Astronomy

Year In Science

Sunday, January 13, 2002

Foggy, Foggy Bang
Fog is the bane of Astronomy, but one type of fog inspires fascination rather than frustration: the universe-spanning haze that formed soon after the Big Bang. It burned away as the first stars lit up, so figuring out when and where that happened will clarify how the universe began its astonishing transition from darkness to light. In August, researchers filled in a big piece of the puzzle, spotting two galaxies at the very edge of the cosmic fog bank.

When the early universe grew cool enough for atoms to form, subatomic particles combined into extensive clouds of neutral hydrogen and helium, which efficiently absorbed ultraviolet light from the earliest stars. "It's like looking at them through sunglasses," says astronomer George Djorgovski of the California Institute of Technology. Over time, however, energetic rays from the stars stripped electrons from the atoms, transforming them into transparent charged ions. In this way, radiation carved out hollows in the haze—like holes in Swiss cheese—that grew ever larger until the clear regions merged. "The clouds are never entirely destroyed," says astronomer David Tytler of the University of California at San Diego. "The last wisps survive to this day."

Attempts to glimpse the earliest birthing stages of stars and galaxies have been thwarted in part by the light-snuffing clouds. Undaunted, two teams (one of them led by Djorgovski, another by Robert Becker of the University of California at Davis) went to work using the giant Keck telescope. The effort paid off: Each team obtained good data on a quasar, a type of active galaxy, that was shining when the universe was about a billion years old, just as the fog was beginning to clear. The findings give the best indication yet of when the process happened. Djorgovski's quasar, which is 100 million years older than the one studied by Becker, appears to be largely in the clear. The younger galaxy is still partly socked in, which suggests that the lifting of the veil occurred in between the formation of the quasars. The timing of that transition confirms cosmologists' models of the early universe.

Probing the edge of the fog bank should help explain how quasars and galaxies managed to form soon after the tumult of the Big Bang. "Right now, it's a bit of a challenge to explain how to make things so quickly," Djorgovski says. "We'll be able to learn some things by looking at how lumpy the edge of the cloud is." In the coming decade, NASA's Next Generation Space Telescope should be able to pierce the fog entirely and reveal, to an eager audience, the first galaxies lighting up one by one.
— Jeffrey Winters


King of the Small Fry
Pluto is the last planet in the pecking order—distant, dim, and so small at 1,400 miles across that some scientists are trying to demote it to an asteroid. Pluto's status grew even more uncertain in May, when astronomers discovered an object roughly half as large in the same region of the solar system. Some regarded it as a challenge to Pluto's planethood; others noted Pluto's larger size still makes it stand out. "You can use this object as ammunition for either side of the debate," says Robert Millis of the Lowell Observatory in Flagstaff, Arizona, who led the team that spotted it.

Judging from its brightness and its distance from Earth, the object, called 2001 KX76, may be 600 to 800 miles across, Millis says. That puts it comfortably ahead of Ceres, long regarded as the largest asteroid. But Millis thinks the comparison is misleading. KX76 belongs to a group of some 500 known objects in the Kuiper belt, a zone on the solar system's fringe. "These objects aren't asteroids; they have a different heritage," Millis says. The two populations are thought to have very different compositions and have probably never mixed. Kuiper belt objects are therefore gaining recognition as a completely separate class of celestial bodies.

There may be 100,000 such objects more than 60 miles wide; a few of them could be the size of Pluto. If so, will that make them planets, or will that make Pluto just another Kuiper belt object? "I'm not interested in what we call them," Millis says. "I just want to find them."
— Jeffrey Winters


The Great Moon Race
Nobody has found a new planet in our solar system since 1930, but astronomers doing a brisk business uncovering new moons. In July, an international group led by Brett Gladman of the Cote d'Azur Observatory in France announced the biggest catch ever— 12 previously unseen satellites, each no more than 20 miles wide, floating in irregular orbits around Saturn. If they all check out, the finds will bring Saturn's moon count to 30, placing it ahead of the longtime champ, Jupiter.

Gladman's team utilized multiple telescopes equipped with sensitive silicon light detectors to survey a large area around Saturn. Similar efforts over the past five years have lifted the number of Jupiter's moons from 16 to 28 and Uranus' from 15 to 17. The boom is far from over, says Brian Marsden of the Harvard-Smithsonian Center for Astrophysics: "Only one-eighth of the area around Jupiter has been searched, so we could find dozens more."

An analysis of the orbits of Saturn's new satellites shows they cluster in groups. Gladman speculates that the giant outer planets captured passing chunks of rock or ice while the solar system was forming. Gravitational forces or subsequent collisions could have fragmented each chunk into a family of small moons. For now, Saturn is the prize example of what happened during those chaotic early days, but Jupiter may soon regain the title.
— Maia Weinstock


Ringing in the Sky
When poets describe the heavens, they often evoke images of diamonds and black velvet. But results from two experiments announced in April suggest a different metaphor: 300,000 years after the Big Bang, the cosmos was ringing like a set of chimes. During that early era, a soup of hot subatomic particles sloshed around like water in a tub, flowing into relatively dense regions of space and flowing out again when the heat from compression overwhelmed the pull of gravity. This push-and-pull battle set off soundlike oscillations all over the universe.

Last year two Antarctic experiments, one flown aboard a balloon, the other based at the south pole, detected subtle signs of this cosmic ringing embedded within the loud buzz of microwave radiation coming from the edge of the universe. "It was like looking at a white wall and subtracting out the whiteness," says physicist John Ruhl of the University of California at Santa Barbara, a member of one of the teams. This year, more precise measurements began revealing details about the early universe buried within the acoustic pattern. The size and spacing of the harmonics indicate that 30 percent of the mass of the universe is made up of mysterious dark matter, and another 65 percent is in the form of dark energy. That the ringing existed at all supports the theory of a rapid period of expansion that occurred just after the Big Bang. NASA's Microwave Anisotropy Probe is now giving the cosmos an even closer listen.
— Jeffrey Winters


Black Hole on a Diet
Because a black hole gobbles everything in its path, you'd think it would always get bigger. But in October, European astronomers discovered a spinning black hole that's losing steam—it's tangled up in a magnetic field. That field slows the black hole's spin, which transfers the energy to a surrounding cloud of gas.


Comet Close-up
Nasa's Deep Space 1 is making a habit of confounding expectations. Scientists initially pinned little hope on the spacecraft because it was built primarily as an engineering experiment to test 12 new technologies, including a superefficient ion propulsion system. Any discoveries that might be made after the technology was proved would be gravy. Then, shortly after Deep Space 1's launch in 1998, even the engineering goals seemed threatened when the ion drive failed to function as expected. Now, three years later, both engineers and scientists couldn't be happier. Not only did all the new technology eventually work, but the little spacecraft also produced some good science. On September 22, Deep Space 1 performed its greatest feat yet, diving through the gas and dust around comet Borrelly and sending back the best-ever images of a comet's nucleus.


Deep Space 1 whizzes by comet Borrelly, propelled by an ion engine whose blue exhaust is exaggerated in this artist's rendering. The probe's snapshots offer the first clear look at a comet's nucleus (inset), a primeval chunk of dust and ice.
Illustration courtesy of NASA/JPL; inset photograph, courtesy of NASA/JPL
Although the European spacecraft Giotto flew to within a few hundred miles of Halley's comet in 1986, its view was obscured by haze. Most of Borrelly's gas and dust emerges from the nucleus along a narrow jet, leaving an open path that allowed Deep Space 1 to get a clear look from a distance of 1,400 miles. The images were surprising: At the heart of the cloud lies an irregular, frozen world, some five miles long, marked by rolling plains, jagged peaks, and deep chasms. "It looks like a foot," says Laurence Soderblom, a geologist at the United States Geological Survey in Flagstaff, Arizona, who helped build the probe's camera. "There's a heel that's raised quite a bit, a low, smooth area in the middle that's like an instep, and rubbly, dark bumps where the toes would be." Soderblom says the images suggest the "instep" is slowly evaporating, meaning that someday the comet will break in two.
— Jeffrey Winters

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