NASA - In search of Earth
new class of planets found!
Posted 61.09.2004

SPACE -- Our planet is not alone. It may not even be lonely.

Astronomers on Tuesday announced the discovery of a new -- and possibly abundant -- class of planets that has more in common with Earth than the uninhabitable gas giants previously discovered.

"We are closer to answering the question, 'Are we alone in the universe?'" said Anne Kinney, director of NASA's Universe Division, Science Mission Directorate. "We aim to answer that question by looking for planets, eventually imaging them and ultimately diagnosing the presence of life on those planets."

Astronomers found the two planets, among the smallest ever detected, orbit different stars less then 50 light years from Earth. One planet circles a red dwarf star, the most abundant in our Milky Way galaxy, igniting hope that the discoveries may just be the beginning.

"We would like to make these discoveries routine and eventually push into the 'super Earth' regime," said Geoffrey Marcy of the University of California at Berkeley, who discovered a planet orbiting working with R. Paul Butler at the Carnegie Institution of Washington.

With evidence of smaller, rocky planets growing, finding another Earth seems more likely.

"It appears that most if not the majority of the remaining 100 billion stars [in the Milky Way galaxy] have some sort of planets orbiting around them," said Butler. "We are edging closer and closer to planet systems that are like our own solar system."

Using a technique that measures the "wobble" of a star caused by a planet's gravitational pull, astronomers inferred the existence of the two extraterrestrial worlds, or exoplanets, as well as traits such as their mass, orbit and speed. The star's movement, or wobble, is found by measuring the Doppler effect on light. The wavelength of the star's light lengthens, or stretches, as it moves with the gravitational pull of the planet reveals much about the planet itself..

The announcement follows on the heels of another by Swiss planet hunters who claimed to discover another planet even smaller than the one announced on Monday. That would add another instance to the new class of planets, although astronomers at Tuesday's conference said recognition of the claim would first require acceptance by a peer-reviewed journal.

There has been an explosion in the number of astronomers scanning the skies for the telltale wobble of distant worlds. Already, about 135 large exoplanets have been discovered. By refining their methods, astronomers can now detect objects even smaller than Saturn. Eventually, they have their sights set on discovering a world the size of our own.

Both of the recently discovered planets are slightly larger than Earth, about the size of Neptune, or about 17 times the size of our planet. Because they are so close to their star, they race through an extraterrestrial "year" in a matter of days.

Beyond that, astronomers can't speculate much about their appearance. They may consist of spheres of gas like Jupiter or look like Neptune itself with a core of rock and ice surrounded by a thick atmosphere of hydrogen and helium.

Given their proximity to the sun, they could also be like a scorched rock resembling Mercury.

The first planet orbits a cool, reddish dwarf star called Gilese 436 in the Leo constellation. Meticulous observation of the star began in July 2003 and detected the planet believed to be at least 21 times the size of Earth. It completes its orbit at the blazing rate of just 2.64 days instead of Earth's 365 days.

The second planet orbits a yellow star like our own, called 55 Cancri in the constellation Cancer, and is part of the first four-planet solar system ever discovered. It is estimated to be about the size of 18 Earths in mass, orbits in 2.81 days and lies about 41 light-years from Earth.

"It's the closest analog we have for our own solar system," said Barbara McArthur, investigator of the study from the University of Texas at Austin.

The planets were discovered using ground-based observations from the W.M. Keck Observatory in Hawaii, the Lick Observatory in California and the McDonald Observatory in Texas. Archived data from the Hubble space telescope was also used.

Both studies will appear in the Astrophysical Journal in December.

NASA will launch a series of missions to find more planets in the future including the Kepler Mission, the Space Interferometry Mission and the Terrestrial Planet Finder to seek out Earth-like worlds.

"These are the three missions that NASA designed to find that pale blue dot orbiting a yellow star that might harbor life," Butler said.