The Shape of Eros

Ostro, S. J., K. D. Rosema, and R. F. Jurgens (1990). Icarus 84, 334-351.

The convex hull of Eros' polar silhouette, estimated from radar echo spectra obtained in 1975 by R. J. Jurgens and R. M. Goldstein (1976, Icarus 28, 1-15), provides new information about this asteroid's shape. Monte Carlo simulations are used to optimize the estimation, to explore the nature and severity of associated errors, and to guide bias-correction procedures. Eros' hull is shaped like a rounded trapezoid, whose long and short bases faced Earth during epochs of primary and secondary maxima, respectively, in the January 1975 optical lightcurves. The non-axisymmetric shape helps to explain odd harmonics in Eros' echo spectral signature as a function of rotation phase, whose presence cannot be accounted for by homogeneous ellipsoid models. The extreme breadths of Eros' polar silhouette are within a few kilometers of 35 and 16 km. Additional constraints of Eros' figure are obtained by inverting an optical lightcurve to estimate the asteroid's "mean cross section," which is a two-dimensional average of the three-dimensional shape. Eros' mean cross section and polar silhouette have similar elongations. The hull estimate permits previously reported radar time-delay and Doppler-frequency measurements to be referenced directly to Eros' center of mass.

Asteroid Radar Astronomy Publications