Comet ISON Is Dead, Officially, But Yielded More Data Than Any Comet Before
It appears the comet ISON's voyage to the sun, which excited skywatchers around Thanksgiving, was a suicide mission in the end. Scientists confirmed Tuesday that the streaking ball of rock and ice has dissolved entirely, but not before researchers collected "one of the largest sets of comet observations of all time," according to NASA.
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Earlier this month, NASA reported that ISON had become "catastrophically fragmented," and one scientist posted an obituary: ISON is "survived by approximately several trillion siblings, Comet ISON leaves behind an unprecedented legacy for astronomers." But the comet wasn't completely dead. Pieces of it survived the closest approach but dissolved on their way out.
Karl Battams, an astrophysicist at the Naval Research Lab, told USA Today that scientists could not determine a "definitive moment" when ISON melted entirely. Rather, he said, "It was kind of a process of heartbreak, really, as we realized the comet was not looking good." Battams and other researchers met at the 2013 Fall American Geophysical Union in San Francisco on Tuesday, where many of them presented findings from the final moments of the comet's life.
What came out of the conference was less heartache than Battams lets on. Scientists learned a lot as we earthlings observed its final days. Since Russian scientists first noticed ISON in August 2012, people have been monitoring its course. By spring they were predicting an earth passing in November. During the week leading up to Thanksgiving, ISON was visible low on the horizon, clear without binoculars or telescope. Some snapped bad photos. Early on, Hubble took a picture of ISON (which stands for the collaboration of scientists who discovered it, the International Scientific Optical Network) that we named one of the coolest photos of the year.
But even in the summer of 2012, ISON was nearing almost certain death. At that time it was still 585 million miles away, but relatively speaking, that was practically the end of the line. "The comet's story begins with the very formation of the solar system," 4.5 billion years ago, Battams said. ISON, like other comets, lived 4.5 trillion miles away (one lightyear is about 5.9 trillion miles) in a place called the Oort Cloud. There, the aged icy leftovers of solar system creation sit idle. Occasionally, something knocks them into orbit around the sun, and gravity does the rest.
In ISON's case, that would've happened a few million years ago, long before the first humans evolved and even before the first species of the genus Homo appeared. An Oort Cloud road trip ain't quick. For all that, scientists were giving ISON a 50/50 chance of surviving perihelion, the point at which it is closest to the sun. By evening on Nov. 28, ISON was nowhere to be found.
But don't dispair, says NASA, "the legacy of the comet will go on for years as scientists analyze the tremendous data set collected during ISON's journey." Some of the first knowledge may be about its size and composition. The nucleus was less than a mile in diameter, they said. And as it burned, scientists couldn't see it using oxygen radars. "The fact that ISON did not show oxygen despite how close it came to the sun provides information about how high was the evaporation temperature of ISON's material," said NASA scientist Dean Pesnell in a statement. "This limits what it could have been made of."
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