Cloud Behavior Expands Habitable Zone of Alien Planets

A planet with clouds and surface water orbits a red dwarf star in this artist’s conception of the Gliese 581 star system. New findings from the University of Chicago and Northwestern University show that planets orbiting red dwarf stars are more likely to be habitable than previously believed. (Credit: Lynette Cook)

A new study that calculates the influence of cloud behavior on climate doubles the number of potentially habitable planets orbiting red dwarfs, the most common type of stars in the universe. This finding means that in the Milky Way galaxy alone, 60 billion planets may be orbiting red dwarf stars in the habitable zone.

Researchers at the University of Chicago and Northwestern University based their study, which appears in Astrophysical Journal Letters, on rigorous computer simulations of cloud behavior on alien planets. This cloud behavior dramatically expanded the habitable zone of red dwarfs, which are much smaller and fainter than stars like the sun.

Current data from NASA’s Kepler Mission, a space observatory searching for Earth-like planets orbiting other stars, suggest there is approximately one Earth-size planet in the habitable zone of each red dwarf. The UChicago-Northwestern study now doubles that number.

“Most of the planets within the Milky Way Galaxy orbit red dwarfs,” aforesaid Nicolas Cowan, a postdoctoral fellow at Northwestern’s Center for knowledge domain Exploration and analysis in uranology. “A thermostat that produces such planets a lot of clement means that we do not have to be compelled to look as way to seek out a livable  planet.”

Cowan is one in every of 3 co-authors of the study, as square measure UChicago’s Greek archimandrite and Jun principle. The trio conjointly offer astronomers with a method of supportive their conclusions with the James Webb area Telescope, scheduled  for launch in 2018.

The formula for conniving the livable  zone of alien planets — wherever they’ll orbit their star whereas still maintaining liquid water at their surface — has remained abundant identical for many years. however the formula mostly neglects clouds, that exert a significant environmental condition influence.

“Clouds cause warming, and that they cause cooling on Earth,” aforesaid archimandrite, associate professor in geology sciences at UChicago. “They replicate daylight to chill things off, and that they absorb actinic radiation from the surface to create a atmospheric phenomenon. that is a part of what keeps the world heat enough to sustain life.”

A planet orbiting a star just like the sun would have to be compelled to complete associate orbit close to once a year to be way enough away to keep up water on its surface. “If you are orbiting around a coffee mass or dwarf star, you’ve got to orbit regarding once a month, once each 2 months to receive identical quantity of daylight that we tend to receive from the sun,” Cowan aforesaid.

Astronomers observing with the James Webb Telescope will be able to test the validity of these findings by measuring the temperature of the planet at different points in its orbit. If a tidally locked exoplanet lacks significant cloud cover, astronomers will measure the highest temperatures when the dayside of the exoplanet is facing the telescope, which occurs when the planet is on the far side of its star. Once the planet comes back around to show its dark side to the telescope, temperatures would reach their lowest point.

Artist's conception of star SO25300.5+165258 w...
Artist’s conception of star SO25300.5+165258 which is a red dwarf about 7.8 light years from the sun (the newest data is 12.578 ly) (Photo credit: Wikipedia)

But if highly reflective clouds dominate the dayside of the exoplanet, they will block a lot of infrared radiation from the surface, said Yang, a postdoctoral scientist in geophysical sciences at UChicago. In that situation “you would measure the coldest temperatures when the planet is on the opposite side, and you would measure the warmest temperatures when you are looking at the night side, because there you are actually looking at the surface rather than these high clouds,” Yang said.

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