Seven Earth-sized planets have been observed by NASA's Spitzer Space Telescope around a tiny, nearby, ultra-cool dwarf star called TRAPPIST-1.
Astronomers are celebrating a new discovery.
Sean Carey, Manager, Spitzer Science Center, Caltech/IPAC: The big news is that around a very nearby cold, small star we've found seven rocky, Earth-sized planets, all of which could potentially have liquid water.
Three of them orbit in the habitable zone around the star. And liquid water could exist on any of the seven planets given the right conditions.
Nikole Lewis, James Webb Telescope Project Scientist, Space Telescope Science Institute: For me, it's mind-blowing. The first time I saw what the system had in it, I was just like, "You got to be kidding me!" Then I looked at the data myself. I'm like, "Yup, there they all are." It's just... I would have never predicted this. It's beyond, you know, anything I could've ever dreamt of.
The planetary system is called TRAPPIST-1 after the Belgian-operated telescope in Chile. TRAPPIST found two planets in 2016. NASA's Spitzer Space Telescope, with the help of ground-based telescopes, discovered five more.
Michael Gillon, Principal Investigator, TRAPPIST, University of Liege, Belgium: I felt super-excited. Amazed by the very existence of this system... was kind of... of, yeah... of shock.
The TRAPPIST-1 planets are extremely close to one another. From a planet's surface you could easily see other TRAPPIST-1 planets in the sky.
Lewis: If you were standing on one of these planets you'd actually see a lot of them sort of in the sky, whipping by on these very short orbital periods.
NASA's James Webb Telescope, launching in 2018, could teach us even more about the TRAPPIST-1 system. It will be able to detect the chemical fingerprints of water, methane and oxygen of potential atmospheres, key ingredients in assessing habitability.
Carey: It is an excellent, fantastic discovery.