Hubble Watches Comet Die a Slow Spinning Death

It's a comet that has survived 4.5 billion years pottering around the solar system. But through a series of gravitational misfortunes, Comet 332P/Ikeya-Murakami was nudged to a new orbit closer to the sun that ultimately doomed it to a lingering, spinning death. And the Hubble Space Telescope was there to capture the aftermath in a very lucky series of images of one very unlucky comet.

For the most part, being a comet is an uneventful existence.

Formed from the ice, dust and chunks of space rocks left over from the birth of the planets, comets will hang out for billions of years in the outer solar system doing, well, nothing. Many of these primordial chunks of icy material sit in the Kuiper Belt, beyond the orbit of Neptune, feeling the weak gravity from our sun.

But should Neptune's chaotic gravitational perturbations jostle them from their previously stable perches, the sun's gravity may win out, causing these icy bodies to make the long fall into the inner solar system. Many comets will end up in stable orbits around the sun, perhaps periodically visiting the inner solar system, while others will vaporize quickly as they play chicken with the sun and lose.

Others, like Comet 332P, may have their orbits modified by the gravity of the planets, causing them to end up in new orbits that that are far enough away from the sun to avoid being blow-torched, but close enough to die a slow solar-powered death.

After surging in brightness, Comet 332P was discovered in 2010 by two Japanese amateur astronomers Kaoru Ikeya and Shigeki Murakami. When a comet's brightness suddenly increases it can mean only one thing: It's being heated. The brightness increase was caused by jets of sublimating ices blasting vapor and dust into space, scattering sunlight.

In January this year, Hubble took a closer look at this fascinating object to see that not only is it generating a lot of vapor and dust, this comet is in the throes of death, ejecting huge building-sized chunks of material. It is currently located in an orbit beyond Mars.

"We know that comets sometimes disintegrate, but we don't know much about why or how they come apart," said David Jewitt, of the University of California at Los Angeles, in a statement. "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."

Although the comet is pretty small as far as comets go, measuring approximately 500 meters wide, its debris field is huge, with a trail extending over 3,000 miles long. But what's causing this comet to break apart?

"In the past, astronomers thought that comets die when they are warmed by sunlight, causing their ices to simply vaporize away," said Jewitt. "Either nothing would be left over or there would be a dead hulk of material where an active comet used to be. But it's starting to look like fragmentation may be more important. In Comet 332P we may be seeing a comet fragmenting itself into oblivion."

Comet 332P is disintegrating as it has been "spun up" by solar heating. As sunlight gradually heats the comet's surface, ices turn from a solid into a vapor without passing through a liquid phase. This process is known as sublimation and causes the comet to fire jets of vapor and dust into space. As this happens, pressure from the jets cause the comet to spin, like a very slow-moving Catherine wheel firework. As comets are composed mostly of loosely-packed material and not solid lumps, this spinning can cause chunks of comet to break away.

This NASA Hubble Space Telescope image reveals the ancient Comet 332P/Ikeya-Murakami disintegrating as it approaches the sun. The observations represent one of the sharpest views of an icy comet breaking apart.

In the case of Comet 332P, that's exactly what Hubble is seeing -- around 25 large chunks are slowly moving away from the main comet after being broken free by the spinning (centrifugal) force. This is how a comet dies in the inner solar system. And it's beautiful.

As Comet 332P has a six-year orbit around the sun, it's going to endure this kind of outburst every six years, allowing astronomers to estimate how long it has until it's completely disintegrated. "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," added Jewitt. "It's the blink of an eye, astronomically speaking. The trip to the inner solar system has doomed it."

Read more at Discovery News