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We determined the mass of asteroid 433 Eros, its lower order gravitational harmonics, and rotation state, using ground-based Doppler and range tracking of the Near Earth Asteroid Rendezvous (NEAR)--Shoemaker spacecraft and images of the asteroid's surface landmarks. The mass of Eros is (6.687 ± 0.003) x [10.sup.18] grams, which, coupled with our volume estimate, implies a bulk density of 2.67 ± 0.03 grams per cubic centimeter. The asteroid appears to have a uniform density distribution. The right ascension and declination of the rotation pole are 11.37 ± 0.05 and 17.22 ± 0.05 degrees, respectively, and at least over the short term, the rotation state of Eros is stable with no measurable free precession of the spin pole. Escape velocities on the surface vary from 3.1 to 17.2 meters per second. The dynamical environment of Eros suggests that it is covered with regolith and that one might expect material transport toward the deepest potential wells in the saddle and 5.5-kilometer crater regions., Radio science analyses offer one of the few techniques available for probing the internal structure of asteroids. Doppler and range measurements of the orbiting spacecraft, together with optical observations of [...]

The Near Earth Asteroid Rendezvous (NEAR) spacecraft flew within 3830 kilometers of asteroid 433 Eros on 23 December 1998. The gravitational perturbation on NEAR was evident in the spacecraft tracking data, Ground-based Doppler and range tracking of the spacecraft as well as spacecraft images of the asteroid's center of figure and surface features were used to determine the mass and rotation pore of Eros. The mass of Eros is (7.2 ± 1.8) x [10.sup.18] grams and, coupled with a volume estimate provided by the NEAR imaging team, this mass suggests a bulk density of 2.5 ± 0.8 grams per cubic centimeter. The rotation pole position is 15.6 (± 3.7) degrees in right ascension and 16.4 (± 1.8) degrees in declination, which is consistent with ground-based and NEAR imaging team observations., Asteroid 433 Eros is second only to 1036 Ganymede as the largest near-Earth asteroid, and its orbital characteristics make it an accessible target for a spacecraft rendezvous mission. Its general [...]

Active asteroids are those that show evidence of ongoing mass loss. We report repeated instances of particle ejection from the surface of (101955) Bennu, demonstrating that it is an active asteroid. The ejection events were imaged by the OSIRIS-REx (Origins, Spectral Interpretation, Resource Identification, and Security-Regolith Explorer) spacecraft. For the three largest observed events, we estimated the ejected particle velocities and sizes, event times, source regions, and energies. We also determined the trajectories and photometric properties of several gravitationally bound particles that orbited temporarily in the Bennu environment. We consider multiple hypotheses for the mechanisms that lead to particle ejection for the largest events, including rotational disruption, electrostatic lofting, ice sublimation, phyllosilicate dehydration, meteoroid impacts, thermal stress fracturing, and secondary impacts., (Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)