Artistic concept of NASA’s Kepler spacecraft. COURTESY OF NASA AMES/JPL CALTECH/T PYLE

On January 6, astronomers and space enthusiasts everywhere celebrated the discovery of the one-thousandth potentially habitable “exoplanet,” a term used to designate any planet from an alien solar system that is not our own.

The discovery has been made possible by NASA’s Kepler spacecraft mission, which uses observation techniques to analyze how similar an exoplanet is to Earth. Although an archive of 1,000 potential new homes may seem like an ample selection to choose from, in reality, determining whether or not an exoplanet could potentially host a human population or even alien life of its own still depends on a large number of restricting factors.

However, new research published just last month in the journal Science suggests that the list of restrictions to a planet’s potential to bear life may not be so insurmountable after all, as at least one of these factors may be far less hindrance than previously believed.

The researchers, including Dr. Jérémy Leconte, who is from the Canadian Institute for Theoretical Astrophysics and is a postdoctoral fellow at the University of Toronto, came upon this conclusion by combining the knowledge of planetary orbit and spin with a 3D atmospheric climate model developed by him and his team.

Physicists who specialize in planetary astronomy and atmospheric science were already aware of the fact that the atmosphere of an orbiting planet can affect how the planet spins on its own axis. This has been observed closer to home by the manner in which Venus orbits around the sun.

According to laws of planetary rotation, Venus is so close to the sun that it should be orbiting in a manner referred to as “synchronous rotation,” where the same side of the planet always faces its star, and thus that half of the planet receives all of the heat and light that the star gives off.

Venus, however, has not been abiding by this rule at all, and is spinning fast enough that different parts of the planet are facing the sun at different times, resulting in Venus having a day-and-night cycle just like Earth does, albeit much slower. Having a cycle in which different parts of the planet are heated up by the sun at different times is a prerequisite for being able to sustain life.

The key to Venus’s orbital delinquency is the fact that it has an atmosphere.

“Although the atmosphere of Venus is only one part in ten thousand of the mass of the planet, it has been able to accelerate Venus’s spin over geological timescales,” Leconte and his colleagues wrote in a press release made public on January 15.

According to the new model, the extent to which Venus is rejecting its expected state of synchronous rotation is not in proportion to the size of its atmosphere. As it turns out, the high density of Venus’s exceptionally cloudy climate is limiting the amount of light from the sun that manages to reach the surface of the planet and heat it up, thus curbing the atmospherically driven increase in rotation speed.

How does this affect our estimate of how many habitable new worlds there could be out there for us? Leconte’s press release reads, “While astronomers are still awaiting observational evidence, theoretical arguments suggest that many exoplanets should be able to keep an atmosphere as massive as that of the Earth. In that case, this new study shows that a large number of known terrestrial exoplanets should not be in a state of synchronous rotation, as initially believed.”

Whether or not the presence of the day-and-night cycle means that a planet has developed life of its own, Leconte says, is still to be seen.




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