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Astronomers using the NASA Swift Satellite are tracking a spectacular comet as it closes in on Earth and sheds gas and dust from its vaporised ice. Lulin will pass closest to Earth on February 24.

The team, which is led by UK astronomers, is studying the comet to find out more about its chemistry and to gather clues about the origin of comets and the solar system. Swift is a NASA mission in collaboration with the Science and Technology Facilities Council (STFC) in the UK and the Italian Space Agency (ASI).

"Swift is the ideal spacecraft with which to observe this comet", said Jenny Carter from the University of Leicester and lead investigator of the team studying the Lulin comet. "We won't be able to send a space probe to Lulin, but Swift is giving us some of the information we would get from just such a mission."

Dr Julian Osborne, leader of the Swift project at Leicester, said "The wonderful ease of scheduling of Swift and its joint UV and X-ray capability make Swift the observatory of choice for observations like these."

"The comet is releasing a great amount of gas, which makes it an ideal target for X-ray observations," said Andrew Read, also at Leicester.

A comet is a clump of frozen gases mixed with dust. These "dirty snowballs" cast off gas and dust whenever they venture near the sun. Comet Lulin, which is formally known as C/2007 N3, was discovered last year by astronomers at Taiwan's Lulin Observatory. The comet is now faintly visible from a dark site. Lulin will pass closest to Earth - 38 million miles, or about 160 times farther than the moon - on February 24.

"The comet is quite active," said team member Dennis Bodewits, from the Goddard Space Flight Center. "The UVOT data show that Lulin was shedding nearly 800 gallons of water each second." That's enough to fill an Olympic-size swimming pool in less than 15 minutes.

Swift can't see water directly. But ultraviolet light from the sun quickly breaks apart water molecules into hydrogen atoms and hydroxyl (OH) molecules. Swift's UVOT detects the hydroxyl molecules, and its images of Lulin reveal a hydroxyl cloud spanning nearly 250,000 miles, or slightly greater than the distance between Earth and the moon.

In the Swift images, the comet's tail extends off to the right. Solar radiation pushes icy grains away from the comet. As the grains gradually evaporate, they create a thin hydroxyl tail. Further from the comet, even the hydroxyl molecule succumbs to solar ultraviolet radiation. It breaks into its constituent oxygen and hydrogen atoms

This interaction, called charge exchange, results in X-rays from most comets when they pass within about three times Earth's distance from the sun. Because Lulin is so active, its atomic cloud is especially dense. As a result, the X-ray-emitting region extends far sunward of the comet.

"We are looking forward to future observations of Comet Lulin, when we hope to get better X-ray data to help us determine its makeup," noted Carter. "They will allow us to build up a more complete 3-D picture of the comet during its flight through the solar system."

Professor Keith Mason, Chief Executive of the Science and Technology Facilities Council (STFC), said, "Swift is an incredibly successful international project with a large degree of UK involvement. It continues to produce amazing results and has already recorded a wealth of information on gamma ray bursts. By using Swift’s cutting edge technology to look at this comet, we may also be able to gather a great deal of new information about comets."

Notes

Images

Images of Comet Lulin taken by Swift are available from the press office or the NASA website http://www.nasa.gov/mission_pages/swift/bursts/lulin.html

Contact

Julia Short

STFC Press Office

Tel: +44 (0)1793 442 012

Email: julia.short@stfc.ac.uk

Julia Maddock

STFC

Tel +44 1793 442094

Email julia.maddock@stfc.ac.uk 

Dr Jenny Carter (email only until 24th Feb) University of Leicester

Tel: 0116 2525244

Email: jac48@star.le.ac.uk

Dr Andy Read

University of Leicester

Tel:0116 2525650

Email: amr30@star.le.ac.uk

Dr Julian Osborne

University of Leicester

Tel:0116 2523598

Email: julo@star.le.ac.uk

UK Swift Science Data Centre - http://www.swift.ac.uk

Swift detects gamma-ray burst and X-ray flashes, and relays their coordinates to the scientific community within seconds. While SWIFT rapidly re-points to continue observations with its high resolution telescopes of the decaying X-ray, UV and optical afterglows that accompany these events, rapid follow-up observations may also be undertaken by other more powerful satellites such as Chandra, the Hubble Space Telescope or XMM satellites and by the European Southern Observatory’s Very Large Telescope (VLT) and other major observatories. These powerful co-ordinated observation programmes, instigated by SWIFT, are slowly unravelling the mystery of star explosions.

Swift, launched in November 2004, is a NASA mission in partnership with the Italian Space Agency and the Science and Technology Facilities Council of 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. Los Alamos National Laboratory provides gamma-ray imaging analysis. The Ultra-Violet -Optical Telescope (UVOT) was constructed at UCL's MSSL. The University of Leicester played a major role in developing Swift's X-Ray Telescope and hosts the UK Swift Science Data Centre.

Science and Technology Facilities Council

The Science and Technology Facilities Council ensures the UK retains its leading place on the world stage by delivering world-class science; accessing and hosting international facilities; developing innovative technologies; and increasing the socio-economic impact of its research through effective knowledge exchange.

The Council has a broad science portfolio including Astronomy, Particle Physics, Particle Astrophysics, Nuclear Physics, Space Science, Synchrotron Radiation, Neutron Sources and High Power Lasers. In addition the Council manages and operates three internationally renowned laboratories:

• The Rutherford Appleton Laboratory, Oxfordshire

• The Daresbury Laboratory, Cheshire