Planets More Like Earth Found Circling Nearby Stars
Posted on: Wednesday, 1 September 2004, 06:00 CDT
Astronomers report finding three worlds close in size to Earth orbiting nearby stars, opening a new era in the search for planets like our own.
A pair of U.S. teams led by astronomer Geoff Marcy of the University of California-Berkeley described a planet orbiting the star Gliese 436 and another orbiting star 55 Cancri. The announcement at a NASA briefing Tuesday follows a report, still under scientific review, from European astronomers last week about a rocky planet orbiting the star mu Arae.
Until now, the roughly 135 planets discovered orbiting nearby stars have essentially been giant balls of gas. The new planets are still hefty, 14 to 20 times heavier than Earth, but they are far smaller than gas giants such as Saturn and Jupiter (95 and 318 times heavier, respectively) and those orbiting other stars.
More important, the weight of the newly discovered planets -- about that of the icy planet Neptune -- suggests that they resemble Earth in that they have a rocky interior.
''It's a unique time in history, finding the first planets reminiscent of those in our own solar system,'' Marcy says. With temperatures that range from 300 to 1,160 degrees Fahrenheit and close orbits to their stars, the planets are too hot to support life. But planets with more life-friendly orbits probably will turn up in coming years, Marcy says.
''The main excitement about this particular discovery is that it bodes extremely well for there being a high frequency of terrestrial planets in our neighborhood of the galaxy,'' says astrophysicist Alan Boss of the Carnegie Institution of Washington, D.C.
The planet orbiting mu Arae shares the star with two gas giants that probably stunted its development, so it is probably a big rock. 55 Cancri's planet, spotted by a University of Texas astronomer, also has gas giant siblings. Astronomers estimate that about 20 billion planetary systems exist in the Milky Way.
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