- Astronomers believe exoplanets that could hold water rotate around their stars at such a speed that they exhibit a day-night cycle similar to Earth
- This contradicts the popular theory that many exoplanets are locked in a rotation which causes only one side of their surface face their sun
But these exoplanets - despite having a chance of holding water - are believed to be locked in a rotation around their sun which causes only one side of their surface face the star.
Now astronomers claim that such exoplanets actually rotate around their stars, and spin at such a speed that they exhibit a day-night cycle similar to Earth – increasing the chance of finding alien life.
'Planets with potential oceans could have a climate that is much more similar to Earth's than previously expected,' said Jérémy Leconte, a postdoctoral fellow at the Canadian Institute for Theoretical Astrophysics (CITA) at the University of Toronto.
'If we are correct, there is no permanent, cold night side on exoplanets causing water to remain trapped in a gigantic ice sheet,' he said. 'Whether this new understanding of exoplanets' climate increases the ability of these planets to develop life remains an open question.'
Dr Leconte and his team reached their conclusions isomg a three-dimensional climate model they developed to predict the effect of a given planet's atmosphere on the speed of its rotation.
'Atmosphere is a key factor affecting a planet's spin, the impact of which can be of enough significance to overcome synchronous rotation and put a planet in a day-night cycle,' said Dr Leconte.
Though astronomers are still awaiting concrete evidence, theoretical arguments suggest that many exoplanets should be able to maintain an atmosphere as massive that of Earth.
In Earth's case - with its relatively thin atmosphere - most of the light from the sun reaches the surface of the planet, maximising the effect of heating throughout the atmosphere and producing a more moderate climate across the planet.
By creating temperature differences at the surface, between day and night and between equator and poles, the solar heating drives winds that redistribute the mass of the atmosphere.
The impact is so significant that it overcomes the effect of tidal friction exerted by a star on whatever satellite is orbiting it, much like Earth does on the moon.
'The moon always shows us the same side, because the tides raised by Earth create a friction that alters its spin,' said Dr 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.'
The researchers say that a large number of known terrestrial exoplanets should not be in a state of synchronous rotation, as initially believed.
While their models show that they would have a day-night cycle making them much more similar to Earth, the duration of their days could last between a few weeks and few months.