Since the discovery in the early 1990's of exoplanets orbiting other stars there has been huge interest in understanding the composition of these planets to determine, among other goals, whether they are suitable for the development of life.
Now a new analysis of data from NASA’s Kepler Space Telescope and ESA’s Gaia satellite indicates that many of the known exoplanets fully one-third of them—or 1,400 of those 4,000—were found to be water-rich worlds. In some cases, as much as 50% water. This is much more than the Earth’s 0.02% (by weight) water content.
“It was a huge surprise to realize that there must be so many water-worlds,” Dr. Zeng said.
Everywhere on Earth you find water, you find life, said Jonti Horner, an astrobiologist at the University of Southern Queensland.
Many of the 4,000 confirmed or candidate exoplanets discovered so far fall into two size categories: those with the planetary radius averaging around 1.5 that of the Earth, and those averaging around 2.5 times the radius of the Earth.
“We have looked at how mass relates to radius, and developed a model which might explain the relationship,” Dr. Zeng said.
Exoplanets similar to Earth. Credit: NASA
Interestingly team’s model indicates corrilation in the fact that those exoplanets which have a radius of around 1.5 Earth radii tend to be rocky planets (typically 5 times the mass of the Earth), while those with a radius of 2.5 Earth radii (with a mass around 10 times that of the Earth) are probably water worlds.
“This is water, but not as commonly found here on Earth,” Dr. Zeng said.
“The surface temperature of these planets is expected to be in the 200 to 500 degree Celsius range.”
“Their surface may be shrouded in a water-vapor-dominated atmosphere, with a liquid water layer underneath.”
“Moving deeper, one would expect to find this water transforms into high-pressure ices before we reaching the solid rocky core.”
“The beauty of the model is that it explains just how composition relates to the known facts about these planets.”
“Our data indicate that about 35% of all known exoplanets which are bigger than Earth should be water-rich,” Dr. Zeng said.
“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.”
Two new tools will soon be available to probe much deeper into these exciting worlds. Li Zeng continued. "The newly-launched TESS mission will find many more of them, with the help of ground-based spectroscopic follow-up. The next generation space telescope, the James Webb Space Telescope, will hopefully characterize the atmosphere of some of them. This is an exciting time for those interested in these remote worlds."