Researchers on Wednesday said they had made one of the most exciting discoveries yet in the search for habitable worlds beyond our own, announcing they had spotted seven Earth-size planets — any of which could have liquid water — orbiting a star 40 light-years away.
“What we really have in this story is a major step forward toward answering one of the questions that are at the heart of so many of our philosophers — of what we’re thinking about when we’re by ourselves, and that basically is: Are we alone out there?” Thomas Zurbuchen, associate administrator of NASA’s Science Mission Directorate in Washington, said during a presentation to announce the discovery.
The finding, based on observations from NASA’s Spitzer Space Telescope, represents the first time that scientists have found so many planets in a single star’s habitable zone, where water might be able to pool on the surface.
And the system’s relative proximity to Earth, along with the fact that the planets can be studied as they move across their sun, opens the door to revelations that were almost inconceivable just a few years ago.
“The discovery gives us a hint that finding a second Earth is not just a matter of if, but when,” Zurbuchen said.
The findings were published Wednesday in the journal Nature by a team including MIT postdoctoral researcher Julien de Wit.
Though it will be a long time before humans have the technology to explore the planets in the system — called TRAPPIST-1 — exoplanet researchers, who study the planets of other stars, said Wednesday the discovery comes at a crucial moment in the search for life.
A number of powerful new telescopes, both on land and in space, are set to come online in coming years. Because the system is so close to Earth, there’s a good chance astronomers will soon be able to see whether the planets might have hospitable atmospheres, water, or basic signs of living things.
“I think it’s huge,” David Charbonneau, a Harvard University astronomy professor who researches exoplanets, said in an interview with the Globe. “What we want to do is look at Earth-like planets and see if there’s evidence of life. The most promising way to do that is to look at the atmospheres of the planets and look for gases that are associated with life.”
Though the planets could potentially have conditions that would support life, they are also likely to be very different from the world we know.
Researchers said the planets are orbiting a small “ultra-cool dwarf” star, which means liquid water could survive on planets much closer to their sun than in our solar system.
They may also be “tidally locked,” which means their same side is always facing the star — some parts permanently in daylight and others eternally darkened by night.
Three of the planets are thought to have the best chance of holding water, which is considered necessary for life as we know it, though researchers emphasized it is possible on any of them.
To find out about the planets, researchers have essentially been looking at the characteristics of the minuscule silhouettes they present in front of their sun. So far, scientists have been able to discern their size and density. The next step will be to find out about their atmospheres.
The system is named for The Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile, which first found planets in the system. The Spitzer data helped scientists find more planets, and suggested they had a rocky composition.
NASA’s Hubble Space Telescope is now looking at four of them, and researchers are waiting to examine them through the agency’s powerful James Webb Space Telescope, which launches in 2018 and could help “detect the chemical fingerprints of water, methane, oxygen, ozone, and other components of a planet’s atmosphere.”
Other ground-based telescopes in Chile, including the Giant Magellan Telescope and the European Extremely Large Telescope, could also help gather more data.
Even if the TRAPPIST-1 planets do not turn out to be conducive to life, they could provide insight into how planets develop and whether other exoplanets are likely to have water and other crucial ingredients, researchers said.
Michael Gillon, lead author of the paper published Wednesday and principal investigator of the TRAPPIST exoplanet survey at the University of Liege, in Belgium, described the system as “the best target yet for studying the atmospheres of potentially habitable, Earth-size worlds.”
Sara Seager, an astrophysicist and planetary scientist at the Massachusetts Institute of Technology who spoke at Wednesday’s announcement, said the findings are another breakout moment for exoplanet studies, which were dismissed in their infancy decades ago as mere “stamp collecting.”
“This is a search that will go on for generations, and just the fact that we’re this close now to finding so many habitable worlds, it’s just really exciting,” she said.