NASA Discovery Reveals Largest Group of Earth-Size Planets In Habitable Zone

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With a view towards the rising host star, TRAPPIST-1, an artist’s conception of what the surface of planet TRAPPIST-1f may look like.

A team of astronomers using NASA’s Spitzer Space Telescope, an orbiting platform that observes the universe exclusively in the InfraRed (heat) region of the spectrum, have discovered a group of Earth-size planets in orbit around the cool, low-mass red dwarf star TRAPPIST-1, three of which are within the star’s habitable zone! As mentioned in yesterday’s post, the habitable zone is the region around every star where water could exist in a liquid state.

The star, named accordingly as the first planet discovered with the TRAPPIST (Transiting Planets and Planetesimals Small Telescope) telescope network (this discovery was made by the southern node in Chile), is approximately 40 light years distant in the constellation Aquarius. In May of last year, three planets in the system were discovered and now, assisted by several ground-based telescopes, including the European Southern Observatory’s Very Large Telescope, Spitzer confirmed the existence of two of these planets and discovered five additional ones, increasing the number of known planets in the system to seven!

Since three of the seven planets lie within the star’s habitable zone, it is possible that any number of them, if not all three, have liquid water on their surfaces. It should be pointed out that the habitable zone scales in distance and extent according to the star’s luminosity, a property of the star that is inexorably linked to its mass. As such, since TRAPPIST-1 is barely above what is known as the Hydrogen-burning mass limit, the habitable zone is quite narrow and begins very close to the star. Any object below the hydrogen-burning mass limit cannot sustain hydrogen-fusion reactions in its core and is thus considered sub-stellar.

The TRAPPIST-1 Family of Planets

The respective orbital periods and distances of the TRAPPIST-1 family of planets compared to our solar system. You will quickly note that even tiny Mercury has a period and distance greater than TRAPPIST-1h at about 20 days and 0.06 AU (1 Astronomical Unit, AU, is the the Earth-Sun distance). 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.


A full compliment of multimedia resources are available at the NASA Exoplanet page for TRAPPIST-1. Additional resources are available, also at NASA’s Exoplanet page for this newly discovered system.

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 at Caltech/IPAC in Pasadena, California. “Spitzer will follow up in the fall to further refine our understanding of these planets so that the James Webb Space Telescope can follow up. More observations of the system are sure to reveal more secrets.”

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. These observations aim at assessing the presence of puffy, hydrogen-dominated atmospheres, typical for gaseous worlds like Neptune, around these planets.

Since the bulk of the light from TRAPPIST-1 is emitted in the InfraRed region of the electromagnetic spectrum, the system makes for a great target for the James Webb Space Telescope, an orbiting platform that, like Spitzer, observes the universe exclusively in the Infrared. JWST is to be launched in the Fall of next year (2018).

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4 thoughts on “NASA Discovery Reveals Largest Group of Earth-Size Planets In Habitable Zone

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