San Diego scientists have helped discover three Earth-sized planets orbiting a tiny nearby star. In a paper published Monday in Nature, the researchers say two of the planets are close enough to the ultracool dwarf star to potentially harbor life.
The planets orbit a very small and faint star, not visible to the naked eye, about 40 light years away from our own sun. They're about as close to their star as Jupiter is to its moons.
"It's a really shrunk-down version of a solar system," said UC San Diego's Adam Burgasser, a co-author of the new paper. "These objects are orbiting around the star on the timescale of days, two to three for some of these planets."
Another UC San Diego scientist, Daniella Bardalez Gagliuffi, also co-authored the paper along with an international team of planet-hunters.
The researchers discovered the planets using a telescope in Chile that helped them look into the infrared spectrum. They detected the planets using the "transit method," essentially watching the star get dimmer at regular intervals as the planets passed in front of it during their orbits.
Burgasser and his colleagues believe the two planets closest to the star lie within the "habitable zone," meaning they receive just enough radiation from the star to potentially contain liquid water at their surfaces.
However, both planets appear to be tidally locked, meaning they have one side permanently facing the star and the other side in perpetually darkness. That could be a challenge for fostering life.
Burgasser said more research on the planet's chemical signatures and atmospheric compositions will be needed to address the question of whether they could harbor life.
Astronomers have discovered a number of potentially habitable planets orbiting other stars. But Burgasser said these planets deviate from the norm because they orbit an unusually small and faint star.
"It could be that many, many terrestrial-sized planets are actually hidden around these little stars, and we are just now starting to build the capabilities to find them and study them," he said.
Burgasser's fellow UC San Diego astronomer, Quinn Konopacky, has also found planets orbiting other stars, but she was not involved in this discovery.
She said the paper was exciting, and that further research on these planets is merited because it will be possible to study their atmosphere and composition.
"We have known that there was the potential to find Earth-sized planets around ultra-cool stars, and this is confirmation of that possibility," she said.
"It really suggests that planets exist in every nook and cranny of the galaxy. And the more planets like this we find, the more confident we feel that life is likely to exist on other worlds."
San Diego State University astronomer Jerome Orosz, another local planet hunter, said, "They do make a good case that meaningful follow-up observations are possible."
But he was less convinced that these planets could harbor life. The two planets receive about two to four times the amount of radiation Earth does, which he said "seems high."
"The bit about the habitable zone is overplayed in my opinion," Orosz said.
Another SDSU astronomer, William Welsh, also had reservations about the planets' habitability, but he said the paper offered some important insights.
"This is important because such low-temperature, low-mass stars are the most common stars in the galaxy," he said. "In other words, Earth-like planets (meaning both Earth-size and Earth temperature) may be even more common than we thought."
