Radar Imaging and Physical Characterization of Near-Earth Asteroid (162421) 2000 ET70

TL;DR

This study used radar imaging to create a detailed 3D shape model of near-Earth asteroid 2000 ET70, revealing its size, surface features, rotation, and low albedo, aiding in trajectory prediction.

Contribution

First detailed radar-based shape and surface characterization of asteroid 2000 ET70, providing insights into its physical properties and rotation state.

Findings

Size approximately 2.6 km x 2.2 km x 2.1 km

Surface features include ridges and concavities

Rotation period of about 8.96 hours

Abstract

We observed near-Earth asteroid (162421) 2000 ET70 using the Arecibo and Goldstone radar systems over a period of 12 days during its close approach to the Earth in February 2012. We obtained continuous wave spectra and range-Doppler images with range resolutions as fine as 15 m. Inversion of the radar images yields a detailed shape model with an effective spatial resolution of 100 m. The asteroid has overall dimensions of 2.6 km X 2.2 km X 2.1 km (5% uncertainties) and a surface rich with kilometer-scale ridges and concavities. This size, combined with absolute magnitude measurements, implies an extremely low albedo (~2%). It is a principal axis rotator and spins in a retrograde manner with a sidereal spin period of 8.96 +/- 0.01 hours. In terms of gravitational slopes evaluated at scales of 100 m, the surface seems mostly relaxed with over 99% of the surface having slopes less than 30 degrees, but there are some outcrops at the north pole that may have steeper slopes. Our precise measurements of the range and velocity of the asteroid, combined with optical astrometry, enables reliable trajectory predictions for this potentially hazardous asteroid in the interval 460-2813.