Radar observations and a physical model of Asteroid 4660 Nereus, a prime space mission target
Abstract
NearEarth Asteroid 4660 Nereus has been identified as a potential spacecraft target since its 1982 discovery because of the low deltaV required for a spacecraft rendezvous. However, surprisingly little is known about its physical characteristics. Here we report Arecibo (Sband, 2380MHz, 13cm) and Goldstone (Xband, 8560MHz, 3.5cm) radar observations of Nereus during its 2002 close approach. Analysis of an extensive dataset of delayDoppler images and continuous wave (CW) spectra yields a model that resembles an ellipsoid with principal axis dimensions X=510±20 m, Y=330±20 m and Z=24110+80 m. The pole direction is approximately located at ecliptic pole longitude and latitude of λ=+25°, β=+80° with the uncertainty radius of 10°. Our modeling yields a refined rotation period of 15.16±0.04 h. Nereus has a circular polarization (SC/OC) ratio of 0.74±0.08, which implies substantial nearsurface centimetertodecimeter scale roughness. Dynamical analysis of our model suggests that YORP alteration of the rotation period may become evident within a few years. Nereus has two stable synchronous orbits where natural material may remain in orbit, while most asteroids observed to date do not have such stable synchronous orbits. We also find that spacecraft orbits about Nereus are feasible.
 Publication:

Icarus
 Pub Date:
 May 2009
 DOI:
 10.1016/j.icarus.2008.12.029
 Bibcode:
 2009Icar..201..153B