Oceans Last for Billions of Years on Distant Super-Earth Exoplanets

When it comes to searching for life on other planets, discovering liquid water is a crucial part of determining whether or not a planet can hold the potential for alien organisms Now, though, scientists have found out that oceans on super-Earths, once established, can actually last for billions of years, which may explain a bit more about our own planet.

"When people consider whether a planet is in the habitable zone, they think about its distance from the star and its temperature," said Laura Schaefer, one of the researchers, in a news release. "However, they should also think about oceans, and look at super-Earths to find a good sailing or surfing destination."

Although water covers 70 percent of Earth's surface, it actually makes up a very small fraction of our planet's overall bulk. Earth is mostly made up of rock and iron, and only about a tenth of a percent of it is made up of water.

That said, water isn't only on Earth's surface. Previous studies have shown that Earth's mantle holds several oceans' worth of water that was dragged underground by plate tectonics and subduction of the ocean seafloor. In theory, Earth's oceans would eventually disappear if it weren't for water returning to the surface via volcanism.

In order to better understand how these processes might occur on super-Earths, the researchers created computer simulations. They studied this recycling process on planets with up to five times the mass of Earth. In addition, they examined the question of how long it would take oceans to form after these super-Earths cooled enough for their crusts to solidify.

In the end, the researchers found that planets two to four times the mass of Earth are actually better at establishing and maintaining oceans than our own planet. The oceans of super-Earth's would last for at least 10 billion years, unless they were boiled away by an evolving red star. That said, a planet with five times the mass of Earth would take about a billion years for its oceans to develop.

"It takes time to develop the chemical processes for life on a global scale, and time for life to change a planet's atmosphere," said Dimitar Sasselov, one of the researchers. "So, it takes time for life to become detectable."

The findings reveal that in the hunt for life, researchers might want to focus on older super-Earths. More specifically, they should examine planets that are about five and a half billion years old, which is about a billion years older than Earth.

The findings were presented at a meeting of the American Astronomical Society.

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