Target NEO: Open Global Community NEO Workshop Report

DRAFT: RELEASED FOR PUBLIC COMMENTWhile there is much we know, there is still much to be learned about the NEO population thatis directly relevant to NASA’s Exploration Systems Mission Directorate (ESMD) concerns. Thesmaller bodies most likely to be visited by humans are not as well studied as the larger ones.We have relatively few density measurements for small asteroids. There is evidence that satellitesform, evolve, and escape from NEOs, with the escaped bodies becoming independent members ofthe NEO population [17, 18]. The internal structure of such escapees is not obvious, however, noris it clear how such objects might systematically differ from their parents. In addition, roughly 10%of NEOs larger than 200 m in diameter are contact binaries, another possible end state of binaryevolution.Table 2, adapted from the National Research Council’s (NRC’s) “Defending Planet Earth: Near-Earth Object Surveys and Hazard Mitigation Strategies” 3 shows the characterization situation.Table 2 shows that most known NEOs have no characterization at all, while a few hundred to afew thousand have some sort of spectral data available. A handful have been characterized verywell by spacecraft. The potential human spaceflight targets are most likely not yet discovered, andas more data are collected they will be better understood until they are suitably characterized orruled out as viable targets. While observations from WISE and Spitzer have increased the numberof NEOs with known albedos and sizes since Table 2 was created [13, 19], it is still true that formost objects all we know is an absolute magnitude and an orbit of varying quality.Table 2: Characterization Levels for NEOsNumberNEOs larger than 50 m diameter (estimated) ≈ 500,000 - 1,000,000 *NEOs currently known (all sizes) 6,278Rotation periods 450Rotation pole directions 25Detected by radar 246Shapes estimated from radar data 25Shapes estimated from optical data 14Shapes estimated from spacecraft data 2Masses estimated from spacecraft data 2Masses estimated from radar data 4Bulk densities estimated from all sources 10Sizes estimated from all sources 108Near-surface densities estimated from radar 17Spectrally classified into taxonomic groups 489 *** Estimate based on current models.** As of February 2011, as reported by the European Asteroid Research Node (http://earn.dlr.de).4.2 Characterization Information Relevant to Human ExplorationUntil recently, the vast majority of NEO data have been collected in support of either basic scientificresearch or in consideration of the general impact hazard. Much of these data, while not specifically3 Found at http://www.nap.edu/catalog.php?record_id=12842DRAFT: RELEASED FOR PUBLIC COMMENT 11