Some massive exoplanets may have oceans and continents, just like Earth

Credit: NASA Ames/JPL-Caltech

A new model has shown that some massive exoplanets may be more like Earth than originally thought. It turns out that there is a very good chance that some “Super-Earth” planets have landscapes a lot like ours, complete with oceans and continents. The model was developed by Nicolas B. Cowan from Northwestern's Center for Interdisciplinary Exploration and Research in Astrophysics (CIERA) and Dorian Abbot from UChicago. Their paper is set to be published in an upcoming edition of the Astrophysical Journal, though they presented their findings this week at the 223rd Meeting of the American Astronomical Society

To qualify as a “Super-Earth” a planet just needs to be more massive than Earth and less massive than Uranus, which has about 15 times the Earth’s mass. There are no other qualifiers for this designation such as chemical composition or habitability. Many Super-Earths are believed to be completely covered in deep water, but this new model challenges that.

By using basic principles of geophysics, in combination with what is known about the planets, the pair were able to determine that quite a bit of the water would likely be tied up in the planet’s mantle, just like on Earth. Because these planets are so massive, the crushing pressure on the seafloor forces water from the ocean down into the mantle. Adding in the factor of plate tectonics, there would be variable sea levels, making the existence of continents a very real possibility. Even if these exoplanets (which are 15 times our mass at most) had 80 times the amount of water as Earth, there still would still be enough exposed rock to have continents.

Why is it a big deal if there are actually continents on these planets? Having a mixture of continents and oceans regulates weather and influences climate. This increases the odds that such a planet in its star’s habitable zone could very well have a climate a lot like Earth’s, which may increase the possibility for finding life similar to our own. Currents in the ocean would mix nutrients around.

Of course, this is just a model and there is no actual evidence as of yet that an exoplanet has these qualities. However, rethinking what is possible may allow us to take new approaches and learn even more about Super-Earths as we search for our planetary twin out in the Universe.

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