Oxygen is a signal of life on our own planet, but that's not necessarily the case elsewhere. Particularly when it comes to young planets, signs of oxygen do not necessarily indicate the presence of biological processes, new research argues.

Water vapor in the upper atmosphere of a young planet could break into hydrogen and oxygen by incoming ultraviolet and extreme ultraviolet rays from the parent star.

"Atomic hydrogen is so light that it can escape to space and lead to the oxidization of the planet," said Robin Wordsworth, a geophysicist at the University of Chicago. "It will just keep continuing and oxidizing the atmosphere. That's what we try and investigate in the paper."

The researchers investigated water photolysis, which happens when a water molecule is torn apart by high-energy photons from the sun. Usually the water (two hydrogen atoms and an oxygen atom) is broken into two parts, OH and H. The H escapes to space because it is so light. Over time, more oxygen molecules build up until eventually O2 (molecular oxygen) form as well.

"The real novelty of our paper was to study the consequences of hydrogen loss from water photolysis, when molecules break down into smaller units after absorbing light," said Wordsworth.

Wordsworth co-led the research with Raymond Pierrehumbert, who is a geophysicist in his department.

The paper, called "Abiotic oxygen-dominated atmospheres on terrestrial habitable zone planets" is available on the pre-publishing site Arxiv and has been accepted for publication in Astrophysical Journal Letters.

Searches for second Earth picking up Due to their diminutive size, Earth-sized planets are hard to spot in telescopes searching for exoplanets. They don't tug on their parent stars as much as the Jupiter-sized worlds, which induce "wobbles" in a star's movement.

If the terrestrial-sized planets pass across the face of their star, their shadow is also incredibly tiny. Trying to pick out details such as land features or even atmospheres is also difficult because of their small size. For now, astronomers expect better success with bigger worlds, of which there are plenty to choose from.

Most planets found outside the Solar System have been Jupiter's size or larger. However, NASA's Kepler Space Telescope has begun spotting more small worlds. A large "planet bonanza" of 715 new worlds was released in February.

Originally posted here:

Oxygen In Exoplanet Atmospheres Could Fool Search For Life