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Green Comet Approaching the Earth

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.

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.

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 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.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.

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.

February 21, 2009 Posted by | Fact, Personal, science | , , , | 6 Comments