Sky Show Tonight: Green "Two-Tailed" Comet Arrives

Victoria Jaggard
National Geographic News
February 23, 2009

A fresh new face has moved into our neighborhood, but once this green-colored comet swings by Earth tonight, it may never come back (picture of green comet Lulin).

Comet Lulin is currently sailing through the inner solar system and is getting closer to our home planet, with its nearest approach expected on February 24.

Although it's hard to glimpse with the naked eye, the comet "should be a fairly easy object [to see using] modest amateur telescopes or even binoculars," said Don Yeomans, a comet expert at NASA's Jet Propulsion Laboratory in Pasadena, California.

Astronomer Mark Hammergren of Chicago's Adler Planetarium added that the icy body has the potential to do something unexpected.

Comet Lulin is arriving from the far reaches of the solar system on a nearly parabolic orbit—"it's almost as if it comes from infinity and goes back out to infinity," he said. (Explore an interactive solar system.)

This means Lulin could be on its first pass by the sun, so the comet should still be encrusted in "fresh" ices preserved by the freezing environment of the outer solar system, Hammergren said.

As Lulin is exposed to the sun's heat for the first time, those ices are vaporizing—activity that could cause the comet to brighten rapidly or even break apart. Even now the comet is spewing cyanogen and diatomic carbon, both gases that glow green in sunlight out in the vacuum of space.

What's more, the comet's orbit is in nearly the same plane as Earth's, but the comet is traveling in the opposite direction. This causes Lulin to appear to move unusually fast and display a rare anti-tail—an optical effect that creates a secondary "tail" pointing toward the sun.

Green Comet Fuzz Ball

Quanzhi Ye, a student at China's Sun Yat-sen University, found comet Lulin in 2007 while examining images from the Lulin Observatory in Taiwan as part of an asteroid survey.

Lulin made its closest approach to the sun on January 10, 2009, and has since been getting brighter in the morning sky.

Tonight the comet will pass nearest to Earth—about 38 million miles (61 million kilometers) away—and will reach peak brightness and fastest apparent speed.

Continued on Next Page >>




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