Mullard Space Science Laboratory

P R E S S  R E L E A S E
12 July 2005
REF: DI120705

Scientists Measure How Deep "Deep Impact" Was, With X-rays

Here come the X-rays, on cue. UK and US scientists, studying the Deep Impact collision using NASA's Swift satellite report that comet Tempel 1 got brighter and brighter in X-ray light over the weekend of July 9-10.

The X-rays provide a direct measurement of how much material was kicked up in the impact. This is because the X-rays are created by the newly liberated material lifted into the comet's thin atmosphere and illuminated by the high-energy solar wind from the Sun. The more material liberated, the more X-rays are produced.

Swift data of the water evaporation on comet Tempel 1 also may provide new insights into how solar wind can strip water from planets such as Mars.

"Prior to its rendezvous with the Deep Impact probe, the comet was a rather dim X-ray source," said Dr. Paul O'Brien of the Swift team at the University of Leicester. "How things change when you ram a comet with a copper probe travelling over 20,000 miles per hour. The X-ray light we detect now is generated by debris created by the collision combined with material naturally coming off the comet. We can get a solid measurement of the amount of material released."

"It takes several days after an impact for surface and sub-surface material to reach the comet's upper atmosphere, or coma," said Dr. Dick Willingale, also of the University of Leicester. "We expected the X-ray production to peak this weekend and it has. These data will enable us to assess how much comet material was released from the impact."

Based on preliminary X-ray analysis, O'Brien estimates that several tens of thousands of tons of material were released, enough to bury a football field under 10 metres of comet dust. Observations and analysis are ongoing in the United Kingdom and at the Swift Mission Operations Centre at Penn State University.

Swift is providing the only simultaneous multi-wavelength observation of this rare event, with a suite of instruments capable of detecting visible light, ultraviolet light, X-rays, and gamma rays. Different wavelengths reveal different secrets about the comet.

The Swift team can compare the satellite's ultraviolet data with the X-ray data. The ultraviolet light was created by material entering into the lower region of the comet's atmosphere; the X-rays come from the upper regions. The Swift data show that the UV light peaked within a day of impact whereas the X-ray light took about 5 days. Professor Keith Mason, from University College London, said "Swift is a nearly ideal observatory for making these comet studies, as it combines both a rapidly responsive scheduling system with both X-ray and optical/UV instruments in the same satellite."

"For the first time, we can see how material liberated from a comet's surface migrates to the upper reaches of its atmosphere," said Prof. John Nousek, Director of Mission Operations at Penn State. "This will provide fascinating information about a comet's atmosphere and how it interacts with the solar wind. This is all virgin territory."

Nousek said Deep Impact's collision with comet Tempel 1 is like a controlled laboratory experiment of the type of slow evaporation process from solar wind that took place on Mars. The Earth has a magnetic field that shields us from solar wind, a particle wind composed mostly of protons and electrons moving at high velocities. Mars lost its magnetic field billions of years ago, and the solar wind stripped the planet of water.

Comets, like Mars and Venus, have no magnetic fields. Comets become visible largely because ice is evaporated from their surface with each close passage around the Sun. Water is dissociated into its component atoms by the bright sunlight and swept away by the fast-moving and energetic solar wind. Scientists hope to learn about this evaporation process on Tempel 1 now occurring quickly - over the course of a few weeks instead of a billion years - as the result of a planned, human intervention.

Swift's "day job" is detecting distant, natural explosions called gamma-ray bursts and creating a map of X-ray sources in the universe. Swift's extraordinary speed and agility enable scientists to follow Tempel 1 day by day to see the full effect from the Deep Impact collision.


For the latest news on Swift analysis of comet Tempel 1, refer to:







High-resolution images and videos are available on the web at:




Dr Paul O'Brien, University of Leicester
Tel: 0116 252 5203. Email:

Dr Dick Willingale, University of Leicester
Tel: 0116 252 3356. Email:

Professor Keith Mason, Mullard Space Science Laboratory, UCL
UK Lead Investigator for UV/Optical Telescope Team.
Tel: 01483 204100. Email:

John Nousek, Penn State University
Tel: +1 814-865-7747. Email:,



Gill Ormrod - PPARC Press Office
Tel: 01793 442012. Mobile: 0781 8013509

Ather Mirza - University of Leicester Press Office
Tel: 0116 252 3335

Lynn Cominsky, Swift PIO, Sonoma State University
Tel: 1 707-664-2655. Email:

Barbara K. Kennedy (PIO), Penn State University
Tel: 1 814-863-4682. Email:



The UK role in Swift has been to provide core elements of the narrow field instruments (the X-ray telescope and the UV/Optical telescope), utilising mature technology already developed for the ESA XMM-Newton mission, and the JeT-X instrument.

University of Leicester

Lead role in the X-ray telescope design, focal plane camera assembly and X-ray design (using past experience from JET-X and XMM-Newton). The UK SWIFT Science DATA Centre, at Leicester, will provide an archive of all SWIFT data, with open access for the wider UK astronomical community.

Mullard Space Science Laboratory, UCL

The major part of the UV/Optical telescope was constructed at MSSL using designs and expertise from the XMM-Newton Optical Monitor.

The Deep Impact mission is managed by NASA's Jet Propulsion Laboratory, Pasadena, California. Swift is a medium-class NASA explorer mission in partnership with the Italian Space Agency and the Particle Physics and Astronomy Research Council in the United Kingdom, and is managed by NASA Goddard. Penn State controls science and flight operations from the Mission Operations Center in University Park, Pennsylvania. The spacecraft was built in collaboration with national laboratories, universities and international partners, including Penn State University; Los Alamos National Laboratory, New Mexico; Sonoma State University, Rohnert Park, Calif.; Mullard Space Science Laboratory in Dorking, Surrey, England; the University of Leicester, England; Brera Observatory in Milan; and ASI Science Data Center in Frascati, Italy.