Scientists have suggested that water worlds might be pretty common elsewhere in the universe, raising the prospects of finding life.
In a talk presented at the Goldschmidt conference in Boston last week, researchers suggested that planets two to four times the size of Earth could contain as much as 50 percent water. For comparison, Earth’s water content is just 0.02 percent of its weight.
"It was a huge surprise to realize that there must be so many water-worlds", said lead researcher Dr Li Zeng from Harvard University in a statement. “Our data indicate that about 35% of all known exoplanets which are bigger than Earth should be water-rich.”
In their research, the scientists used data from NASA’s Kepler telescope and ESA’s Gaia telescope. They found that of the 4,000 exoplanets found so far, most were about 1.5 or 2.5 times the radius of Earth.
Developing a model on the structure of these planets, the researchers found that the smaller ones were likely to be rocky, with up to five times the mass of Earth. But the larger ones, with masses 10 times that of Earth, are probably water worlds.
However, there was a caveat. Many of these worlds might have extremely hot surface temperatures of about 200 to 500°C (390 to 930°F). So it’s thought the planets could be covered in water vapor atmospheres, with a liquid water layer lower down.
“These water worlds likely formed in similar ways to the giant planet cores (Jupiter, Saturn, Uranus, Neptune) which we find in our own Solar System,” said Dr Li Zeng.
It’s hoped that a newly launched NASA mission, the Transiting Exoplanet Survey Satellite (TESS), could help find even more of these worlds. It is expected to find about 20,000 exoplanets over the course of its mission, ranging from Earth-sized to hot gas giants.
The next step in exoplanet research will be to start studying some of the atmospheres of these planets in detail. Scientists are hoping to use NASA’s delayed James Webb Space Telescope (JWST), and work out if other planets do indeed contain a lot of water.
And that’s important, because where we find water on Earth, we find life. If we can find other watery places too, then it raises the prospect of finding habitable locations beyond the Solar System.
“Life could develop in certain near-surface layers on these water worlds, if the pressures, temperatures and chemical conditions are appropriate,” said Dr Li Zeng, reported New Scientist. The only issue now is, can you ever have too much water for life?