Summary:
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.
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