"Long before it's in the papers"
January 28, 2015


“Green Comet” visits neighborhood

Feb. 21, 2009
Courtesy Uni­ver­s­ity of Leices­ter
and World Science staff

As­tro­no­mers are keep­ing a close eye on a green­ish com­et fast ap­proach­ing Earth’s vicin­ity, reach­ing its near­est point to us on Feb. 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 false-color im­age of Com­et Lulin tak­en Jan. 28 merges da­ta ac­quired by Swift's Ul­tra­vi­o­let 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/ et al.)

This will be the com­et’s first vis­it to the Earth’s in­ner so­lar sys­tem. 

Re­search­ers from the Uni­ver­s­ity of Leices­ter, U.K. are us­ing NASA’s Swift sat­el­lite to mon­i­tor Com­et Lulin as it closes on Earth. The space­craft can re­cord images of a com­et sim­ul­ta­ne­ously in ul­tra­vi­o­let and X-ray light. “Swift is the ide­al space­craft with which to ob­serve this com­et,” said Jen­ny Cart­er, an as­tron­o­mer at the uni­ver­s­ity.

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, Md. The tel­e­scope da­ta “show that Lulin was shed­ding nearly 800 gal­lons of wa­ter each sec­ond,” enough to fill an Olympic-sized 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 mo­le­cules. Swift’s tel­e­scope de­tects the hy­drox­yl mo­le­cules. Its im­ages of Lulin show a hy­drox­yl cloud span­ning nearly 250,000 miles, or slightly great­er than the dis­tance be­tween Earth and the moon.

* * *

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Astronomers are keeping a close eye on a greenish comet fast approaching Earth’s vicinity, 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. Researchers from the University of Leicester, U.K. 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, an astronomer at the university. 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, Md. The telescope data “show that Lulin was shedding nearly 800 gallons of water each second,” 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 molecules. Swift’s telescope detects the hydroxyl molecules. Its images of Lulin show a hydroxyl cloud spanning nearly 250,000 miles, or slightly greater than the distance between Earth and the moon.