Earth and Planetary Science
EPS Near-Surface Geochemistry and Geobiology

Prof. Imke de Pater Obtains New Observations on the Largest M-class Asteroid in the Main Belt

Tuesday, August 23, 2016

Professor Imke de Pater is co-author of “Radar observations and shape model of asteroid 16 Psyche.” The manuscript has been accepted by Icarus and is available online from 12 August 2016 onward.

Using the S-band radar at Arecibo Observatory, the authors observed 16 Psyche, the largest M-class asteroid in the main belt. They then obtained 18 radar imaging and 6 continuous wave runs in November and December 2015, and combined these with 16 continuous wave runs from 2005 and 6 recent adaptive-optics (AO) images to generate a three-dimensional shape model of Psyche. Their model is consistent with a previously published AO image (Hanus et al., 2013) and three multi-chord occultations. Our shape model has dimensions 279 × 232 × 189 km (± 10%), Deff = 226 ± 23 km, and is 6% larger than, but within the uncertainties of, the most recently published size and shape model generated from the inversion of lightcurves (Hanus et al., 2013). Psyche is roughly ellipsoidal but displays a mass-deficit over a region spanning 90° of longitude. There is also evidence for two ∼50–70 km wide depressions near its south pole. Their size and published masses lead to an overall bulk density estimate of 4500 ± 1400 kgm−3. Psyche's mean radar albedo of 0.37 ± 0.09 is consistent with a near-surface regolith composed largely of iron-nickel and ∼40% porosity. Its radar reflectivity varies by a factor of 1.6 as the asteroid rotates, suggesting global variations in metal abundance or bulk density in the near surface. The variations in radar albedo appear to correlate with large and small-scale shape features. Finally their size and Psyche's published absolute magnitude lead to an optical albedo of pv = 0.15 ± 0.03, and there is evidence for albedo variegations that correlate with shape features.

Professor de Pater is jointly appointed in the Berkeley Departments of Astronomy and Earth & Planetary Science. She is broadly interested in adaptive optics and radio observations of giant planets, their rings and satellites.

For the full-length article please click here.