Spectral properties of near-Earth and Mars-crossing asteroids using Sloan photometry

Abstract

International audienceThe nature and origin of the asteroids orbiting in near-Earth space, including those on a potentially hazardous trajectory, is of both scientific interest and practical importance. We aim here at determining the taxonomy of a large sample of near-Earth and Mars-crosser asteroids and analyze the distribution of these classes with orbit. We use this distribution to identify the source regions of near-Earth objects and to study the strength of planetary encounters to refresh asteroid surfaces. We measure the photometry of these asteroids over four filters at visible wavelengths on images taken by the Sloan Digital Sky Survey (SDSS). These colors are used to classify the asteroids into a taxonomy consistent with the widely used Bus-DeMeo taxonomy (DeMeo et al. [2009]. Icarus 202, 160–180) based on visible and near-infrared spectroscopy. We report here on the taxonomic classification of 206 near-Earth and 776 Mars-crosser asteroids determined from SDSS photometry, representing an increase of 40% and 663% of known taxonomy classifications in these populations. Using the source region mapper by Greenstreet et al. (Greenstreet, S., Ngo, H., Gladman, B. [2012]. Icarus, 217, 355–366), we compare for the first time the taxonomic distribution among near-Earth and main-belt asteroids of similar diameters. Both distributions agree at the few percent level for the inner part of the main belt and we confirm this region as a main source of near-Earth objects. The effect of planetary encounters on asteroid surfaces are also studied by developing a simple model of forces acting on a surface grain during planetary encounter, which provides the minimum distance at which a close approach should occur to trigger resurfacing events. By integrating numerically the orbit of the 519 S-type and 46 Q-type asteroids in our sample back in time for 500,000 years and monitoring their encounter distance with Venus, Earth, Mars, and Jupiter, we seek to understand the conditions for resurfacing events. The population of Q-type is found to present statistically more encounters with Venus and the Earth than S-types, although both S- and Q-types present the same amount of encounters with Mars

Implications for Planetary System Formation from Interstellar Object 1I/2017 U1 (‘Oumuamua)

“…However, we note that a red spectral slope over this range is not unexpected and is characteristic of many primitive objects in our Solar System, (Cruikshank et al 1998;Jewitt & Luu 1999;Bus & Binzel 2002;Sheppard 2010;Carry et al 2016). Whether this slope is something intrinsic to the bulk properties of 1I or a consequence of its surface being altered via energetic processing is unclear.…”

Some things special about NEAs: Geometric and environmental effects on the optical signatures of hydration

“…Rivkin and DeMeo (2018) calculated the theoretical amount of hydrated NEAs according to their spectral group and found 17 ± 3% for the Ch-group and 43 ± 6% corresponding to C-complex bodies. However, observations from Stuart and Binzel (2004) and Carry et al (2016) resulted in the statistics of 6 ± 3% of NEAs showing signs of Ch asteroids, and 16 ± 7% showing signatures of C-complex asteroids. While NEAs are certainly more accessible for sample-return purposes, it is not known today whether they experienced specific, or more intense, geological processes when compared to main-belt asteroids.…”

How Many Hydrated NEOs Are There?

“… Note . Source citation codes are as follows: R12 = Rivkin (); F14 = Fornasier et al (); B05 = Bottke et al (); B02 = Bus and Binzel (); D16 = DeMeo and Carry (); B04 = Binzel et al, ; S04 = Stuart and Binzel (); C16 = Carry et al (); Met Bull = Meteoritical Bulletin ( https://www.lpi.usra.edu/meteor/metbull.php, 9 February 2018 update); NEOs = near‐Earth objects.…”