The most recent discoveries bring the number of known exoplanets – planets outside our solar system – to 236, the researchers said on Monday.
“We are beginning to see that our home is not a rarity in the universe,” said Geoffrey Marcy, a professor of astronomy at the University of California Berkeley in the US, who led the team.
“We are easily able to detect giant planets like Jupiter and Saturn around other stars. Most orbit far from the star like our own Jupiter and Saturn orbit from the sun,” Marcy said.
Four of the systems also have multiple planets, like our own solar system. The researchers have posted details of their findings at exoplanets.org.
“The attribute which really has us excited is this new planet which we found three years ago,” Marcy said. The Neptune-like planet orbiting the star Gliese 436 has intrigued scientists because it
appears to be covered with water – albeit rock-hard, hot water in a most un-Earthlike chemical state because of the intense pressures on the planet.
Lngredients of Life
Earlier this month, Swiss and Belgian researchers imaged the star as this planet crossed between it and the Earth. The tiny change in the star’s light gave them the planet’s diameter and density.
“Now we are very sure it has a rocky core and this giant thick envelope of water,” Marcy said. “It is the first time we have determined the structure of one of these extrasolar planets. It is rocky like Earth but it has a lot of water which is the essential ingredient for life.”
Scientists had theorised this for decades but now the hard evidence is pouring in, Marcy said.
“Our Milky Way galaxy has 200 billion stars. I would estimate that 10 per cent of them, perhaps, have planets that are habitable,” Marcy said. “There are hundreds of billions of galaxies, all of which are more or less like our Milky Way galaxy, which is tens of billions of planets like our own.”
There is one unusual property to our solar system: the nearly circular orbits, which gives a consistent dose of radiation from the Sun. Other solar systems seen so far usually run in elongated or elliptical orbits.
“We enjoy nearly constant temperatures throughout the year,” he added. “If the Earth got too close to the Sun, the Earth would heat up, the water would boil off and that would be bad.” Too far, and it would freeze. “An elongated orbit could not sustain life,” Marcy said.