Standard asteroid physical characteristics

For the majority of numbered asteroids, almost nothing is known apart from a few physical parameters and orbital elements and some physical characteristics are often only estimated. The physical data is determined by making certain standard assumptions.

Data from the IRAS minor planet survey or the Midcourse Space Experiment (MSX) minor planet survey (available at the Planetary Data System Small Bodies Node (PDS)) is the usual source of the diameter.

For many asteroids, lightcurve analysis provides estimates of pole direction and diameter ratios. Pre-1995 estimates collected by Per Magnusson are tabulated in the PDS, with the most reliable data being the syntheses labeled in the data tables as "Synth". More recent determinations for several dozens of asteroids are collected at the web page of a Finnish research group in Helsinki which is running a systematic campaign to determine poles and shape models from lightcurves.

These data can be used to obtain a better estimate of dimensions. A body's dimensions are usually given as a tri-axial ellipsoid, the axes of which are listed in decreasing order as a×b×c. If we have the diameter ratios μ = a/b, ν = b/c from lightcurves, and an IRAS mean diameter d, one sets the geometric mean of the diameters ${\displaystyle d=(abc)^{\frac {1}{3}}\,\!}$ for consistency, and obtains the three diameters:

Barring detailed mass determinations, the mass M can be estimated from the diameter and (assumed) density values ρ worked out as below.

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