Heat Prevents 'Mirage Earth' Exoplanets from Being Habitable

It seems that certain exoplanets are just too hot to handle. Far-away planets referred to as "mirage Earths" once boasted intense heat during their formation, which unfortunately prevented them from ever becoming habitable, according to a new study.

Scientists believe more and more than we are not alone in the Universe, and have since dedicated their efforts towards finding life outside of Earth. Planets orbiting close to low-mass stars - the most common stars in space - are prime targets in their search for extraterrestrials and habitable worlds. But some of these promising exoplanets may have duped astronomers.

"Because of the oxygen they build up, they could look a lot like Earth from afar - but if you look more closely you'll find that they're really a mirage; there's just no water there," researcher Rodrigo Luger, a doctoral student at the University of Washington, said in a statement.

Low-mass stars, also called M dwarfs, are smaller and less luminous than the Sun, which makes their planets better able to cling onto habitable zones, where temperatures are just right for water to form. And considering that M stars make up about 75 percent of the stars in our galaxy, the potential for discovering an Earth-like world seems more than likely.

But what scientists don't realize upon first look at these "mirage Earths" is that their M stars were much more active early in their life, which can create some hot and sweaty conditions.

"Planets around these stars can form within 10 million years, so they are around when the stars are still extremely bright," Luger explained. "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."

So any water that might have existed on these exoplanets would simply have dried up. And in a cruel trick of the eye, as astronomers observe and measure these worlds - using the dimming in light during transit, or the star's slight "wobble" due to gravity - they will see a buildup of oxygen in their atmospheres, indicating life. But really the gas was just split off, along with hydrogen, from the boiled water molecules.

"Searches for life often rely on oxygen as a tracer of extraterrestrial life - so the abiological production of such huge quantities of oxygen could confound our search for life on exoplanets," added co-author Rory Barnes.

Though the findings, published in the journal Astrobiology, may prove to be true, scientists will no doubt continue in their search for life in the Universe.

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