U.S. astronomers have found a second example of what could be a strange new class of planet. Peering outside our solar system, they have spotted the largest planet ever observed, but one so light that it would float on water. Other astronomers have devised techniques to try to determine if life exists on other planets.
Since 1995, scientists have found nearly 200 planets outside our solar system, but the new one is the biggest yet detected. It is one-and-a-third times bigger in diameter than Jupiter, the largest planet in Earth's neighborhood, and its volume is 2.5 times more.
But to everyone's surprise, it is so light that it is like a big ball of cork in space, confounding current theories about planetary evolution and structure.
"We have discovered a very bizarre new object," said Co-discoverer Robert Noyes of the Smithsonian Astrophysical Observatory near Boston.
He says its density is only half that of Jupiter, which is a sphere of gas around a central core. He notes that Jupiter would sink in a cosmic bathtub, but the newly found planet would bob on its surface.
Noyes says it is only the second very low density planet found, but the bigger of the two - 24 percent bigger than current theories say is possible for a planet.
"There is actually another one almost as bizarre, so now we have two of them. So the people who do the theoretical structure models are left scratching their heads as to what possibly be going on."
Noyes and his colleagues detected the planet orbiting one of a pair of stars in the constellation Lacerta about 450 million light years away, the time it takes light to travel that distance. They calculated the planet's size and density by observing how much the light of the star dimmed as the planet blocked it while it passed in front.
Noyes says the only way the planet could be so big and light is if an interior heat source is puffing it up. It must also lack a solid core of material like those in our solar system whose gravity holds material in tighter.
Co-researcher Dimitar Sasselov of the Harvard University Origins of Life Initiative says the planet is the strangest yet encountered.
"Today we have a new challenge, yet another kind of extreme planet, and it's a real mystery," he said. "It is actually a hallmark of an age of exploration, and I truly believe that we are in the beginning stages of a new age of exploration of these kinds of objects."
The scientists say the big, puffy planet could not harbor life as we know it, since it is too close to its sun, and therefore too hot.
They point out that life is more likely on an Earth-sized planet around a distant star. With telescopes and techniques improving, they say it is only a matter of time before an Earth-like planet is found. But if so, could we tell whether it had life?
Another group of Smithsonian astronomers has devised a method to do this. Wesley Traub and colleagues say the composition of its atmosphere would be an important clue.
"The only way we can tell about what's going on in the oceans and on the ground is by looking at the waste gases that go from these animals into the atmosphere," he explained.
This would be methane, oxygen, and nitrous oxide, detectable by measuring the color of their light with a spectrograph.
Their abundance would vary depending on the stage of life development, but Traub says it would be far from the level of mammals.
"The kind of life that we're looking for is really bugs, bacteria, and slime," he explained. "You know, it's not people walking around at the surface. It's slimy little things on the ocean and the surface, but that's life!"
Traub and his colleague Lisa Kaltenegger propose using Earth's atmospheric history as a guide. By mapping its composition through time, they propose looking for similar atmospheric conditions on other planets to determine if life exists and at what evolutionary stage.
"This for us is a fingerprint. It's an ID card," she said.