‘Super-Earths’ study reveals strange new oceans with potential for life

It’s easy to think of Earth as a watery world, with its vast oceans and beautiful lakes, but compared to many worlds, Earth is especially wet. The icy moons of Jupiter and Saturn also have much more liquid water than Earth. Earth is unusual not because it has liquid water but because it has liquid water in the warm habitable zone of the Sun Nature communications shows, Earth may be even more unusual than we thought.

Water is one of the most common molecules in the universe. Hydrogen is the most abundant element in the cosmos, and oxygen is easily produced as part of the CNO stellar fusion cycle. So we would expect water-rich planets to be abundant in star systems. But that’s not to say that liquid water will be plentiful. In our Solar System, two types of worlds have liquid water. Terrestrial and gaseous giant moons.

Like other hot terrestrial planets like Venus and Mars, Earth had liquid water in its youth. Mars was too small to hold its water. Much of it evaporated into space, while some froze into its surface crust. Venus was large enough to hold water, but its extreme heat boiled much of it in its thick atmosphere. We’re still not entirely sure how Earth managed to maintain its oceans, but it was likely a combination of a strong magnetic field and an extra helping of water from asteroids and comets during the heavy bombardment period.

The icy moons of Jupiter and Saturn are another story. They were far enough from the Sun to retain the water of their formation. They quickly formed a thick layer of ice to prevent water from evaporating into space. But these moons are small worlds and would have solidified very quickly were it not for the tidal forces exerted by their gas giant.

Since cold gaseous planets are likely to have icy moons, the general thinking is that we’d be much more likely to find life on a Europa-like world than an Earth-like one. But this new study begs to differ. He argues that liquid water is much more likely to be found on super-Earths.

Number of exoplanets discovered by the Kepler mission in May 2016.

Credit: W. Stenzel/NASA Ames

Super-Earths cover a mass range from a couple of Earth masses to the mass of Neptune. In general, they are likely to be gaseous worlds with thick atmospheres. On the small side, they are likely to be more Earth-like. Based on the exoplanets we’ve found so far, super-Earths are by far the most common. And it is likely that most of them are found outside the habitable zone of their stars, in the cold regions of the star system. So they are probably rich in water. But they’re also unlikely to be in orbit around a gas giant, so it’s generally assumed that their ice sheet would be mostly frozen in time.

The reason has to do with the various freezing and melting points of the ice. The kind of ice we have on Earth melts at about 0 degrees Celsius. But this is only true around Earth’s atmospheric pressure. At higher pressures, there are different varieties of ice with different melting points. While it’s a bit tricky, generally, at higher pressures, ice can have a much higher melting point. So even if a super-Earth is geologically active, it might not be hot enough to melt the ice.

This new study shows that super-Earths don’t have to be hot enough to create a deep ocean. Through geothermal and nuclear heating, it can melt a thin layer of water on its surface, and thanks to fissures and various phase transitions of water, the water can creep up to the layer just below the frozen surface. This process would be enough to create a rich ocean layer of liquid water. Because a super-Earth’s heat lasts for billions of years, it could maintain a liquid ocean long enough for life to evolve.

Based on what we know about exoplanets, super-Earth’s oceans could be 100 times more common than those of Earth-like worlds or icy moons. And that means life has even more possible homes than we thought.

This article was originally posted on Universe Today by Brian Koberlein. Read the original article here.

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Image Source : www.inverse.com

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