Detection of λ = 2 cm emission from minor planet 704 Interamnia

λ = 2 cm emission from 704 Interamnia was detected on June 28, 1984, using the VLA. At this time, 704 Interamnia was 2.0 AU distant from Earth. A flux density of 953±53 μJy was measured at 14.9 GHz (50-MHz bandwidth). If 338 km is adopted for the diameter, a disk temperature of 190±15°K results. This temperature is consistent with a rapidly rotating black sphere with 704 Interamnia's diameter. Using published 20-μm infrared data, we infer that a dust-like layer (depth ≥3 cm) covers 704 Interamnia. Most probably, the bulk composition of this layer is identical to that of the outermost shell of the asteroid. Comparison with observations of 15 Eunomia reported earlier suggest that smaller main belt asteroids are covered by a few centimeters of impact gardened material. The physical properties of this layer (especially its depth) make it impossible to infer the dielectric properties of the underlying surface with radio measurements at frequencies above 8 GHz.