The artist’s concept depicts Kepler-69c, a super-Earth-size planet in the habitable zone of a star like our sun, located about 2,700 light-years from Earth in the constellation Cygnus. Living on a planet with one side in perpetual sunlight and the other in perpetual darkness would pose some significant challenges for survival the sunny side of the planet might reach boiling temperatures while the dark side might be completely frozen. This scenario occurs when a planet’s rotation (its day) becomes synched with its orbit (its year), meaning only one side of the planet ever faces its parent star.
This scenario occurs when a planet’s rotation (its day) becomes synched with its orbit (its year), meaning only one side of the planet ever faces its parent star. Earth’s moon experiences this “synchronous rotation,” which is why only one side of the moon ever faces the Earth. Some researchers fear that many of the new exoplanets being discovered around other stars are at risk of experiencing this synchronous rotation, which might lower the odds that those planets support life.
Synchronous rotation is also known as tidal locking, because tides are at the heart of why these orbits arise, the researchers explain in their paper. The moon’s pull on the Earth creates tides in the ocean — in turn, the Earth exerts a tidal pull on the moon. The tidal force slows down the rotation of the moon (or planet), until it is synchronized with the body’s orbit.
Planetary atmospheres are not totally spherical — they can move, shift and bulge in some areas. As the atmosphere shifts, its mass exerts a force on the planet, and computer simulations show that this atmospheric force can be enough to counter the frictional force of the tides, potentially stopping the planet from falling into a synchronous rotation.
The reason has to do with the heating of the planet’s atmosphere. Differences in temperature generate strong winds that redistribute the atmosphere, distorting it in such a way that it tends to counter the drag of tidal forces.
As for exoplanets, Leconte writes, “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.” Read more…