Radar Observations and the Shape of Near-Earth Asteroid 2008 EV5

TL;DR

This study used radar observations to determine that near-Earth asteroid 2008 EV5 has an oblate spheroid shape with a prominent equatorial ridge and a large concavity, suggesting a rubble-pile structure shaped by YORP spin-up and impact events.

Contribution

First detailed radar-based shape model of asteroid 2008 EV5 revealing its unique features and potential formation history.

Findings

Asteroid 2008 EV5 is a 400m oblate spheroid with a prominent equatorial ridge.

The asteroid's surface is mostly smooth with a large concavity likely caused by an impact.

The shape features suggest a rubble-pile structure shaped by YORP spin-up and impacts.

Abstract

We observed the near-Earth asteroid 2008 EV5 with the Arecibo and Goldstone planetary radars and the Very Long Baseline Array during December 2008. EV5 rotates retrograde and its overall shape is a 400 /pm 50 m oblate spheroid. The most prominent surface feature is a ridge parallel to the asteroid's equator that is broken by a concavity 150 m in diameter. Otherwise the asteroid's surface is notably smooth on decameter scales. EV5's radar and optical albedos are consistent with either rocky or stony-iron composition. The equatorial ridge is similar to structure seen on the rubble-pile near-Earth asteroid (66391) 1999 KW4 and is consistent with YORP spin-up reconfiguring the asteroid in the past. We interpret the concavity as an impact crater. Shaking during the impact and later regolith redistribution may have erased smaller features, explaining the general lack of decameter-scale surface structure.