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"Diamond Planets" Hint at Dazzling Promise of Other Worlds

Stefan Lovgren
for National Geographic News
February 8, 2005
 
The universe beyond our solar system just got wilder.

Astronomers meeting in Colorado this week said they have found a disk of planet-building material around a small, "failed star" called a brown dwarf. The discovery raises the possibility that there may be pint-size solar systems where planets orbit objects far smaller than our sun.

Another team of scientists theorized that some faraway planets could be made mostly out of carbon, and may have a thick layer of diamonds hiding under the surface.

And yet another astronomer announced that he had spotted the smallest planet ever detected outside our solar system.

The results were presented to reporters on Monday in a teleconference from an extra-solar planet meeting held by the American Astronomers Association at the Aspen Center for Physics in Colorado.

Smallest Planet

Once, scientists believed that planetary systems might be very rare. But since the first planet outside our solar system was found in 1992, more than a hundred planets orbiting stars beyond our system have been discovered.

"This dramatic increase in the number of planets discovered … is not by chance," said Michel Mayor, a prominent astronomer at the Geneva Observatory in Switzerland. "It's the … improvement of the quality of the spectrometers during these years" that have made the discoveries possible.

Spectrometers separate radiation, including light, into different wavelengths. This allows astronomers to detect bodies that they can't see with telescopes alone.

Up to 20 new planets are being announced this week at the 2005 Winter Conference on Astrophysics, which features more than 200 scientists from around the world.

Alex Wolszczan, the Penn State University astronomer who found the first planets outside our solar system, announced that his team had found the smallest planet yet—in the same system as that earlier discovery.

The newly discovered planet, which is about one-fifth the mass of Pluto, is immersed in an extended cloud of gas. It orbits a pulsar—a former star that exploded and collapsed into a dense object and now spins 160 times per second—1,500 light-years away in the constellation Virgo.

The three previously discovered planets around the pulsar have their orbits in almost exact proportion to the spacings among Mercury, Venus, and Earth. Wolszczan says the whole planetary system looks like a scaled-down copy of our own inner solar system.

Forming Planets

Astronomers are increasingly using bigger and better telescopes to look beyond the brightest objects in the cosmos, such as supernova explosions and giant galaxies. Now they're focusing on exotic planets that could harbor life.

Scientists using NASA's Spitzer Space Telescope recently discovered a dusty disk around a so-called brown dwarf—a star that failed to grow big enough to ignite and burn hydrogen, as our sun does. The finding suggests that there may be mini-solar systems in which planets orbit objects that are barely bigger than a planet itself.

The failed star, known as OTS 44, is about 500 light-years away. It is among the smallest known brown dwarfs—just 15 times the mass of Jupiter. It is also the smallest object yet found with a disk of material around it.

A disk of such material once surrounded our sun, and the Earth is believed to have formed from it. The presence of a disk around brown dwarfs suggests that terrestrial planets could form around an object that is too small to shine via nuclear fusion, as our sun does.

"We have identified the smallest body that is known to have the building blocks around it for making planets," said Kevin Luhman, lead author of a study by the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts.

Glittering Planets

Meanwhile, another team of scientists theorized that some faraway planets could be mostly carbon, with a thick layer of diamonds hiding under the surface.

Earth, Mars, and Venus are "silicate planets," consisting mostly of silicon-oxygen compounds condensed from a disk of gas orbiting the sun. Carbon planets, though, might form more differently, the scientists said.

In gas with extra carbon or too little oxygen, carbon compounds like carbides and graphite could form instead of silicates, said Marc Kuchner, an astronomer at Princeton University in New Jersey.

Any condensed graphite would then change into diamond under high pressure and potentially form diamond layers. Inside the planets such layers could be several miles thick.

Kuchner said the galaxy is becoming richer in carbon as it gets older. "It may become so carbon rich that all planets formed in the future may be carbon planets," he said. "Just wait a couple of billion years."

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