Feb. 22 (UPI) -- NASA announced the discovery of seven Earth-sized planets surrounding a single star at a press conference on Wednesday -- three of which are entirely within the planetary system's habitable zone.
Scientists found the seven planets orbiting an ultra-cool dwarf named TRAPPIST-1. Scientists used the Spitzer Telescope to measure the planets' sizes, masses and orbits.
"This is the most exciting discovery we've had yet with the Sptizer Telescope," Sean Carey, manager of the Spitzer Science Center, said during the NASA press conference.
All three exoplanets in the habitable zone are prime targets for further exploration, but all seven could potentially host liquid water given the right conditions. Future surveys by the Hubble Space Telescope -- and eventually the James Webb Space Telescope -- will study each of the planet's atmospheres.
"Finding a second earth is not a matter of if but when," said Thomas Zurbuchen, associate administrator of the Science Mission Directorate at NASA Headquarters.
All seven of the planets are extremely close together. From the surface of any one of them, the viewer would see be able to see planetary neighbors moving across the sky. The exoplanets feature relatively short orbital periods.
The three potentially habitable exoplanets are TRAPPIST-1d, TRAPPIST-1e and TRAPPIST-1f. Trappist-1d receives an amount of light similar to Earth, and is most likely to feature temperatures comparable to Earth. Trappist-1e receives an amount of light similar to Mars. Initial investigations of its chemical composition suggest it could host liquid water.
Researchers say the results of future TRAPPIST surveys in the next five years could yield insights into the presence of important greenhouse gases -- oxygen, methane, hydrogen, CO2 -- in the exoplanets' atmospheres. These insights could help confirm whether any of the three habitable planets host water and could support life.