7 Earth-Sized Planets Found Orbiting Nearby Star – 3 of them are in the Habitable Zone

On February 22, 2017, NASA has announced that seven Earth-sized planets have been observed by NASA’s Spitzer Space Telescope around TRAPPIST-1, a tiny, nearby, ultra-cool dwarf star located 39 light-years (12 parsecs; 370 petametres) away from Earth in the constellation Aquarius. The good news is: three of these planets are firmly in the habitable zone. The new discovery may be a great breakthrough in search for extraterrestrial life.

Possible surface of TRAPPIST-1f
This illustration shows the possible surface of TRAPPIST-1f, one of the newly discovered planets in the TRAPPIST-1 system. Scientists using the Spitzer Space Telescope and ground-based telescopes have discovered that there are seven Earth-size planets in the system.
Credits: NASA/JPL-Caltech

In fact, three of these seven planets are already known: In 2015 a team of astronomers headed by Michaël Gillon of the Institut d’Astrophysique et Géophysique at the University of Liège in Belgium discovered three Earth-sized planets orbiting the dwarf star. Gillon and his team used transit photometry with the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) at the La Silla Observatory in Chile. On February 22, 2017, astronomers announced four additional exoplanets around TRAPPIST-1.

All seven of TRAPPIST-1’s planets orbit much closer than Mercury orbits the Sun. (Mercury’s orbit is not a perfect circle, so its distance from the sun varies. The minimum distance from the sun to Mercury is 28.5 million miles / 45.86 million km. The maximum distance is 43.5 million miles / 70 million km.) But, since it is a ultra-cool dwarf star, and considering the amount of energy they receive from the star, three of them (e, f, g) orbit the habitable zone (1). The planets also are very close to each other: the distance between the orbits of TRAPPIST-1b and TRAPPIST 1c is only 1.6 times the distance between the Earth and the moon (which is roughly 384,400 km / 238,855 mi). According to NASA, “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.”

TRAPPIST-1 system
TRAPPIST-1 system. Three of (e, f, g) seven Earth-sized planets of TRAPPIST-1 orbit the habitable zone. Image: NASA
TRAPPIST-1 System vs Solar System
TRAPPIST-1 System vs Solar System: the known data on each of the seven planets of TRAPIST-1 compared to the rocky planets (Mercury, Benus, Earth, Mars) in our Solar System.

Alien life?

Despite three of the planets are in the habitable zone, this does not mean we found extraterrestrial life: the life itself depends on a number of factors: for example, we still don’t know if these planets have atmospheres allow water to remain as liquid. And, since the star is 10 times further away than Proxima Centauri (from Latin, meaning “nearest [star] of Centaurus”) in the Alpha Centauri system, we don’t have much hope of sending a spacecraft to this system in the near future.

The planets may also be tidally locked to their star, making alien life less likely. Tidal locking is the name given to the situation when an object’s orbital period matches its rotational period. A great example of this is our own Moon. If they are tidally locked, this means the same side of the planet is always facing the star, therefore each side is either perpetual day or night. This could mean they 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.

On the surface

The 360-degree panorama below depicts the surface of a newly detected planet, TRAPPIST-1d, part of a seven planet system some 40 light years away. You can explore this artist’s rendering of an alien world by moving the view using your mouse or your mobile device.

The depiction is based on the latest scientific data about this planetary system, and this world’s sister planets can be seen as bright points of light in a dark sky. Each world is roughly in Earth’s size range, in terms of both mass and diameter. Further observations will be needed to determine whether any or all of these worlds might be habitable.


  1. In astronomy and astrobiology, the circumstellar habitable zone (CHZ), or simply the habitable zone, is the range of orbits around a star within which a planetary surface can support liquid water given sufficient atmospheric pressure.


  • TRAPPIST-1 on wikipedia
  • “NASA Telescope Reveals Largest Batch of Earth-Size, Habitable-Zone Planets Around Single Star” on NASA.gov (press release)

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