Researchers determined that a "fluctuating tilt" in a planet does not necessarily mean it cannot harbor life.
These planets (fondly called "tilt-a-worlds" by astronomers) are less likely to freeze over than planets with a fixed spin, a University of Washington news release reported. This phenomenon occurs because heat from the host star is more evenly distributed; this has only been observed in the outer realms of a star's habitable zone (a distance from the star in which water can exist).
This new finding significantly increases the amount of planets that could potentially host life. The planet's irregular tilt would cause the poles to sometimes point towards the star, melting the ice caps and creating liquid water.
"Without this sort of 'home base' for ice, global glaciation is more difficult," UW astronomerRory Barnes said in the news release. "So the rapid tilting of an exoplanet actually increases the likelihood that there might be liquid water on a planet's surface."
"[Neighbor planets] can tug on each other from above or below, changing their poles' direction compared to the host star," First author isJohn Armstrongof Weber State, who earned his doctorate at the UW, said in the news release. This occurs when the planets are at angles to each other.
The researchers used a computer model to see how these neighbors interact with each other and what Earth would be like if it had "similar neighbors."
The new research also disputes the idea that a planet needs a large satellite, like our moon, in order to host life.
"We're finding that planets don't have to have a stable tilt to be habitable," Barnes said. "This study suggests the presence of a large moon might inhibit life, at least at the edge of the habitable zone."
The finding could double the number of potentially habitable planets in the Milky Way and could also change the way we think about our own stellar neighborhood.
"It would give the ability to put Earth, say, past the orbit of Mars and still be habitable at least some of the time - and that's a lot of real estate," Armstrong said.
