This artist's concept appeared on the February 23rd, 2017 cover of the journal Nature announcing that the TRAPPIST-1 star, an ultra-cool dwarf, has seven Earth-size planets orbiting it. Any of these planets could have liquid water on them. Planets that are farther from the star are more likely to have significant amounts of ice, especially on the side that faces away from the star. 

The system has been revealed through observations from NASA's Spitzer Space Telescope and the ground-based TRAPPIST (TRAnsiting Planets and PlanetesImals Small Telescope) telescope, as well as other ground-based observatories. The system was named for the TRAPPIST telescope.

NASA's Jet Propulsion Laboratory, Pasadena, California, manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate, Washington. Science operations are conducted at the Spitzer Science Center at Caltech in Pasadena. Spacecraft operations are based at Lockheed Martin Space Systems Company, Littleton, Colorado. Data are archived at the Infrared Science Archive housed at Caltech/IPAC. Caltech manages JPL for NASA.
Boasting 7 Earth-Sized Planets, TRAPPIST-1 Is the New Solar System to Know
published during a waning crescent moon.

Learn the name of TRAPPIST-1. Loaded with Earth-sized planets, this solar system will provide astronomers with the exciting opportunity to learn more about rocky worlds like our own. Three of its planets are even located within the habitable zone, meaning there could be a high chance they support liquid water.

earth-sized planets

This artist’s concept shows what the TRAPPIST-1 planetary system may look like, based on available data about the planets’ diameters, masses, and distances from the host star. Credit: NASA/JPL-Caltech/R. Hurt, T. Pyle (IPAC)

At just forty light-years away, the alien worlds orbit a nearby ultra-cool dwarf star, TRAPPIST-1. The star is both smaller and cooler than our Sun, which means its habitable zone — the distance at which a planet is most likely to have liquid water — is closer to the star than it is in our solar system. For some perspective, all seven Earth-like planets are closer to their star than Mercury is to the Sun. In fact, the orbits are so close that if we were to stand on the surface of one of Trappist-1’s planets and gaze up, the other planets would sometimes appear even bigger than the Moon does in the skies above Earth, as you can see in this video:

Similar to Mercury and our Sun, some of the planets may be tidally locked to their star, resulting in perpetual days and eternal nights. The strong temperature differentials between these two sides would likely create some extreme weather conditions, such as intense winds.

The TRAPPIST-1 system was observed by the Spitzer Space Telescope nearly continuously for 500 hours in the fall of 2016.  “This is the most exciting result I have seen in the 14 years of Spitzer operations,” said Sean Carey, manager of NASA’s Spitzer Science Center in a press release. Spitzer is scheduled to make follow-up observations in the autumn of 2017, giving scientists the chance to examine the planets’ atmospheres.

earth-sized planets

An artist’s fantasy of the surface of TRAPPIST-1e, a stop on a tour of this seven-world system. Credit: NASA-JPL/Caltech

However, Spitzer isn’t the only one getting in on the game. Exoplanet-hunting powerhouse, Kepler Space Telescope, will wrap up their observations in early March 2017. The Hubble Space Telescope has also begun its investigation of the solar system by setting its sights on the atmospheres of the two planets closest to the sun. More observations are planned for another four planets, including three in the habitable zone. So far, these observations support the idea that these Earth-sized planets are also rocky terrestrial worlds like ours.

earth-sized planets

This artist’s concept allows us to imagine what it would be like to stand on the surface of the exoplanet TRAPPIST-1f, located in the TRAPPIST-1 system in the constellation Aquarius. Credit: NASA/JPL-Caltech/T. Pyle (IPAC)

All this data will be used to help plan a more detailed investigation by the James Webb Space Telescope after it launches in 2018. The powerful new space observatory is designed to be able to detect key components of atmospheres around alien worlds, identifying water, methane, oxygen, ozone, along with planets’ temperature and surface pressure. These future observations will help to establish whether or not TRAPPIST-1’s Earth-like worlds have liquid water.

“This is a search that will go on for many generations,” exclaimed astronomer and planetary scientist Sara Seager during the NASA press conference. “We’re this close now to finding so many habitable worlds.”