¹Z.A. Landsman, ¹H. Campins, ²N. Pinilla-Alonso, ³J. Hanuš, ⁴V. Lorenzi
¹Department of Physics, University of Central Florida, 4111 Libra Drive, PS 430, Orlando, FL 32826
²Department of Earth and Planetary Sciences, University of Tennessee, 1412 Circle Drive, Knoxville, TN 37996
³UNS-CNRS-Observatoire de la Côte d’Azur, BP 4229, 06304 Nice Cedex 4, France
⁴Fundación Galileo Galilei-INAF, Rambla José Ana Fernández Pérez 7, 38712, Breña Baja, TF, Spain

We obtained 2-4 μμm spectra of six M-type asteroids using the SpeX spectrograph at NASA’s Infrared Telescope Facility. We find evidence for hydrated minerals on all six asteroids, including two that were previously thought to be dry. One of our targets, (216) Kleopatra, shows rotational variability in the depth of its 3-μμm feature. We also studied three of these asteroids in the 0.8 – 2.4 μμm range using the NICS instrument at the Telescopio Nazionale Galileo (TNG) in La Palma, Spain. The discovery of spectral signatures of hydrated minerals on so many M-types is difficult to reconcile with a highly thermally evolved composition. It has been suggested that the hydrated minerals could have been delivered to M-types via impacts with primitive objects, or that the M-types may actually have primitive compositions that are not represented in meteorite collections. Understanding the origin and type of hydration on these asteroids will help determine which of these interpretations is correct.

Reference
Landsman ZA, Campins H, Pinilla-Alonso N, Hanuš J, Lorenzi V (2015) A new investigation of hydration in the M-type asteroids. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.01.021]
Copyright Elsevier

¹Lucille Le Corre, ¹Vishnu Reddy, ¹Juan A. Sanchez, ²Tasha Dunn, ³Edward A. Cloutis, ³Matthew R.M. Izawa, ³Paul Mann, ⁴Andreas Nathues
¹Planetary Science Institute, 1700 East Fort Lowell, Suite 106, Tucson, AZ 85719, USA
²Colby College, Department of Geology, 5800 Mayflower Hill, Waterville, ME 04901
³Department of Geography, University of Winnipeg, 515 Portage Avenue, Winnipeg, Manitoba, Canada R3B 2E9
⁴Max-Planck-Institute for Solar System Research, Göttingen, Germany

The detection of olivine on Vesta is interesting because it may provide critical insights into planetary differentiation early in our Solar System’s history. Ground-based and Hubble Space Telescope (HST) observations of asteroid (4) Vesta have suggested the presence of olivine on the surface. These observations were reinforced by the discovery of olivine-rich HED meteorites from Vesta in recent years. However, analysis of data from NASA’s Dawn spacecraft has shown that this “olivine-bearing unit” is actually impact melt in the ejecta of Oppia crater. The lack of widespread mantle olivine, exposed during the formation of the 19 km deep Rheasilvia basin on Vesta’s South Pole, further complicated this picture. Ammannito et al. (2013a) reported the discovery of local scale olivine-rich units in the form of excavated material from the mantle using the Visible and InfraRed spectrometer (VIR) on Dawn. These sites are concentrated in the walls and ejecta of Arruntia (10.5 km in diameter) and Bellicia (41.7 km in diameter) craters located in the northern hemisphere, 350-430 km from Rheasilvia basin’s rim. Here we explore alternative sources for the olivine in the northern hemisphere of Vesta by reanalyzing the data from the VIR instrument using laboratory spectral measurements of meteorites. Our rationale for using the published data set was to bypass calibration issues and ensure a consistent data set between the two studies. Our analysis of the VIR data shows that while the interpretation of their spectra as an olivine-rich unit is correct, the nature and origin of that olivine could be more complicated. We suggest that these olivine exposures could also be explained by the delivery of olivine-rich exogenic material. Our rationale for this study is supported by meteoritical evidence in the form of exogenic xenoliths containing significant amount of olivine in some of the HED meteorites from Vesta. Previous laboratory work on HEDs show that potential sources of olivine on Vesta could be different types of olivine-rich meteorites, either primitive achondrites (acapulcoites, lodranites, ureilites), ordinary chondrites (H, L, LL), pallasites, or carbonaceous chondrites (e.g. CV). Based on our spectral band parameters analysis, the lack of correlation between the location of these olivine-rich terrains and possible mantle-excavating events, and supported by observations of HED meteorites, we propose that a probable source for olivine seen in the northern hemisphere are remnants of impactors made of olivine-rich meteorites. Best match suggests these units are HED material mixed with either ordinary chondrites, or with some olivine-dominated meteorites such as R-chondrites.

Reference
Corre LL, Reddy V, Sanchez JA, Dunn T, Cloutis EA, Izawa MRM, Mann P, Nathues A (2015) Exploring Exogenic Sources for the Olivine on Asteroid (4) Vesta. Icarus (in Press)
Link to Article [doi:10.1016/j.icarus.2015.01.018]

Copyright Elsevier

The most popular papers in January on Cosmochemistry Papers were:

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