Comet Lulin arrives tonight - break out your telescopes

Sky map drawn by Xephem
Comet Lulin will make its closest approach to Earth on Monday night. The circled X shows the comet's position at seen from Boston at 10 p.m. local time. It appears in the southeastern sky near Saturn, at the tip of Leo the Lion's hind leg.

Over the next three nights, skywatchers should expect their best views yet of Comet Lulin. It makes its closest approach to Earth -- some 38 million miles away -- on Tuesday, Feb. 24.

To the naked eye, the comet looks like a fuzzy patch of hazy light against the night sky. Use binoculars or telescopes, and you'll be able to pick out its brighter center, along with its dual tail -- a brighter tail of dust, and a dimmer one of ionized gases the comet sheds as its sun-warmed ices change directly from a solid to a gas.

Lulin, formally known as C/2007 N3, will dim quickly through March, thanks to the kick it's gotten from the sun's gravity. Then it's Oort-a here -- heading back out to its kin in the Oort Cloud, a vast collection of icy construction debris left over from the formation of the solar system some 4.6 billion years ago.

The far edge of the Oort cloud reaches some 18 trillion miles beyond the sun. That's a lot of space for literally billions of icy objects to inhabit. Scientists estimate that the combined mass of all those objects is about 40 times that of Earth.

While amateur skywatchers brave a chilly winter's night or two (in the higher latitudes of the northern hemisphere) with a thermos of hot chocolate and their favorite viewing tools, Neil Dello Russo is looking to the comet's flyby for a serious cosmic chemistry lesson.

Some serious comet-watching

Dr. Dello Russo, with the Johns Hopkins University's Applied Physics Laboratory in Laurel, Md., has snagged some telescope time on one of the Keck Observatory's two 10-meter telescopes on Hawaii's Mauna Kea. He and an international team are watching emissions from Lulin, as well as those from comet 22P/Kopff. Unlike Lulin, Kopff is a short-period comet, originating in a band of icy objects beyond Neptune's orbit. The band is called the Kuiper Belt.

Since an initial post on Lulin at the beginning of the month, you learn an extra thing or two -- such as the length of the comet's orbital period. It isn't just a million years; it's nearly 50 million years. Kuiper Belt objects like 22P/Kopff return every 200 years or less. Comet Halley is one high-profile example. Comet 22P/Kopff returns once nearly every seven years. It's next closest approach to the sun takes place in May.

Dello Russo and his colleagues are looking at Lulin and 22P/Kopff to compare the relative amounts of different gases they give off. Among them: organic compounds like ethane, hydrogen cyanide, acetylene, ammonia, methanol, and, of course, water.

When emissions from these two comets are added to the data the team has already accumulated, the information should help give astronomers a better handle on how conditions in different parts of the solar system affected the chemical makeup of comets and, over time, how that makeup was altered with each pass by the sun.

Meanwhile, National Aeronautics and Space Administration's SWIFT spacecraft has been gathering images of the comet at ultraviolet and x-ray wavelengths. The research team using the craft, led by the University of Leicester's (England) Jenny Carter, also is interested in analyzing Lulin's emissions.

At the end of January, for instance, the comet was unleashing about 800 gallons of water (about $17,000 worth of Evian) a second, according to team member Dennis Bodewits, with NASA's Goddard Space Flight Center in Greenbelt, Md.

Upcoming comet encounters

And opportunities for new insights into comets don't stop there. NASA has two extended missions -- Deep Impact (now EPOXI) and Stardust (now Stardust-NExT)-- bound for comet encounters over the next two years.

Deep Impact, you may recall, buzzed Comet Tempel 1 on July 4, 2005, and launched a projectile at the comet. The two collided, releasing as much energy as nearly 5 tons of TNT. The collision carved a crater in the comet's nucleus. But the Deep Impact spacecraft got a very limited look at the crater, thanks to all the dust the impact kicked up.

The Stardust-NExT spacecraft is slated to fly by Tempel 1 in 2011. If all goes well, it will capture images of the crater as well as measure the properties of the dust it encounters. Since Stardust already has sampled Comet Wild 2 (and returned those samples to Earth), the Tempel 1 flyby gives astronomers a unique opportunity to observe different comets with the same instruments.

Meanwhile, EPOXI is scheduled to fly by Comet Hartley 2 on Nov. 4, 2010. And NASA's New Horizons mission is outbound for Pluto and its companion Charon, and then into the Kuiper Belt to buzz one or two objects there. The Pluto flyby currently is slated for July 14, 2015. Look for the Kuiper object encounters in 2016 and 2020.

And if for some reason you miss Lulin -- you know, cloudy skies, wrong setting on the alarm clock, those kinds of things -- try this video.

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