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Spitzer discovers star system with seven orbiting Earth-sized planets

Spitzer discovers TRAPPIST-1 system

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. Image & Caption Credit: NASA-JPL/Caltech

A star system, approximately 40 light-years from Earth, with seven Earth-sized planets, including three in the habitable zone, has been discovered by NASA’s Spitzer Space Telescope.

Named TRAPPIST-1 because it was discovered by the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile, the star is an ultra-cool M-type dwarf star with eight percent the mass of the Sun and half its temperature, located in the direction of the constellation Aquarius.

NASA announced the discovery at a news conference on Wednesday, February 22, at 1:00 p.m. EST. Researchers who took part in the news conference, which was followed by a question and answer period, include the following:

  • Thomas Zurbuchen, associate administrator for NASA’s Science Mission Directorate in Washington, DC.
  • Michael Gillon, an astronomer at the University of Liege in Belgium.
  • Sean Carey, manager of NASA’s Spitzer Science Center at Caltech/IPAC in Pasadena, California.
  • Nikole Lewis, an astronomer at the Space Telescope Science Institute in Baltimore, Maryland.
  • Sara Seager, professor of planetary science and physics at the Massachusetts Institute of Technology (MIT) in Cambridge, MA.

The seven planets of TRAPPIST-1

Spitzer: Transit Illustration of TRAPPIST-1

The TRAPPIST-1 system consists of seven Earth-sized planets orbiting a red dwarf star. Image Credit: NASA / JPL-Caltech / R. Hurt (IPAC)

All seven planets orbit closer to the star than Mercury orbits the Sun. Their densities indicate they could all be rocky worlds while their cool temperatures indicate that under the right atmospheric conditions, all could host liquid water on their surfaces.

Being rocky and capable of harboring liquid water are two of the primary conditions necessary for life as we know it to exist.

Scientists are especially interested in the three planets located in the star’s habitable zone, as they are the ones most likely to have liquid water.

Three of the planets were discovered in May 2016 by scientists in Chile using TRAPPIST. Following the discovery, several other ground-based telescopes, including the European Southern Observatory’s (ESO) Very Large Telescope, as well as NASA’s Spitzer Space Telescope were trained on the system.

Spitzer not only confirmed the presence of the first two planets but also discovered five more orbiting the same star. The data provided by Spitzer enabled the scientists to accurately determine the planets’ sizes and estimate the masses of all but one.

With knowledge of their masses and sizes, the scientists were able to make decent estimates of their densities. By knowing or closely estimating a planet’s density, the scientists were able to gain an insight as to whether the planet is gaseous or rocky.

“This discovery could be a significant piece in the puzzle of finding habitable environments, places that are conducive to life,” Zurbuchen stated during the news conference. “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.”

Four of the system’s planets were observed with the Hubble Space Telescope, which found no evidence for their having the puffy, hydrogen-heavy atmospheres typical of gaseous planets.

“The TRAPPIST-1 system provides one of the best opportunities in the next decade to study the atmospheres around Earth-size planets,” noted Nikole Lewis, who co-led the Hubble study of the system.

Spitzer: Surface of TRAPPIST-1f

Imagine standing on the surface of the exoplanet TRAPPIST-1f. This artist’s concept is one interpretation of what it could look like. Image & Caption Credit: NASA/JPL-Caltech

TRAPPIST-1’s seven planets orbit so close to each other that a person standing on one of them would be able to see the disks of the others in the sky. The close orbits also mean the planets perturb one another. Their layout is more akin to that of Jupiter’s moons than to that of the Solar System.

Mercury orbits the Sun at a distance of 0.39 AU (astronomical units, with one AU equal to the average Earth-Sun distance: 93 million miles or 150 million kilometers). In contrast, the closest TRAPPIST-1 planet orbits its star at 0.01 AU and the furthest at 0.06 AU.

While the planets’ densities suggest they are rocky, the question of whether they have water will require additional observations. Some scientists think that the system’s outermost planet is icy, though its mass has not yet been determined.

Spitzer: The TRAPPIST-1 Habitable Zone

The TRAPPIST-1 habitable zone in comparison to the Solar System. Image Credit: NASA/JPL-Caltech

As an infrared telescope, Spitzer is ideal for studying this system because the star glows in infrared wavelengths. During the last quarter of 2016, Spitzer observed the system for 500 hours, monitoring transits of the planets in front of the star.

Because the planets are in such close orbits around TRAPPIST-1, some or all of them may be tidally locked, which means that they always present the same side to the star and the opposite side away from the star.

That configuration may cause extreme temperature variations that could limit the planets’ habitability. It could also result in extreme weather events, with strong winds blowing from one side of a planet to the other side.

Additionally, red dwarf stars, especially young ones, can experience superflares that emit high levels of radiation, which can strip away a planet’s atmosphere and prevent life from getting started.

However, unlike Proxima Centauri, TRAPPIST-1 is a quiet, middle-aged star.

Spitzer: TRAPPIST-1 Statistics Table

This chart shows, on the top row, artist concepts of the seven planets of TRAPPIST-1 with their orbital periods, distances from their star, radii, and masses as compared to those of Earth. Image Credit: NASA / JPL-Caltech / R. Hurt, T. Pyle (IPAC)

Follow-up observations

NASA’s K2 extended Kepler exoplanet search mission is now studying the TRAPPIST-1 system while Spitzer and Hubble will conduct follow-up observations in preparation for study by the James Webb Space Telescope (JWST), set to launch in 2018.

The highly sensitive JWST will be capable of probing the planets’ atmospheres in a search for bio-signatures, as well as detecting evidence of water, methane, oxygen, ozone, carbon dioxide, and various other gases; plus, it will analyze their surface pressures and temperatures.

Another research team is constructing Speculoos, a more powerful version of TRAPPIST, which will search for planetary systems around other red dwarf stars.

Findings of the TRAPPIST-1 study have been published in the journal Nature.

Various visual simulations, including “Exoplanet Surface in 360 VR“, as well as additional photos and videos, and the TRAPPIST-1 system in the free, downloadable desktop app, “Eyes on Exoplanets”, or on mobile, “TRAPPIST-1 system in 3D”, can all be accessed at this website.

Video Courtesy of NASA Jet Propulsion Laboratory

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.

Video & Caption Courtesy of NASA Jet Propulsion Laboratory



Laurel Kornfeld is an amateur astronomer and freelance writer from Highland Park, NJ, who enjoys writing about astronomy and planetary science. She studied journalism at Douglass College, Rutgers University, and earned a Graduate Certificate of Science from Swinburne University’s Astronomy Online program. Her writings have been published online in The Atlantic, Astronomy magazine’s guest blog section, the UK Space Conference, the 2009 IAU General Assembly newspaper, The Space Reporter, and newsletters of various astronomy clubs. She is a member of the Cranford, NJ-based Amateur Astronomers, Inc. Especially interested in the outer solar system, Laurel gave a brief presentation at the 2008 Great Planet Debate held at the Johns Hopkins University Applied Physics Lab in Laurel, MD.

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