The puzzling case of the deep-space debris WT1190F: A test bed for advanced SSA techniques

Abstract

We report on somewhat unique photometric and spectroscopic observations of the deep-space debris WT1190F, which entered Earth atmosphere off the Sri Lanka coast, last 2015 November 13. This striking case has been imposing to the worldwide SSA community as an outstanding opportunity to effectively assess origin and physical nature of such extemporary impactors and appraise their potential threat for Earth. Our observations indicate for WT1190F an absolute magnitude R = 32.45 ± 0.31, with a flat dependence on the phase angle, and slope 0.007 ± 0.002 mag deg−1. The detected short-timescale variability suggests a “four-facet” geometry, with the body likely spinning with a period P = 2.9114 ± 0.0009 s. In the BVRI color domain, WT1190F closely resembled the Planck deep-space probe, a feature that points to an anthropic origin of the object. This match, together with a depressed reflectance around 4000 and 8500 Å may be suggestive of a “grey” (aluminized) surface texture. An analysis is in progress to assess the two prevailing candidates to WT1190F’s identity, namely the Athena II upper stage of the Lunar Prospector mission, and the ascent stage of the Apollo 10 lunar module (LEM LM-4) “Snoopy”, by comparing observations with the synthetic photometry from accurate mock-up modeling and reflectance rendering.