The M- ⁄X-asteroid menagerie: Results of an NIR spectral survey of 45 main-belt

asteroids

Paul S. HARDERSEN1*, Edward A. CLOUTIS2, Vishnu REDDY1, Thais MOTHE-DINIZ3,and Joshua P. EMERY4

1Department of Space Studies, Box 9008, University of North Dakota, Grand Forks, North Dakota 58202, USA2Department of Geography, University of Winnipeg, Winnipeg, Manitoba R38 2E9, Canada

3Universidade Federal do Rio de Janeiro ⁄Observatorio do Valongo, Lad. Pedro Antonio, 43 – 20080-090, Rio de Janeiro, Brazil4Department of Earth and Planetary Sciences, University of Tennessee, Knoxville, Tennessee 37996, USA

*Corresponding author. E-mail: Hardersen@space.edu

(Received 13 February 2009; revision accepted 12 October 2011)

Abstract–Diagnostic mineral absorption features for pyroxene(s), olivine, phyllosilicates, andhydroxides have been detected in the near-infrared (NIR: approximately 0.75–2.50 lm) spectra for 60% of the Tholen-classified (Tholen 1984, 1989) M- ⁄X-asteroidsobserved in this study. Nineteen asteroids (42%) exhibit weak Band I (approximately 0.9 lm)± Band II (approximately 1.9 lm) absorptions, three asteroids (7%) exhibit a weak Band I(approximately 1.05–1.08 lm) olivine absorption, four asteroids (9%) display multipleabsorptions suggesting phyllosilicate ± oxide ⁄hydroxide minerals, one (1) asteroid exhibitsan S-asteroid type NIR spectrum, and 18 asteroids (40%) are spectrally featureless in theNIR, but have widely varying slopes. Tholen M-asteroids are defined as asteroids exhibitingfeatureless visible-wavelength (k) spectra with moderate albedos (Tholen 1989). TholenX-asteroids are also defined using the same spectral criterion, but without albedoinformation. Previous work has suggested spectral and mineralogical diversity in theM-asteroid population (Rivkin et al. 1995, 2000; Busarev 2002; Clark et al. 2004; Hardersenet al. 2005; Birlan et al. 2007; Ockert-Bell et al. 2008, 2010; Shepard et al. 2008, 2010;Fornasier et al. 2010). The pyroxene-bearing asteroids are dominated by orthopyroxene withseveral likely to include higher-Ca clinopyroxene components. Potential meteorite analogsinclude mesosiderites, CB ⁄CH chondrites, and silicate-bearing NiFe meteorites. The Eosfamily, olivine-bearing asteroids are most consistent with a CO chondrite analog. Theaqueously altered asteroids display multiple, weak absorptions (0.85, 0.92, 0.97, 1.10, 1.40,and 2.30–2.50 lm) indicative of phyllosilicate ± hydroxide minerals. The spectrallyfeatureless asteroids range from metal-rich to metal-poor with meteorite analogs includingNiFe meteorites, enstatite chondrites, and stony-iron meteorites.

INTRODUCTION

The M- and X-asteroid taxonomic designations ofTholen (1984, 1989) are based on visible k spectra andalbedo information. The X-class includes all asteroids inthe ECAS data set (Zellner et al. 1985) that havefeatureless visible-k spectra as the only classificationcriterion. The X-class becomes nondegenerate if objectalbedo information is available as a second criterion. Thisproduces three subclasses, the E-, M-, and P-asteroids

that have relatively high, moderate, and low albedos,respectively. For example, the 38 Tholen M ⁄MU ⁄MU:asteroids in this work have an albedo rangeapproximately from 7 to 30% (Tedesco et al. 2002). TheMU and MU: variants of the M-class designation indicate‘‘unusual’’ and ‘‘unusual and noisy’’ data (Tholen 1989).The five X- ⁄XD-class asteroids have a wider albedo range,from 6 to 34% (Tedesco et al. 2002). The one TholenS-asteroid in this article, 71 Niobe, has an albedo ofapproximately 31% (Tedesco et al. 2002).

� The Meteoritical Society, 2011. 1910

Meteoritics & Planetary Science 46, Nr 12, 1910–1938 (2011)

doi: 10.1111/j.1945-5100.2011.01304.x

Prior to 2001 and the introduction of the SpeX 0.8–5.5 lm spectrograph at the NASA Infrared TelescopeFacility (IRTF; Rayner et al. 2003, 2004), M-asteroidNIR spectra were reported as being spectrally featureless,which led to the suggestion that enstatite chondrites andNiFe meteorites were the most likely analogs for theseasteroids (Chapman and Salisbury 1973; Gaffey andMcCord 1979). Polarimetric observations by Dollfuset al. (1979) supported the metallic interpretation bysuggesting that particulate metallic surfaces with graindiameters of 20–50 lm as being the most consistent withtheir polarimetric data. Lupishko and Belskaya (1989),however, suggested that the M-asteroids 16 Psyche, 21Lutetia, 22 Kalliope, 69 Hesperia, and 110 Lydia, have asilicate surface component with enstatite chondrites andstony-iron meteorites as the most consistent options.Jones et al. (1990) reported that 55 Pandora and 92Undina, both M-asteroids, displayed 3 lm absorptions,whereas 16 Psyche did not. The work by Jones et al.(1990) was the first suggestion of a hydrous mineralcomponent for some M-asteroids, which were previouslythought to be anhydrous.

In addition, radar observations suggest that the M-asteroid population displays both a larger average radaralbedo and larger overall radar albedo variability (Magriet al. 1999; Shepard et al. 2010). A high radar albedo isthe most robust indicator suggesting the presence ofmetal on the surfaces of atmosphereless bodies (Ostro1993). Ostro et al. (1985) reported differing radaralbedos for 16 Psyche and 97 Klotho, with 16 Psyche asthe most likely one to have a significant surface metalcomponent. Mitchell et al. (1995) reported a high radaralbedo for 216 Kleopatra (0.44 ± 0.15), which wassubsequently revised upward to 0.7 (Ostro et al. 2000)and 0.68 ± 0.28 (Magri et al. 2007). Shepard et al.(2008) reported an all-observation radar albedo averagefor 216 Kleopatra of 0.60 ± 0.15.

Three-micron and visible k spectra from Rivkinet al. (1995, 2000) and Busarev (2002) suggested thepresence of hydrous mineralogical environments (i.e.,phyllosilicates, hydrated salts, etc.) for some M-asteroids, which provided additional hints of mineralogicvariability within this taxonomic group. Rivkin et al.(1995, 2000) reported that 21 Lutetia, 22 Kalliope, 55Pandora, 77 Frigga, 92 Undina, 110 Lydia, 129Antigone, 135 Hertha, 136 Austria, and 201 Penelopedisplay a 3 lm absorption feature. Mineralogically, theimplication of a 3 lm absorption feature in an asteroid’sNIR spectrum is the presence of H2O- or OH-bearingminerals, such as the phyllosilicate group of minerals andvarious hydroxide minerals (Calvin and King 1997).However, a 3 lm absorption is not diagnostic and maymask otherwise anhydrous objects (Gaffey et al. 2002,and references therein).

Clark et al. (2004) and Hardersen et al. (2005)reported the detection of weak approximately 0.9 lmabsorptions in the NIR spectra for some M- ⁄X-asteroids.Clark et al. (2004) reported approximately 0.9 lmfeatures in the NIR spectra of 16 Psyche, 110 Lydia, 216Kleopatra, and 785 Zwetana, whereas Hardersen et al.(2005) reported similar features for 16 Psyche, 69Hesperia, 110 Lydia, 125 Liberatrix, 201 Penelope, and216 Kleopatra.

Since then, several research teams have undertakenboth radar and NIR spectral studies of the M- ⁄X-asteroid population (Birlan et al. 2007; Ockert-Bell et al.2008, 2010; Shepard et al. 2008, 2010; Fornasier et al.2010; this paper). Birlan et al. (2007) reported featurelessNIR spectra of eight M-asteroids (325 Heidelberga, 497Iva, 558 Carmen, 687 Tinette, 860 Ursina, 909 Ulla, 1280Baillauda, and 1564 Srbija) that are most consistent witha NiFe meteorite analog via spectral curve matching.One additional asteroid, 766 Moguntia, exhibits a weakolivine absorption feature with a band depth ofapproximately 7% (Birlan et al. 2007). Spectral curvematching, MGM modeling, and application of theShkuratov scattering model suggest the CV3 chondrite,Allan Hills (ALH) 84028, and the H6 ordinarychondrite, Ozona, as the best analogs for 766 Moguntia.Nedelcu et al. (2007) reported rotationally resolved NIRspectra of 21 Lutetia. Their spectra exhibit slopevariations and they suggest enstatite chondrites (EL6)and carbonaceous chondrites (CI1, CV3) as the bestmeteorite analogs, depending on the nature of each NIRspectral slope for 21 Lutetia.

Shepard et al. (2008, 2010) and Ockert-Bell et al.(2008, 2010) have conducted coordinated radar and NIRspectral observations of members of the M- ⁄X-asteroidpopulation in an effort to better constrain themineralogic and meteoritic diversity of these asteroids.Shepard et al. (2008, 2010), as well as previous workers,have obtained radar observations for 19 M- ⁄X-asteroids.These include 16 Psyche, 21 Lutetia, 22 Kalliope, 83Beatrix, 97 Klotho, 110 Lydia, 129 Antigone, 135Hertha, 216 Kleopatra, 224 Oceana, 325 Heidelberga,347 Pariana, 497 Iva, 678 Fredegundis, 758 Mancunia,771 Libera, 779 Nina, 785 Zwetana, and 796 Sarita(Shepard et al. 2010). As a group, their radar albedosvary from 0.07 to 0.60 with 13 of the asteroids havingradar albedos <0.30 (Shepard et al. 2010). Due to thewide range of variability in radar albedo seen forsome of their asteroids and the presence of silicateminerals (Hardersen et al. 2005; Ockert-Bell et al. 2008,2010; Fornasier et al. 2010), Shepard et al. (2010)suggested that most M-asteroids are collisionalmixes, mostly analogous to stony-iron meteorites andhigh-Fe carbonaceous chondrites. However, individualanalogs for specific asteroids suggested by Shepard

NIR spectra for 45 M- ⁄X-asteroids 1911

et al. (2010) span a wide range that includes NiFemeteorites, CH ⁄CB chondrites, enstatite chondrites, andstony irons.

Ockert-Bell et al. (2008, 2010) and Fornasier et al.(2010) presented M- ⁄X-asteroid NIR spectra for 22 and30 asteroids, respectively. While Ockert-Bell et al. (2008)focused on analyzing asteroid NIR continuum slopes,they reported weak, approximately 0.9 lm band depthsfor 16 Psyche and 129 Antigone of approximately 1.2–1.5%. Examination of fig. 2 in Ockert-Bell et al. (2008)suggests the presence of weak, approximately 0.9 lmfeatures for 55 Pandora, 110 Lydia, 216 Kleopatra, and872 Holda. Ockert-Bell et al. (2010) reported weak,approximately 0.9 lm features for 16 Psyche, 22 Kalliope,77 Frigga, 129 Antigone, 135 Hertha, 136 Austria, 250Bettina, 441 Bathilde, 497 Iva, 678 Fredegundis, 771Libera, and 872 Holda. They report approximately0.9 ± 1.9 lm features for 55 Pandora, 110 Lydia, 216Kleopatra, 347 Pariana, 758 Mancunia, 779 Nina, and785 Zwetana (Ockert-Bell et al. 2010). Ockert-Bell et al.(2010) note that the highest radar albedo asteroids tendto also have weak approximately 0.9 and 1.9 lmabsorption features.

Fornasier et al. (2010) report weak visible-k and ⁄orNIR absorptions for 17 M-asteroids that include 16Psyche, 22 Kalliope, 55 Pandora, 69 Hesperia, 110Lydia, 129 Antigone, 132 Aethra, 498 Tokio, 516Amherstia, 755 Quintilla, and 872 Holda. Visible-kabsorptions are either at approximately 0.43 lm or0.50 lm; NIR absorptions span a wider range, butdominate in the Band I region from approximately 0.87to 1.16 lm. NIR absorptions at longer wavelengths arereported for 755 Quintilla and 516 Amherstia (range:approximately 1.37–1.95 lm) (Fornasier et al. 2010). Thecollection of absorption features identified by Fornasieret al. (2010) are attributed to minerals that includechlorites, serpentinites, antigorite, pigeonite, augites, ortho-pyroxene, Fe-bearing pyroxene, olivine, oldhamite ⁄troilite, and unknown phases.

Taken as a cumulative body of research, the availableevidence suggests that the mineralogic and meteoriticdiversity of the M- ⁄X-asteroid taxonomic classescontinues to expand. The intent of this article is to add tothe existing knowledge of theM- ⁄X-asteroid taxons and tosearch for additional evidence of mineralogic, meteoritic,and spectral diversity.

OBSERVATIONS AND DATA REDUCTION

All observations were conducted at the NASAInfrared Telescope Facility, Mauna Kea, Hawai’i, usingthe SpeX spectrograph in the prism mode (i.e., lowresolution, R approximately 95), 0.75 to 2.50 lm,0.8¢¢ · 15¢¢ slit (Rayner et al. 2003, 2004). The full

observational protocols are described in Hardersen et al.(2004, 2005, 2006a), but the standard procedure involvesobtaining NIR spectra of the target asteroids, standard(i.e., extinction) stars (as close to G2V as possible) formodeling the first-order extinction coefficients aboveMauna Kea, and solar analog stars to correct for slopedifferences when using non-G2V extinction stars. Tominimize spectral data dispersion and to securely detectweak NIR spectral absorption features, a signal-to-noiseratio (SNR) ‡100 is desired for each nightly averageasteroid spectrum. Oftentimes, the nightly asteroidspectrum is an average of only those spectra with the besttelluric corrections (i.e., the least data scatter in the telluricwater vapor regions at approximately 1.4 and 1.9 lm). SeeTable 1 for a compilation of the observing circumstancesfor the asteroids reported in this article.

Observations for the August 2005 IRTF observingrun did not utilize solar analog (i.e., G2V) stars. Withinthis article, this applies to the NIR spectra of 129Antigone, 184 Dejopeja, 417 Suevia, 441 Bathilde, 739Mandeville, and 758 Mancunia. Extinction correctionsfor these asteroids utilized either F9V or G3V stars. Theoverall NIR spectral slope for the asteroids using theF9V standard stars (129 Antigone, 417 Suevia, 441Bathilde) will be somewhat decreased, mostly at theshorter k. The variations will be relatively minor as thespectral classes only span three subclasses from G2Vstars; the overall slope change for the asteroids usingG3V standard stars (184 Dejopeja, 739 Mandeville, 758Mancunia) will be trivial.

NIR spectra were reduced using either IRAF ⁄SpecPR (Gaffey 2003) or Spextool (Cushing et al. 2004).Both programs perform the same primary functions,which include flux summation and extraction, extinctioncorrections, channel shifting, and spectral averaging.SpecPR performs additional analysis functions such asabsorption feature continuum removal, polynomialfitting, and band center ⁄band area calculations.Spextool, an IDL routine, does not include analysisfunctions. However, analysis functions equivalent tothose for SpecPR are accomplished using MATLABsubroutines.

Infrared Telescope Facility ⁄SpeX LXD observationsof 22 Kalliope were also conducted for this study. Bothprism mode and cross-dispersed spectra (approximately1.9–4.1 lm) were obtained and used to compare withsimilar observations by Rivkin et al. (2000). The SpeXLXD data are reduced using standard NIR spectralreflection techniques, which include dark and flat fieldcorrections, and application of a bad pixel mask. Theraw cross-dispersed data is different from prism data, asit is vertically offset across six spectral orders on theCCD chip. The data were extracted as a 1-D flux array,clipped at the ends to exclude low SNR data, and only

1912 P. S. Hardersen et al.

Table

1.Summary

oftheobservationalcircumstancesforthe45asteroidsobserved

attheNASA

InfraredTelescopeFacility

(IRTF).Individual

asteroid

and

stellar

spectra

were

limited

toindividualexposure

times

of120s.

Stellar

spectralclassifications

obtained

from

the

Sim

bad

AstronomicalDatabase

(http://sim

bad.u-strasbg.fr/simbad/).Asteroid

apparentmagnitudes

obtained

from

theJP

LHorizonsephem

erisduringtime

ofobservation(http://ssd.jpl.nasa.gov/?horizons).UT

start

⁄stoptimes

representeither

(1)thetimeintervalbetweenthebeginningofthefirstand

last

setofobservations,or(2)thetimeintervalforcontinuousset(s)

ofobservations.

Asteroid

Date(s)of

observation

(UT)

Apparent

magnitude

No.of

spectra

obtained

No.of

spectra

usedto

produce

spectrum

Start

time

(UT)

Stop

time

(UT)

Total

integration

time(s)

Airmass

rangeof

observations

Extinctionstar

used

Solaranalog

starused

Weather

notes

16Psyche

3⁄22

⁄2002

10.7

120

120

705

1135

1800

1.167–1.268

HD

95868

(G2V)

SAO

120107

(G5III)

Clear

21Lutetia

8⁄16

⁄2008

12.1

68

68

1318

1428

2720

1.245–1.574

HD

285660

(G0V)

HD

28099

(G2V)

Initialsummit

cloudsin

early

evening;

otherwise,

clear

22Kalliope

5⁄9

⁄2004

11.4

20

51205

1229

800

1.406–1.417

HD

155415

(G2V)

SAO

120107

(G5III)

Clear

22Kalliope

2⁄27

⁄2008

11.2

70

60

1232

1521

700

1.020–1.201

SAO

119805

(G1V)

SAO

120107

(G5III)

Clear

55Pandora

1⁄22

⁄2007

12.6

164

100

1010

1445

8610

1.087–1.380

HD

94794

(F8V)

SAO

120107

(G5III)

Clear

69Hesperia

5⁄3

⁄2001

12.2

54

54

1126

1454

2150

1.304–1.364

SAO

141608

(G2V)

SAO

120107

(G5III),

SAO

31899

(G3V)

Clear

69Hesperia

5⁄4

⁄2001

12.2

16

16

1329

1425

880

1.197–1.288

SAO

141608

(G2V)

SAO

31899

(G3V)

Clear

71Niobe

1⁄6

⁄2009

12.9

40

30

520

658

4800

1.092–1.405

SAO

74132

(G4V)

HD

28099

(G2V)

Mostly

clear,

butsomecirrus

cloudsare

present

77Frigga

1⁄23

⁄2007

13.2

30

6517

631

3600

1.077–1.286

HD

9986

(G5V)

SAO

120107

(G5III)

Clear

97Klotho

5⁄9

⁄2004

12.5

40

13

842

1254

3000

1.246–1.321

HD

141308

(G2V)

SAO

120107

(G5III)

Clear

97Klotho

5⁄10

⁄2004

12.5

54

12

826

1344

5450

1.369–1.488

HD

141308

(G2V)

SAO

120107

(G5III)

Lightcirrus

presentacross

thesky

110Lydia

5⁄2

⁄2001

12.6

30

30

624

920

2100

1.066–1.144

SAO

119191

(G0V)

SAO

120107

(G5III)

Clear

NIR spectra for 45 M- ⁄X-asteroids 1913

Table

1.Continued.Summary

oftheobservationalcircumstancesforthe45asteroidsobserved

attheNASA

InfraredTelescopeFacility

(IRTF).

Individualasteroid

andstellarspectrawerelimited

toindividualexposure

times

of120s.

Stellarspectralclassificationsobtained

from

theSim

bad

AstronomicalDatabase

(http://sim

bad.u-strasbg.fr/simbad/).Asteroid

apparentmagnitudes

obtained

from

theJP

LHorizonsephem

erisduringtime

ofobservation(http://ssd.jpl.nasa.gov/?horizons).UT

start

⁄stoptimes

representeither

(1)thetimeintervalbetweenthebeginningofthefirstand

last

setofobservations,or(2)thetimeintervalforcontinuousset(s)

ofobservations.

Asteroid

Date(s)of

observation

(UT)

Apparent

magnitude

No.of

spectra

obtained

No.of

spectra

usedto

produce

spectrum

Start

time

(UT)

Stop

time

(UT)

Total

integration

time(s)

Airmass

rangeof

observations

Extinctionstar

used

Solaranalog

starused

Weather

notes

110Lydia

5⁄3

⁄2001

12.6

38

18

545

959

3540

1.127–1.284

SAO

119191

(G0V)

SAO

120107

(G5III),

SAO

31899

(G3V)

Clear

110Lydia

5⁄4

⁄2001

12.6

16

16

915

1030

1760

1.153–1.467

SAO

119191

(G0V)

SAO

31899

(G3V)

Clear

125Liberatrix

3⁄23

⁄2002

13.3

80

80

535

915

4800

1.036–1.396

SAO

118176

(G1V)

SAO

120107

(G5III)

Clear

129Antigone

8⁄19

⁄2005

11.4

10

10

630

647

150

1.412–1.503

HD

141247

(F9V)

None.

Mostly

clear

skies.Overhead

cirrusat

beginningof

night

129Antigone

8⁄20

⁄2005

11.4

30

30

605

637

690

1.322–1.465

HD

141247

(F9V)

None.

Mostly

clear

skies.Cirrus

nearhorizons

only

129Antigone

8⁄21

⁄2005

11.4

40

6604

631

800

1.331–1.450

HD

141247

(F9V)

None.

Cirrusoverhead

beginningof

night.

Otherwiseclear

remainder

of

night

132Aethra

5⁄21

⁄2008

12.8

20

20

1158

1250

2400

1.402–1.410

SAO

185949

(G5V)

SAO

27996

(G5V)

Variable

abundance

of

cirrusclouds

presentaround

thesky

132Aethra

8⁄18

⁄2008

14.3

10

10

539

607

1200

1.200–1.215

HD

154067

(G2

⁄G3V)

HD

28099

(G2V)

Clear

135Hertha

10

⁄3⁄2004

10.2

110

15

841

944

1190

1.037–1.130

HD

6302

(G8V)

HD

1835

(G3V)

Clear

136Austria

3⁄22

⁄2002

12.8

50

50

825

1405

3500

1.100–1.514

SAO

139102

(G8V)

SAO

120107

(G5III)

Clear

1914 P. S. Hardersen et al.

Table

1.Continued.Summary

oftheobservationalcircumstancesforthe45asteroidsobserved

attheNASA

InfraredTelescopeFacility

(IRTF).

Individualasteroid

andstellarspectrawerelimited

toindividualexposure

times

of120s.

Stellarspectralclassificationsobtained

from

theSim

bad

AstronomicalDatabase

(http://sim

bad.u-strasbg.fr/simbad/).Asteroid

apparentmagnitudes

obtained

from

theJP

LHorizonsephem

erisduringtime

ofobservation(http://ssd.jpl.nasa.gov/?horizons).UT

start

⁄stoptimes

representeither

(1)thetimeintervalbetweenthebeginningofthefirstand

last

setofobservations,or(2)thetimeintervalforcontinuousset(s)

ofobservations.

Asteroid

Date(s)of

observation

(UT)

Apparent

magnitude

No.of

spectra

obtained

No.of

spectra

usedto

produce

spectrum

Start

time

(UT)

Stop

time

(UT)

Total

integration

time(s)

Airmass

rangeof

observations

Extinctionstar

used

Solaranalog

starused

Weather

notes

184Dejopeja

8⁄20

⁄2005

13.1

20

71139

1326

2000

1.183–1.518

HD

211839

(G3V)

None.

Mostly

clear

skies.Cirrus

nearhorizons

only

201Penelope

5⁄2

⁄2001

12.2

40

40

1038

1237

2700

1.140–1.293

SAO

140198

(G2V)

SAO

120107

(G5III)

Clear

201Penelope

5⁄3

⁄2001

12.2

50

42

900

1232

2980

1.138–1.272

SAO

140198

(G2V)

SAO

120107

(G5III),

SAO

31899

(G3V)

Clear

201Penelope

7⁄29

⁄2006

10.9

70

70

1000

1041

1320

1.197–1.203

HD

194428

(G2

⁄G3V)

SAO

31899

(G3V)

Earlyevening

fog.Otherwise,

clear

216Kleopatra

4⁄29

⁄2001

12.6

39

39

600

928

4470

1.090–1.434

SAO

138119

(G8V)

SAO

120107

(G5III)

Variablecirrus

cloudspresent

duringthe

observations

216Kleopatra

5⁄4

⁄2001

12.7

24

24

619

848

2480

1.086–1.332

SAO

138119

(G8V)

SAO

31899

(G3V)

Clear

224Oceana

10

⁄2⁄2004

12.1

74

15

703

917

5580

1.072–1.620

HD

6302

(G8V)

HD

1835

(G3V)

Clear

250Bettina

4⁄19

⁄ 2005

12.7

50

20

550

1024

2700

1.001–1.629

HD

88371

(G2V)

SAO

120107

(G5III),

SAO

31899

(G3V)

Clearskies,low

relative

humidity

325Heidelberga

4⁄29

⁄2001

14.2

44

735

749

480

1.155–1.167

SAO

138119

(G8V)

SAO

120107

(G5III)

Variablecirrus

cloudspresent

duringthe

observations

325Heidelberga

1⁄23

⁄2007

15.0

34

91259

1407

4080

1.485–1.977

HD

121867

(G2V)

SAO

120107

(G5III)

Clear

NIR spectra for 45 M- ⁄X-asteroids 1915

Table

1.Continued.Summary

oftheobservationalcircumstancesforthe45asteroidsobserved

attheNASA

InfraredTelescopeFacility

(IRTF).

Individualasteroid

andstellarspectrawerelimited

toindividualexposure

times

of120s.

Stellarspectralclassificationsobtained

from

theSim

bad

AstronomicalDatabase

(http://sim

bad.u-strasbg.fr/simbad/).Asteroid

apparentmagnitudes

obtained

from

theJP

LHorizonsephem

erisduringtime

ofobservation(http://ssd.jpl.nasa.gov/?horizons).UT

start

⁄stoptimes

representeither

(1)thetimeintervalbetweenthebeginningofthefirstand

last

setofobservations,or(2)thetimeintervalforcontinuousset(s)

ofobservations.

Asteroid

Date(s)of

observation

(UT)

Apparent

magnitude

No.of

spectra

obtained

No.of

spectra

usedto

produce

spectrum

Start

time

(UT)

Stop

time

(UT)

Total

integration

time(s)

Airmass

rangeof

observations

Extinctionstar

used

Solaranalog

starused

Weather

notes

338Budrosa

7⁄30

⁄2006

13.1

80

80

1018

1323

9600

1.059–1.352

SAO

146477

(F8V)

SAO

31899

(G3V)

Earlyfogand

highrelative

humidity,

followed

by

clearskies

347Pariana

5⁄9

⁄2004

11.9

56

19

821

1229

3100

1.143–1.537

HD

141308

(G2V)

SAO

120107

(G5III)

Clear

369Aeria

4⁄19

⁄2005

13.2

60

27

1153

1503

7200

1.215–1.463

HD

157842

(G2V)

SAO

120107

(G5III)

Clearskies,

lowrelative

humidity

382Dodona

4⁄21

⁄2005

12.3

40

20

929

1024

2400

1.307–1.338

HD

115106

(G2V)

SAO

120107

(G5III)

Clear

413Edburga

4⁄20

⁄2005

15.8

100

14

526

932

12000

1.007–1.307

HD

104076

(G0V)

SAO

120107

(G5III)

Clearskies,low

relativehumidity

417Suevia

8⁄20

⁄2005

14.0

50

50

847

1359

6000

1.060–1.385

HD

217786

(F8V)

None.

Mostly

clearskies.

Cirrusnear

horizonsonly

417Suevia

8⁄21

⁄2005

14.0

30

16

937

1306

3600

1.061–1.184

HD

217786

(F8V)

None.

Cirrusoverhead

beginning

ofnight.

Otherwise

clearremainder

ofnight

418Alemannia

1⁄23

⁄2007

14.5

46

14

1034

1228

5520

1.148–1.555

HD

98281

(G8V)

SAO

120107

(G5III)

Clear

418Alemannia

1⁄24

⁄2007

14.5

70

70

1027

1332

8400

1.106–1.575

HD

98281

(G8V)

SAO

120107

(G5III)

Clear

441Bathilde

8⁄19

⁄2005

12.8

30

30

940

1147

1350

1.112–1.378

HD

198273

(G2V)

None.

Mostly

clear

skies.Overhead

cirrusat

beginningof

night

497Iva

4⁄21

⁄2005

16.0

80

20

512

813

9600

1.000–1.188

SAO

98655

(F8V)

SAO

120107

(G5III)

Clear

1916 P. S. Hardersen et al.

Table

1.Continued.Summary

oftheobservationalcircumstancesforthe45asteroidsobserved

attheNASA

InfraredTelescopeFacility

(IRTF).

Individualasteroid

andstellarspectrawerelimited

toindividualexposure

times

of120s.

Stellarspectralclassificationsobtained

from

theSim

bad

AstronomicalDatabase

(http://sim

bad.u-strasbg.fr/simbad/).Asteroid

apparentmagnitudes

obtained

from

theJP

LHorizonsephem

erisduringtime

ofobservation(http://ssd.jpl.nasa.gov/?horizons).UT

start

⁄stoptimes

representeither

(1)thetimeintervalbetweenthebeginningofthefirstand

last

setofobservations,or(2)thetimeintervalforcontinuousset(s)

ofobservations.

Asteroid

Date(s)of

observation

(UT)

Apparent

magnitude

No.of

spectra

obtained

No.of

spectra

usedto

produce

spectrum

Start

time

(UT)

Stop

time

(UT)

Total

integration

time(s)

Airmass

rangeof

observations

Extinctionstar

used

Solaranalog

starused

Weather

notes

498Tokio

10

⁄9⁄2001

11.5

66

1306

1315

450

1.487–1.539

SAO

53622

(G2V)

SAO

31899

(G3V)

Clear

504Cora

1⁄22

⁄2007

13.9

26

20

505

748

3120

1.011–1.131

HIP

15904

(G0V)

SAO

120107

(G5III)

Clear

504Cora

1⁄23

⁄2007

13.9

20

10

714

751

2400

1.071–1.147

HIP

15904

(G0V)

SAO

120107

(G5III)

Clear

516Amherstia

10

⁄4⁄2004

13.1

26

7831

906

3120

1.066–1.136

HD

7352

(G0V)

HD

1835

(G3V)

Patchycirrus

present

558Carm

en1

⁄22

⁄2004

12.9

68

50

811

1127

6120

1.004–1.281

HD

75528

(G1V)

HD

28099

(G2V)

Clear

739Mandeville

8⁄21

⁄2005

12.8

40

8806

853

4800

1.296–1.401

HD

203619

(G3V)

None.

Cirrusoverhead

beginningofnight.

Otherwiseclear

remainder

ofnight

758Mancunia

8⁄19

⁄2005

12.6

40

40

919

1212

2400

1.219–1.389

HD

214414

(G3V)

None.

Mostly

clear

skies.Overhead

cirrusat

beginningof

night

766Moguntia

1⁄20

⁄2004

14.5

80

19

618

1023

9600

1.053–1.195

HD

41330

(G0V)

HD

28099

(G2V)

Clear

785Zwetana

4⁄19

⁄2005

11.7

30

30

1108

1234

750

1.040–1.162

BD+

062840B

(G0V)

SAO

120107

(G5III)

Clearskies,low

relativehumidity

796Sarita

1⁄24

⁄2007

15.3

10

10

1416

1443

1200

1.442–1.586

HD

129485

(G6V)

SAO

120107

(G5III)

Clear

798Ruth

8⁄18

⁄2008

15.3

20

51308

1401

2400

1.183–1.407

SAO

76384

(G4V)

HD

28099

(G2V)

Clear

857Glasenappia

8⁄17

⁄2008

15.9

20

91334

1428

2400

1.266–1.571

HD

28099

(G2V)

HD

28099

(G2V)

Clear

857Glasenappia

8⁄18

⁄2008

15.9

88

1417

1444

960

1.200–1.303

HD

28099

(G2V)

HD

28099

(G2V)

Clear

NIR spectra for 45 M- ⁄X-asteroids 1917

Table

1.Continued.Summary

oftheobservationalcircumstancesforthe45asteroidsobserved

attheNASA

InfraredTelescopeFacility

(IRTF).

Individualasteroid

andstellarspectrawerelimited

toindividualexposure

times

of120s.

Stellarspectralclassificationsobtained

from

theSim

bad

AstronomicalDatabase

(http://sim

bad.u-strasbg.fr/simbad/).Asteroid

apparentmagnitudes

obtained

from

theJP

LHorizonsephem

erisduringtime

ofobservation(http://ssd.jpl.nasa.gov/?horizons).UT

start

⁄stoptimes

representeither

(1)thetimeintervalbetweenthebeginningofthefirstand

last

setofobservations,or(2)thetimeintervalforcontinuousset(s)

ofobservations.

Asteroid

Date(s)of

observation

(UT)

Apparent

magnitude

No.of

spectra

obtained

No.of

spectra

usedto

produce

spectrum

Start

time

(UT)

Stop

time

(UT)

Total

integration

time(s)

Airmass

rangeof

observations

Extinctionstar

used

Solaranalog

starused

Weather

notes

860Ursina

8⁄16

⁄2008

13.4

50

40

752

1125

6000

1.117–1.460

HD

209712

(F6V)

HD

28099

(G2V)

Initialsummit

cloudsin

early

evening;

otherwise,

clear

860Ursina

1⁄7

⁄2009

15.6

10

4446

515

1200

1.396–1.583

HD

215763

(F9V)

HD

28099

(G2V)

Clear

872Holda

10

⁄3⁄2004

14.0

34

11

633

752

4080

1.143–1.431

HD

223498

(G7V)

HD

1835

(G3V)

Clear

931Whittemora

4⁄19

⁄2005

14.6

30

29

643

901

3600

1.006–1.205

SAO

100038

(G2V)

SAO

120107

(G5III)

Clearskies,

lowrelative

humidity

1210Morosovia

1⁄22

⁄2007

15.4

36

36

548

805

4320

1.011–1.195

HIP

15904

(G0V)

SAO

120107

(G5III)

Clear

1210Morosovila

1⁄24

⁄2007

15.5

30

20

509

557

3600

1.011–1.022

HIP

15904

(G0V)

SAO

120107

(G5III)

Clear

1461Jean-Jacques

7⁄29

⁄2006

15.5

36

5639

748

4320

1.206–1.314

HD

146720

(G3V)

SAO

31899

(G3V)

Earlyevening

fog.Otherwise,

clear

1918 P. S. Hardersen et al.

the highest SNR images were used in the final average.Error bars are the standard deviation of the mean ofeach channel. Wavelength calibration in the K-band usesargon lines obtained by SpeX and in the L-band usingatmospheric absorption lines. The data are normalized at2.2 lm.

Individual NIR absorption bands are isolated using alinear continuum that meets the local maximum on eitherside of an absorption feature. A continuum-removedfeature is calculated as the ratio of the reflectance of theabsorption feature to the linear continuum. A polynomialis then fit to the isolated feature to estimate the bandcenter. Reported band centers are averages of multiplepolynomial fitting attempts. Band error estimates aredominated by the point-to-point data scatter of thefeature, but are typically smaller for approximately 0.9–1.0 lm (Band I) features than the approximately 1.9–2.0 lm (Band II) features.

Continuum-removed features were corrected fortemperature effects, when necessary, because NIR mineralabsorptions become narrower and ⁄or experience awavelength shift compared with equivalent laboratoryspectra obtained at room temperature (approximately293 K) (Singer and Roush 1985; Moroz et al. 2000;Hinrichs and Lucey 2002). Asteroid surface temperaturesat the time of observation were calculated using theThermflx program of M. J. Gaffey using the StandardThermal Model (STM; Lebofsky and Spencer 1989) withinputs that include the semimajor axis, phase angle,albedo, emissivity (0.856), and beaming factor (0.75)across an arbitrary wavelength interval (i.e., 0.4–20.0 lm).Using the techniques in Burbine et al. (2009), all Band Itemperature shifts are smaller than the errors in thereported band centers and usually amounts to a shift ofonly 0.001 lm. Asteroids with measurable Band IIfeatures, however, experienced substantially largertemperature-induced shifts and were corrected by themethods of Burbine et al. (2009).

Pyroxene chemistry estimates are determined fromthe methods of Gaffey et al. (2002) and Burbine et al.(2009), where the former is based on the work ofAdams (1974) and Cloutis and Gaffey (1991). Thepyroxene chemistry calculations are most precise whenorthopyroxene ± Type B clinopyroxene are the solemafic silicates present. Pyroxene chemistry estimates canbe skewed by the presence of olivine and Type Aclinopyroxene that can shift the Band I centers (Gaffeyet al. 2002). The presence of Type A and ⁄or Type Bhigh-Ca clinopyroxene can be inferred based on theposition of the band parameters in the pyroxeneband-band plot (Gaffey et al. 2002), and Type Aclinopyroxene can be directly detected by the presenceof a uniquely invariant double Band I minimum inthe approximately 1 lm region (Schade et al. 2004;

Hardersen et al. 2006a). The Burbine et al. (2009)calibration is based on the howardite, eucrite, diogenite(HED) meteorites, where pyroxene is the dominant maficsilicate mineral present. Both techniques are used in thisarticle for comparison.

MINERAL MIXTURES

Laboratory VNIR spectra of several mineral, metal,and meteorite samples were obtained to allowcomparison of the laboratory spectra to the asteroidspectra. All new spectra were obtained at the Universityof Winnipeg using an Analytical Spectral Devices (ASD)FieldSpec Pro HR spectrometer (Cloutis et al. 2006).Absolute reflectances from 0.35 to 2.50 lm was measuredfor all samples, which were uniformly ground to <45 lmparticle size fractions. Spectra were measured at aviewing geometry of i = 30�, e = 0�. Olivine (OLV003),orthopyroxene (PYX042), metal (Meteorite Hills [MET]101), and CH chondrite (Pecora Escarpment [PCA]91467) samples were used in this work. PYX042 has achemistry of Wo0.4Fs12.8 and Al2O3 abundance of0.09 wt%. OLV003 has a chemistry of Fo90.4. Thepyroxene within PCA 91467 has a chemistry of Fs1–5 thatranges as high as Fs16 (Score and Lindstrom 1993). Thissample has a weathering grade of B ⁄C, which indicatesmoderate to severe weathering (Score and Lindstrom1993). The reflectance spectra measured at the NASA-supported RELAB facility were measured at i = 30�,e = 0� in bidirectional reflectance mode relative to halonfor the approximately 0.3–2.5 lm region at 5 nmintervals, and corrected for minor irregularities in halon’sabsolute reflectance in the 2.0–2.5 lm region. Details ofthe RELAB facility are available at the RELAB website(http://www.planetary.brown.edu/relab/).

VNIR spectra were obtained for olivine:metal andorthopyroxene:metal mixtures to study the effects ofchanging relative amounts of powdered metal on theoverall NIR spectral slope and the reduction of mineralabsorption band depths. Mixtures were sampled at10 wt% intervals for olivine:metal and orthopyroxene:metal mixtures. The laboratory VNIR spectra were alsocompared with asteroid spectra to attempt to constrainthe potential abundance of metal on asteroid surfaces.

RESULTS

Physical and Dynamic Characteristics

As a group, the asteroids in this article do notpossess any distinct or uniquely identifiable dynamical orphysical characteristics that suggest they are geneticallyrelated. Of the Tholen M-asteroids in this article, 30 of38 have an IRAS albedo within the range from 0.14 to

NIR spectra for 45 M- ⁄X-asteroids 1919

0.25 (Tedesco et al. 2002). Seven M-asteroids have IRASalbedos <0.14, and one (55 Pandora) has an IRASalbedo >0.30 (Tedesco et al. 2002; Shepard et al. 2010).Two of the Tholen X- ⁄XD-asteroids have an IRASalbedo <0.14, three have an IRAS albedo in the rangefrom 0.14 to 0.25, and one (504 Cora) has an IRASalbedo >0.30 (Tedesco et al. 2002).

Dynamically, these asteroids range in semimajor axisfrom approximately 2.15–3.20 AU. There is no large-scale preference of dynamical groupings of theseasteroids when plotting eccentricity versus semimajoraxis or sine of the orbital inclination versus semimajoraxis. However, several asteroids are members of a fewdifferent asteroid families. All the olivine-bearingasteroids in this article—766 Moguntia, 798 Ruth, and1210 Morosovia (see discussion below)—are members ofthe Eos dynamical family (Zappala et al. 1990). Fiveasteroids: 77 Frigga, 110 Lydia, 125 Liberatrix, 201Penelope, and 224 Oceana, are members of the Kozai 30family (Kozai 1979). Fifty-five Pandora, 441 Bathilde,and 872 Holda are members of the Kozai 36 family(Kozai 1979). Both 755 Quintilla and 758 Mancunia aremembers of the Kozai 60 family (Kozai 1979). A total of325 Heidelberga and 382 Dodona are members of theKozai 63 family (Kozai 1979). 338 Budrosa and 558Carmen are members of the Williams 124 family(Williams 1979, 1989, 1992). It is important to note thatcommon family membership is not a guarantee of adirect genetic relationship due to the presence ofinterlopers.

Pyroxene-Bearing Asteroids

Seventeen Tholen M ⁄MU-asteroids, two Tholen X-asteroids, and one Tholen XD-asteroid exhibit weakapproximately 0.9 lm (Band I) ± approximately 1.9 lm(Band II) absorptions with continuum-removed banddepths that range from approximately 1 to 14%. Table 2lists these asteroids with their band parameters andcomplementary data, such as radar albedo and 3 lmabsorptions. The band parameters for the six asteroidswith weak pyroxene features from Hardersen et al.(2005) have been remeasured and included in Table 2.Table 3 includes the band parameters for the fiveasteroids with Band I and Band II absorptions, whichinclude temperature-corrected band centers and thederived pyroxene chemistries using the Gaffey et al.(2002) and Burbine et al. (2009) calibrations. Figures 1and 2 show the average NIR spectrum for eachpyroxene-bearing asteroid, except for 857 Glasenappia.Figure 3 shows the continuum-removed Band Iabsorptions for 250 Bettina, 347 Pariana, 497 Iva, and516 Amherstia, which are typical Band I absorptions forthese asteroids.

For the asteroids in Table 2 that only exhibit a BandI absorption, the Band I centers for all but two asteroids(417 Suevia and 857 Glasenappia) range fromapproximately 0.89 to 0.95 lm. Without a measurableBand II feature, it is not possible to use the existingcalibrations to estimate the average surface pyroxenechemistry for each asteroid. However, it is instructive tonote that all but three of the orthopyroxene laboratorysamples measured for the pyroxene band–band plot fromGaffey et al. (2002) have Band I centers £0.936 lm. InTable 1, nine asteroids (69 Hesperia, 110 Lydia, 125Liberatrix, 129 Antigone, 216 Kleopatra, 250 Bettina,347 Pariana, 418 Alemannia, 796 Sarita) have Band Icenters <0.930 lm. While a few higher-Ca Type Bclinopyroxene samples in the band–band plot have bandcenters <0.930 lm, the vast majority have band centersthat range from approximately 0.95 to 1.07 lm (Gaffeyet al. 2002). This suggests that most of these asteroidshave a surface mineralogy dominated by orthopyroxeneor an orthopyroxene ⁄Type B clinopyroxene mixture.

Sixteen Psyche, 201 Penelope, 382 Dodona, and 558Carmen have Band I centers that range from 0.930 to0.945 lm. Compared with the asteroids showing theshorter-k Band I centers, these asteroids have a higherproportion of Type B clinopyroxene on their surfaces.417 Suevia’s Band I feature has a relatively flat bottomthat extends from approximately 0.82 to 1.17 lm, whichprevents a determination of a Band I center. The breadthof this feature suggests a multipyroxene ± olivinesurface mineralogy that accounts for the breadth of thisfeature and the presence of multiple overlapping weakabsorptions (Cloutis and Gaffey 1991; Gaffey et al. 2002;Schade et al. 2004).

Olivine-Bearing Asteroids

The average NIR spectral and physical characteristicsof the three Tholen MU- ⁄MU:-olivine-bearing asteroids(766 Moguntia, 798 Ruth, 1210 Morosovia) are shown inTable 4 and Fig. 4. Figure 4 also shows the continuum-removed Band I feature for 766 Moguntia. Band I centersrange from 1.047 to 1.068 lm and band depths rangefrom approximately 4 to 10%. The three asteroids aremembers of the Eos dynamical family (Zappala et al.1990) and show similar NIR olivine features in the workof Birlan et al. (2007) andMothe-Diniz et al. (2008).

Olivine calibrations using derived Band I centers arepoorly constrained due to the small change in bandcenter with increasing Fe2+ content in olivine (King andRidley 1987; Burns 1993; Reddy et al. 2011). However,applying the recent calibration from Reddy et al. (2011)yields olivine chemistry values of Fo60±7 for 766Moguntia and Fo84±7 for 798 Ruth showing thatthese asteroids have rather Mg-rich olivine chemistries.

1920 P. S. Hardersen et al.

Table

2.Physical,orbital,andtaxonomiccharacteristics

ofthepyroxene-bearingM-⁄X-asteroids.

Name

Tholen

class

IRAS

diameter

(km)

IRAS

albedo

a(A

U)

BandI(lm)

BandI

depth

(%)

BandII

(lm)

Radaralbedo

3lm

feature?

IRAS

albedo

16Psyche

M253.16

0.1203

2.921

0.932±

0.008

�1–2

–0.42±

0.10

No

0.1203

69Hesperia

M138.13

0.1402

2.989

0.923±

0.011;

0.909±

0.009

�2

1.78–1.83c

––

0.1402

110Lydia

M86.09

0.1808

2.732

0.914±

0.006;

0.914±

0.004;

0.903±

0.005

�2

1.75–1.90c

0.20±

0.12

Yes

0.1808

125Liberatrix

M43.58

0.2253

2.743

0.920±

0.006

�2–3

––

No

0.2253

129Antigone

M–

0.18a

2.867

0.918±

0.003;

0.930±

0.008

�3

–0.36±

0.09

Yes

0.1800

184Dejopeja

X66.47

0.1897

3.179

0.931±

0.004

�2

––

No

0.1897

201Penelope

M68.39

0.1604

2.678

0.932±

0.005;

0.945±

0.008;

0.917±

0.010

�2

1.82–1.83c

–Yes

0.1604

216Kleopatra

M135.07

0.1164

2.791

0.923±

0.003

�2

1.79–1.80c

0.60±

0.15

No

0.1164

250Bettina

M79.75

0.2581

3.148

0.914±

0.007

�2

––

–0.2581

338Budrosa

M63.11

0.1766

2.911

0.939±

0.008

�1–2

1.933±

0.018

––

0.1766

347Pariana

M51.36

0.1845

2.612

0.919±

0.008

�2–3

–0.36±

0.09

–0.1845

369Aeria

M60.00

0.1919

2.649

0.920±

0.003

�2

1.865±

0.023

–No(?)

0.1919

382Dodona

M58.37

0.1610

3.119

0.934±

0.007

�1–2

––

–0.1610

417Suevia

X40.69

0.1960

2.807

See

textfor

discussion

�2

––

–0.1960

418Alemannia

M34.10

0.1878

2.593

0.922±

0.010;

0.910±

0.005

�2–3

––

–0.1878

497Iva

M31±

60.085±

0.010b

2.850

0.941±

0.006

�1–2

1.918±

0.019

0.24±

0.08

No

0.0850

516Amherstia

M73.10

0.1627

2.676

0.927±

0.003

�4–5

1.911±

0.039

––

0.1627

558Carm

enM

59.31

0.1161

2.907

0.940±

0.006

�2–3

––

–0.1161

796Sarita

XD

44.96

0.1966

2.635

0.914±

0.008

�2

1.846±

0.027

0.25±

0.10

No

0.1966

857Glasenappia

MU

15.03

0.2318

2.190

Flatfeature

rom�0.94to

1.08

lm

�14%

1.958±

0.028

–No(?)

0.1572

Taxonomicclassificationsfrom

Tholen(1984,1989).

IRASalbedo

⁄diameter

from

Tedesco

etal.(2002).

3lm

data

from

Rivkin

etal.(2000).

a129Antigonealbedofrom

Shepard

etal.(2008)andreferencestherein.

bData

from

Shepard

etal.(2010)andreferencestherein.Morrison(1977)reportsaradiometricalbedo=

0.18±

0.04.Radardata

from

Shepard

etal.(2010).BandII

centers

listed

in

Table

2are

thenontemperature-correctedvalues.

cData

from

BandII

averages

from

Hardersenet

al.(2005).

NIR spectra for 45 M- ⁄X-asteroids 1921

The Band I center for 1210 Morosovia is at a shorter-kdue to a pyroxene component, and olivine calibrationscannot be used (Reddy et al. 2011).

Mothe-Diniz et al. (2008) report Fo�85–95 for 766Moguntia and Fo�40–70 for 798 Ruth, which aresomewhat more Mg-rich and Mg-poor, respectively,compared with the results in Table 3. Mothe-Diniz et al.(2008) reported a larger range of Fo values for Eosfamily members and suggest analogs that include Rchondrites, CK chondrites, and partial melts. Birlanet al. (2007) note the weak Band I absorption feature for766 Moguntia and attribute the relatively shallow banddepth to opaque minerals on Moguntia’s surface thatwere suppressing the olivine absorption.

Hydrated Mineral-Bearing Asteroids

Three Tholen M-asteroids: 22 Kalliope, 55 Pandora,and 132 Aethra, and an S3OS2-Tholen X-asteroid (Lazzaroet al. 2004), 504 Cora, display NIR spectral slopes andabsorption features consistent with the presence ofphyllosilicate ± hydroxide minerals. Table 5 and Fig. 5display the dynamical and physical characteristics, andaverage NIR spectra of these asteroids, respectively.

132 Aethra was observed in May and August 2008,respectively, and a comparison of their average spectra isshown in Fig. 6. The May 2008 spectrum is an averageof 20 spectra, and the August 2008 spectrum is anaverage of 10 spectra.

Table 3. Band parameters and pyroxene chemistry estimates for 338 Budrosa, 369 Aeria, 497 Iva, 516 Amherstia,and 796 Sarita. Band centers have been temperature-corrected via the methods in Burbine et al. (2009).

Asteroid Band I (lm) Band II (lm)Gaffey et al. (2002)Pyroxene chemistry

Burbine et al. (2009)Pyroxene chemistry

338 Budrosa 0.939 1.919 Wo12Fs38 Wo8Fs39369 Aeria 0.920 1.886 Wo3Fs22 Wo3Fs26497 Iva 0.939 1.937 Wo11Fs39 Wo9Fs41516 Amhertia 0.928 1.898 Wo8Fs25 Wo5Fs31796 Sarita 0.914 1.846 Wo0Fs11 Wo0Fs18

Fig. 1. Average NIR reflectance spectra of 16 Psyche, 69Hesperia, 110 Lydia, 125 Liberatrix, 129 Antigone, 184Dejopeja, 201 Penelope, 216 Kleopatra, 250 Bettina, and 338Budrosa.

Fig. 2. Average NIR reflectance spectra of 347 Pariana, 369Aeria, 382 Dodona, 417 Suevia, 418 Alemannia, 497 Iva, 516Amherstia, 558 Carmen, and 796 Sarita.

1922 P. S. Hardersen et al.

The May 2008 spectrum has a significantly steeperslope than the August 2008 spectrum and exhibits weakabsorptions at approximately 0.90, 1.10, and 1.40 lm,along with a more prominent and broader absorptionranging from approximately 2.28 to 2.50+ lm. TheAugust 2008 spectrum has a shallower, but significantlyreddish slope; however, it is largely absent the features inthe May 2008 spectrum. The features in the May 2008NIR spectrum at approximately 0.90 and 1.10 lm can beassigned to Fe2+ crystal field transitions and theapproximately 1.40 and 2.28–2.50 lm absorptions can beassigned to Mg-OH, H2O, or OH vibrational overtones(Burns 1993; Calvin and King 1997). The spectraldifferences from the two observing runs can possiblybe attributed to variable abundances of surfacephyllosilicates with rotation, variable abundances ofopaque surface minerals with rotation, the presence of aneclipsing satellite with a different surface mineralogythan the primary, or unidentified observational andinstrumental artifacts. A rigorous review of the data doesnot indicate an obvious observational or instrumentalreason(s) to explain the spectral differences.

Comparison of the May 2008 spectrum with multipleRELAB samples of chamosite show the best slope andabsorption feature match with Fe-rich sample CHM102.The spectral match is very close from approximately 1.2 to2.5 lm. The ground chamosite sample has a purity of 98%;no other minerals were identified via X-ray diffractionanalysis. The NIR spectra of Fe-poor chamosites aresignificantly less red (i.e., shallower slopes) than CHM102(by a factor of 4+), while still displaying multiple weakabsorption features attributable to Fe2+, Fe3+, OH, andH2O.

CHM102 displays weak absorptions at approximately0.70 (Fe2+-Fe3+ IVCT), 0.90 (Fe2+ crystal fieldtransition) and 1.10 lm (Fe2+ crystal field transition), andstronger absorptions at approximately 1.92 lm (H2O),2.34 lm (metal-OH), and 2.51 lm (metal-OH and ⁄orH2O). Mg-bearing phyllosilicates are characterized by abroad Fe2+ absorption from 0.6 to 1.8 lm that issuperimposed on a red NIR slope and includes a weakFe2+- Fe3+ IVCT absorption at approximately 0.70 lmand weak Fe2+ crystal field transitions at approximately0.90 and 1.10 lm (Calvin and King 1997). Chamosite is anintermediate Fe- ⁄Mg-bearing phyllosilicate (Fe2+, Mg,Fe3+)5Al(Si3Al)O10(OH,O)8 from the chlorite group andexhibits greater spectral reflectance with increasing Alcontent (Calvin and King 1997). This relative brightnessis consistent with 132 Aethra’s IRAS albedo ofapproximately 19% (Tedesco et al. 2002) and would moreeasily allow the appearance of weak absorption features inthe NIR spectrum.

Visible-k spectra from Bus and Binzel (2002) andFornasier et al. (2010) show an approximately 0.49 lmfeature possibly attributable to oldhamite (Burbine et al.2002); this feature is also seen in the spectra of someE-type asteroids (Clark et al. 2004; Fornasier et al. 2007,2008). The coexistence of sulfides and phyllosilicates doesoccur terrestrially in some ore deposits (King and Clark1989). Some RELAB samples of glauconite, nontronite,and saponite display a similar absorption feature, whichis consistent with a hydrated mineral environment(Stewart et al. 2006).

The average NIR spectrum of 504 Cora is shown inFig. 5, and a magnified view of the Band I region isshown in Fig. 7. Reynolds (2007) and Reynolds et al.

Fig. 3. Continuum-removed Band I absorption features for 250Bettina, 347 Pariana, 497 Iva, and 516 Amherstia. Band depthsfor the pyroxene-bearing asteroids in this article range fromapproximately 1 to 5%.

Table 4. Physical, orbital, and taxonomic characteristics of the olivine-bearing M-asteroids.Name Tholen class IRAS D (km) IRAS albedo a (AU) Band I (lm) Band I depth (%) Family Fo %

766 Moguntia MU 31.28 0.1572 3.022 1.068 ± 0.004 �10% Eos 60

798 Ruth MU 43.19 0.1587 3.015 1.056 ± 0.004 �4–5% Eos 841210 Morosovia MU 33.65 0.1695 3.012 1.047 ± 0.009 �8–9% Eos –

Family classifications from Zappala et al. (1990).

Forsterite % calculated from Reddy et al. (2011).

IRAS diameters and albedos from Tedesco et al. (2002).

NIR spectra for 45 M- ⁄X-asteroids 1923

(2007) initially reported 504 Cora as a low-Fe pyroxene-bearing asteroid, but reanalysis reveals what is seen inFig. 7, which is a set of weak, narrow absorptions atapproximately 0.85 and 0.92 lm that are superimposedon a broader absorption, and another weak feature atapproximately 1.08 lm. The weak approximately 1.6 lmabsorption in Fig. 5 is telluric.

The relatively high reported IRAS albedo for 504Cora, approximately 30%, is inconsistent with a metaland pyroxene mixture (Cloutis et al. 2010). Theapproximately 0.85 lm feature is consistent with Fe3+

spin-forbidden bands in hydroxide ⁄oxide minerals suchas ferrihydrite and hematite. The same feature has alsobeen reported in the laboratory spectrum of CMcarbonaceous chondrites (Gaffey and McCord 1979). Theapproximately 0.92 and 1.08 lm weak absorptions couldbe attributed to Fe2+-bearing phyllosilicate (Calvin andKing 1997).

55 Pandora has spectral and albedo characteristicsthat are very similar to those of 504 Cora. The NIRspectrum is broadly similar to that for 504 Cora, mostnotably in the approximately 0.7–1.2 lm spectral region.

Table 5. Physical, orbital, and taxonomic characteristics of the phyllosilicate ⁄hydroxide-bearing M- ⁄X-asteroids.Name Tholen class IRAS D (km) IRAS albedo a (AU) Band minima (lm) 3 lm feature?

22 Kalliope M 181.00 0.1419 2.909 0.94–(?), 2.30–2.50+ Yes

55 Pandora M 66.70 0.3013 2.760 0.85–(?), 0.92–(?), 0.97–(?) 1.10 Yes132 Aethra M 42.66 0.1718 2.610 0.91–, 1.10–, 1.40–, 2.28–2.50+ –504 Cora – 30.02 0.3407 2.721 0.85–, 0.91–, 1.07– –

3 lm data from Rivkin et al. (2000).

Fig. 4. Average NIR reflectance spectra for 766 Moguntia, 798 Ruth, and 1210 Morosovia, and the Band I continuum-removedabsorption for 766 Moguntia.

1924 P. S. Hardersen et al.

While the Band I region for 55 Pandora is somewhatnoisier than 504 Cora’s data, there are suggestions ofweak absorptions at approximately 0.85, 0.92, 0.97, and1.10 lm. The 0.97 lm feature is seen in the spectrum ofsome CM chondrites (Cloutis et al. 2011), whereas theother features are consistent with phyllosilicate phases,as discussed previously.

55 Pandora and 504 Cora have similar IRAS albedoswithin the range from 0.30 to 0.35. A 3 lm feature hasalso been detected for 55 Pandora (Jones et al. 1990;Rivkin et al. 2000). The combination of weak absorptionsthat are indicative of hydroxide ⁄oxide and phyllosilicateminerals suggest a surface mineral environment similar to504 Cora’s—a heavily hydrated, relatively bright surfacethat argues for extensive aqueous alteration of the parentasteroid.

An average spectrum for 22 Kalliope is shown inFig. 5 and includes a weak, yet broad absorption in theapproximately 2.30–2.50 lm region that can be attributedto Mg-OH vibrational overtones seen in Mg-serpentinesand chamosite (Calvin and King 1997). There is a

Fig. 5. Average NIR reflectance spectra for 22 Kalliope, 55 Pandora, 132 Aethra, and 504 Cora. The 22 Kalliope spectra includesL-band data that increases the spectral coverage to approximately 4.1 lm.

Fig. 6. Overlay of the average spectrum for 132 Aethra fromMay 2008 (20 spectra) and August 2008 (10 spectra). The steepred slope and weak features in the May 2008 spectrum areabsent from the August 2008 spectrum. Unpublished spectrafrom J. Emery (December 2010–February 2011) are alsofeatureless and more similar to the August 2008 spectrum.

NIR spectra for 45 M- ⁄X-asteroids 1925

possible weak feature at approximately 0.94 lm, but thecontinuum-removed feature seems too narrow forattribution to pyroxene. There is no indication of the weakFe2+ and Fe3+ absorptions that have been identified inthe May 2008 NIR spectrum of 132 Aethra. It is alsonotable that the spectral slope for 22 Kalliope is notextremely red, as is the case for 132 Aethra and theCHM102 sample.

L-band data from approximately 1.9–4.1 lm werealso obtained on the same night. While the L-bandspectrum shows a weak absorption in the 3 lm region,the weak feature in the SpeX data from 2.3 to 2.5 lm isabsent. The difference in the time of observation of 22Kalliope for the NIR and L-band data was <1 h, andKalliope’s surface would have rotated <90� based on itsrotation period of 4.148 h (Warner 2007). A separateNIR spectrum of 22 Kalliope obtained on May 9, 2004UT did not show any indication of a 2.30–2.50 lmabsorption (Hardersen et al. 2006b). Rivkin et al. (2000)reported a 3 lm absorption for 22 Kalliope and thepossibility of band depth variations.

22 Kalliope has a known satellite companion(Margot and Brown 2003). An initial bulk density of2.37 ± 0.4 g cm)3 was reported (Margot and Brown2003), but was later revised upward to 3.35 ± 0.33 g cm)3

(Descamps et al. 2008). The former density is consistentwith the bulk densities of some CM chondrites, but ishigher than measured for CI chondrites (Britt andConsolmagno 2003). The higher value is inconsistent withboth CI and CM chondrites (Britt and Consolmagno2003). 22 Kalliope’s IRAS albedo (approximately 14%) isalso inconsistent with CI and CM chondrite albedos

(Gaffey 1976). Chlorite- and serpentine-group mineralshave densities ranging from 2.5 g cm)3 to 3.3 g cm)3

(Klein and Hurlbut 1993).

Spectrally Featureless Asteroids

Fifteen Tholen M-asteroids, one Tholen S-asteroid,and two Tholen X-asteroids in this article arespectrally featureless in the NIR. Average NIR spectraare shown in Figs. 8 and 9 and related characteristicsin Table 6. As seen in Figs. 8 and 9, these asteroidsexhibit a wide variety of spectral slopes. Most of theasteroids in Table 5 exhibit a generally red NIR slopeacross most or all of the wavelength range fromapproximately 0.8 to 2.5 lm. However, the spectra of97 Klotho and 441 Bathilde are flat, and the spectrumof 498 Tokio is distinctly bluish with a pronouncednegative slope.

Various reflectance ratios and slopes have beenmeasured and analyzed for featureless M- ⁄X-asteroidNIR reflectance spectra (Ockert-Bell et al. 2008, 2010;this work) and laboratory NIR spectra for plausiblemetallic surfaces (powdered and slab) for M-asteroids(Cloutis et al. 2010; and references therein). Theasteroids in Table 5 have 1.8 ⁄0.8 lm reflectance ratiosthat range from 0.754 to 1.452 with 10 of the asteroidshaving ratios > 1.20. Reflectance ratios for variousmetallic powders and slabs range from approximately1.0–1.7 (Cloutis et al. 2010). The blue NIR spectral slopefor 498 Tokio and reflectance ratio = 0.754 isinconsistent with the metal NIR spectra from Cloutiset al. (2010) and the NIR spectrum in Fornasier et al.(2010). The remaining asteroids in Table 6 are consistentwith both works.

Meteorite analogs for spectrally featureless asteroidsare more difficult to constrain, but enstatite chondritesand NiFe meteorites—assuming moderate albedos fromapproximately 10 to 20%—remain viable options.Particulate metallic surfaces require red spectral slopesand albedos of approximately 10–15% at 0.56 lm(Cloutis et al. 2010). If IRAS albedos (Tedesco et al.2002) are equivalent to 0.56 lm albedos, then 21 Lutetia,71 Niobe, 97 Klotho, 498 Tokio, 739 Mandeville, 872Holda—and possibly 931 Whittemora and 1461 Jean-Jacques—are not likely to have metallic surfaces.

The recent Rosetta flyby of 21 Lutetia revealed anasteroid with a regolith of varying thickness and analbedo of approximately 19% (consistent with Muelleret al. 2006; inconsistent with Morrison and Zellner1979), suggesting that the surface is not metallic (Barucciet al. 2010). Shepard et al. (2008, 2010) derived a radaralbedo of 0.24 ± 0.07 for 21 Lutetia, which is consistentwith enstatite chondrites, CH chondrites, and silicate-bearing iron meteorites. CH chondrites display a weak

Fig. 7. The 0.6–1.2 lm region of the SMASS II visible-k (opensquares; Bus and Binzel 2002) and average IRTF ⁄SpeX NIRspectrum (black diamonds) for 504 Cora. The broader featurein the figure occurs at the overlap of the SMASS II and SpeXdata sets. Note the distinct, weak absorptions at 0.85, 0.92, and1.08 lm in the NIR spectrum. The absorptions are attributedto Fe2+ and Fe3+ crystal field absorptions found in hydroxideand phyllosilicate minerals.

1926 P. S. Hardersen et al.

approximately 0.9 lm pyroxene absorption (i.e., PCA91467: this work); silicate-bearing iron meteorites maydisplay a pyroxene absorption depending on the surfacepyroxene abundance. Orthopyroxene ⁄metal laboratorymixtures produce a weak approximately 0.9 lmabsorption feature with a 10 ⁄90 wt% mixture oforthopyroxene and powdered metal. The available datacurrently suggests that enstatite chondrites are the mostviable meteorite analog for 21 Lutetia with silicate-bearing iron meteorites (with <10 wt% opx ⁄metalmixture) as another possibility.

Radar albedos have also been obtained for 71Niobe, 97 Klotho, 135 Hertha, 224 Oceana, 325Heidelberga, 758 Mancunia, and 785 Zwetana (Shepardet al. 2008, 2010), among which 758 Mancunia and 785Zwetana have relatively high, and variable, radaralbedos, which makes the iron meteorite analogapplicable to these asteroids (Shepard et al. 2008, 2010).Ockert-Bell et al. (2008) found a correlation betweentheir ‘‘NIR2’’ continuum slope (1.70–2.45 lm) and radaralbedo, which may assist in identifying metal-richasteroids via NIR spectra.

135 Hertha, 224 Oceana, and 325 Heidelberga haveradar and NIR spectral properties consistent withenstatite chondrites, but CH chondrites can be ruled out,as discussed above (Shepard et al. 2008, 2010). 71 Niobe

and 97 Klotho are mostly consistent with enstatitechondrites, but their IRAS albedos are higherthan typically measured for this meteorite type (Gaffey1976).

857 Glasenappia

This asteroid is unique in this study, because it is theonly asteroid with two well-defined and relatively deepabsorptions in the approximately 0.9 and 1.9 lm regions,akin to the NIR spectral characteristics of S-asteroids(Gaffey et al. 1993); see Fig. 10. The continuum-removedBand I absorption is quite broad and extends fromapproximately 0.80 to 1.60 lm. The bottom of thecontinuum-removed feature is relatively flat and extendsfrom approximately 0.92 to 1.08 lm with an inflection atapproximately 1.20 lm. A Band I center could not bedetermined due to the flatness of the feature, but thebreadth of the feature suggests the presence ofoverlapping absorptions from at least two distinct maficsilicate minerals. The Band II center = 1.958 ± 0.028lm. The calculated band area ratio (BAR: Band II ⁄BandI) = 0.64.

From Cloutis et al. (1986), the BAR suggests anapproximately 68% relative olivine abundance in anolivine ⁄orthopyroxene mixture on the asteroid’s surface.The rounded Band I feature is also consistent with the

Fig. 8. Average NIR reflectance spectra of 21 Lutetia, 71Niobe, 77 Frigga, 97 Klotho, 135 Hertha, 136 Austria, 224Oceana, 325 Heidelberga, and 413 Edburga.

Fig. 9. Average NIR reflectance spectra of 441 Bathilde, 498Tokio, 739 Mandeville, 758 Mancunia, 785 Zwetana, 860Ursina, 872 Holda, 931 Whittemora, and 1461 Jean-Jacques.

NIR spectra for 45 M- ⁄X-asteroids 1927

S-II asteroids in Gaffey et al. (1993), who note that theshape of this feature is mostly unique to this S-asteroidsubtype. The position of the Band II center is consistentwith an average surface pyroxene that is either mostlyorthopyroxene or an orthopyroxene ⁄Type B clinopyroxenemixture (Gaffey et al. 2002).

Possible meteorite analogs for 857 Glasenappiainclude L and LL chondrites, which is based on the BARand Band II center (Gaffey 1976; Gaffey et al. 2002)similarities between the derived olivine abundance and thenormative abundances from McSween et al. (1991). Otherpotential analogs include clinopyroxene-bearing ureilites,brachinites, and olivine ⁄ clinopyroxene cumulates (Gaffeyet al. 1993).

ANALYSIS AND INTERPRETATIONS

Pyroxene-Bearing Asteroids

For the pyroxene-bearing asteroids that exhibit ameasurable Band I feature, Hardersen et al. (2005)offered four possible interpretations: (1) low-Fe pyroxenemantling metallic cores, (2) CB ⁄CH chondrites, (3)smelting products, and (4) collisional debris. Thepresence of weak pyroxene absorptions rules out theenstatite chondrite and iron meteorite interpretations forthese asteroids (Hardersen et al. 2005, and referencestherein).

The M- ⁄X-asteroids with shorter-k Band I centers(<0.93 lm) would be consistent with the low-Fe pyroxene

mantle ⁄core and CB ⁄CH-chondrite interpretations due totheir inferred low Fe2+ content (Brearley and Jones 1998).A continuum-removed absorption for CH-chondrite, PCA91467, has a band center of approximately 0.92 lm and aband depth of approximately 3%, which is consistent withmany of the asteroid band centers in Table 2.

Conversely, those asteroids with Band I centers>0.94 lm (16 Psyche, 201 Penelope, 417 Suevia, 558Carmen) would be inconsistent with CB ⁄CH chondritesand represent a more Fe-rich pyroxene environment. Theasteroids in Table 2 are also inconsistent with CB ⁄CH

Table 6. Physical, orbital, and taxonomic characteristics of the near-infrared spectrally featureless M- ⁄X-asteroids.

NameTholenclass

IRAS D(km)

IRASalbedo a (AU)

1.8 ⁄ 0.8 lmratio Radar albedo

3 lmfeature?

21 Lutetia M 95.76 0.2212 2.435 1.109 0.24 ± 0.07 Yes71 Niobe S 83.42 0.3052 2.756 1.079 ⁄ 1.100 0.19 ± 0.05 –

77 Frigga MU 69.25 0.1440 2.671 1.381 – Yes97 Klotho M 82.83 0.2285 2.666 0.981 ⁄ 1.004 0.26 ± 0.05 –135 Hertha M 79.24 0.1436 2.429 1.277 0.18 ± 0.05 Yes136 Austria M 40.14 0.1459 2.287 1.137 – Yes

224 Oceana M 61.82 0.1694 2.645 1.267 0.25 ± 0.10 –325 Heidelberga M 75.72 0.1068 3.201 1.414 0.17 ± 0.08 –413 Edburga M 31.95 0.1466 2.583 1.289 – –

441 Bathilde M 70.32 0.1410 2.809 – – –498 Tokio M 81.83 0.0694 2.651 0.754 – –739 Mandeville X 107.53 0.0608 2.742 – – –

758 Mancunia X 85.48 0.1317 3.190 – 0.55 ± 0.14 No785 Zwetana M 48.54 0.1245 2.573 1.170 0.33 ± 0.08 No860 Ursina M 29.32 0.1618 2.796 1.215 ⁄ 1.292 – –

872 Holda M 30.04 0.2127 2.731 1.261 – –931 Whittemora M 45.27 0.1704 3.178 1.322 – –1461 Jean-Jacques M 32.94 0.1613 3.128 1.452 – –

Radar data from Shepard et al. (2008, 2010).

3 lm data from Rivkin et al. (2000).

Fig. 10. Average NIR reflectance spectrum of 857Glasenappia.

1928 P. S. Hardersen et al.

chondrites as they are more Fe-rich than typically seen inCB ⁄CH chondrites (Brearley and Jones 1998).

The pyroxene-bearing asteroids with Band I and IIcenters, shown in Table 3, are plotted on the pyroxeneband–band plot in Fig. 11. The band centers for 369Aeria and 516 Amherstia plot within the orthopyroxeneregion (Gaffey et al. 2002). The derived pyroxenechemistries for 369 Aeria are Wo3Fs22 (Gaffey et al.2002) and Wo3Fs26 (Burbine et al. 2009). The derivedpyroxene chemistries for 516 Amherstia are Wo8Fs25(Gaffey et al. 2002) and Wo5Fs31 (Burbine et al. 2009).These estimates suggest that orthopyroxene is thedominant mafic silicate mineral on these asteroids’surfaces, although minor ⁄accessory amounts of Type Bclinopyroxene and olivine may also be present (Cloutiset al. 1986). The 338 Budrosa and 497 Iva plot slightlyabove the pyroxene trend in Fig. 11. This suggests thepresence of either an olivine or high-Ca pyroxene phasein addition to orthopyroxene ± Type B clinopyroxene(Gaffey et al. 2002).

369 Aeria displays an NIR spectral slope that issimilar to that seen in some mesosiderite NIR spectra(Gaffey 1976). The asteroid’s average pyroxenechemistry is also consistent with the pyroxene chemistryrange for some mesosiderites (Weigand 1975; Hewins1979) and diogenites (Rubin 1997; Mittlefehldt et al.1998). Weak Band I and Band II features would beexpected for an asteroid with a surface composition oforthopyroxene and metal (Vernazza et al. 2009).Laboratory mixtures of orthopyroxene and metal(10 ⁄90 wt%) produce a VNIR spectrum with weakpyroxene features, but the slope of the laboratoryspectrum is much steeper than the 369 Aeria spectrum.Mesosiderite NIR spectra will vary significantlydepending on the proportions of pyroxene and metal(Burbine et al. 2007).

Vernazza et al. (2009) suggested 201 Penelope, 250Bettina, and 337 Devosa as potential mesosiderite-likeasteroids. NIR spectra of untreated and ion-irradiatedsamples of the mesosiderite Vaca Muerta were comparedwith spectra of the three asteroids. Associations weresuggested based on the similarities between thecontinuum-removed spectra of the meteorite andasteroids, similar albedos, and the presence of weakpyroxene features in the approximately 0.9 and 1.9 lmregions. The Band I centers reported for 250 Bettina byOckert-Bell et al. (2010), Fornasier et al. (2010), and thiswork are inconsistent with HED band parameters(Gaffey 1997). For 201 Penelope, the Band I and Band IIcenters reported by Hardersen et al. (2005, this work) areat wavelengths inconsistent with HED band parametersand chemistries (Gaffey 1997).

516 Amherstia exhibits a pyroxene chemistrysomewhat more Fe-rich than 369 Aeria and has the

deepest Band I feature of the pyroxene-dominatedasteroids in Tables 2 and 3. Spectrally, the asteroid looksto be a composite of an S-type and an M-type spectrum,which suggest that a NIR spectral continuum may existbetween these two taxonomic classes. The asteroid’sspectrally derived Fs content is more Fe-rich thanordinary chondrites (Rubin 1997), but overlaps the upperend of the Fs range for diogenites and mesosideritepyroxenes (Weigand 1975; Hewins 1979; Mittlefehldtet al. 1998).

338 Budrosa and 497 Iva have larger calculated Fsvalues (approximately 39–40%), but their positionsslightly above the pyroxene trend line in the band–bandplot suggest additional mafic silicate phases (i.e., olivine)that may be causing an over-estimate of the Fsabundance. Shepard et al. (2010) suggest stony-ironmeteorites (i.e., mesosiderites, pallasites) and CHchondrites as potential analogs for 497 Iva. Pallasites canbe ruled out due to the lack of abundant pyroxene withinpallasites (Mittlefehldt et al. 1998) and an NIR pallasitespectrum that should be dominated by olivine. Thederived pyroxene chemistry for 497 Iva, even taking intoaccount an olivine phase, will probably be too Fe-richfor CH chondrites. Mesosiderites remain a possibleanalog.

796 Sarita displays the lowest-Fe pyroxenes ofthese asteroids with a surface mineralogy that isdominated by orthopyroxene. The moderate radaralbedo (0.25 ± 0.10) led Shepard et al. (2010) to suggestmesosiderites as a potential analog. The derived Fscontents (Fs11–18) for 796 Sarita in Table 3 overlap themost Fe-poor mesosiderite pyroxenes (Mittlefehldt et al.1998) and could represent a mesosiderite-like object withdiogenitic surface pyroxenes. Mesosiderite asteroidswith higher-Fe pyroxenes, however, can be ruled out.

Fig. 11. Pyroxene Band I versus Band II plot with band centerdata for 338 Budrosa, 369 Aeria, 497 Iva, 516 Amherstia, and796 Sarita.

NIR spectra for 45 M- ⁄X-asteroids 1929

Mesosiderites represent a wide range of metalabundances (17–90 wt%; Mittlefehldt et al. 1998). As10 ⁄90 wt% mixtures of opx ⁄metal produce a weakBand I pyroxene feature, this suggests that the vastmajority of mesosiderite bodies in the asteroid belt willexhibit Band I ⁄ II pyroxene absorptions with varyingband depths.

Olivine-Bearing Asteroids

766 Moguntia, 798 Ruth, and 1210 Morosovia, aswell as the Eos family asteroids in Birlan et al. (2007)and Mothe-Diniz et al. (2008), display weak olivine ±pyroxene absorption features. Only 1210 Morosoviadisplays a weak Band II feature, which indicates asurface pyroxene component. Possible mechanisms forthis band weakening include surface metal, opaqueminerals, or space weathering (Cloutis et al. 1990; Clarket al. 2002; Birlan et al. 2007). Olivine ⁄metal mixtureswith olivine relative abundances of approximately 50–80 wt% reduce olivine band depths to approximately4–13%. This is compared with a band depth ofapproximately 45% for a pure olivine NIR spectrum.This result is consistent with the band depths of theolivine-bearing asteroids in this work. Progressivelyincreasing amounts of metal, beginning around60 ⁄40 wt% olivine ⁄metal mixtures, imparts a red slopeto the NIR spectrum that is not observed in the asteroidNIR spectrum (Birlan et al. 2007; Mothe-Diniz et al.2008; this work).

Laboratory spectra of brachinites (i.e., Brachina),ureilites (18 RELAB samples1), CO3 chondrites (ALH82101, Frontier Mountain [FRO] 95002, FRO 99040,MET 00737), CK (3–5) chondrites (MET 01149, PCA91470, DAV 92300, ALH 85002, Elephant Moraine[EET] 83311), a CV3 chondrite (Queen Alexandra Range[QUE] 93744), and an R3 chondrite (PRE 95404)produce weak Band I ± Band II features similar to theEos family asteroids. Band areas and centers for thesemeteorite samples were measured to compare bandparameters with the olivine-bearing asteroid spectra.CO3 chondrite Band I centers range from 1.059 to1.069 lm and Band II centers range from 1.940 to2.044 lm. About 8 vol% of bulk CO3 chondritescontain olivine and pyroxene, whereas 40–50 vol% ofthe matrix consists of olivine and pyroxene (Brearley andJones 1998). Besides metal, opaque phases in thegroundmass include magnetite and pyrrhotite (Brearleyand Jones 1998). Olivine and pyroxene chemistries

range from Fa�1–60 and Fs<10 in unequilibrated CO3chondrites, but Fa�35–60 in more equilibrated CO3chondrites (Brearley and Jones 1998). The Band II centerfor 1210 Morosovia, 1.883 ± 0.049 lm is consistentwith an orthopyroxene component (Gaffey et al. 2002),but is at a somewhat shorter-k compared with the CO3chondrite Band II centers.

CV3 chondrite, QUE 93744, has a Band Icenter = 1.063 lm. CV chondrite chondrule olivinechemistries are generally Mg-rich as, for example, themean Allende olivine chondrule chemistry is Fo76

2

(Brearley and Jones 1998). Fe-bearing pyroxenes have awide chemistry range and include clinoenstatite, low-Capyroxene, and augite (Brearley and Jones 1998). Matrixolivine is generally ferroan (often mean Fa�50), but thechemistry depends on the degree of equilibration and theamount of aqueous alteration (Brearley and Jones 1998).Meteorite albedo values (Gaffey 1976) are below thosefor all Eos family members except one (513 Centesima)(Mothe-Diniz et al. 2008).

CK chondrite Band I centers range from 1.064 to1.068 lm. Four of the five samples have a Band IIabsorption, but two of the features are very weak. TheBand II centers range from 1.980 to 2.075 lm. Band Idepths vary from 9.4 to 15.1%. CK chondrites arethermally metamorphosed consisting mostly of matrixwith an olivine chemistry of Fo67–71, a pyroxene chemistryof Fs23–29, and an opaque matrix component (mostlymagnetite) of approximately 1–8 vol% (Mittlefehldt et al.1998). The sole CK chondrite sample, EET 83311, lackinga Band II center has an olivine chemistry of Fo64±7

(Reddy et al. 2011).A single R chondrite, PRE 95404, yields a Band I

center = 1.064 lm, Band II center = 2.163 lm, and aBAR = 0.24. The band center data for PRE 95404produces an olivine chemistry of Fo68±7, which overlapsthe known olivine chemistry of R chondrites, Fo60–63(Brearley and Jones 1998; Reddy et al. 2011). Rchondrite pyroxene mineralogy includes low-Capyroxene, augites, and diopside; the Band II centersuggests that the augite and diopside mineralogy isdominating the Band II center, and is inconsistent withthe Band II center for 1210 Morosovia.

The single sample of Brachina has a Band Icenter =1.057 lm with no Band II feature. The banddepth is approximately 28%. The Reddy et al. (2011)olivine calibration produces an olivine chemistry ofFo82±7. Brachinite olivine chemistries vary from Fo65–70(Mittlefehldt et al. 1998). The second most abundantmineral in brachinites is augites (4–15%; Wo39-47Fs52–56;

1EET 87720, MET 01085, Graves Nunatak 95205, EET 87517, Y-

791538, ALHA77257, Lewis Cliff 88201, ALH 82130, ALHA81101,

PCA 82506, EET 96042, Grosvenor Mountains 95575, Dar al Gani

319, Novourei, Kenna, META78008, NWA 1500, Goalpara.

2Figure 45 from Brearley and Jones (1998) incorrectly shows the mean

Allende chondrule olivine chemistry as Fa76. It should read Fo76, which

is correctly discussed in the text on page 3–53.

1930 P. S. Hardersen et al.

Mittlefehldt et al. 1998), which can potentially produce aBand II feature in the NIR spectra. Brachinites havebeen described as both primitive achondrites and olivinecumulates, but either environment requires parent bodyexposure to temperatures >825 �C (Mittlefehldt et al.1998).

Ureilite Band I centers range from 0.920 to 1.075 lm,although 16 of the samples have Band I centers£0.962 lm. Band II centers range from 1.852 to 2.041 lm.The sample with Band I = 1.075 lm, Northwest Africa(NWA) 1500, is an olivine-rich ultramafic meteorite.Recent work suggests that NWA 1500 may not be aureilite and has affinities more closely associated with thebrachinites (Mittlefehldt and Hudon 2004; Kita et al.2009).

Band I and II centers have been derived for fiveadditional Eos family asteroids from Mothe-Diniz et al.(2008). Band I and II centers for 633 Zelima, 661 Cloelia,669 Kypria, 1413 Roucarie, and 1416 Renauxa rangefrom 1.044 to 1.067 lm and 1.897 to 1.940 lm,respectively. Combined with the band center data for1210 Morosovia, the new data suggests that themeasured Eos family asteroids have a surface mineralogyof olivine ± orthopyroxene ⁄Type B clinopyroxene.

Band Area Ratio (BAR) values for the Eosasteroids, 1210 Morosovia, and the above meteoritesrange from lowest to highest as follows: CK chondrites(0.02–0.17), R chondrite (0.24), 1210 Morosovia (0.58 ±0.04), ureilites (0.19–0.67), CO3 chondrites (0.58–0.85),and the CV3 chondrite (0.76).

Mothe-Diniz et al. (2008) suggest R chondrites asthe best analog for the Eos family, while suggesting thatCR and CV chondrites remain possible options. Thisanalysis shows that the CO3 chondrite band parametersare most consistent with the Eos family band parameters(i.e., Band I ⁄ II centers, band depths, BAR, estimatedmineral chemistries).

If the Eos family asteroids originate from a singleparent body that formed in a specific region of the solarnebula and the family members now observed originatefrom that parent body, then that parent body shouldhave an oxygen isotopic composition that is commonamong its family members. This would require meteoriteanalogs for the Eos family members to include onlythose analogs with similar oxygen isotope ratios. Oxygenisotopic ratios for the CO, CK, and CV chondritesoverlap in a region of d17O ⁄ d18O space, but the Rchondrites occupy a different region of this plot(Brearley and Jones 1998). This suggests that theCO ⁄CK ⁄CV chondrites could potentially compose theEos parent body either singly or as a combination of twoor more of these meteorite types. Recent work byGreenwood et al. (2010) suggests an affinity between theCK and CV chondrites, but not the CO chondrites. This

suggests that the Eos family may have originated from aparent body with a CO chondrite, CV ⁄CK-chondrite, orR chondrite origin, but not an original mixture of thesemeteorite types from the solar nebula.

Phyllosilicate-Bearing Asteroids

This article presents the first NIR spectral evidence inthe wavelength range of approximately 0.8–2.5 lm forphyllosilicate ± hydroxide minerals on asteroid surfaces,although absorptions at visible and 3 lm wavelengths havebeen previously reported (Vilas 1994; Rivkin et al. 1995,2000). The suggestion of Fe-rich chamosite or chlorites,more generally, is consistent with the hydrous mineralogywithin CI and CM chondrites (Brearley and Jones 1998).CI ⁄CM chondrites are not, however, meteorite analogsfor 22 Kalliope, 55 Pandora, 132 Aethra, and 504 Corabecause of albedo and ⁄or overall spectral slopedissimilarities (Gaffey 1976; Tedesco et al. 2002).

The combination of multiple NIR absorptionfeatures attributable to phyllosilicates and hydroxides,moderate albedos significantly brighter than CI ⁄CMchondrites, and variably red NIR spectral slopesconsistent with laboratory phyllosilicate NIR spectrasuggests that these asteroids represent a population ofextensively hydrated asteroids that do not have meteoriteanalogs in the terrestrial collection. This suggestion issupported by these asteroids’ locations beyond the 2:1mean-motion resonance at 2.5 AU.

The 26Al accretionary heating model of Grimm andMcSween (1993) predicts a heliocentric-based temperaturegradient throughout the asteroid belt based on asteroidsize and semimajor axis. Using current asteroid diameterscan begin to constrain the greatest semimajor axis wherean asteroid should reside based on the inferredtemperature environment that it experienced in this model.For example, 22 Kalliope has an IRAS diameter of181 km. Assuming T = 300 K for the hydrous andanhydrous models of Grimm and McSween (1993), 22Kalliope should reside at a semimajor axis ofapproximately 2.86 AU and 3.00 AU, respectively. 22Kalliope’s current semimajor axis is at 2.92 AU.Increasing this asteroid’s diameter will not change itssemimajor axis in these models.

55 Pandora, 132 Aethra, and 504 Cora have currentdiameters ranging from approximately 30 to 70 km,but they are probably fragments from larger parentasteroids. Using current diameters results in predictedminimum semimajor axes of approximately 2.6–2.7 AU;their maximum semimajor axes will be no more thanapproximately 2.9–3.0 AU, depending on the parentasteroids’ original diameters. The location of these fourpotentially hydrous asteroids is consistent with thepredicted locations of extensive asteroid belt

NIR spectra for 45 M- ⁄X-asteroids 1931

hydrothermal alteration in the models of Grimm andMcSween (1993). It also suggests the approximately 2.6–3.0 AU region in the main asteroid belt may be a goodlocation to look for hydrous asteroids with detectableNIR absorption features.

SUMMARY OF EXISTING DATA

A summary of the derived band centers from theworks of Hardersen et al. (2005), Ockert-Bell et al. (2008,2010), Fornasier et al. (2010), and this article arepresented in Table 7. A comparison of the data inTable 7 shows that the results from different researchgroups are often divergent when reporting the presenceof NIR absorption features and the derived bandcenter(s) for individual asteroids. The data in Table 7shows differing results for 22 Kalliope, 69 Hesperia, 77Frigga, 110 Lydia, 125 Liberatrix, 129 Antigone, 135Hertha, 136 Austria, 201 Penelope, 216 Kleopatra, 250Bettina, 338 Budrosa, 347 Pariana, 369 Aeria, 382Dodona, 441 Bathilde, 497 Iva, 498 Tokio, 516Amherstia, 558 Carmen, 758 Mancunia, 785 Zwetana,and 872 Holda. The possible causes for the differencesare numerous and could include compositional variationswith rotation, measurement difficulties due to absorptionband weakness, telluric effects, data reductionprocedures, and observational circumstances (Ockert-Bell et al. 2008).

3 lm Correlations

Three pyroxene-bearing M-asteroids: 110 Lydia, 129Antigone, and 201 Penelope exhibit both approximately0.9 ± 1.9 lm and approximately 3.0 lm absorptions,whereas seven asteroids (16 Psyche, 125 Liberatrix, 184Dejopeja, 216 Kleopatra, 369 Aeria, 497 Iva, 796 Sarita)have approximately 0.9 ± 1.9 lm features, but noapproximately 3.0 lm feature. 857 Glasenappia has acomplex olivine ⁄pyroxene NIR spectrum, but does nothave an approximately 3.0 lm feature with someuncertainty (Rivkin et al. 2000). Four asteroids (21Lutetia, 77 Frigga, 135 Hertha, 136 Austria) have anapproximately 3.0 lm feature, but are spectrallyfeatureless in the NIR. 758 Mancunia and 785 Zwetanalack both NIR spectral features and a approximately3.0 lm absorption. One of the potentially phyllosilicate-bearing M-asteroids, 22 Kalliope, has an approximately3.0 lm absorption.

Any number of scenarios can account for thesecombinations of absorption features and spectral shapesin the VNIR region. Assuming that an approximately3.0 lm feature is due to a hydrated mineral phase on anasteroid’s surface, collisional mixing can account for thepresence of abundant hydrous and anhydrous phases on

an asteroid’s surface. A noncollisional mechanism couldinvolve a parent body with internal ice that heated andmelted during the early solar system heating event(Herbert et al. 1991; Grimm and McSween 1993). Theinternal water could have mobilized and aqueouslyaltered only portions of the interior prior to disruption.The coexistence of moderately reducing minerals (i.e.,low-Fe pyroxenes) with ice seems unlikely, but could befacilitated in middle regions of the main asteroid belt(approximately 2.6–3.0 AU) where the chemical andmixing conditions are quite variable (Grimm andMcSween 1993).

Implications of Space Weathering

An uncertainty in our results involve the effects ofspace weathering on the asteroid NIR spectra and, hence,the resulting interpretations. Space weathering is generallydefined as a spectral effect that causes either VNIRspectral slope reddening, absorption band weakening, andsurface material darkening due to either micrometeoriteimpacts causing the deposition of nano-phase Fe or solarwind sputtering (Clark et al. 2002). A variety oflaboratory and observational efforts have been underwayto try to better understand and constrain the effect as itrelates to asteroids (Moroz et al. 1996; Hiroi et al. 2006;Lazzarin et al. 2006; Gaffey 2010 and references therein).

Gaffey (2010) showed that asteroids might beexperiencing multiple types of space weatheringprocesses. Plots of band depth versus albedo and spectralslope versus albedo for 243 Ida and 433 Eros differ bothfrom lunar-style space weathering trends and eachother’s trends. Band analysis techniques (i.e., bandcenters) and mineralogical determinations (i.e., Gaffeyet al. 2002) appear to be immune from whatever spaceweathering effects are occurring (Gaffey 2010). It is alsoimportant to note that VNIR spectral slopes and mineralband depth changes can be attributed to a wide varietyof observational and compositional effects, which are noteasy to distinguish (Cloutis et al. 1990; Birlan et al. 2007;Ockert-Bell et al. 2008).

The pyroxene-only bearing asteroids in this articledisplay systematically weaker Band I ± Band IIabsorptions compared with the olivine-bearing asteroids.A pure orthopyroxene sample will display a Band I depthof approximately 50%, whereas the band depths of thepyroxene-bearing asteroids range from approximately 1to 5%. No obvious trend is apparent when plotting BandI depth versus semimajor axis for these asteroids,although the asteroids with the mildly deeper Band Idepths (approximately 3–5%) are located at semimajoraxes from 2.6 to 2.7 AU, whereas those asteroids withBand I depths of 1–2% are found along the entire 2.6–3.2 AU semimajor axis range.

1932 P. S. Hardersen et al.

Table 7. Compilation of reported M- ⁄X-asteroid band centers from Hardersen et al. (2005), Fornasier et al. (2010),Ockert-Bell et al. (2008, 2010), and this work.

AsteroidHardersen et al.Band I center (lm)

Hardersen et al.Band II center(lm)

Ockert-Bell et al.Band I center (lm)

Ockert-Bell et al.Band II center (lm)

Fornasier et al.All band centers

16 Psyche 0.932 ± 0.008 – 0.95 ± 0.01 – 0.430 ± 0.0040.949 ± 0.008

21 Lutetia – – – – No data22 Kalliope 0.94-(?) – 0.90 ± 0.01 0.434 ± 0.005;

0.903 ± 0.008

55 Pandora 0.85-(?), 0.92-(?),0.97-(?) 1.10

– 0.93 ± 0.01 1.94 ± 0.02 0.91 ± 0.010

69 Hesperia 0.923 ± 0.011;

0.909 ± 0.009

1.71–1.85 No data No data 0.430 ± 0.004;

0.951 ± 0.00971 Niobe – – No data No data No data77 Frigga – – 0.87 ± 0.01 – No data97 Klotho – – – – –

110 Lydia 0.914 ± 0.006;0.914 ± 0.004;0.903 ± 0.005

1.71–1.90 0.88 ± 0.01 1.75 0.942 ± 0.008

125 Liberatrix 0.920 ± 0.006 – No data No data –129 Antigone 0.918 ± 0.003;

0.930 ± 0.008– 0.89 ± 0.01 – 1.028 ± 0.010

132 Aethra 0.91-, 1.10-, 1,40-,2.28–2.50+

– No data No data 0.498 ± 0.004

135 Hertha – – 0.91 ± 0.01 – 0.515 ± 0.005;

0.905 ± 0.008136 Austria – – 0.85 ± 0.01 – No data161 Athor No data No data No data No data –184 Dejopeja 0.931 ± 0.004 – No data No data No data

201 Penelope 0.932 ± 0.005;0.945 ± 0.008;0.917 ± 0.010

– No data No data –

216 Kleopatra 0.923 ± 0.003 – 0.91 ± 0.01 1.99 ± 0.02 0.429 ± 0.004;0.969 ± 0.008

224 Oceana – – – – –

250 Bettina 0.914 ± 0.007 – 0.91 ± 0.01 – 0.885 ± 0.010325 Heidelberga – – No data No data –338 Budrosa 0.939 ± 0.008 1.933 ± 0.018 No data No data 0.425 ± 0.004;

0.876 ± 0.010

347 Pariana 0.919 ± 0.008 – 0.94 ± 0.01 1.79 ± 0.02 0.871 ± 0.008369 Aeria 0.920 ± 0.003 1.865 ± 0.023 No data No data 0.884 ± 0.008382 Dodona 0.934 ± 0.007 – No data No data –

413 Edburga – – No data No data No data417 Suevia Flat feature from �

0.82 to 1.17– No data No data No data

418 Alemannia 0.922 ± 0.010;0.910 ± 0.005

– No data No data –

441 Bathilde – – 0.87 ± 0.01 – –

497 Iva 0.941 ± 0.006 1.918 ± 0.019 0.90 ± 0.01 – No data498 Tokio – – No data No data 0.430 ± 0.005;

1.159 ± 0.008504 Cora 0.85-, 0.91-, 1.07- – No data No data No data

516 Amherstia 0.927 ± 0.003 1.911 ± 0.039 No data No data 0.965 ± 0.008;1.949 ± 0.010

558 Carmen 0.940 ± 0.006 – No data No data –

678 Fredegundis No data No data 0.91 ± 0.01 – No data739 Mandeville – – No data No data No data

NIR spectra for 45 M- ⁄X-asteroids 1933

A pure olivine sample will display a Band I depth ofapproximately 45%, whereas the band depths of theolivine-bearing asteroids range from approximately 4 to10%. The band depths of the olivine-bearing asteroids,however, are consistent with the band depths for the CO,CK, and R chondrites in this study. The opaque mineralcomponent of these meteorite types (discussed above) isthe likely cause of the resulting spectral band depthweakness and does not require a space weatheringmechanism.

The four potentially phyllosilicate-bearing asteroidsexhibit one or more weak absorption features, but thesefeatures are similarly weak in laboratory VNIR spectraof the same minerals (Calvin and King 1997). Theweakness of these features is attributed to crystal fieldtransitions (Burns 1993).

The cause(s) of mineral absorption band weakness(or absence) in asteroid NIR spectra include spaceweathering, surface opaque minerals, the absence ofFe2+-bearing minerals, and metal. If space weathering isthe cause of the band weakness for these asteroids, thenthe mechanism must be able to explain differential,mineral-dependent space weathering effects. Continuingwork is necessary to disentangle these variables to enablea more robust understanding of this mechanism and itseffects on NIR spectra.

CONCLUSIONS

Significant advances in understanding themineralogicaland compositional nature of the M- ⁄X-asteroid

population has been made in the past 15 yr. This articlereports significant mineralogical and spectral diversityamong a group of 45 M- ⁄X-asteroids. The primaryresults include:1. Weak NIR absorption features in the approximately

0.9 ± 1.9 lm region are common and include 42%of the asteroids in this study. These asteroids arefound throughout the main asteroid belt, exhibitband depths from approximately 1 to 5%, and BandI centers typically at k < 0.93 lm. These asteroidsare dominated by surface orthopyroxene, whereas afew asteroids with Band I > 0.94 lm includesorthopyroxene and Type B clinopyroxene. Meteoriteanalogs for these asteroids include mesosiderites,silicate-bearing iron meteorites, CB ⁄CH chondrites,and metallic cores of differentiated asteroid parentbodies with remnant mantle surface pyroxene.

2. The three olivine-bearing asteroids reported here arerestricted to the Eos dynamical family. As a group,these olivine ± pyroxene-bearing asteroids havepossible affinities to the CO chondrites, CKchondrites, CV chondrites, ureilites, brachinites, andR chondrites. The band parameters for several Eosfamily asteroids and the above meteorite typessuggest that CO chondrites are most consistent withthe spectral traits of the measured Eos familyasteroids.

3. Four potentially phyllosilicate ± hydroxide-bearingasteroids are located in the central region of themain asteroid belt. We report what appears to be thefirst NIR spectral absorption features in the

Table 7. Continued. Compilation of reported M- ⁄X-asteroid band centers from Hardersen et al. (2005), Fornasieret al. (2010), Ockert-Bell et al. (2008, 2010), and this work.

AsteroidHardersen et al.Band I center (lm)

Hardersen et al.Band II center(lm)

Ockert-Bell et al.Band I center (lm)

Ockert-Bell et al.Band II center (lm)

Fornasier et al.All band centers

755 Quintilla No data No data No data No data 0.904 ± 0.010;1.369 ± 0.010;

1.610 ± 0.008;1.864 ± 0.010

758 Mancunia – – 0.87 ± 0.01 1.90 ± 0.02 No data

766 Moguntia 1.068 ± 0.004 – No data No data No data771 Libera No data No data 0.90 ± 0.01 – No data779 Nina No data No data 0.93 ± 0.01 1.78 ± 0.02 No data

785 Zwetana – – 0.62 ± 0.01 1.68 ± 0.02 –796 Sarita 0.914 ± 0.008 1.846 ± 0.027 No data No data No data798 Ruth 1.056 ± 0.004 – No data No data –849 Ara No data No data No data No data –

857 Glasenappia Flat feature from �0.94 to 1.08 1.958 ± 0.028 No data No data No data860 Ursina Weak inflection? – No data No data –872 Holda Weak inflection? – 0.95 ± 0.01 – 0.965 ± 0.020

931 Whittemora Weak inflection? – No data No data No data1210 Morsovia 1.047 ± 0.009 – No data No data No data1461 Jean-Jacques – – No data No data No data

1934 P. S. Hardersen et al.

approximately 0.8–2.5 lm range consistent withphyllosilicate or hydroxide minerals. Fe-richchamosite is suggested as a primary surface mineralfor some regions on 132 Aethra. The locations ofthese asteroids are consistent with the predictedlocations of hydrous asteroids heated by 26Al via themodel of Grimm and McSween (1993). CI ⁄CMchondrites are not meteorite analogs due to themuch higher albedos reported for these asteroids.This suggests that these asteroids are from objectsnot represented in the terrestrial meteorite collection.

4. M- ⁄X-asteroids with featureless NIR spectracompose 40% of our sample, but display noticeablevariations in spectral slope. Enstatite chondrites andNiFe meteorites remain viable interpretations formost of the asteroids in this group.

5. While taxonomies are useful tools to categorizeasteroids into similar groups, their utility in exploringthe mineralogical diversity of a taxonomic group’smembers is limited. Higher-quality instrumentationand data reduction protocols, along with the ability toreliably detect weak NIR spectral absorptionfeatures, allow enhanced opportunities to discovermineralogical diversity within a single taxonomicclass.

6. The asteroids in this article are, for the most part,genetically unrelated. Interpretations and potentialmeteorite analogs for these asteroids should bedecoupled; each asteroid should be consideredindividually and usually assumed to derive from aunique parent body.

Acknowledgments––The authors thank reviewers LucyMcFadden, Taki Hiroi, Maureen Ockert-Bell, and theMAPS Associate Editor, Beth Clark, for comments thatimproved this manuscript. This work has been supportedby NASA Planetary Astronomy Program grantNNG05GH01G. The contributions of Driss Takir,Sherry Fieber-Beyer, Beth Reynolds, Paul Abell, andMichael Gaffey to this work are noted and appreciated.The authors thank the NASA Infrared TelescopeFacility, Alan Tokunaga, Bobby Bus, John Rayner, andtelescope operators Bill Golisch, David Griep, PaulSears, and Eric Volquardsen for facilitating the results ofthis paper. Please forgive the lead author (PSH) fornearly burning out the brakes on an IRTF vehicle duringhis first-ever observing run in April 2001.

Thanks to the Canadian Space Agency, the CanadaFoundation for Innovation, the Manitoba ResearchInnovations Fund, NSERC, and the University ofWinnipeg for providing funding to EAC to establish andoperate the Planetary Spectrophotometer Facility at theUniversity of Winnipeg.

Author T. Mothe-Diniz was supported by theConselho Nacional de Desenvolvimento Cientıfico eTecnologico––CNPq ⁄Brasil and by the Fundacao deAmparo a Pesquisa do Estado do Rio de Janeiro––FAPERJ.

Editorial Handling––Dr. Beth Ellen Clark

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