Space

22 Methane Rain Falls Mainly on Titan's Plain

Astronomers hoped the Huygens probe would reveal a global ocean of methane when it parachuted to the surface of Titan, Saturn's largest moon, on January 14, 2005. Instead of landing with a splash, the spacecraft made more of a splat. "It landed in mud," says planetary scientist Christopher McKay of NASA's Ames Research Center. And that mud was wet with methane. Studies have detected methane rain on Titan and more than 20 lakes of methane at the moon's north pole. Alien as this may seem, Titan's atmosphere—rich in nitrogen and organic compounds—may be similar to the atmosphere of early Earth.

Courtesy of NASA

On Titan, where temperatures range around –300 degrees Fahrenheit, methane can be solid, liquid, or gas. McKay and his colleagues suspect there is a thin layer of liquid methane clouds beneath a higher, thicker cloud bank composed of methane ice crystals. The lower clouds produce a constant drizzle amounting to about two inches of precipitation a year. "That kind of system, in motion like that, with a contained weather cycle—it's just ideal for a methane-based organism," McKay says. Perhaps Earth is not the only place where creatures slither through the mud.

Richard Morgan

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45 Alien Planets Get Smaller, Fatter, Faster, and Hotter

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This year ushered in at least two dozen more planets outside our own solar system, including some of the oddest ones yet.

In January astronomers introduced the least massive extrasolar planet yet discovered. Weighing in at just 5.5 times the Earth's mass, planet OGLE-2005-BLG-390Lb, most likely an ice-covered ball of rock, circles a cool red dwarf star some 21,000 light-years away.

In September another extrasolar planet rewrote the record books. HAT-P-1 is about 1.5 times the width of Jupiter, yet remarkably, only half Jupiter's mass. Less dense than cork, it would float in water.

In October astronomers revealed the fastest known planet, named SWEEPS-10, with a "year" just 10 hours long and a surface temperature of perhaps 3,000 degrees Fahrenheit. If its home star were any hotter, the planet might have simply boiled away.

Stephen Ornes

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48 Nearby Universe Mapped

After two decades of research on three continents, astrophysicists have produced the largest and most detailed full-sky map of the nearby universe. The three-dimensional plot, known as the 2MASS Redshift Survey, covers 600 million light-years in all directions, reconstructing the positions and velocities of 25,000 galaxies. One cool detail: Our home galaxy, the Milky Way, and our sister galaxy, Andromeda, move at 1.4 million miles per hour relative to the ubiquitous background energy left over from the Big Bang, a standard frame of reference for astronomers.

Alex Stone

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51 Ice Volcanoes Seen On Saturnian Moon

Saturn's small moon Enceladus—just 300 miles wide—turned in one of the biggest discoveries from NASA's Cassini probe, now orbiting the ringed planet. Data published in March showed a geyser on Enceladus shooting jets of water and fine icy particles hundreds of miles into space. The jets also contained simple carbon compounds. These findings suggest that liquid water may lurk

Courtesy of NASA

beneath the moon's surface, adding Enceladus to the list of alien locations that could harbor organic chemistry, if not actual life.

Carolyn Porco, head of the Cassini imaging team at the Cassini Imaging Central Laboratory for Operations in Boulder, Colorado, has determined that ice from Enceladus's plume swirls around Saturn to form one of the planet's signature rings. Nobody knows why Enceladus is so active; the leading theory is that the stretching force of Saturn's gravity has heated the moon's interior more efficiently than expected.

  Richard Morgan

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