Washington: Alien planets would likely have a leap year too similar to the 366-day year that comes in every four years in our calender, scientists say.
An extra day, February 29, is added to the second month of the year every four years to keep our calendar in line with the seasons that depend on Earth`s revolution around the Sun.
That`s because the year, or the time it takes Earth to make one circuit around the Sun, can`t be evenly divided into days -- the time it takes Earth to make one full rotation.
"We have a leap year because the spin rate of the Earth, which is 23 hours and 56 minutes, doesn`t divide completely evenly into the length of the year, which is 365.242374 days," astronomer Greg Laughlin of the University of California was quoted as saying by SPACE.com.
And the same is probably true for most alien planets as well, said Laughlin, who is the co-investigator of the Lick Carnegie Exoplanet Survey which hunts for planets around other stars using the Keck telescope in Hawaii. More than 700 such planets have so far been found by astronomers.
Most extrasolar planets "will all have spin periods that don`t fit neatly into their orbital periods," Laughlin said.
"So one could image you would have to design leap year-like systems for them. The degree to which they mismatch would be random."
An exception are those planets found orbiting extremely close to their stars, which have become tidally locked, bound by their star`s gravity to spin exactly once a year.
These planets only ever show one face to the star, the other side permanently turning away, just as the moon orbits Earth, never showing us its far side, the researchers said.
For all other planets, though, there shouldn`t be any relationship between the planet`s spin and its orbital period.
"If tidal locking hasn`t occurred then there`s nothing to inform the planet about how fast it`s spinning relative to its year," Laughlin said. "The spin of the planet depends on the gory details of its history."