Earth-like Exoplanets May Have Burned Away Their Chances at Cultivating Life

Exoplanets may have burned away their chances to cultivate life. Scientists have discovered that planets orbiting close to low-mass stars, which are thought to be prime targets in the search for extraterrestrial life, may have had their water at atmospheres burned away by their host stars while they were still forming.

Low-mass stars, also called M dwarfs, are smaller than the sun and also less luminous. This means that their habitable zone tends to be fairly close in. These low-mass stars are easily the most common in the universe, which means that there are more chances to find life on their planets.

Planets that are close to their host stars are also easier for astronomers to find than their siblings further out. This means that it's easier to scientists to spot and study them.

Now, though, researchers have found that some planets close to low-mass stars likely had their water and atmospheres stripped away while they were still forming. This means that it's unlikely they can harbor life.

"All stars form in the collapse of a giant cloud of interstellar gas, which releases energy in the form of light as it shrinks," said Rodrigo Luger, one of the researchers, in a news release. "But because of their lower masses, and therefore lower gravities, M dwarfs take longer to fully collapse-on the order of many hundreds of millions of years. Planets around these stars can form within 10 million years, so they are around when the stars are still extremely bright. And that's not good for habitability, since these planets are going to initially be very hot, with surface temperatures in excess of a thousand degrees. When this happens, your oceans boil and your entire atmosphere becomes steam."

In addition, M dwarf stars emit a lot of X-ray and ultraviolet light. This heats the upper atmosphere to thousands of degrees and causes gas to expand so quickly that it leaves the planet and is lost to space. This means that a lot of planets in the habitable zone of M dwarfs could have dried up early on.

The findings reveal that these planets may not be able to harbor life, even though they were prime targets in the past. Instead, they lose their atmospheres.

The findings are published in the journal Astrobiology.

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