28 newfound planets in Milky Way spur hunt for Earth look-alikes

An artist's concept of the Neptune-sized planet GJ436b (right) orbiting an M dwarf star, Gliese 436, at a distance of only 3 million miles. With a density similar to that of Neptune, the exoplanet is an ice giant and probably has a rocky core and lots of water that forms ice in the interior under high pressure and temperature. GJ436b was discovered in 2004 by the California and Carnegie Planet Search team, and found by Belgian astronomer Micha�l Gillon in May 2007 to transit its star. Credit: Copyright Lynnette Cook / UC Berkeley Handout. less An artist's concept of the Neptune-sized planet GJ436b (right) orbiting an M dwarf star, Gliese 436, at a distance of only 3 million miles. With a density similar to that of Neptune, the exoplanet is an ice ... more Photo: Lynnette Cook Photo: Lynnette Cook Image 1 of / 1 Caption Close 28 newfound planets in Milky Way spur hunt for Earth look-alikes 1 / 1 Back to Gallery

All of a sudden the Milky Way is filling up with far-off solar systems never seen before -- more and more planets of all shapes and sizes, wheeling in orbits around their own sunlike stars.

Astronomers on teams from UC Berkeley and Australia reported the discovery of 28 new planets all at once on Monday, and their leader -- working through the night all this week at the world's biggest telescope in Hawaii -- is now on the hunt for rocky planets that might resemble Earth.

"An overarching question now is whether our own solar system is really alone," said Geoffrey Marcy, the Berkeley astronomer whose team has led in the discovery of what are now widely known as "exoplanets."

Marcy and many of his colleagues are in Honolulu for a meeting of the American Astronomical Society, and in telephone interviews and e-mails he said he and Katie Peek, 26, a Berkeley graduate student, are scanning 70 more stars right now to seek still more of the increasingly common objects.

"It's all most amazing and fascinating," Jason Wright, a Berkeley postdoctoral fellow, said in a telephone conversation. He and colleague John Asher Johnson described the group's findings in detail at the astronomy meeting.

The 28 planets they and their Anglo-Australian colleagues reported bring the total number of exoplanets discovered to 236 since the first one was detected barely a dozen years ago, and now the rush is on.

The two teams reporting Monday said that besides the 28 planets they discovered during the past year, they also found seven brown dwarfs -- huge and strange objects much larger than Jupiter that are called "failed stars" because they never grew to a size and mass big enough to turn on their nuclear fires and blaze forth as true stars.

But among the confirmed solar systems detected during the past year, four of the stars hold at least two planets in orbit and maybe more that are as yet undetected, the astronomers said. Two other stars hold objects that are even more puzzling: They could be either giant gas planets or brown dwarfs, and only more investigations with more sensitive instruments will be able to identify them for certain.

Some of the new-found exoplanets, Marcy said, are "massive super-Jupiters," orbiting far from their suns, while others are "hot Jupiters" orbiting less than 3 million miles out -- only a fraction of the distance Earth is from our own sun, about 93 million miles.

Marcy and Wright singled out one extraordinary planet that orbits a star called Gliese 436 that is much like our own sun and only 30 light-years away. The Berkeley team found the planet two years ago, and only two weeks ago Michael Gillon of the University of Liege in Belgium detected it crossing the face of its sun and was able to determine its diameter for the first time. Although Gliese 436's planet is the size of Neptune, the Berkeley team's measurements show its mass is 17 times greater.

Most of the exoplanets are detected by the wobble their gravity causes in the suns they orbit, but the one around Gliese 436 is known as a "transiting" planet because its orbital path crosses directly in front of its sun as viewed from Earth.

Among the three Neptune-like exoplanets around other stars, Marcy said, "This one is the Rosetta stone. It must be composed of a rocky core surrounded by large amounts of water compressed into a solid by the planet's gravity" -- very much like Neptune and Uranus in our own solar system.

"The overarching theme is that many of the properties of our solar system are suddenly noticeably common among planetary systems in general," Marcy said. "Apparently, our solar system is structurally common (with others elsewhere in the galaxy) and its planetary inhabitants must have a common composition."

And as Wright put it: "They're starting to look more and more like real solar systems -- like our own."

Whether the giant exoplanets fly in orbit close-in or far-out from their stars, both Marcy and Wright agree that smaller rocky planets like Earth and Mars could well be orbiting there, too -- some at "habitable distances" from their suns, where temperatures are benign and liquid water and the properties necessary for life could exist.

As the technology for detection improves -- and perhaps even now -- the chances of finding such distant exoplanets will improve, too, they agreed.

Marcy is hunting more exoplanets every night this week at the W. M. Keck Observatory atop Mauna Kea on the Big Island of Hawaii, where the twin telescopes are the world's largest.

His team includes Debra Fischer of San Francisco State University, Paul Butler of the Carnegie Institution in Washington, and Steven Vogt of UC Santa Cruz. The Anglo-Australian group's leaders include Chris Tinney of the University of New South Wales and Hugh Jones of Britain's University of Hertfordshire.