Eros: Calibration of Radar-Based Shape Constraints from First NEAR Images

Eros is the first asteroid for which a shape model based on radar observations is available that has been imaged at useful resolutions by a spacecraft.

Mitchell, Hudson, Ostro, and Rosema (Icarus 131, 4-14, 1998) used new analysis techniques to constrain the shape of 433 Eros with Goldstone radar data obtained during the asteroid's close approach in 1975. A previous analysis of these data (Ostro, Rosema, and Jurgens, Icarus 84, 334-351, 1990) used estimates of the echo's spectral edge frequencies as a function of asteroid rotation phase to constrain the pole-on silhouette's convex envelope (the solid curves in the figure; the dots define the uncertainty). The more sophisticated approach used the echo's full Doppler-frequency distribution (~15 times more data points) to constrain concavities within this convex envelope. The radar echoes are weak and north-south ambiguous, so the resolution of any shape model is necessarily low, and the pole-on silhouette is the only aspect of the shape that could be constrained. The shaded shapes in the figure show results of two approaches to finding that silhouette. Both approaches yielded models tapered along their lengths, with one or more prominent concavities on one side but not the other. There wasn't enough information to determine the exact nature of the concavities.

Recent images of Eros obtained by the NEAR Spacecraft show the asteroid's shape in detail.