Radar observations and a physical model of contact binary Asteroid 4486 Mithra

Marina Brozovic, Lance A.M. Benner, Christopher Magri, Steven J. Ostro, Daniel J. Scheeres, Jon D. Giorgini, Michael C. Nolan, Jean Luc Margot, Raymond F. Jurgens, Randy Rose

Research output: Contribution to journalArticlepeer-review

23 Scopus citations


Arecibo (2380. MHz, 12.6. cm) and Goldstone (8560. MHz, 3.5. cm) delay-Doppler radar images obtained in July and August of 2000 reveal that 4486 Mithra is an irregular, significantly bifurcated object, with a central valley ~380. m deep and a long axis potentially exceeding 2. km. With its bimodal appearance, Mithra is a strong candidate for a contact binary asteroid. Sequences of Goldstone images spanning up to 3. h per day show very little rotation and establish that Mithra is an unusually slow rotator. We used Goldstone and Arecibo data to estimate Mithra's 3D shape and spin state. We obtain prograde (λ=337°, β=19°) and retrograde (λ=154°, β=-19°) models that give comparable fits, have very similar shapes roughly resembling an hourglass, and have a rotation period of 67.5 ± 6.0 h. The dimensions of these two models are very similar; for the prograde solution the maximum dimensions are X=2.35 ± 0.15. km, Y=1.65 ± 0.10. km, Z=1.44 ± 0.10. km. Dynamical analysis of our models suggests that in the past, Mithra most likely went through a period of even slower rotation with its obliquity close to 90°. The spin rate is predicted to be increasing due to thermal torque (YORP), while the obliquity, which is currently +68° and +106° for the prograde and retrograde models, respectively, is predicted to move away from 90°.

Original languageEnglish (US)
Pages (from-to)207-220
Number of pages14
Issue number1
StatePublished - Jul 2010
Externally publishedYes


  • Asteroids
  • Radar observations

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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