Far away, around a star in the constellation Cancer the crab, scientists say they have discovered new evidence that we may not be alone.
A group of scientists working in Hawaii and California reported today that the star 55 Cancri has a complete solar system -- five planets, in almost circular orbits, at least one of which seems to be in the star's "habitable zone," where temperatures are likely to be right for liquid water to exist.
It has been more than a decade since astronomers found the first so-called "exoplanets" -- planets orbiting other stars -- and the total count is now more than 250.
But most of them were vastly larger than the Earth and followed lopsided, elliptical orbits. If they orbited close enough to their host stars to be warm, they would alternately fry and freeze -- not the best conditions for life to take root.
"This discovery of the first-ever quintuple planetary system has me jumping out of my socks," said Geoff Marcy, an astronomer at the University of California at Berkeley who is one of the world's leading discoverers of far-away planets. "We now know that our sun and its family of planets is not unusual."
Marcy and other scientists have been scanning the heavens, openly hoping to find planets like Earth.
"This discovery shows that our Milky Way contains billions of planetary systems," said Marcy.
The scientists who reported the find today said they have been watching 55 Cancri for 18 years, using the Keck Observatory in Hawaii and the Lick Observatory in California as part of a project funded by NASA and the National Science Foundation.
The star is 41 light years away, more than 240 trillion miles. Because of the great distances, they could not directly see the planets, but they could watch the star wobbling, ever so slightly, because of the gravity exerted on it by the planets as they orbited.
Then they did the math. They concluded that one of the planets is in an orbit about 72.5 million miles from the star, taking 260 Earth days to circle it once. It's therefore closer to its host star than the Earth is to the sun (93 million miles) -- but they said that is a promising sign because 55 Cancri is slightly fainter than the sun is.
"This object," said Jonathan Lunine of the University of Arizona at Tucson, "would have a very temperate climate. It would be a little bit warmer than the Earth, but not very much."
Is there a prospect for life on that distant world? Any answer to that question, said the scientists, would be pure conjecture. But Debra Fisher, an astronomer from San Francisco State University, pointed out that our Earth would be too small to be seen from other stars if there were anyone out there using technology like ours.
It's quite possible, she said, that 55 Cancri has more planets in its temperate zone -- and even moons around those planets -- that we cannot see.
"There could be Earths, there could be 10 Earth-mass planets, and we would just not have detected them," she said.
This discovery, said the researchers, raises the odds other worlds are capable of supporting life. Space telescopes of the future, flying above the Earth's atmosphere, may be able to spot them.
"There may be terrestrial planets around most stars," said Lunine. We just haven't found them yet."