M-type asteroids are a relatively rare type of asteroid in the main asteroid belt, located between Mars and Jupiter. Some of them are made of nickel-iron. While they are mostly reddish un color it is very difficult to determine whether an asteroid is metallic with optical telescopes, so the best instrument is radiotelescope. The most known and the largest of M-type asteroids is 16 Psyche which is thought to be metallic core of protoplanet that was fragmented by impacts.
Radar observations performed by Arecibo allowed to generate 3D shape model of Psyche with a resolution of about 15 km.
Image: Arecibo observatory
All sides of the asteroid are shown. Colors represent the deviation in topography from the surface mean. The numbers in the top left corner of each image are the longitude and latitude, respectively, of the image center. The most interesting features are two ∼50-70 km wide very deep depressions near its south pole (lower right picture), probably impact craters. It is possible that in these craters metals, much heavier than iron could be found as heavy elements go down in molten alloys.
The shape model has dimensions 279 × 232 × 189 km (± 10%), and is 6% larger than, but within the uncertainties of, the most recently published size and shape model based on optical observations.
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. It is highly possibly that the surface of Psyche consists of metal rubble - this confirm new measured data about mean density which is 4500 ± 1400 kg/m3.
The new data are of great importance for NASA as it develops mission to Psyche with start in 2022 and arrival in 2026.
Image: SSL/ASU/P. Rubin/NASA/JPL-Caltech
Sources:
[1] http://adsabs.harvard.edu/abs/2017Icar..281..388S
[2] http://outreach.naic.edu/ao/blog/radar-observations-and-shape-model-asteroid-16-psyche