Astronomers have long assumed that, to be habitable, an exoplanet needs to be a rocky planet that lies within the habitable territory. That is the area of distance from a star at which water can exist on a planet’s surface as a liquid. However, new research means that even frozen. Icy planets might be theoretically able to support life.
“You might have these planets that traditionally you might consider not habitable, and this means that perhaps they are often,” Adiv Paradise, an astronomer and physicist at the University of Toronto and lead author of the new research, stated in a statement.
The analysis looked at “snowball planets,” that are the size of Earth and which have oceans which can be frozen all the way to their equators. The researchers simulated different climates of snowball planets, by manipulating variables like the amount of sunlight which a planet received and the way the continents have been positioned. An essential variable was the quantity of carbon dioxide within the atmosphere, as carbon dioxide retains heat trapped and warms the surface of a planet.
If the level of carbon dioxide in a planet’s atmosphere is low, it can’t trap sufficient heat, and it becomes a snowball. This could happen when there’s heavy rainfall which absorbs the carbon dioxide, turning it into acid which causes erosion of the surface rock. The acid is broken down within the course of and sinks to the seafloor, gradually removing carbon dioxide from the atmosphere.