### 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.