According to a news release from the University of Chicago, A new study that determines the influence of cloud behavior on climate doubles the number of potentially habitable planets circling red dwarfs, which means that in the Milky Way galaxy alone, 60 billion alien planets could support alien life.
The study is based on exacting computer simulations of cloud behavior on alien planets. This cloud behavior significantly amplified that habitable zone of red dwarfs, which are a lot smaller and fainter than stars like the Sun.
Previously, data from NASA’s Kepler Mission suggested that there is approximately one Earth-size planet in the habitable zone of each red dwarf. This study doubles that number.
According to co-author Nicolas Cowan, a postdoctoral fellow at Northwestern’s Center for Interdisciplinary Exploration and Research in Astrophysics, “a thermostat that makes such planets more clement means we don’t have to look as far to find a habitable planet.”
The researchers point out that the formula for determining the habitable zone of alien planets, the region that is the proper distance from the star for those planets to have water remain liquid, has changed very little for decades. However, the formula fails to take clouds, which wield a major climatic influence, into consideration.
Dorian Abbot, an assistant professor in geophysical science at the University of Chicago, notes that clouds cause warming and cooling on Earth. Not only do they reflect sunlight to cool things off, they also absorb infrared radiation from the surface to create a greenhouse effect.
According to Cowan, a planet orbiting a low mass or dwarf star would have to orbit approximately once a month or once every two months to get the same amount of sunlight that the Earth receives from the Sun.
Interestingly, planets in such a tight orbit would eventually become tidally locked with their sun, meaning that they would always keep the same side facing the sun. According to the University of Chicago-Northwestern team, the star-facing side of the planet would experience powerful convection and highly reflective clouds in the sub-stellar region. In this region, the sun always sits directly overhead.
The astronomers calculated for the first time the impact of water clouds on the inner edge of the habitable zone. The simulations that they used are similar to the global climate simulations that scientists utilize to predict Earth climate.
According to Cowan, it is impossible to accurately measure the influence of clouds on the inner edge of the habitable zone in one-dimension; a three-dimensional model allowed the astronomers to simulate the way air travels and the way moisture travels through the entire atmosphere of the planet.
These new simulations reveal that if there is any surface water on the planet, water clouds form as a result. The simulations also reveal that cloud behavior has a major cooling effect on the inner portion of the habitable zone, allowing planets to keep liquid water on their surfaces much closer to their sun.
Using the James Webb Telescope, astronomers will be able verify these findings by determining the temperature of the planet at various points in its orbit. If a tidally locked exoplanet has a dearth of cloud cover, astronomers will measure the highest temperatures when the dayside of the exoplanet is facing the telescope. When the planet reveals its dark side to the telescope, astronomers will measure the lowest temperatures.
However, if highly reflective clouds rule the dayside of the alien planet, they will block a lot of infrared radiation from the surface, according to Jun Yang, a postdoctoral scientists in geophysical science at the University of Chicago. Yang says that if this is the case, astronomers would measure the lowest temperatures when the planet is on the opposite side, and they would measure the highest temperatures when they are looking at the night side, because there you are actually observing the surface as opposed to these high clouds.
Cowan notes that a similar situation has been observed by Earth-watching satellites. Brazil or Indonesia, for example, have looked cold from space but that is because the satellites are looking at the cloud deck.
The study’s findings are described in greater detail in Astrophysical Journal Letters.