On 2015 November 13, the small artificial object designated WT1190F entered the Earth atmosphere above the Indian Ocean offshore Sri Lanka after being discovered as a possible new asteroid only a few weeks earlier. At ESA's SSA-NEO Coordination Centre we took advantage of this opportunity to organize a ground-based observational campaign, using WT1190F as a test case for a possible similar future event involving a natural asteroidal body.

Estimated impact location at ground level assuming a purely ballistic entry (no atmospheric drag), computed from different subsets of astrometric data. Dates are in decimal UT days of 2015 November, times are UT of 2015 November 13. The table uses IAU codes for each station: 130=Lumezzane, 309=Paranal (VLT), 598=Loiano, Z66=DeSS. The nominal prediction from the JPL final trajectory reconstruction (Farnocchia 2015b) is reported in the last entry, for comparison purposes. Error bars quoted in the table are semiaxes of the uncertainty ellipses at the 1σ level.

An illustrative astrometric image, taken along the night of 2015 November 12, just a few hours before the WT1190F atmosphere entry, with the 1.52m "Cassini" telescope of the Loiano Observatory (Italy). The telescope was tracking non-sidereally at the apparent angular motion of the target (which appears as a point source near the center of the field), therefore all astrometric reference stars in the frame are severely trailed (approximately 1 arcmin in this example). A correct astrometric reduction of a frame like this requires to fit every reference star with a trailed model, to properly determine their centroid.

The sky-subtracted spectrum of WT1190F obtained on 2016 November 06 with the FORS2 camera of the ESO VLT telescope (in red) with the superposed sky background (in black). The absolute calibration allowed to assess WT1190F's inherent colors, which resulted only slightly redder than the Sun and closely matching those of a typical red giant star of spectral type K3.