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Comet could be a stunner (or not)

IfA / Pan-STARRS 1

    An animated image shows C/2011 L4 in motion.

A newly discovered comet from the farthest reaches of the solar system could become a sky spectacle in 2013, astronomers say. No guarantees, though.

Comet C/2011 L4 (PANSTARRS) was detected on the night of June 5-6 using the Pan-STARRS 1 telescope in Hawaii. The next night, astronomers checked it out using the Canada-France-Hawaii Telescope and confirmed that it was indeed a comet.

Calculations suggest that the comet will come within about 30 million miles (50 million kilometers) of the sun in early 2013. That's roughly equivalent to the distance between the sun and Mercury, the University of Hawaii's Institute for Astronomy said today in a news release.

"The comet has an orbit that is close to parabolic, meaning that this may be the first time it will ever come close to the sun, and that it may never return," said University of Hawaii astronomer Richard Wainscoat.

Pan-STARRs' primary job is to detect potentially hazardous asteroids that might hit Earth someday, but the orbital calculations for C/2011 L4's path have ruled out any chance that this comet will hit us. The iceball is nevertheless interesting for two big reasons.

First, the comet is coming in fresh from an unspoiled cosmic frontier, trillions of miles away — and is thus likely to be composed of the fluffy stuff from which the solar system was made. That's a golden opportunity for astronomers who are trying to piece together the grand saga of planetary formation.

Second, it could be a heck of a show.

Right now the comet is 700 million miles (1.2 billion kilometers) from the sun, well beyond the orbit of Jupiter. Its brightness is magnitude 19, which means it can be spotted only with telescopes equipped with sensitive electronic detectors. But observers expect that the comet will be visible to the naked eye when it comes closest to the sun, around March 2013. C/2011 L4 could put on a nightly show in western skies just after sun set. Some even say it has the potential to become "the brightest comet of the decade."

But most astronomers are reluctant to make predictions about brightness, particularly so soon after the discovery. A comet's brightness depends not only on how close it comes to the sun and how big it is, but also on how much ice it contains. The transformation of a comet's ice to gas is a major contributor to its brightness. "More accurate brightness predictions will not be possible until the comet becomes more active as it approaches the sun and astronomers get a better idea of how icy it is," the Institute for Astronomy said.

C/2011 L4 is inherently unpredictable because this will be its first and perhaps its last journey through the inner solar system. Some comets, such as Comet Halley and Tempel-Tuttle, follow orbits that take them around the sun on a regular, relatively short timetable (every 76 years for Halley, every 33 years for Tempel-Tuttle). But the comets from the Oort Cloud, also known as long-period comets, are infrequent visitors. Examples include Comet Hale-Bopp (which became famous in 1997) and Kohoutek (which fell short of expectations in 1973).

Long-period comets spend most of their time amid the huge reservoir of icy objects that extends a quarter of the way to the next star over. They're thought to come into the inner solar system only when they're diverted by gravitational interaction with the other objects out there.

It's worth noting that some astronomers suspect that a large celestial object — perhaps a brown dwarf or a so-called "Planet X" — may lie in the Oort Cloud and be responsible for variations in the flux of long-period comets. You can read all about the search for such objects, including a little bit about Pan-STARRS, in "The Case for Pluto," my book about Pluto and other weird worlds.

You'll probably be hearing more doomsday talk about Planet X, Nibiru, Nemesis and other supposed denizens of the Oort Cloud due to the hype over 2012. Who knows? Maybe Comet C/2011 L4 will provide some with an excuse to whip up the doomsday talk again. But don't be misled — and whatever you do, DON'T PANIC.

More about comets:

Most comets are named after their discoverers, but so many scientists collaborated on the C/2011 L4's discovery that the comet took the PANSTARRS name instead. Among the collaborators are Larry Denneau, Richard Wainscoat, Robert Jedicke, Mikael Granvik and Tommy Grav, who designed the software that searches through Pan-STARRS 1 telescope imagery for moving objects. Denneau, Harry Hsieh and Jan Kleyna wrote other software that analyzes the moving objects for the telltale fuzzy appearance of a comet. Wainscoat and Marco Micheli confirmed the comet observations on the Canada-France-Hawaii Telescope.

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