• Seeds of life: Many researchers believe that comets played an important role in providing water to a young, dry Earth. Comets may also have supplied some of the chemical ingredients used as the building blocks of life. Other researchers speculate that comets harbor bacteria or other life forms and could therefore have delivered life to Earth in a ready-made form. This more controversial view is part of a broad concept called panspermia, which holds that the seeds of life are everywhere in the universe. Full Story

• Hammers of death: Earth was frequently bombarded by comets and asteroids until about 3.8 billion years ago. Though impacts are less frequent now, they still occur. A comet or asteroid is thought to have wiped out the dinosaurs 65 million years ago, for example. And recent research suggests that such impacts occur with a regularity that dooms most species, eventually, and makes way for others to prosper. Even humanity has to face this fact, some scientists say. Full Story

• Origin of sex: A billion years ago, life was pretty boring. Pond scum made progeny with no help, no courtships nor any of the subsequent machinations familiar to most adult animals nowadays. But would you believe it? It may have been comets that rocked the scum into action. Full Story

• Human evolution: Are we human because of comets? In the 5 million years or so that it took for apes to become human, a dozen or so human-like species didn't survive. One controversial argument suggests that catastrophic asteroid or comet impacts might have created climate conditions that competing species couldn't handle. Full Story

GENERAL COMET INFORMATION Table -->

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	A 1994 image of Comet Borrelly on one of its swings around the Sun.
	Some comets are attracted to an abrupt ending. In 1994, a crumbling Comet P/Shoemaker-Levy 9 smashed into Jupiter, ripping holes in its atmosphere and leaving dark scars that lasted for weeks. This Hubble Telescope image shows icy fragments stretching across 710,000 miles (1.1 million kilometers) of space.
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	SPECIAL REPORT: Aged and Wounded Spacecraft Photographs Comet
	A Comet's Life: Icy Adventure From Birth to Death
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• Birth of comets: Like planets and asteroids, comets are thought to have formed from the detritus of the Sun's birth: gas, ice and dust swirling around the young star in a giant, flat disk. But did comets form when knots of material collapsed under gravity, or did they build up over time via multiple collisions of smaller objects? A recent study of a comet that peeled apart in layers indicates latter may be true. Full Story

• Exocomets: Two recent studies provide strong evidence that comets may have formed around other stars. The research supports the idea that our solar system, and the way it developed, is not unusual. If true, then Earth-like planets might orbit other stars, possibly harboring life. Full Story

• Famous comets: Comet Borrelly doesn't get bright enough to enthrall non-astronomers, and so it has never achieved the fame of a Halley or a Hale-Bopp, which graced the skies in 1997. Meanwhile, earlier this year, astronomers found that Hale-Bopp was still sloughing off material even while nearly 1.2 billion miles (2 billion kilometers) from the Sun. Full Story

• Total Amateurs: While much of what we know about comets has been learned by professional astronomers using high-powered telescopes, most comets are in fact discovered by amateurs. Full Story

FUTURE COMET MISSIONS

• Rosetta: This European mission, scheduled for launch in 2003, will attempt to put the first spacecraft in orbit around a comet at close quarters and deploy a lander onto the surface of a comet nucleus. Full Story

• Stardust: The Stardust spacecraft plans to fly through the cloud of dust that surrounds the nucleus of comet Wild-2 in 2004 and, for the first time ever, bring cometary material back to Earth. Full Story

• Deep Impact: No planned mission will be as dramatic as Deep Impact, recently approved by NASA. On Independence Day 2005, mission planners expect to send a camera-packing copper probe headlong into Comet Tempel 1. Scientists hope for head-on collision that will rend and reveal the comet's innards. Full Story

• Deep Space 1 -- Saturday's flyby: Deep Space 1 is "aged and wounded," says a NASA mission manager, and may well fail in its attempt to find and photograph Comet Borrelly. But that's not stopping the attempt. Full Story