Space

3 Cosmic Collision Brings Dark Matter Into View
A violent collision has turned up the most direct evidence yet of dark matter...

10 Pluto Demoted
Pluto now falls under the quaint designation "dwarf planet"...

13 Probe Snaps Baby Picture of the Cosmos
A detailed snapshot of what the universe was like as a trillionth-of-a-second-old newborn...

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22 Methane Rain Falls Mainly on Titan's Plain
The Huygens probe made a splat. "It landed in mud"...

45 Alien Planets Get Smaller, Fatter, Faster, and Hotter
This year ushered some of the oddest extrasolar plaents ever found...

48 Nearby Universe Mapped
Astrophysicists have produced the most detailed full-sky map of the nearby universe...

51 Ice Volcanoes Seen On Saturnian Moon
NASA's Cassini probe showed a geyser shooting jets of water and fine icy particles hundreds of miles into space...

56 Comet Dust Records Solar System Chaos
One-third of a milligram of dust from comet Wild 2 landed on Earth last January...

67 Complex Organic Molecules Formed in Outer Space
Astronomers have identified eight new complex molecules in space...

75 Astro-Hotel Launched
Bigelow Aerospace last July launched Genesis 1, the first inflatable space station...

93 Renegade Planet Pair Defy Explanation
A pair of celestial objects circling one another have fed a growing debate over the dividing line between planets and stars...

96 Strange Swirls Spotted at Venus's Pole
Venus is Earth's near-twin in size and mass, yet bafflingly different in other particulars...

100 Saturn Sunburst
The Cassini spacecraft captured an extraordinary backlit image of Saturn and its gossamer rings...

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3 Cosmic Collision Brings Dark Matter Into View

A violent collision between a pair of massive galaxy clusters 3 billion light-years from Earth has turned up the most direct evidence yet of dark matter, the invisible substance thought to make up 80 percent of the matter in the universe. To catch dark matter in action, astrophysicists at Stanford University's Kavli Institute and the universities of Arizona and Florida compared X-ray images of visible matter in the clusters with a map of the total mass, which they obtained by measuring the degree to which light from distant galaxies was bent as it passed by, a phenomenon known as gravitational lensing.

Courtesy of NASA

When the researchers compared the two images, "the two didn't line up," says Kavli Institute astrophysicist Marusa Bradac. "This tells us there must be something there, and that it is dark matter." Because dark matter doesn't interact with regular matter, or with itself, it passes right through everything. So when the two galaxy clusters smashed together at a staggering 10 million miles per hour, visible matter slowed down in the crush of the collision, but dark matter flew through unfettered. "The visible matter created a kind of traffic jam in the middle, whereas dark matter has its own highway," Bradac says. The different locations of the two kinds of matter are seen in the image, where red represents visible matter and blue represents the dark stuff.

If dark matter exists, it should be present on Earth too. "There are dark matter particles around me and you right now," says Bradac. The next big step for physicists is to detect it in a terrestrial laboratory. That effort got a major boost two months after the Kavli crew announced its discovery, when the most sensitive—and recently upgraded—dark matter detector in the world went online. The Cryogenic Dark Matter Search (CDMS), buried half a mile deep in an old Minnesota iron mine to shield it from cosmic rays, searches for collisions between dark-matter particles called WIMPS and ordinary atoms in 19 hockey-puck-size hunks of germanium. The apparatus is tuned to spot heat energy deposited by these rare impacts, known as scattering events, so the temperature of the instrument's underground silicon and germanium detectors is held at a chilly –459.58 degrees Fahrenheit, just above absolute zero.

Physicists could detect dark matter in the next five years, says Bradac, assuming it has the properties scientists expect. CDMS physicist Dan Akerib of Case Western Reserve University is wagering that it does. "If WIMPS are just around the corner, we might be able to see something," he says. "I'm betting 10 years of my life that they are."

Alex Stone

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10 Pluto Demoted

For such a small planet—sorry, dwarf planet—Pluto caused a big uproar this year. In August a 424-person vote by the International Astronomical Union (IAU) in Prague settled the long-standing debate over how many planets our solar system contains, bumping Pluto and fixing the number at a modest eight. Due to a new requirement that planets dominate their gravitational domains, Pluto now falls under the quaint designation "dwarf planet," which applies to objects orbiting the sun that are not satellites and are "nearly round." The decision was met with responses ranging from praise to protest. (Some perplexed elementary-school teachers even held vigils.) But the brief period of national mourning over Pluto's demotion

Courtesy of NASA

soon gave way to new debate. Although the IAU's conservative description barred many celestial bodies access to the title of planet, it generated a new set of questions. What constitutes a dwarf planet? And what is instead merely a "small solar system body," the default category for the tens of thousands of asteroids and comets floating around the sun? At least 12 other candidates, including three asteroids and nine ice balls, are already up for dwarf status, with heated dispute and more votes sure to follow. Who knew astronomy could be so contentious?

Alex Stone

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13 Probe Snaps Baby Picture of the Cosmos

For five years, the Wilkinson Microwave Anisotropy Probe (WMAP) has been mapping cosmic microwave background radiation, the ubiquitous afterglow of the Big Bang. In March, the WMAP team released new data that provide the most detailed snapshot of what the universe was like as a trillionth-of-a-second-old newborn. The new portrait expands on the probe's initial results from 2003, which showed fluctuations in the microwave background caused by events 400,000 years after the Big Bang. Since 2003,

Courtesy of NASA

WMAP researchers have made more precise energy measurements of the microwaves that allow them to look farther back in time. Led by Charles Bennett of Johns Hopkins University, the team accounted for distortions in the microwaves due to collisions with distant clouds of electrons. As a result, researchers could study signals 100 times weaker than what was previously detectable. The findings suggest that the first stars lit up around 400 million years after the Big Bang, 200 million years later than originally estimated. The analysis also yielded a breakdown of the cosmic makeup: The universe consists of 22 percent dark matter and 74 percent dark energy. Dark energy seems to cause the expansion of the universe to accelerate, while dark matter helps hold galaxies and galaxy clusters together. And what of the other 4 percent? That's plain old matter—the stuff we're made of.

Stephen Ornes

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