Hubble witnesses death throes of ancient comet
Astronomers have witnessed the beginning of the end of an ancient comet. After billions of years, Comet 332P may only have a century and a half left to live, as the Hubble Space Telescope captured detailed images of it fragmenting, throwing dozens of building-sized pieces into space. The observation is helping scientists learn about the life and death of comets.
Named 332P/Ikeya-Murakami, astronomers believe the comet spent about 4.5 billion years in the Kuiper Belt, the rocky region beyond Neptune, before it was dislodged and sent hurtling towards the inner solar system. Jupiter's enormous mass then set it in motion on its current orbit.
This journey may kill the comet, but it gives scientists a perfect opportunity to study that process. Over three days in January this year, Hubble snapped photos of Comet 332P some 67 million miles from Earth, revealing the size, speed and rotation of the parent body and its fragments, as well as how many pieces it's splintering into, and how and why that might be happening.
"We know that comets sometimes disintegrate, but we don't know much about why or how they come apart," says lead researcher, David Jewitt. "The trouble is that it happens quickly and without warning, and so we don't have much chance to get useful data. With Hubble's fantastic resolution, not only do we see really tiny, faint bits of the comet, but we can watch them change from day to day. And that has allowed us to make the best measurements ever obtained on such an object."
The Hubble data suggests that as the 1,600 ft (488 m) wide comet warms up in the sunlight, jets of gas are exploding out from under its surface. That's causing it to spin rapidly, at a rate of one rotation every two to four hours, which in turn is the likely cause of the breakup, as it shakes loose chunks of rock ranging from 65 ft (20 m) to 200 ft (61 m). These are then strolling away from the parent body at about a human walking pace, and may succumb to their own fragmentation.
"Our analysis shows that the smaller fragments are not as abundant as one might expect based on the number of bigger chunks," says Jewitt. "This is suggestive that they're being depleted even in the few months since they were launched from the primary body. We think these little guys have a short lifetime."
Although it has endured for billions of years out in the frigid Kuiper Belt, the trip to warmer conditions has shortened its life dramatically. The researchers believe that the comet may have split in two in 2012 (visible in the images as a second small bright dot, right next to the main body), and that the fragments seen in the Hubble images were probably ejected between October and December last year. Judging by its current size, Comet 332P will probably disintegrate completely after another 25 outbursts.
"If the comet has an episode every six years, the equivalent of one orbit around the sun, then it will be gone in 150 years," says Jewitt. "It's the blink of an eye, astronomically speaking. The trip to the inner solar system has doomed it."
The research was published in The Astrophysical Journal Letters.