Deep Impact

The movie was put together by Peter Bunclark from observations made by Simon Hodgkin, Gavin Dalton and Will Sutherland.

Object 2008 TC3 was an asteroid that hit the Earth (and debris has since been located in the Sudan: wikipedia). The meteoroid was discovered by Richard A. Kowalski at the Catalina Sky Survey (CSS) 1.5-meter telescope at Mount Lemmon, north of Tucson, Arizona, USA, about a day before the impact.

Observations taken with VISTA on the night of 2008-08-06/7 were produced by tracking the telescope on a fixed sky postion ahead of the asteroid, and taking a hundred exposures during the time it took the object to traverse the entire detector array. The frames, in the J filter and each of 1 second, were processed using the Data Reduction Library written at CASU (for delivery to ESO and for use in the UK VISTA Science pipeline) to produce calibrated pawprints. Normally, “jittered” images of the same field are optimally combined to produce science-quality output; however, for such high time-resoloution work, single, but calibrated, frames must be used.

The object was picked out visually in the ds9 display server, and the pan parameter set to centre it at a number of positions across the detector array. Quadratic polynomials were fitted to relate object (x,y) positions to time of exposure; these functions were then used to centre 2008tc3 in every pawprint (even those in which it fell between detectors). Thus it was possible to pan the “virtual camera” to smoothly follow the asteroid on its rapidly changing course.

Each displayed frame was saved and impressed with the observation time; finally these frames were converted using ImageMagick command-line tools into the animated gif.