An international team of astronomers has detected at least four new planets orbiting two distant stars very similar to our Sun. The discovery raises the possibility of finding potentially habitable worlds in other solar systems in the near future.
The discoveries include three planets orbiting the sun-like star 61 Virginis - a relatively close neighbor, about 28 light years away. All of the planets detected around the star are considerably larger than Earth, including a so-called "super Earth" that is five times the mass of our planet.
Astronomers also detected another giant Earth-like planet orbiting a star called HD1461, 76 light years away. The planet is 7.5 times Earth's mass, but much smaller than giant planets like Jupiter or Saturn. And scientists say there might two other planets in the HD1461 solar system.
Astronomers say the stars 61 Virginis and HD1461 are very similar to the Sun in terms of their mass, brightness and composition, something that has made them the objects of study by planet hunters.
Gregory Laughlin, an astronomer at the University of California, Santa Cruz, helped analyze combined observational data from telescopes in Hawaii and Australia that led to the discoveries.
"The planets that we've found, they could be Earth-like in the sense that they could be made largely of rock and metal," said Gregory Laughlin. "But the excitement in these discoveries is that they point the way toward the detection of truly Earth-like planets in a very short period of time, within the next few years."
Astronomers detected the new planets using indirect observations. Laughlin says the ground-based observations used the Doppler wobble method that is becoming an increasingly common way of detecting planets outside our solar system.
"When a planet is going around a star, it pulls the star back and forth," he said. "When the star is coming toward you, its light is ever-so-slightly bluer. And when it's going away from you, its light is ever-so-slightly redder. And we have a spectrograph instrument that can detect those very, very subtle changes. And it allows us to infer the presence of the planets orbiting a star."
Laughlin says the Doppler method that astronomers now use is quite effective for detecting new planets.
"And it's pretty clear that the ease we're making detections now is going to allow us to probe in to a regime where we're looking at planets that are potentially habitable and potentially truly Earth-like," said Laughlin.
Around 400 planets outside our solar system have now been discovered, and during the past year, scientists have said it is evident that planets commonly orbit neighboring stars.
Two papers describing the new planets are published this week in The Astrophysical Journal.