Binary Asteroid Systems: Tidal End States and Estimates of Material Properties

The locations of the fully despun, double synchronous end states of tidal evolution are derived for spherical components. With the exception of nearly equal-mass binaries, binary asteroid systems are in the midst of lengthy tidal evolutions, far from their fully synchronous tidal end states. Calculations of material strength indicate that binaries in the main belt with 100-km-scale primary components are consistent with being made of monolithic or fractured rock as expected for binaries likely formed from sub-catastrophic impacts in the early solar system. To tidally evolve in their dynamical lifetime, near-Earth binaries with km-scale primaries or smaller must be much weaker mechanically than their main-belt counterparts even if formed in the main belt prior to injection into the near-Earth region. Small main-belt binaries with primary components less than 10 km in diameter, depending on their ages, could either be as strong as large main-belt binaries or as weak as near-Earth binaries because the inherent uncertainty in the age of a binary system can affect the calculation of material strength by orders of magnitude. Several other issues are considered, though these typically affect the calculation of material strength by no more than a factor of two. We also find indirect evidence within all three groups of binary asteroids that the inter-component separation may evolve via another mechanism(s) with the binary YORP effect being a likely candidate.Comment: 39 pages, 3 tables, 6 figures, published in Icaru

Orbital period change of Dimorphos due to the DART kinetic impact

The Double Asteroid Redirection Test (DART) spacecraft successfully performed the first test of a kinetic impactor for asteroid deflection by impacting Dimorphos, the secondary of near-Earth binary asteroid (65803) Didymos, and changing the orbital period of Dimorphos. A change in orbital period of approximately 7 min was expected if the incident momentum from the DART spacecraft was directly transferred to the asteroid target in a perfectly inelastic collision1, but studies of the probable impact conditions and asteroid properties indicated that a considerable momentum enhancement (β) was possible2, 3. In the years before impact, we used lightcurve observations to accurately determine the pre-impact orbit parameters of Dimorphos with respect to Didymos4–6. Here we report the change in the orbital period of Dimorphos as a result of the DART kinetic impact to be −33.0 ± 1.0 (3σ) min. Using new Earth-based lightcurve and radar observations, two independent approaches determined identical values for the change in the orbital period. This large orbit period change suggests that ejecta contributed a substantial amount of momentum to the asteroid beyond what the DART spacecraft carried

Successful Kinetic Impact into an Asteroid for Planetary Defense.

While no known asteroid poses a threat to Earth for at least the next century, the catalog of near-Earth asteroids is incomplete for objects whose impacts would produce regional devastation1,2. Several approaches have been proposed to potentially prevent an asteroid impact with Earth by deflecting or disrupting an asteroid1-3. A test of kinetic impact technology was identified as the highest priority space mission related to asteroid mitigation1. NASA's Double Asteroid Redirection Test (DART) mission is the first full-scale test of kinetic impact technology. The mission's target asteroid was Dimorphos, the secondary member of the S-type binary near-Earth asteroid (65803) Didymos. This binary asteroid system was chosen to enable ground-based telescopes to quantify the asteroid deflection caused by DART's impact4. While past missions have utilized impactors to investigate the properties of small bodies5,6, those earlier missions were not intended to deflect their targets and did not achieve measurable deflections. Here we report the DART spacecraft's autonomous kinetic impact into Dimorphos and reconstruct the impact event, including the timeline leading to impact, the location and nature of the DART impact site, and the size and shape of Dimorphos. The successful impact of the DART spacecraft with Dimorphos and the resulting change in Dimorphos's orbit7 demonstrates that kinetic impactor technology is a viable technique to potentially defend Earth if necessary