On Wednesday, NASA announced the discovery of as many as seven exoplanets that orbit a dwarf star called TRAPPIST-1 just 39 light years (235 trillion miles) away. The discovery was also detailed in the journal Nature. Finding a planet similar to Earth is the first step in finding life as we know it in the outer world. It means the planet has to be rocky, and at the right distance from its parent star to hold liquid water on its surface. They have to be in the habitable zone of their star.

NASA TRAPPIST-1
Image Credit: NASA / JPL / YouTube Video (screenshot)

Planets orbiting TRAPPIST-1 could have ‘life on the surface’

NASA said three of the seven newly discovered planets are directly in the habitable zone of their star.  The TRAPPIST-1 star system is located in the Aquarius constellation. All the seven planets are rocky, and almost the same size as our Earth. Lead researcher Michaël Gillon of the University of Liege said during a press conference that it was the first time so many Earth-like planets were found orbiting the same star.

Gillon added that these exoplanets “could have some water and maybe life on the surface.” The discovery could help us find new environments that support life forms. Temperatures on these planets range between zero and 100 degrees Celsius. The exoplanets were discovered by NASA’s Spitzer Space Telescope, which was assisted by many other ground-based telescopes.

At least one planet highly likely to have a ‘water-rich composition’

Using data from Spitzer, astronomers were able to measure the sizes of all the seven planets, and masses of six of them. That’s how they confirmed that the planets are rocky. Gillon said in a statement that one of the planets in the habitable zone has a mass that “strongly” suggests a “water-rich composition.” Astronomers believe that the other planets could also hold liquid water, depending on their atmospheric composition.

TRAPPIST-1 is an “ultra-cool” dwarf star with a mass only 1/10th of our Sun. Its brightness is estimated to be 1/1000th of the Sun. Due to its low mass, the planets orbit the star very closely. The closest one has a “year” of just over one day. The most distant one completes one orbit around the star in 20 days. When searching for exoplanets, scientists look for a temporary dimming of a star, which indicates that a planet is passing in front of it.

James Webb would study their atmospheres

Gillon said these planets are “very well suited” for further atmospheric study. For now, researchers are studying the exoplanets’ atmospheres using existing telescopes, which have certain limitations. NASA is set to launch the James Webb Telescope in 2018 that will be capable of measuring the chemical composition of an exoplanet’s atmosphere. We will get to know a lot about these seven planets in the coming years.

While Gillon indicated the possibility of alien life forms on at least one of these exoplanets, NASA has been trying to temper such expectations. The US space agency said the likelihood of alien life there was slim. Astronomers are still working to figure out whether the planets have atmospheres and telltale gases like oxygen, methane, and ozone.