Hailed by astronomers as the “comet of the century,” scientists around the world are waiting to see whether a “relic” from the far reaches of the solar system will survive a trip around the sun.
Already, the comet ISON has become the most watched and studied comet in the history of NASA. But if it isn’t vaporized in the sun’s radiating heat, scientists say it could offer even more clues to how the solar system was formed.
“The comet is a relic – it’s a dinosaur bone of solar system formation,” said Carey Lisse, head of NASA’s Comet ISON Observing Campaign, who noted that comets are the building blocks of planets.
Soon after the comet ISON slingshots around the sun today, astronomers will know whether it has managed to stay intact. But the comet will likely not be visible to backyard astronomers – if at all – until after Saturday.
“If it goes around the sun, it could break up into pieces or not survive at all,” Lisse said. “If you ask me, as a betting man, I personally think that ISON may have fallen apart – but a big chunk is still there.”
Lisse said he believes enough of ISON will survive to offer a “fantastic series of images” from research telescopes. Currently NASA has six telescopes trained at the comet.
Amateur astronomers may not have binoculars or land-based telescopes powerful enough to pick up the comet or its burning fragments. And yet, there is a small chance the comet may burn bright enough to be seen by the naked eye.
Blame all the uncertainty on comets behaving like comets.
“Quite simply, comets are like bears – you never know what one is going to do – until it happens,” said Liam McDaid, an astronomy professor at Sacramento City College. “This is why astronomers are loath to make predictions.”
The best viewing opportunities, if there are any, are expected to happen during the first and second week of December as the comet moves away from the sun.
The best case scenario for ISON viewing is that it will be as bright as Venus in the sky. It will be seen only in the Northern Hemisphere and seen right before dawn or just after dusk. Its position in the sky will be low, near the horizon when looking east-southeast. As December progresses, ISON will move higher and higher.
The concern that ISON will not survive its meeting with sun has to do with its relatively small mass. The last comet that was easily seen by the naked eye in the Northern Hemisphere was the Hale Bopp, which came closest to Earth in 1997. That comet was almost 20 miles wide.
In its present state, ISON is thought to be less than a mile and a half wide.
“ISON will come within 800,000 miles of the solar surface,” said Patricia Boeshaar, senior lecturer in physics at UC Davis. “The sun has a diameter of approximately 100 million miles ... so that’s within about 0.8 solar diameter ... and will heat up to several thousand degrees. This is why there are some bets ISON will get bright after solar passage ... that’s if it’s not destroyed.”
Scientists believe there may be good viewing even if the comet breaks up. Last year, the comet Lovejoy, which was visible only in the Southern Hemisphere, grazed the sun and lost its tail as a result. Still, Lovejoy provided a spectacular series of sightings through telescopes and binoculars after it reappeared.
ISON was discovered a year ago by two Russian astronomers. Its name is an acronym for the International Scientific Optical Network, a group of night sky observatories in 10 countries.
The appearance of “sungrazing” comets – those whose path takes them around the sun – is no rarity. However, ISON is no ordinary comet, scientists say.
“It’s probably the first time a comet has come in from a very large distance,” said Jim Green, director of planetary science at NASA.
Scientists believe ISON originated in the far outer reaches of the solar system in a region called the Oort cloud. That cloud is like an outer space trailer park filled with frozen comets over a billion years old. Oort cloud comets are sometimes roused from their slumber when snagged by the gravitational pull of a star. For the comet, this triggers an event-filled, elliptical road trip.
The sun’s gravitational pull likely snagged ISON more than a million years ago – roughly the same time as the dawn of man, Lisse said.
But its potential swing by Earth is a one-time thing. Unlike other comets that make regular swings around our solar system, ISON’s origination in the Oort Cloud and its elliptical path assures it will never return to the solar system, Lisse said.