Friday, 14 Dec 2018
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SPACE | Exoplanets may be water balls: study

WASHINGTON — Scientists have shown that water is likely to be a major component of planets orbiting other stars that are between two to four times the size of Earth.

The study presented at this week’s Goldschmidt conference held in Boston will have implications for the search of life in our Galaxy.

A new evaluation of data from the exoplanet-hunting Kepler Space Telescope and the Gaia mission indicated that many of the known planets might contain as much as 50 percent water, much more than the Earth’s 0.02 percent water content by weight.

“It was a huge surprise to realize that there must be so many water-worlds,” said lead researcher Li Zeng at Harvard University.

Scientists have found that 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,” said Li.

Li’s model indicated that those exoplanets which have a radius of around 1.5 time Earth radius tend to be rocky planets, while those with a radius of 2.5 time Earth radius are probably water worlds.

“This is water, but not as commonly found here on Earth,” said Li. “Their surface temperature 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,” said Li.

Li said about 35 percent of all known exoplanets which are bigger than Earth should be water-rich and 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.

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