Intense heat may have made 'mirage earth' exoplanets uninhabitable

A new study has revealed that "mirage earth" exoplanets, planets orbiting close to low-mass stars, might have lost chance at hosting life long ago due to intense heat during their formative years.

University of Washington indicated that low-mass stars, also called M dwarfs, are smaller than the sun, and also much less luminous, so their habitable zone tends to be fairly close in. The habitable zone was that swath of space that was just right to allow liquid water on an orbiting planet's surface, thus giving life a chance.

Planets close to their host stars are easier for astronomers to find than their siblings farther out. Astronomers discover and measure these worlds by studying the slight reduction in light when they transit, or pass in front of their host star; or by measuring the star's slight "wobble" in response to the planet's gravity, called the radial velocity method.

However, the researchers found through computer simulations that some planets close to low-mass stars likely had their water and atmospheres burned away when they were still forming.

Rodrigo Luger said that also boding ill for the atmospheres of these worlds was the fact that M dwarf stars emit a lot of X-ray and ultraviolet light, which heats the upper atmosphere to thousands of degrees and causes gas to expand so quickly it leaves the planet and would be lost to space.

A side effect of this process was that ultraviolet radiation can split up water into its component hydrogen and oxygen atoms. The lighter hydrogen escapes the atmosphere more easily, leaving the heavier oxygen atoms behind. While some oxygen is clearly good for life, as on Earth, too much oxygen can be a negative factor for the origin of life.

The study is published in the journal Astrobiology.