We have already discovered several exoplanets around the nearby stars, thanks to NASA. The agency is expected to find more once the James Webb Space Telescope (JWST) begins its search. However, the main challenge for the scientists is to comprehend which star-planet combinations are more likely to support life forms.
Recently, a new study by the scientists at the space agency has found out that planets orbiting small stars like Trappist-1 have the potential to retain their oceans for billions of years, even if they're quite close. However, the star needs to emit the right amount of infrared radiation.
If a planet is too cold, any water will freeze into ice there, making life formation almost impossible. On the other hand, if it's too hot, the water will evaporate and gather into the stratosphere, where it will then get broken into hydrogen and oxygen by the star's UV (ultraviolet) light. Eventually, this state, called a "moist greenhouse," also leads to the loss of all water bodies, killing any chances for life.
As per a report by Engadget, unlike Earth, planets on the red dwarf stars' systems are often tidally locked, which means the same of the planet points towards the star all the time. It leads to overheating of one side and overcooling of the other. However, such planets can zip around their stars quick enough to create a circulating atmosphere, states the report.
Now, a team of scientists from NASA's Goddard Institute for Space Studies and the Earth-Life Science Institute at the Tokyo Institute of Technology, have conducted a new study, in which they have simulated the atmospheric circulation on a planet in a hypothetical red dwarf system using an advanced 3D atmospheric model, reported NASA.
"We found an important role for the type of radiation a star emits and the effect it has on the atmospheric circulation of an exoplanet in making the moist greenhouse state," said Yuka Fujii of NASA's Goddard Institute for Space Studies (GISS), New York and also the lead author of the study, which has been published in the Astrophysical Journal.
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Until now, scientists had believed that if a planet's surface is too warm, around 150 degrees F, it would create an ocean-destroying moist greenhouse state. However, the new research discovered that on red dwarf, Trappist-1 type planets, that wasn't always the case. In this system, if a star emitted enough near-infrared radiation, it could throw off a moist greenhouse effect. The model also showed that, surprisingly, if an exoplanet was closer to its parent star, the infrared heating increased the moisture in the atmosphere more slowly. This means that, contrary to previous findings, it can actually remain habitable.
If the study proves to be valid, it will help the scientists immensely to narrow down the habitable exoplanet candidates. First, they can measure the radiation of a star and then, possibly they can measure its planet's atmospheric composition using spectroscopic methods.
"As long as we know the temperature of the star, we can estimate whether planets close to their stars have the potential to be in the moist greenhouse state," said co-author of the Anthony Del Genio from NASA. "If there is enough water to be detected, it probably means that planet is in the moist greenhouse state."
