Kepler spacecraft finds more than 1,000 planets
Published 4:00 am, Thursday, February 3, 2011
The Kepler spacecraft, searching far beyond our solar system, has found more than 1,000 possible planets orbiting distant stars, and at least 54 of them are within their suns' "habitable zones," where temperature could support liquid water and potentially life.
Borucki and his team announced the long-awaited results Wednesday of the first four months of data from Kepler's search for planets among 156,000 stars more than 2,000 light-years away from Earth.
Of the 54 planets whose orbits lie in those habitable zones, Borucki said, five are very close to Earth's size while others range from twice the size of Earth to as large as our solar system's gas giant, Jupiter.
In all, Kepler has found 1,235 planets - called exoplanets because they exist outside our solar system. Most of them are a weird assortment: 288 are "super-Earths," at least twice the size of our own, 662 are the size of Neptune, 165 are Jupiter size, and 19 are much larger than Jupiter.
The spacecraft's search has focused on a region of space where the constellations Lyra and Cygnus exist.
"Kepler has blown the lid off everything we've known about exoplanets," said Debra Fisher, a Yale astronomer and a planet hunter on a team using different methods to detect and measure planets in the same area of space.
"I'm amazed," she said of the huge variety of planets in the team's report on the Kepler mission, which began in March 2009.
5 planets and a giant
Among Kepler's new discoveries was a mini-solar system with five tightly packed small planets orbiting close to their star in addition to a giant planet flying in orbit farther out.
The "amazing" planetary system is unlike any other found so far, said Jack Lissauer, a member of the Kepler team.
All five small, inner planets fly in the same plane - much like the planets of our solar system. They vary from two to four times the size of Earth, and because their orbits are so tightly clustered, each one's gravity is perturbing the orbit of the others, Lissauer said.
The planets have such low masses that the outer density of each is sort of like a marshmallow, while their cores are "probably like hard candy," he said.
All five have atmospheres of hydrogen and helium, suggesting, he said, that they could well be models of how all planets everywhere formed billions of years ago - by condensing from flattened and swiftly rotating "proto-planetary" disks of gas and dust. But none of them appears capable of supporting life because their orbits are so close to their sun - similar to those of our solar system's close-in planets, Mercury and Venus.
A report by Lissauer's team on the unusual solar system will be published today in the journal Nature.
Much work to do
The other new planets announced by Borucki's team are still listed as "candidates" - meaning that the scientists must do much more work by computer to confirm that they really are planets and to precisely determine their size, mass and orbits.
Kepler's telescope is only surveying 1/400 of the spacecraft's field of view in the visible sky, Borucki noted. And that would mean, he said, that within 3,000 light-years from Earth there must be at least 20,000 exoplanets now in orbit within the habitable zones of their suns.
The spacecraft's eye stares at 156,000 stars simultaneously every 30 minutes and measures infinitely small changes in their brightness. Those changes could indicate that some object like a planet is passing in front of the star and dimming its light - an indication that the planet is "transiting" the star.
From that kind of ultra-precise observation, Kepler's scientists and their super-smart computers can confirm that the spacecraft has spotted a real planet, determine its orbit, and even measure its size and its mass - measurements that can then be further confirmed by powerful ground-based telescopes, like the Keck in Hawaii.