It’s been a few months since Comet ISON has been in the news again, but fear not: the hurtling pile of ice and gas is still on its trajectory inside the Solar System. Boffins at JPL tell us today that the “soda pop comet” has just begun shedding carbon dioxide and dust, turning on something akin to a fog machine as it gets closer to the sun:
“We estimate ISON is emitting about 2.2 million pounds (1 million kilograms) of what is most likely carbon dioxide gas and about 120 million pounds (54.4 million kilograms) of dust every day,” said Carey Lisse, leader of NASA’s Comet ISON Observation Campaign and a senior research scientist at the Johns Hopkins University Applied Physics Laboratory in Laurel, Md. “Previous observations made by NASA’s Hubble Space Telescope and the Swift Gamma-Ray Burst Mission and Deep Impact spacecraft gave us only upper limits for any gas emission from ISON. Thanks to Spitzer, we now know for sure the comet’s distant activity has been powered by gas.”
As comets get closer to stars, they begin to warm up. “Warm,” in this case, being a relative term. Carbon dioxide freezes at -78C and its much, much colder than that in space. But as ISON gets closer to the sun, the sun’s energy begins warming the flying snowball, creating the signature tail, which is a trail of debris being shed from the comet.
This explains why the tail doesn’t necessarily trail out behind the comet: the tail points in the same direction as the solar wind that is creating it, pushing debris off the comet.
In ISON’s case, once it arrives in the inner atmosphere, scientists think it could become extremely bright. Brighter, in fact, than the moon. That’s because it is both large and made of chemicals known to cause nice, bright tails. But that’s only one possibility. Another is that the comet breaks apart from the heat.
We won’t know what will happen until it happens. For now, scientists are busy gathering data they believe will “help explain how and when the solar system first formed.” But then, let’s be honest: they always say that.