At a news conference in Washington D.C. today (February 22, 2017), NASA announced that its Spitzer Space Telescope has observed the first known system of seven Earth-size planets around a single star. Three of these planets are firmly located in what’s called the habitable zone, the area around the parent star where a rocky planet is most likely to have liquid water – key to life as we know it. The discovery sets a new record for greatest number of known planets in a star’s habitable zone. After all, our solar system has only two planets in the habitable zone: Earth and Mars. This exoplanet system – called TRAPPIST-1 – has three.
Because they are located outside of our solar system, these planets are scientifically known as exoplanets.
Only about 40 light-years (235 trillion miles) from Earth, in the direction to our constellation Aquarius, TRAPPIST-1 – classified as an ultra-cool dwarf. It’s so cool that liquid water could survive on planets orbiting very close to it, closer than is possible on planets in our solar system. All seven of the TRAPPIST-1 planetary orbits are closer to their host star than Mercury is to our sun. According to a NASA statement:
The planets also are very close to each other. If a person was standing on one of the planet’s surface, they could gaze up and potentially see geological features or clouds of neighboring worlds, which would sometimes appear larger than the moon in Earth’s sky.
The researchers say that the planets might also be tidally locked to the TRAPPIST-1 star. That means that the same side of the planet is always facing the star, therefore each side is either in perpetual day or night. If that’s true, the planets could have weather patterns totally unlike those on Earth, such as strong winds blowing from the day side to the night side, and extreme temperature changes.
According to the study – published today in the journal Nature – all of the TRAPPIST-1 planets are likely to be rocky. Further observations will hopefully reveal whether any have liquid water on their surfaces. The mass of the seventh and farthest exoplanet hasn’t yet been estimated. Scientists believe it could be an icy, “snowball-like” world.
Michael Gillon, lead author of the paper and the principal investigator of the TRAPPIST exoplanet survey at the University of Liege, Belgium. Gillon said in a statement:
The seven wonders of TRAPPIST-1 are the first Earth-size planets that have been found orbiting this kind of star. It is also the best target yet for studying the atmospheres of potentially habitable, Earth-size worlds.
Following up on the Spitzer discovery, NASA’s Hubble Space Telescope has initiated the screening of four of the planets, including the three inside the habitable zone.
This 360-degree panorama depicts the surface of a newly detected planet, TRAPPIST 1-d, part of a seven planet system some 40 light years away. Explore this artist’s rendering of an alien world by moving the view using your mouse or your mobile device.
Thomas Zurbuchen is associate administrator of NASA’s Science Mission Directorate in Washington. He said in a statement:
This discovery could be a significant piece in the puzzle of finding habitable environments, places that are conducive to life. Answering the question ‘are we alone’ is a top science priority and finding so many planets like these for the first time in the habitable zone is a remarkable step forward toward that goal.
Bottom line: NASA’s Spitzer Space Telescope has observed 7 Earth-sized planets orbiting a tiny star called TRAPPIST-1. Three of them are firmly in the habitable zone.
Eleanor Imster has helped write and edit EarthSky since 1995. She was an integral part of the award-winning EarthSky radio series almost since it began until it ended in 2013. Today, as Lead Editor at EarthSky.org, she helps present the science and nature stories and photos you enjoy. She also serves as one of the voices of EarthSky on social media platforms including Facebook, Twitter and G+. She and her husband live in Tennessee and have two grown sons.