There May Be Billions More Habitable Exoplanets than We Thought
When searching for extraterrestrial life, the "holy grail," so to speak, has long been a planet with liquid water. But thus far, there have been no serious candidates for habitability outside of our own solar system, as it was thought that exoplanets were too dark and cold to host liquid oceans. Now, a new study from the University of Toronto shows that certain exoplanets may be able to provide an environment that is conducive to liquid water, and therefore they may be much more habitable than previously thought.
Astronomers have long believed that planets outside of our solar system spun in such a way that their rotation was synchronized with their star, meaning that the same side of the planet would always face towards their Sun. This would mean that one half of the planet would always be facing away from the star, and would resemble an arctic wasteland as a result. If a planet has synchronized rotation, it would be impossible for liquid oceans to exist, as they would be trapped underneath a permanent sheet of ice. Earth's asynchronous rotation allows for the day/night cycle, which in turn allows for liquid oceans and the emergence of life forms.
But now, this new study purports to demonstrate that many exoplanets may exhibit asynchronous rotation as long as they are able to maintain an atmosphere as thick as Earth's, which is relatively thin. The assumption that exoplanets exhibited synchronous rotation came out of the notion that their rotation was controlled by tidal forces, much like our Moon, which is in synchronous rotation with Earth. But, according to the researchers, this ignores the solar heating effects of the atmosphere, which could overcome the effect of tidal friction.
"The Moon always shows us the same side, because the tides raised by Earth create a friction that alters its spin," said Leconte. "The Moon is in synchronous rotation with Earth because the time it takes to spin once on its axis equals the time it takes for it to orbit around Earth. That is why there is a dark side of the moon. The tidal theory, however, neglects the effects of an atmosphere."
If the researchers' models prove correct, then there are not only billions more candidates for watery exoplanets, but several of the planets that we've already discovered may be more conducive to liquid water than we thought. Although we can't say for sure that this would make these planets habitable to life as we know it, it's definitely a step in the right direction.
"If we are correct, there is no permanent, cold night side on exoplanets causing water to remain trapped in a gigantic ice sheet. Whether this new understanding of exoplanets' climate increases the ability of these planets to develop life remains an open question."