2 More Planets Found Beyond Solar System

Pursuing a tip from a college sophomore in England, a California astronomer has discovered two new planets orbiting distant suns--raising the total number of known planets outside our solar system to 12.

The discovery potentially brings dreams of inhabited worlds beyond the sun one step closer to reality.

Although neither Jupiter-sized orb seems likely to support life, one of the new planets is the first found to orbit its star at a leisurely earthlike pace, with a 437-day year. Instead of circling its sun, however, the planet traces a wide ellipse, zooming in closer than Venus is to our sun, then looping out beyond the distance of Mars, creating a climate alternately furnace-hot and sub-freezer-cold. Still, it is the nearest thing to an earthlike orbit yet seen in the skies beyond our solar system.

The other new planet skims perilously close to its parent star, orbiting in just three days.

The discovery was announced Wednesday by San Francisco State University astronomer Geoffrey Marcy. Along with his colleague, Paul Butler of the Anglo-Australian Observatory, Marcy has discovered nine of the 12 known extrasolar planets.

The newest members of the planetary family are also notable because they are the first discovered with the Keck Telescope on Hawaii’s Mauna Kea, the sharpest optical telescope in the world. Keck is scanning more than 400 stars for signs of planets, and Marcy strongly hints that he has found others that he isn’t quite ready to announce.

“We sit on prospective planets for six to 12 months [before we announce them],” Marcy said. “Right now we’re like mother hens, sitting on unhatched eggs.”

At least one of the new planets orbits a star suggested out of the blue by a student and amateur astronomer at the University of Sussex. For some time, Kevin Apps had been studying available data for stars likely to have planets, based on their sizes, ages and types. He e-mailed Marcy, offering assistance in the astronomer’s planet search.

“I had never heard of him,” Marcy said. “I thought, ‘What arrogance!’ An amateur astronomer who thought he could select stars better than we could.”

Grudgingly, Marcy said, he checked out Apps’ suggestions. Now the student is in charge of selecting target stars for Marcy’s group.

Since the planets are too dim to be seen directly, astronomers detect their presence by telltale wobbles in the path of the parent star as it gets pulled about by the planet’s gravity. These wobbles stretch the light from the star, distorting its spectrum.

The Keck Telescope, says Marcy, is the world’s best at resolving these stellar signals.

Still, the astronomers need to carefully plot the positions of the star for at least a year. “At first, you don’t see much of a wobble,” Marcy said. “It takes a while to literally connect the dots.”

Once they see the telltale pattern, the astronomers wait for at least six months to make sure before announcing results. “Because of the sordid history of planet searching, we consider it very important to maintain high credibility,” Marcy said.

Until a few years ago, most newly discovered “planets” turned out to be illusions. The few that were confirmed follow extreme orbits--either far more distant, or far closer, to their suns than Earth to its sun. “We were wondering whether nature avoids the zone our Earth is in,” said Marcy. Only an earthlike orbit can produce the temperate climate thought essential to the evolution of life.

With Keck, however, astronomers believe that discoveries of planets should become increasingly everyday events. “The precision of measurement is such that it’s becoming almost routine,” said William Cochran, a University of Texas astronomer who also uses Keck to hunt for planets.

Based on their distance from its star, Harvard astronomer Dimitar Saselov has calculated that the planet skimming near the yellow sun known as HD187123 should loom as a huge violet-blue marble in the sky. The planet with the earthlike orbit around HD210277, according to Saselov, probably looks a lot like Jupiter. “While any new planet is exciting,” he said, “these two are special.”