Astronomers Find 1st Rocky Planets Beyond Solar System
Peering at dim specks of stars light-years from Earth, U.S. and European astronomers have made the first discovery of rocky planets beyond our solar system, a scientific leap that bolsters the possibility of Earth-like planets in the cosmos.
Until now, the only known extrasolar planets were gas giants, akin to Jupiter and Saturn, that are at least 300 times the size of Earth.
The three newly discovered planets are 15 to 20 times the mass of Earth but small enough that scientists believe they are composed primarily of rock and ice.
One of the new extrasolar planets, moreover, is the fourth planet discovered circling its star, making it part of the most complex known planetary system outside our own.
“We are beginning to see smaller and smaller planets. Earth-like planets are the next destination,” said astronomer Geoff Marcy of UC Berkeley, co-leader of one of the discovery teams.
“Up until now, the technology has limited planet detection to those in the Jupiter- and Saturn-mass range,” added his coauthor, Paul Butler of the Carnegie Institution of Washington.
“We’ve entered a new era for planet hunting.”
Two of the new discoveries were revealed at a NASA-sponsored news conference Tuesday. A third was announced Monday by Swiss researchers.
Reflecting the intense, though friendly, competition in the race to discover planets, the Americans dismissed the Europeans’ priority claim because their paper had not yet been accepted for publication, whereas the Americans’ had.
“Using an Olympics analogy, we would have to award the Swiss only a bronze medal,” said astronomer Alan Boss of the Carnegie Institution, who was not involved in the research.
All the teams deserve medals for a very important reason, he added. “This is evidence for a new class of planets about which we have not had any information,” he said.
“The fact that we are discovering a new class is very reassuring for the possibility that we would find new Earth-like planets.”
Anne Kinney, NASA’s director of astronomy and physics missions, said the discoveries may help answer a simple question: Are we alone in the universe?
Until nine years ago, astronomers had discovered no planets outside our solar system, and many researchers did not think such observations were feasible. Now astronomers know of 139.
Marcy and Butler pioneered the field using modestly sized telescopes to study the wobble of stars caused by the gravitational influence of one or more planets.
Because they were using relatively small telescopes to perfect their technique, the first planets they found were rather large ones circling relatively close to their stars.
The stars were also relatively large because of the need to gather sufficient quantities of light to measure the wobble.
Now that the technique has been refined, teams have moved to the largest Earth-based telescopes, where they can look at smaller, dimmer stars and detect smaller planets.
“We’ve got a factor-of-100 improvement from the original observations,” said astronomer Stein Sigurdsson of Pennsylvania State University. “We are only a factor of 10 away from finding Earths.”
That may require use of a space-based telescope called Kepler that is scheduled for launch in 2007.
Marcy and Butler used the massive Keck Telescope in Hawaii to find a new planet circling a small star called Gliese 436, which is only 30 light-years from Earth in the constellation Leo.
Gliese 436 is an M-class star, a so-called red dwarf, which is about 40% the size of our sun and produces only 2% to 3% the amount of light. About 70% of the stars in the Milky Way galaxy are M-class stars, but they have not been thoroughly studied in the search for planets because they are so dim.
The newly discovered planet, the second known to orbit an M-class star, is about 15 to 18 times the mass of Earth and is much closer to its star -- only 38% of Earth’s distance from the sun.
Because it is so close, its surface temperature would be about 300 to 400 degrees Fahrenheit, Marcy said. It orbits its star in about 2 1/2 Earth days.
Astronomer Barbara McArthur of the University of Texas at Austin used the large Hobby-Eberly telescope in West Texas to find a planet circling a star called 55 Cancri, about 41 light-years away in the constellation Cancer. The star is 5 billion years old, roughly the age of our sun, and about the same size.
Researchers had previously discovered three gas giant planets circling 55 Cancri every 15, 44 and 4,250 days. The new planet, with a mass about 18 times that of Earth, lies inside the orbits of the other three and orbits the star every three days.
The team calls the planet 55 Cancri e.
The Swiss scientists, from the Geneva Observatory, announced Monday that they had used the European Southern Observatory in Chile to detect a planet, about 14 times the mass of Earth, circling the bright star named mu Arae in the southern constellation Ara.
It is the second planet discovered circling this star and completes an orbit in 9 1/2 days.
