Goldstone radar imaging of near-Earth Asteroid 2003 MS2

Abstract We report radar observations of near-Earth Asteroid (NEA) 2003 MS2 with Goldstone (8560 MHz, 3.5 cm) on June 28, 29, and July 4, 2003, shortly after the asteroid’s discovery. Delay-Doppler images with resolutions as fine as 19 m/pixel reveal an unusually angular object with pronounced facets. The longest sequence of images was obtained on July 4 when the asteroid rotated ∼140 deg in 2.7 h. During this interval, bandwidths varied by a factor of ∼1.5 and indicate that 2003 MS2 is an elongated object. The rotation and bandwidth variations evident in the radar images are consistent with the 7 h rotation period and the 0.7 magnitude lightcurve amplitude reported by Muinonen et al. (Muinonen, K. et al. [2007]. Spins, shapes, and orbits for near-Earth objects by Nordic NEON. In: Milani, A., Valsecchi, G.B., Vokrouhlický, D. (Eds.), Near Earth Objects, our Celestial Neighbors: Opportunity and Risk. Cambridge University Press, Cambridge, pp. 309–320). If we adopt the 7 h period, then the maximum and minimum bandwidths place lower bounds on the pole-on dimensions of (0.33 × 0.19) km/cos  δ , where δ is the unknown subradar latitude. The radar and photometric observations by Muinonen et al. constrain the pole directions to ( λ , β ) = (20 ± 20 deg, 0 ± 40 deg) and (200 ± 20 deg, 0 ± 40 deg). The circular polarization ratio of 0.31 ± 0.02 is comparable to that of 25143 Itokawa, suggesting a similar degree of near-surface roughness at decimeter spatial scales.