While most Americans are sitting down to Thanksgiving dinner Thursday, astronomers will be looking up at an unusual comet passing near the sun.
The story of comet ISON started in September 2012 when a pair of astronomers in Russia spotted it out beyond the orbit of Jupiter. Two things stood out right away: First, ISON was really bright; second, it was going to pass close to the sun and Earth.
Some media outlets began making incredible claims — that ISON might, for example, become brighter than the moon in the night sky.
"I don't even know who came up with that — that's just patently ridiculous," says Karl Battams, an astrophysicist at the U.S. Naval Research Laboratory in Washington, D.C., who studies comets. "Straightaway there were unrealistic expectations of it, but nonetheless, we knew it was going to be interesting."
That's because ISON is unique in a couple of ways. First, it's a chunk of ice and rock from the Oort cloud, a huge field of debris beyond Pluto that's filled with leftovers from the solar system's formation.
"It has never been into our solar system before," Battams says. "It's a 4.5-billion-year-old, frozen chunk of what our solar system was made of."
Comet ISON is also passing very close to the sun. It's on an orbit, Battams says, that will take it "through the sun's atmosphere."
Using solar-observing spacecraft, Battams hopes to see the comet boil as it passes by. "The surface is going to be vaporizing furiously, and that's going to release a lot of interesting material that hopefully we can study," he says.
It could yield clues about how our solar system formed. And because much of the stuff released will get tangled in the sun's magnetic fields, it could also work as a sort of dye, illuminating the magnetic workings of our nearest star.
Battams and other astronomers will be spending Thanksgiving Day watching the comet from atop Kitt Peak in Arizona. "We're going to be roasting a ball of ice while people are roasting their turkeys," he says.
Assuming the comet survives its roasting, it could become easily visible in the December sky. Amateur astronomers like Mike Hankey are gearing up for what they hope could be quite a show. "My whole month of December is planned around this comet," Hankey says.
But that will only happen if the comet survives its trip around the sun. "At any moment it could fall apart, it could fizzle out, big chunks could break off," Battams warns. Even if it can stand the heat, the sun's gravity could tear it to shreds.
Only time will tell whether ISON reappears from behind the sun as a dramatic streak of fiery ice, a small smudge or nothing at all. "Comets are like cats," Battams says. "They've got tails, and they do exactly what they please."
STEVE INSKEEP, HOST:
This week, while most of us are sitting down to a Thanksgiving meal, astronomers around the world will be working, looking up at an unusual comet passing near the sun. NPR's Geoff Brumfiel has the story of what some are calling the comet of the century.
GEOFF BRUMFIEL, BYLINE: The story of comet ISON started in September of last year, when a pair of astronomers in Russia spotted it out beyond the orbit of Jupiter. Two things stood out right away: First, ISON was really bright. Second, it was going to pass close to the sun and the Earth. That's led to a lot of excitement. The Science Channel even has a documentary in the works.
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UNIDENTIFIED MAN: ISON has arrived. But where does it go from here?
KARL BATTAMS: The media caught wind of it before reasonable astronomers could catch wind of it. And so, suddenly, everybody started talking about the comet of the century.
BRUMFIEL: Karl Battams is a reasonable astrophysicist as the Naval Research Laboratory. Despite the hype, the comet isn't easily visible to most of us. Only a few amateur astronomers have seen it. But for the pros, ISON is interesting on a couple of fronts: It's a chunk of ice and rock from the Oort cloud, a huge field of debris beyond Pluto, filled with leftovers from the solar system's formation.
BATTAMS: It has never been into our solar system before. It's a four-and-a-half-billion-year-old, frozen chunk of what our solar system was made of. Comet ISON is also a sun-grazing comet, which means it's on an orbit that's going to take it extremely close to the sun and go through the sun's atmosphere.
BRUMFIEL: Using solar-observing spacecraft, Battams hopes to see the comet boil as it passes the sun.
BATTAMS: The surface is going to be vaporizing furiously, and that's going to release a lot of interesting material that hopefully we can study.
BRUMFIEL: It could yield clues about how our solar system formed. It's all happening on Thanksgiving Day.
BATTAMS: We're going to be roasting a ball of ice while people are roasting their turkeys.
BRUMFIEL: If the comet survives its roasting, it could become easily visible in the December sky. But that's a big if.
BATTAMS: The next week is really, really critical for the comet. And any moment, it could fall apart. It could fizzle out. Big chunks could break off.
BRUMFIEL: Even if it can stand the heat, the sun's gravity could rip it to shreds. But Battams is staying positive.
BATTAMS: This morning, my gut is telling me that it's actually going to survive past the sun in some appreciable form.
BRUMFIEL: It could be a small smudge, or a dramatic streak of fiery ice. For now, Battams is staying away from the comet of the century.
BATTAMS: Comet of the decade. We'd definitely be more comfortable with comet of the decade. And comet of the year, it's nailed it, at this point.
BRUMFIEL: It's anyone's guess just how cool it will be. Battams says comets are like cats: They have tails, and do whatever they want. Geoff Brumfiel, NPR News. Transcript provided by NPR, Copyright NPR.