A space telescope that usually studies the most powerful explosions in the universe has set its sights on an approaching comet. Its observations at ultraviolet and X-ray wavelengths should help reveal the comet鈥檚 composition, structure and its interaction with the solar wind.
Comet Lulin, which was discovered in 2008 by astronomers at the Lulin Observatory in Taiwan, will make its closest pass near Earth on 24 February. At that time, it will come within 61 million kilometres, or 40% the Sun-Earth distance, from our planet.
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Amateur astronomers have been watching the approaching comet, which is bright enough to be visible with the naked eye from dark sites (see this image taken by Jack Newton).
Now, NASA鈥檚 Swift space telescope, designed to study cosmic explosions called gamma-ray bursts, has released an image of the comet.
鈥楺uite active鈥�
The icy body is shedding gas and dust as it nears the Sun, whose ultraviolet light breaks apart the comet鈥檚 water molecules into hydrogen atoms and hydroxyl (OH) molecules. Swift鈥檚 Ultraviolet/Optical Telescope (UVOT), which can detect the hydroxyl molecules, found that they fill a cloud more than 400,000 km across.
鈥淭he comet is quite active,鈥� team member Dennis Bodewits of NASA鈥檚 Goddard Space Flight Center in Maryland said in a statement. 鈥淭he UVOT data show that Lulin was shedding nearly 800 gallons of water each second鈥� 鈥� enough to fill an Olympic-size swimming pool in less than 15 minutes.
Farther from the comet, solar ultraviolet radiation also breaks up hydroxyl molecules 鈥� into oxygen and hydrogen atoms.
鈥淭he UV will [teach] us about the composition of the comet,鈥� Bodewits told New 杏吧原创, adding that such studies are interesting because comets might have brought water to Earth several billion years ago.
Glowing wind
Studying the comet in X-rays reveals how it interacts with the solar wind, a stream of charged particles from the Sun. That鈥檚 because positive ions in the solar wind steal electrons from neutral gases, such as hydroxyl, that they hit.
Since the stolen electrons are in an excited state, 鈥渢his makes the solar wind glow when it interacts with a comet鈥�, says Bodewits.
The observations could lend insight into why Mars has such a thin atmosphere. 鈥淭he Earth is lucky because we have a magnetic field that protects us from most of the solar wind,鈥� he continues. 鈥淏ut Mars, lacking such a shield, might have lost its atmosphere because of the interaction with the solar wind.鈥�
Jenny Carter of the University of Leicester in the UK, who is leading Swift鈥檚 studies of the comet, says the team plans to continue its observations. 鈥淲e are looking forward to future observations of Comet Lulin, when we hope to get better X-ray data to help us determine its makeup,鈥� she said. 鈥淭hey will allow us to build up a more complete 3D picture of the comet during its flight through the solar system.鈥�
