Astronomers have discovered three exoplanets in a nearby star system that may be comparable to the size of Earth and Venus and one of them may also be located at distance from its star to experience temperatures similar to our planet.
The planets are about 40 light years from our planet and orbit a dwarf star that is about one-eighth the size of our sun, or approximately the size of Jupiter. The dwarf star, which astronomers consider to be “ultracool,” is so much cooler than our sun that the system’s habitable zone is much closer to it than in our solar system.
A star’s habitable zone is the area of its star system in which temperatures may be hospitable to environmental conditions amenable to life.
Two of the exoplanets have orbital periods of less than three days; they probably receive two-to four times the amount of solar radiation that Earth does.
The third and most distant of the exoplanets experiences a year that is at least four and as many as 73 days long.
“These planets are so close, and their star so small, we can study their atmosphere and composition, and further down the road, which is within our generation, assess if they are actually inhabited,” Julien de Wit, a postdoctoral researcher at Massachusetts Institute of Technology and a co-author of the paper announcing the discovery, said.
The two exoplanets closest to their star are likely tidally locked to it, meaning that one side of the planet always faces the star. Those two planets are generally too hot on their day-sides, and too cold on their night sides, to support life, though the team of scientists that published the paper describing them said that there may be small areas on their western hemispheres that might be temperate enough to do so.
The third planet from the star could be in its habitable zone, meaning liquid water could occur on its surface.
The three exoplanets are the first ever discovered orbiting an ultracool dwarf star.
Researchers used the TRAPPIST instrument in Chile to find the exoplanets. Because their star emits so little radiation, compared to larger stars, it cannot be seen with an optical telescope.
TRAPPIST, which is an acronym for TRAnsiting Planets and PlanetesImals Small Telescope, detects radiation in the infrared band of the spectrum. Starting in September 2015 the scientists periodically detected a lessening of the amount of the star’s infrared radiation detected by the instrument. That indicated the likelihood that several objects were passing in front of it.
The paper describing the discovery of the exoplanets was published online in the May 12 edition of Nature.