ExploreNEOs III: Size, Albedo, And Thermal History Of 58+ Low-deltaV NEOs

Abstract

Space missions to NEOs are being planned at all major space agencies, and recently President Obama announced the goal of a manned mission to an NEO. Efforts to find and select suitable targets (plus backup targets) are severely hampered by our lack of knowledge on the physical properties of dynamically favorable NEOs. In particular, current mission scenarios tend to favor primitive low-albedo objects. For the vast majority of NEOs the albedo is unknown. We report new constraints on the size and albedo of NEOs with rendezvous deltaV < 7 km/s. Our results are based on thermal flux data obtained in the framework of our ongoing ExploreNEOs survey (Trilling et al., 2010) using NASA's "Warm Spitzer" space telescope. As of this writing, we have results for 253 objects in hand (including the 58 low-deltaV NEOs presented here); before the end of 2011 we expect to have measured the size and albedo of ~700 NEOs (including probably ~160 low-deltaV NEOs). Due to the nature of our observations, our results are generally more accurate for low-albedo objects than for their high-albedo counterparts. While there are reasons to believe that primitive volatile-rich materials are universally low in albedo, the converse need not be true: The orbital evolution of some objects caused them to lose their volatiles by coming too close to the Sun. For all our targets, we give the closest perihelion distance they are likely to have reached (using orbital integrations from Marchi et al., 2009) and corresponding upper limits on the past surface temperature. Low-deltaV objects for which both albedo and thermal history suggest a primitive composition include (162998) 2001 SK162, (68372) 2001 PM9, and (100085) 1992 UY4. This work is based on observations made with the Spitzer Space Telescope, which is operated by JPL, Caltech under a contract with NASA.