Pivoting planets that lean one way and then change orientation within a short geological time period might be surprisingly habitable, NASA scientists have found.
Tilted orbits might make some planets wobble like a top that's almost done spinning, an effect that could maintain liquid water on the surface, researchers said.
The climate effects generated on these wobbling worlds could prevent them from turning into glacier-covered ice lockers, even if those planets are somewhat far from their stars, they said.
And with some water remaining liquid on the surface long-term, such planets could maintain favourable conditions for life.
"Planets like these are far enough from their stars that it would be easy to write them off as frozen, and poor targets for exploration, but in fact, they might be well-suited to supporting life," said Shawn Domagal-Goldman, astrobiologist at NASA's Goddard Space Flight Center in Greenbelt.
"This could expand our idea of what a habitable planet looks like and where habitable planets might be found," said Domagal-Goldman.
The new modelling considers planets that have the same mass as Earth, orbit a Sun-like star and have one or two gas giants orbiting nearby.
In some cases, gravitational pulls from those massive planets could change the orientation of the terrestrial world's axis of rotation within tens to hundreds of thousands of years - a blink of an eye in geologic terms.
Though it might seem far-fetched for a world to experience such see-sawing action, scientists have already spotted an arrangement of planets where this could happen, in orbit around the star Upsilon Andromedae.
There, the orbits of two enormous planets were found to be inclined at an angle of 30 degrees relative to each other.
Compared to our solar system, that arrangement looks extreme. The orbits of Earth and its seven neighbouring planets differ by 7 degrees at most.
Even the tilted orbit of the dwarf planet Pluto, which really stands out, is offset by a relatively modest 17 degrees.
"Knowing that this kind of planetary system existed raised the question of whether a world could be habitable under such conditions," said Rory Barnes, a scientist at the University of Washington in Seattle.
The study was published in the journal Astrobiology.
