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The Way a Comet Crumbles
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For a comet, breaking up is not so hard to do.
A comet called 73P/Schwassmann-Wachmann 3 has been disintegrating for years, but the pace has picked up in recent weeks. The comet has already broken into at least 59 pieces. As it gets closer to the sun, scientists are expecting it to crumble even more.
Comets are giant, fragile balls of ice and dust that take odd orbits around the sun. Sometimes, they're really far away from the sun. Sometimes, they're really close. When a comet is near the sun, some of its ice melts, which produces its distinctive tail.
Comet 73P/Schwassmann-Wachmann 3 orbits the sun every 5.4 years. Over the past month, the Hubble Space Telescope and other instruments have watched the comet's biggest 36 chunks break up into dozens of smaller bits. These pieces measure between 20 and 30 meters (66 to 98 feet) across.
The breakup shows that the cores of comets "are as fragile as the meringue in lemon-meringue pie," says Casey Lisse of the Johns Hopkins Applied Physics Laboratory in Laurel, Md.
Images from the Spitzer Space Telescope show lots of tiny specks of dust between the comet chunks. One theory is that comets lose material mostly by releasing millimeter-size dust particles.
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Saturn's Strangely Warm Moon |
| Weird things are happening on Saturn's moon Enceladus.
The small moon, only 505 kilometers (314 miles) wide, was thought to be cold and icy. But new findings suggest that Enceladus (pronounced en-SELL-ah-dus) is oozing heat. And there might be pools of liquid water just below its surface.
That's a surprise because Saturn orbits, on average, about 1.3 billion kilometers (more than 800 million miles) from the sun. "You expect everything to be cold and frozen" out there, says Andrew Ingersoll. He's a planetary scientist at the California Institute of Technology in Pasadena.
Instead, Enceladus appears to be one of the few planets or moons in the solar system that generates detectable heat of its own. |
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New mysteries |
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The recent observations have raised a slew of new mysteries.
For example, scientists had assumed that Enceladus' geysers would contain ammonia, a common chemical that softens ice and allows it to flow like lava. The presence of ammonia would explain why parts of the moon's surface appear smooth instead of pockmarked by craters.
Cassini's instruments, however, haven't detected any ammonia. But in addition to water, the plumes of material spewing from Enceladus do contain nitrogen, along with methane, carbon dioxide, and other carbon-containing molecules.
Why the moon's hot spot is in the southern polar region is also perplexing. On Earth, the poles are some of the coldest places on the planet.
Cassini will pass by Enceladus again in 2008. On that trip, the spacecraft will snap detailed photos of various surface features and maybe even peer inside the moon's canyons. |
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