In March 2013 amateur astronomers at EUMETSAT used weather satellites to spot a comet.
For the first time, they found the Meteosat Second generation satellite, Meteosat-9, had captured an image of a comet.
Observing comets with weather satellites is not easy and it requires an element of luck for a comet to pass the satellite’s field of view at around midnight, during a short period of some weeks around the equinoxes (March and September).
Some time ago members of the EUMETSAT Astronomy Club — Daniel Risquez, Theo Steenbergen and Milan Klinc — set out to prove that comets should actually be visible in satellite imagery, specifically that taken from Meteosat Second Generation in its geostationary orbit, from where it covers parts of open space.
Only the raw Level 1.0 data can be used, where the black area around the Earth disk in the MSG image still represents outer space.
In March 2013 the club got lucky, as the PANSTARRS comet appeared, travelling through the closest point around the sun and visible from the ground with the naked eye.
Initially it was hoped some of the 15-minute time slots of the SEVIRI instrument on board Meteosat-10 would observe the comet, but none of these showed any signs.
The amateur astronomers realised that they might have a better chance with Meteosat-9, which was in rapid scanning mode, scanning more frequently but in shorter time intervals of five minutes.
Some advanced image processing produced a tiny blob of bright pixels at exactly the position predicted in the field of view of channel 4 or Fire Channel (3.9 microns wavelength).
This channel appeared to be the only one where anything was visible due to its higher dynamic range, i.e. higher sensitivity. All together the comet was located in six time slots (animated GIF, 537 KB) from 23:50 UTC on 14 March to 01:00 UTC on 15 March.
Carsten Schaefer, from the EUMETSAT Astronomer Club said: "This was not only the first time ever that a comet was observed with a EUMETSAT satellite instrument, but, as far as we know, with any other meteorological satellite. There was great euphoria when that tiny blob of bright pixels was found."