Deep Impact: UKIRT tells NASA "You hit it!"

On July 4, the Deep Impact mission aimed a dustbin-sized block of copper at a nearby comet, known as 9P/Tempel-1. For a couple of anxious minutes around 7:52pm Hawaii Standard Time - 05:52 UT - NASA's Jet Propulsion Laboratory in Pasadena waited with bated breath for news that they had struck home. That news came from the United Kingdom InfraRed Telescope (UKIRT), on the top of Mauna Kea, Hawaii.

The UKIRT observing team, led by Professor Steve Miller, comprised Dr Tom Stallard and Bob Barber, from University College London (UCL), and Dr Paul Hirst and Tim Carroll, from UKIRT. UKIRT had done an amazingly good job at detecting the impact. Impact Time was supposed to have been at 05:52 UT, and sure enough, just a few seconds after this time, the telescope guider camera detected a flash as the impactor struck home!

Prof. Miller noted afterwards that there had been a moment's confusion as someone from another observatory came onto the observing telecommunication network (the "telecom") and said impact had been delayed. The UKIRT team looked at the guider and saw immediately that this was impossible - the comet had suddenly become so bright.

As part of UKIRT's preparations for Deep Impact, staff members Chris Davis, Tom Kerr and Thor Wold took a quick look at the comet a week or so before impact. This UFTI image comprises short exposures taken in J, H and K-band filters.

The team immediately got onto the telecom and reported to NASA and the other observers around the world that impact had occurred, and had occurred on time. The comet had doubled in brightness in the course of just over a minute, and it continued to brighten steadily for the next hour.

The purpose of the Deep Impact mission was to improve our understanding of what comets are made of and how they behave. The impactor was designed to punch a hole through the outermost crust, and create a crater ~100 metres across. The whole process was observed by the cameras on board the main spacecraft, as well as by telescopes around th world.

UKIRT's camera picked up the initial explosive flash of impact, plus a jet of hot gas which streamed back out of the whole punched by the impactor for about 70 seconds. Then the rock, ice and dust created by the actual cratering process itself took over, as sunlight was reflected back off the newly created debris. The UKIRT observations showed that material from the crater flew away from the comet into space at around 300 metres per second.

UKIRT also took several spectra of the gases formed after the impact using the CGS4 spectrometer. These are currently being analysed at UCL, but almost certainly show that water vapour was formed from the ice melted by impact. Information from the spacecraft and ground-based observatories around the world are being combined to maximise the scientific return from the missions. Prof. Miller and his team agreed that there's still an awful lot more for us to get out of this exciting event.

Information, images and videos from the Deep Impact mission can be found at: http://deepimpact.jpl.nasa.gov/home/index.html