Scientists Probe Green Comet

Feb 20, 2009
Scientists Probe Green Comet
This image of Comet Lulin taken Jan. 28 merges data acquired by Swift's Ultraviolet/Optical Telescope (blue and green) and X-Ray Telescope (red). At the time of the observation, the comet was 99.5 million miles from Earth and 115.3 million miles from the sun. Credit: Univ. of Leicester/NASA/Swift/Carter et al.

(PhysOrg.com) -- Space scientists from the University of Leicester are keeping a close eye on a ‘green comet’ fast approaching the Earth - reaching its nearest point to us on February 24.

Comet Lulin will streak by the earth within 38 million miles - 160 times farther than the moon -and is expected to be visible to the naked eye. Discovered only a year ago, the comet gains its green colour from poisonous cyanogen and diatomic carbon gases in its atmosphere.

This will be the comet’s first visit to the Earth’s inner solar system- and will enable the team from the University of Leicester to gain valuable insights into the comet.

They are using NASA's Swift satellite to monitor Comet Lulin as it closes on Earth. The spacecraft has recorded simultaneous ultraviolet and X-ray images of a comet.

“Swift is the ideal spacecraft with which to observe this comet”, said Jenny Carter, a scientist working with Dr Andrew Read at the University of Leicester, UK. “We alerted the Swift team that the comet might be visible” said Dr Read “and they quickly responded to take images using both the X-ray (XRT) and Ultraviolet/Optical Telescopes (UVOT) on-board.”

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.'

Carter added: “It is important to carry out these observations as they give us clues about the origin of comets and the solar system".

As the University of Leicester has played a major role in developing Swift's X-Ray Telescope and is an important centre for the study of high-energy emission from objects within our Solar System, it is an ideal place for this study to be carried out.

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.

On Jan. 28, Swift trained its Ultraviolet/Optical Telescope and X-Ray Telescope on Comet Lulin. "The comet is quite active," said team member Dennis Bodewits, a NASA Postdoctoral Fellow at the Goddard Space Flight Center in Greenbelt, Maryland, USA. "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.

The UVOT includes a prism-like device called a grism, which separates incoming light by wavelength. The grism's range includes wavelengths where the hydroxyl molecule is most active. "This gives us a unique view into the types and quantities of gas a comet produces" Bodewits explains.

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 tail of hydroxyl molecules.

Farther from the comet, even the hydroxyl molecule succumbs to solar ultraviolet radiation. It breaks into its constituent oxygen and hydrogen atoms. "The solar wind -- a fast-moving stream of particles from the sun -- interacts with the comet's broader cloud of atoms. This causes the solar wind to light up with X-rays, and that's what Swift's XRT sees," said Stefan Immler, also at Goddard.

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 and is losing a lot of gas, its X-ray emitting region extends in a large cloud far sunward of the comet.

Geronimo Villanueva completes the team working on the comet data at Goddard.

“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,” notes Carter. “They will allow us to build up a more complete 3-D picture of the comet during its flight through the solar system.”

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.

Provided by University of Leicester

Explore further: NASA spacecraft almost to Pluto: Smile for the camera!

add to favorites email to friend print save as pdf

Related Stories

Davos elites warned about catastrophic cyberattacks

8 hours ago

Attacks on power plants, telecommunications and financial systems, even turning all of Los Angeles' traffic lights green: Davos elites were warned Saturday of the terrifying possibilities of modern cyber ...

Recommended for you

Elon Musk's SpaceX drops lawsuit against Air Force

6 hours ago

A spacecraft company run by billionaire Elon Musk has dropped a lawsuit alleging the U.S. Air Force improperly awarded a contract to launch military satellites to a joint venture between Boeing and Lockheed Martin.

NASA spacecraft almost to Pluto: Smile for the camera!

Jan 23, 2015

It's showtime for Pluto. NASA's New Horizons spacecraft has traveled 3 billion miles and is nearing the end of its nine-year journey to Pluto. Sunday, it begins photographing the mysterious, unexplored, icy ...

Gullies on Vesta suggest past water-mobilized flows

Jan 23, 2015

(Phys.org)—Protoplanet Vesta, visited by NASA's Dawn spacecraft from 2011 to 2013, was once thought to be completely dry, incapable of retaining water because of the low temperatures and pressures at its ...

SOHO and Hinode offer new insight into solar eruptions

Jan 23, 2015

The sun is home to the largest explosions in the solar system. For example, it regularly produces huge eruptions known as coronal mass ejections – when billions of tons of solar material erupt off the sun, ...

User comments : 2

Adjust slider to filter visible comments by rank

Display comments: newest first

barakn
1 / 5 (1) Feb 20, 2009
"Comet Lulin, which is formally known as C/2007 N3, was discovered last year by astronomers at Taiwan's Lulin Observatory."

Last year was 2008.
seanpu
not rated yet Feb 23, 2009
"A comet is a clump of frozen gases mixed with dust. These 'dirty snowballs'"

the dirty snowball theory has been thrown out. every comet / asteroid we've visited has no relation to a dirty snowball.

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.