Comets are fantastic targets for scientific study. They stay chilly in their far-flung orbits, and the ancient masses of dirt, ice and rock contain relatively pristine materials from the earliest days of the solar system. But these dirty snowballs can't last forever. When their orbital path brings them close to the sun, they begin to warm up and break apart. A comet's icy core, or nucleus, sublimates from solid to gas under the sun's hot rays, creating a "coma" of vapor around and behind it.
Eventually, after enough trips around our star, a comet will either totally disintegrate or turn into an iceless, rocky husk of its former self. Now scientists have captured the most detailed images of a comet's self-destruction, revealing an ancient space rock's tumble into crumbled oblivion.
“We know that comets sometimes disintegrate, but we don’t know much about why or how they come apart,” David Jewitt of the University of California at Los Angeles said 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."
But over the course of three days in January, images from the Hubble Space Telescope revealed the destruction of a comet called 32P/Ikeya-Murakami, or Comet 332P. The telescope was able to show faint bits of comet, capturing some 25 chunks in action as they ambled away from the comet at about the walking speed of a human adult — forming a trail 3,000 miles long.
“In the past, astronomers thought that comets die when they are warmed by sunlight, causing their ices to simply vaporize away,” added Jewitt, one of the authors of a study on Comet 332P published in the Astrophysical Letters. “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 thought to be 4.5 billion years old, which puts its birthday just 100 million years or so after the formation of our solar system. That's roughly the same age as the planets, but Comet 332P has spent that time very differently. Until (relatively) recently, the hunk of ice and dirt lived in the Kuiper belt, the region of our solar system beyond Neptune. Objects in the Kuiper belt are kept so cold as to preserve some of the solar system's first molecular building blocks.
But as with many comets, something about Neptune's gravity knocked 332P out of place. Eventually, a pinball-like jaunt through the solar system's gravitational fields left it on a six-year orbit around the sun. Considering how much farther away it used to be — Pluto, one of the closest objects in the Kuiper belt, takes 248 Earth years to circle the sun — it's no surprise that 332P is feeling a little bit peaky.
At 150 million miles from the sun, Comet 332P was seen doing the usual business of heating up and giving off gas. But based on the new Hubble images, which show fragmented debris trailing behind the comet, researchers believe these powerful gas jets are acting like engines, speeding up the comet's spin and making it break apart.
Although the fragments, which range from about 65 to 200 feet in diameter, are moving slowly — just a few miles per hour — they already make up about 4 percent of the body's original volume. Scientists believe the smaller fragments are continuing to break up as they slowly spin out into space.
“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,” Jewitt said in a statement. “It’s the blink of an eye, astronomically speaking. The trip to the inner solar system has doomed it.”