The Trajectory Dynamics of Near-Earth Asteroid 101955 (1999 RQ36)
Abstract
101955 (1999 RQ36) is a 500-m diameter Potentially Hazardous Asteroid and the target of the OSIRIS-REx sample return mission. September 2011 radar ranging from the Arecibo Observatory to 1999 RQ36 unambiguously reveals the action of the Yarkovsky effect, which manifests as a mean semimajor axis drift, da/dt = -18.99±0.10 ×10-4 AU/My. Here da/dt is primarily dependent on the body’s thermal inertia Γ, bulk density ρ, diameter, and obliquity. From radar we have an excellent estimate of the last two of these, while modeling of Spitzer and Herschel space telescope observations indicates Γ=600±150 Jm-2s-0.5K-1 [1,2]. Using these data and applying the Yarkovsky model described in [3] leads to an estimate of the bulk density of ρ=0.97±0.15 g/cm3. This suggests a macroporosity of 50-60%, assuming a material density of 2-2.5 g/cm3. The new orbit for 1999 RQ36 is extraordinarily precise, as measured by the 6 m formal uncertainty in the osculating semimajor axis. Eleven approaches to Earth closer than 0.05 AU over a span of 481 years, from 1654 to 2135, can be confidently predicted. Prior work showed a cumulative impact probability 10-3 late in the 22nd century, with most of the risk associated with a potential Earth encounter in 2182 [4]. The new radar astrometry allows us to eliminate the 2182 impact hazard, but we find that the increased orbital precision increases the impact probabilities of those potential impacts that persist, as well as revealing new potential impacts in the same timeframe that were previously too remote to resolve. Thus, the tabulation of potential impacts is qualitatively similar, with the cumulative impact probability still of order 10-3. References: [1] Emery et al. (2010) LPS XLI, Abstract #1533. [2] Mueller et al. (2012), A&A, in prep. [3] Vokrouhlický, Milani, Chesley (2000), Icarus, 148, 118-138. [4] Milani et al. (2009) Icarus, 203, 460-471.
- Publication:
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AAS/Division of Dynamical Astronomy Meeting #43
- Pub Date:
- May 2012
- Bibcode:
- 2012DDA....43.0708C