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Chart showing that most of the five new planets are much hotter and bigger than any planet in our solar system

Most of the five new planets are much hotter and bigger than any planet in our solar system.

Illustration courtesy William Borucki, NASA

Victoria Jaggard in Washington, D.C.

National Geographic News

January 4, 2010

Five new planets have been found orbiting distant stars—the first confirmed new worlds from NASA's recently launched Kepler space telescope mission, astronomers announced today.

Like many of the more than 400 exoplanets—planets outside our solar system—found to date, the new planets are so-called hot Jupiters. They're about the same mass as Jupiter and orbit very close to their host stars, which makes the planets relatively easy to spot from Earth.

The smallest of the new planets is about the same size as Neptune, though much more massive. All of the planets are hotter than molten lava and could turn gold to goo, according to NASA temperature estimates.

Dubbed Kepler 4b, 5b, 6b, 7b, and 8b, the five new planets range in temperature from 2,000 to 3,000 degrees Fahrenheit (1,090 to 1,650 degrees Celsius), William Borucki, Kepler's principal investigator, said today during a press briefing at the American Astronomical Society's annual meeting in Washington, D.C.

One of the worlds, Kepler 7b, is among the lowest-density planets yet found, with about the same density as Styrofoam, he said. (Related: "'Backward' Planet Has Density of Foam Coffee Cups.")

These planets are "certainly no place to look for life—that will be coming later," with discoveries of Earth-like planets, Borucki said.

Kepler "Working So Well"

Kepler's main goal is to find rocky, Earthlike planets orbiting in stars' habitable zones—the regions in which planets receive enough heat from their stars for liquid water to exist.

While the new finds don't meet those criteria, they do show that the instrument is working as expected—offering "a tantalizing hint at what we can expect in a few years' time," noted Greg Laughlin, an astronomer at the University of California, Santa Cruz.

"It's wonderful to see Kepler working so well."

How to Find New Planets

Kepler looks for extrasolar planets by spying the decrease in starlight as a planet transits, or crosses in front of, its host star, as seen from Earth.

The orbiting telescope, which launched last March, spotted the five new worlds in its first six weeks of operation.

Each planet's existence was later confirmed using a method called radial velocity, which looks for the wobble in a star's orbit caused by the gravitational pull of an orbiting planet.

The radial velocity observations were "a beautiful match" for Kepler's data, Borucki said. "It completely confirms that we really have planets here."

Having both sets of data creates a "truly valuable situation" in planet hunting, UCSC's Laughlin added.

That's because each method does more than just help confirm the other. Each technique provides different types of information, which help build a more complete picture of the alien world.

Radial velocity, for example, gives details about a planet's mass and orbit, while transits can reveal a planet's size relative to its star. This in turn tells astronomers about the planet's density.

Planet-hunting missions such as Kepler have shown us that the densities of exoplanets are all over the map, Laughlin said.

Some of the biggest worlds, for instance, have been found to be unexpectedly "puffed up" by an as-yet unexplained heat source.

Kelper 5b, for instance, is much more massive than Jupiter but is much less dense then water, said mission co-investigator Dimitar Sasselov.

"It's like looking at a football team," Laughlin said. "You might guess that they're all 250 to 300 pounds. But then you find out that some of them are 25 pounds—that would come as a surprise."

Hundreds of Candidates for New Planets

Although Kepler's five new planets are the only ones confirmed by the mission so far, the telescope's first few months of data actually contain hundreds of candidates.

The Kepler mission, expected to last at least three and a half years, will likely announce many more new worlds in coming years as astronomers are able to confirm the planets' existence.

But it will take several Earth years before Kepler scientists can be sure they've seen an Earth-size world in its star's habitable zone, Laughlin said.

That's because a planet orbiting at the right distance from its star will be farther out than a hot Jupiter and so will take much longer to complete an orbit of its star—making transits much rarer.

To be sure you've seen a planet, "you have to watch long enough to see three to four transits," Laughlin said.

Overall, though, the new finds help make it clear that planets with otherwise similar traits can have very different personalities, Laughlin noted.

"It's not a situation of, You've seen one, you've seen them all."

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