NASA’s February 22, 2017 announcement of seven Earth-sized planets orbiting TRAPPIST-1, three in the habitable zone, became the most Earth-like exoplanet system ever discovered.
The System
TRAPPIST-1, an ultra-cool red dwarf 40 light-years away, hosts seven rocky planets similar in size to Earth. Three orbit in the habitable zone where liquid water could exist. All seven planets are closer to their star than Mercury is to our Sun - the entire system fits inside Mercury’s orbit.
Tidal Locking
All seven planets likely show the same face to their star always. The “terminator zone” between permanent day and night sides might harbor habitable conditions. Orbital resonances (planet periods in simple ratios) stabilize the system - when one planet orbits twice, another orbits three times, etc.
NASA’s Announcement
The press conference went viral - Google created a doodle, trending #1 globally. NASA emphasized the planets’ potential for atmospheres and water. The discovery proved Earth-sized planets are common, not rare cosmic flukes.
James Webb Follow-Up
In 2023, JWST analyzed TRAPPIST-1c’s atmosphere, finding no thick CO2-rich atmosphere like Venus - good news for habitability hopes. TRAPPIST-1b showed no significant atmosphere. Webb will study the other five planets, searching for biosignatures like oxygen and methane.
The Reality Check
Red dwarfs are volatile - TRAPPIST-1 likely bombards its planets with radiation and flares. Any atmospheres may have been stripped early in the system’s history. Still, red dwarfs are the most common stars (70% of the galaxy), and they live trillions of years - far longer than Sun-like stars. If life can exist there, it’s everywhere.
Source: NASA TRAPPIST-1 Discovery