One of the instruments tuned into Deep Impact is NASA's Swift satellite, normally designed to detect and analyze gamma ray bursts. Swift has been watching the expanding debris cloud, and detected increasing numbers of X-rays every day. This has enabled scientists to accurately measure the total amount of material released. So far, it appears that several tens of thousands of tonnes of debris were blasted off the comet into space; enough to bury a football field under 9 metres (30 feet) of dust.