November 25, 2013

On comet! Gaining speed, celestial body zooms toward sun

The moment of truth occurs on Thanksgiving, when it will fry or shatter – or endure to put on a celestial show in December.

By Marcia Dunn
The Associated Press

CAPE CANAVERAL, Fla. — For months, all eyes in the sky have pointed at the comet that’s zooming toward a blisteringly close encounter with the sun.

click image to enlarge

Comet ISON’s tail is seen in this three-minute exposure taken last week from the Marshall Space Flight Center in Huntsville, Ala. If the comet survives its close encounter with the sun, it could put on a nice show in December. Earthlings are not in danger, scientists say.

The Associated Press/NASA

The moment of truth comes Thursday – Thanksgiving Day.

The sun-grazing Comet ISON, now thought to be less than a mile wide, will either fry and shatter, victim of the sun’s incredible power, or endure and quite possibly put on one fabulous celestial show.

Talk about an astronomical cliffhanger.

Even the smartest scientists are reluctant to lay odds.

Should it survive, ISON would be visible with the naked eye through December, at least from the Northern Hemisphere. Discernible at times in November with ordinary binoculars and occasionally even just the naked eye, it already has dazzled observers and is considered the most scrutinized comet ever by NASA. But the best is, potentially, yet to come.

Detected just over a year ago, the comet is passing through the inner solar system for the first time. Still fresh, this comet is thought to bear the pristine matter of the beginning of our solar system.

It’s believed to be straight from the Oort cloud on the fringes of the solar system, home to countless icy bodies, most notably the frozen balls of dust and gas in orbit around the sun known as comets. For whatever reason, ISON was propelled out of this cloud and drawn toward the heart of the solar system by the sun’s intense gravitational pull.

The closer the comet gets to the sun, the faster it gets.

In January, it was clocked at 40,000 mph.

By last Thursday, with just a week to go, it had accelerated to 150,000 mph.

By the time ISON slingshots around the sun, it will be moving at a mind-boggling 828,000 mph.

Whether it survives or is torn apart, earthlings have nothing to fear.

The comet will venture no closer to us than about 40 million miles, less than half the distance between Earth and the sun. That closest approach to Earth will occur Dec. 26. Then it will head away in the opposite direction forever, given its anticipated trajectory once it flies by the sun.

ISON is named after the International Scientific Optical Network, used by a pair of Russian astronomers to detect the comet in September last year. But it officially is known as C/2012 S1, a designation indicating when it was discovered.

Take heart: The “C” means it is not expected here again.

NASA wasted no time jumping on ISON. The space agency’s Deep Impact spacecraft observed ISON back in January from a distance of about 500 million miles.

Since then, the observations have stacked up.

Among NASA’s space telescopes taking a look: Swift, Hubble, Spitzer, Mars Reconnaissance Orbiter, Solar and Heliospheric Observator, Chandra, Mercury-orbiting Messenger, and the Stereo twin spacecraft.

“Every spacecraft that has a camera, we’re turning on it,” said John Grunsfeld, NASA’s science mission director.

The newly launched Maven spacecraft en route to Mars will gaze at ISON the second week of December.,

“That’s well after closest approach to the sun,” the University of Colorado’s Nick Schneider, who’s in charge of the instrument, said in an email. So it’s not known “whether we’ll see a comet, comet bits or the last wisps of comet vapor.”

Besides ISON, NASA is spying on Comet Siding Spring, another Oort cloud comet discovered in January by the Australian observatory of the same name. Siding Spring will pass within tens of thousands of miles of Mars next October, so close that scientists believe the coma of the comet – its thin but expansive atmosphere – will envelop the red planet.

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