New study increases the likelihood of discovering habitable exoplanets

As of 2014, nearly 2,000 planets outside of our solar system have been identified. Known as exoplanets, these distant celestial bodies have been the subject of dedicated astronomical research and speculation on the possibility of life beyond Earth.

According to phys.org, there are a number of criteria put in place to determine the habitability of distant planets. One such criteria is known as obliquity, or the angle of the planet’s axis relative to its orbit around a star. Since Earth has a low obliquity, it has long been speculated that a low obliquity would be required to support life. However, a new study indicates this may not be the case.

Scientists at MIT now believe that even if a planet rotates on a horizontal axis, imagine a rotisserie, it could still support life provided it was covered by water. These oceans would help to keep the surface temperatures in the hospitable range. In fact, the oceans could be as shallow as 50 meters and still host a multitude of organisms.

David Ferreira, a former research in MIT’s Department of Earth, Atmospheric and Planetary Sciences, points out that a planet with high obliquity would be an extreme environment. There would be six months of daylight followed by six months of darkness as the planet rotated around its star.

“The expectation was that such a planet would not be habitable. It would basically boil and freeze, which would be really tough for life,” says Ferreira. “We found that the ocean stores heat during the summer and gives it back in winter, so the climate is still pretty mild, even in the heart of the cold polar night. So in the search for habitable exoplanets, we’re saying don’t discount high-obliquity ones as unsuitable for life.”

Life on a high-oblique aquaplanet would thrive, but only to a point. Ferreira found that a planet with oceans shallower than 10 meters could not regulate the temperatures effectively. In that scenario, as soon as some ice formed on the dark side of the planet, it would spread rapidly across the surface. Even as the iced portion rotated into the sunlight, it would be too late to stop the spreading of ice. The entire planet would eventually be forever covered in ice.

Darren Williams, a professor of physics and astronomy at Pennsylvania State University, puts the new statistics into perspective.

“There are one or two terrestrial-sized planets exoplanets out of a thousand that appear to have densities comparable to water, so the probability of an all-water planet is at least .1 percent. The upshot of all this is that exoplanets at high obliquity are not necessarily devoid of life, and are therefore just as interesting and important to the astrobiology community.”

The study can be found in the scientific journal Icarus.

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