  Using 8m-10m class telescopes and their Adaptive Optics (AO) systems, we
conducted a long-term adaptive optics campaign initiated in 2003 focusing on
four binary asteroid systems: (130) Elektra, (283) Emma, (379) Huenna, and
(3749) Balam. The analysis of these data confirms the presence of their
asteroidal satellite. We did not detect any additional satellite around these
systems even though we have the capability of detecting a loosely-bound
fragment (located at 1/4 x RHill) ~40 times smaller in diameter than the
primary. The orbits derived for their satellites display significant
eccentricity, ranging from 0.1 to 0.9, suggesting a different origin. Based on
AO size estimate, we show that (130) Elektra and (283) Emma, G-type and P-type
asteroids respectively, have a significant porosity (30-60% considering CI-CO
meteorites as analogs) and their satellite's eccentricities (e~0.1) are
possibly due to excitation by tidal effects. (379) Huenna and (3749) Balam, two
loosely bound binary systems, are most likely formed by mutual capture. (3749)
Balam's possible high bulk density is similar to (433) Eros, another S-type
asteroid, and should be poorly fractured as well. (379) Huenna seems to display
both characteristics: the moonlet orbits far away from the primary in term of
stability (20% x RHill), but the primary's porosity is significant (30-60%).

Astrophysics