TY - JOUR
T1 - The Nature of Low-albedo Small Bodies from 3μm Spectroscopy
T2 - One Group that Formed within the Ammonia Snow Line and One that Formed beyond It
AU - Rivkin, Andrew S.
AU - Emery, Joshua P.
AU - Howell, Ellen S.
AU - Kareta, Theodore
AU - Noonan, John W.
AU - Richardson, Matthew
AU - Sharkey, Benjamin N.L.
AU - Sickafoose, Amanda A.
AU - Woodney, Laura M.
AU - Cartwright, Richard J.
AU - Lindsay, Sean
AU - McClure, Lucas T.
N1 - Funding Information:
This work is the result of years of effort and numerous discussions. The authors wish to recognize and acknowledge the very significant cultural role and reverence that the summit of Maunakea has always had within the indigenous Hawaiian community. We are most fortunate to have the opportunity to conduct observations from this mountain, and we recognize that we are guests. We thank those who work at the NASA Infrared Telescope Facility, without whom this would have been impossible: the telescope operators, day crew, instrument scientists, administrators, admin assistants, and others. We similarly thank the staff at Hale Pohaku, even including the kitchen crew that was not as good as the other one. Thanks to Eric Volquardsen for allowing us to use the data he collected, and thanks to the online IRTF Legacy Archive and the IRTF Data Archive at IRSA for enabling that use. Consistent support from the NASA Planetary Astronomy program, including grants NNX14AJ39G, NNX09AB45G, NNG05GR60G, and NAG5-10604, enabled these observations and analysis. The SSERVI RESOURCE team and their PI Jen Heldmann provided support for the finishing stages of this project. This research has made use of NASA’s Astrophysics Data System.
Publisher Copyright:
© 2022. The Author(s).
PY - 2022/7/1
Y1 - 2022/7/1
N2 - We present evidence, via a large survey of 191 new spectra along with previously published spectra, of a divide in the 3 μm spectral properties of the low-albedo asteroid population. One group (“sharp types,” or STs, with band centers <3 μm) has a spectral shape consistent with carbonaceous chondrite meteorites, while the other group (“not sharp types,” or NSTs, with bands centered >3 μm) is not represented in the meteorite literature but is as abundant as the STs among large objects. Both groups are present in most low-albedo asteroid taxonomic classes, and, except in limited cases, taxonomic classifications based on 0.5–2.5 μm data alone cannot predict whether an asteroid is an ST or NST. Statistical tests show that the STs and NSTs differ in average band depth, semimajor axis, and perihelion at confidence levels 98% while not showing significant differences in albedo. We also show that many NSTs have a 3 μm absorption band shape like comet 67P and likely represent an important small-body composition throughout the solar system. A simple explanation for the origin of these groups is formation on opposite sides of the ammonia snow line, with the NST group accreting H2O and NH3 and the ST group only accreting H2O, with subsequent thermal and chemical evolution resulting in the minerals seen today. Such an explanation is consistent with recent dynamical modeling of planetesimal formation and delivery and suggests that much more outer solar system material was delivered to the main asteroid belt than would be thought based on the number of D-class asteroids found today.
AB - We present evidence, via a large survey of 191 new spectra along with previously published spectra, of a divide in the 3 μm spectral properties of the low-albedo asteroid population. One group (“sharp types,” or STs, with band centers <3 μm) has a spectral shape consistent with carbonaceous chondrite meteorites, while the other group (“not sharp types,” or NSTs, with bands centered >3 μm) is not represented in the meteorite literature but is as abundant as the STs among large objects. Both groups are present in most low-albedo asteroid taxonomic classes, and, except in limited cases, taxonomic classifications based on 0.5–2.5 μm data alone cannot predict whether an asteroid is an ST or NST. Statistical tests show that the STs and NSTs differ in average band depth, semimajor axis, and perihelion at confidence levels 98% while not showing significant differences in albedo. We also show that many NSTs have a 3 μm absorption band shape like comet 67P and likely represent an important small-body composition throughout the solar system. A simple explanation for the origin of these groups is formation on opposite sides of the ammonia snow line, with the NST group accreting H2O and NH3 and the ST group only accreting H2O, with subsequent thermal and chemical evolution resulting in the minerals seen today. Such an explanation is consistent with recent dynamical modeling of planetesimal formation and delivery and suggests that much more outer solar system material was delivered to the main asteroid belt than would be thought based on the number of D-class asteroids found today.
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U2 - 10.3847/PSJ/ac7217
DO - 10.3847/PSJ/ac7217
M3 - Article
AN - SCOPUS:85138929102
SN - 2632-3338
VL - 3
JO - Planetary Science Journal
JF - Planetary Science Journal
IS - 7
M1 - 153
ER -