Radar Observations of Asteroid 1998 ML14

S. J. Ostro, R. S. Hudson, L. A. M. Benner, M. C. Nolan, J. D. Giorgini, D. J. Scheeres, R. F. Jurgens, and R. Rose.

Meteoritics Planet. Sci. 36, 1225-1236 (2001).

Abstract:

Goldstone and Arecibo delay-Doppler radar imaging of asteroid 1998 ML14 shortly after its discovery reveals a 1-km-diameter spheroid with prominent topography on one side and subdued topography on the other. The object's radar and optical properties are typical for S-class near-Earth asteroids. The gravitational slopes of a shape model derived from the images and assumed to have a uniform density are shallow, exceeding 30° over only 4% of the surface. If 1998 ML14's density distribution is uniform, then its orbital environment is similar to a planetary body with a spheroidal gravitational field and is relatively stable. Integration of a radar-refined orbit reveals that the 1998 apparition was the asteroid's closest approach to Earth since at least 1100 and until 2283, when it approaches to within 2.4 lunar distances. Outside of that time interval, orbit uncertainties based on the present set of observations preclude reliable prediction.

The gravitational slope is the acute angle that a plumb line (e.g., a rock hanging from a string) would make with the local surface normal. On almost all of 1998 ML14, the slope is shallower than typical angles of repose of unconsolidated piles of particles. The following figures show the radar-derived computer model of 1998 ML14, with the surface color-coded for gravitational slope. The object rotates about the z axis, which is the principal axis with maximum moment of inertia. The x axis has the minimum moment of inertia.

Nine views (with scale bar and color bar)

One view

This object was the first asteroid imaged by the upgraded Arecibo telescope.