Move over, TRAPPIST-1 and Proxima Centauri b. A recently found exoplanet has astronomers even more excited, as it appears that this new world might be the best place to look for signs of life beyond our solar system.
“This is the most exciting exoplanet I’ve seen in the past decade,” Jason Dittmann of the Harvard-Smithsonian Center for Astrophysics (CfA), lead author of a new paper in Nature, said in a statement. “We could hardly hope for a better target to perform one of the biggest quests in science — searching for evidence of life beyond Earth.”
The exoplanet, named LHS 1140b, is located in the habitable zone of a faint red dwarf star located just 40 light-years away from Earth, in the constellation of Cetus. Dittman and his team were able to determine the planet is a so-called “super-Earth” — a planet between the size of Earth and Neptune.
The planet was found using the transit method. When a planet transits or passes in front of its star, it blocks a small portion of the star’s light, like a mini eclipse. By measuring how much light LHS 1140b blocks, the team determined the planet is about 11,000 miles (18,000 km) in diameter, or about 40 percent larger than Earth.
Additionally, the team found this exoplanet is about 6.6 times the mass of Earth, meaning it is very likely a dense, rocky world. It orbits the star, LHS 1140, every 25 days. Since the star is so dim and cool, its habitable zone is quite close to the star. But even in that close orbit, it receives about half as much sunlight from its star as Earth.
Perhaps most enticing, the researchers think this planet likely has an atmosphere, making it one of the most promising targets for ongoing atmospheric studies of exoplanets using the Hubble Space Telescope and other observatories.
The conditions on the planet have likely changed over the life of the star, since when red dwarf stars are young they are known to emit radiation that can strip away atmospheres of the planets that orbit them. But later, the stars settle down to be less active.
The researchers see a possible scenario where the planet’s large size means that a magma ocean could have existed on its surface for millions of years. As the star calmed down, the cooling ocean of lava could release steam, creating an atmosphere and putting water on the surface of the planet.
“Based on the fact that the star is slowly rotating and relatively inactive, we are actually fairly sure that the system is older than 5 billion years old in age,” Dittman told Seeker via email. “To contrast, the Earth and Sun are about 4.5 billion years old. So we actually think that this planet is older in age than the Earth, plenty of time for life to have possibly sprung up!”
According to their paper, Dittman and his team have been observing this star and the transiting planet for several years to garner as much information as possible. They made their first detection in September 2014 with the MEarth observatory, a dual facility that uses the Fred Lawrence Whipple Observatory in Arizona and the Cerro Tololo Inter-American Observatory in Chile. Later follow-up observations were made with ESO’s HARPS instrument, the High Accuracy Radial velocity Planet Searcher.
“When we first had hints of this planet’s existence, we actually did not know the orbital period of planet, so we couldn’t tell if it was in the habitable-zone or not,” Dittman told Seeker. “The duration of the transit was long, so we at least suspected the period was fairly long. However, it took a long time after that first tantalizing hint of the planet to really confirm that it was in the habitable zone.”
Since the planet passes directly in front of the star from our vantage point, that means the star’s light will be filtered through any atmosphere and provide clues to the atmosphere’s composition. Work has already begun to study the planet’s atmosphere with the Hubble Space Telescope.
“We have already been awarded time from Hubble to look at the planet’s atmosphere, and the first of that data was gathered in January,” Dittman said. “I haven’t fully delved into the data, and we need much more data, but the process of further studying this planet is already underway! We have more time with Hubble awarded but yet to be scheduled, and we have also asked for additional time in this year’s call for Hubble Space Telescope proposals, so we’re very excited to see what we find out!”
Astronomers are also looking forward to studying this world with even more powerful telescopes.
“This planet will be an excellent target for the James Webb Space Telescope when it launches in 2018, and I’m especially excited about studying it with the ground-based Giant Magellan Telescope, which is under construction,” said co-author David Charbonneau of the Harvard Center for Astrophysics.
Unlike the crowded seven-planet TRAPPIST-1 system, no other exoplanets around LHS 1140 have been found so far. Multi-planet systems are thought to be common around red dwarfs, so it is possible that additional exoplanets have gone undetected so far because they are quite small.
But overall, the researchers feel this super-Earth may be the best candidate yet to study and characterize an exoplanet’s atmosphere.
“The LHS 1140 system might prove to be an even more important target for the future characterization of planets in the habitable zone than Proxima b or TRAPPIST-1,” said European team members Xavier Delfosse and Xavier Bonfils. “This has been a remarkable year for exoplanet discoveries.”