Comets are often described as dirty snowballs. They're composed mostly of water ice, frozen gases and dust. Scientists believe they carry some of the solar system's original construction debris. By analyzing and comparing comets' composition, researchers gain insights into the physical makeup and environmental conditions of the solar system as the planets formed 4.5 billion years ago.
Lulin is very active, scientists say, perhaps because it is near the sun for the first time and reacting to the heat and bombardment by solar particles.
"There is really a lot of gas evaporating off the comet's nucleus," said Dennis Bodewits, a post-doctoral fellow at Goddard. A comet specialist, he has been observing Lulin in X-ray and ultraviolet wavelengths with NASA's orbiting Swift Observatory.
Most of that gas is water that has evaporated from the comet's icy nucleus. Bodewits estimated the comet is losing water at 800 gallons a second, enough to fill an Olympic pool in 15 minutes.
A handful of spacecraft have flown close to other comets to photograph them and scoop up matter from their tails and "comas," the halo of gas and dust surrounding the tiny nucleus. In 2005, a spacecraft called Deep Impact, on a mission led by a University of Maryland scientist, hurled a projectile onto the nucleus of Comet Tempel 1, then examined the resulting crater and the material blasted into space by the impact.
But mostly scientists study comets from a vast distance, by analyzing the sunlight they reflect or the X-rays they give off as their water molecules are struck by the solar wind. The task becomes more difficult as sunlight hits the gas and dust coming off the comet, and those molecules break down into other substances.
"Our question is, 'How does what we're seeing relate to what the comet is made of?' " Bodewits said. As Lulin draws nearer, he said, "Pretty much all the observatories are on it. It's the only bright comet at this moment."
For the rest of us, it's simply a rare opportunity to see a comet. The last naked-eye comet visible from Maryland was Comet Holmes, in October and November 2007. In 1997, Comet Hale Bopp passed by. Comet Hyakutake, with its classic sweeping tail, made a naked-eye appearance for Marylanders in 1996.
To find Lulin on Monday: Look about halfway up in the southeastern sky, just below the hook-shaped constellation Leo. You should see two bright stars. One is Regulus, the brightest star in Leo. The second is the planet Saturn, a faintly yellow object below and slightly to the left of Regulus.
