NASA discovers seven Earth-size exoplanets 40 light-years away, three of which are in the habitable zone

The National Aeronautical and Space Administration (NASA) announced the discovery of seven Earth-sized exoplanets today, three of which are located in the habitable zone, the area around the parent star where a rocky planet is most likely to have liquid water. The discovery set the record for the most number of habitable-zone planets found around a single star outside our solar system.
The exoplanets are revolving around an ultra-cool dwarf star. The system has been named TRAPPIST-1 by NASA after the Transiting Planets and Planetesimals Small Telescope in Chile, which first discovered three of the planets in this system in May 2016. It is located in the constellation Aquarius about 40 light-years (378 trillion kilometres) from Earth.

“The seven wonders of TRAPPIST-1 are the first Earth-size planets that have been found orbiting this kind of star,” said Michael Gillon, lead author of the paper and the principal investigator of the exoplanet survey at the University of Liege, Belgium. “It is also the best target yet for studying the atmospheres of potentially habitable, Earth-size worlds.”
Using data from NASA’s Spitzer Space Telescope, an estimate of the planets’ densities was made which suggests that all seven could be rocky. Further observations will reveal whether any of the planets could have liquid water on their surfaces.
Understandably, a discovery of this scale led to some amusing commentary on social media and even inspired a Google Doodle.