This artist’s illustration imagines the view from the surface of one of the planets in the TRAPPIST-1 planetary system. Astronomers think that some of the planets in this system may have a substantial ocean of water, a necessary ingredient for life.
Credit: NASA/JPL-Caltech

One of the most stunning astronomical discoveries of the last decade was an entire system of exoplanets, relatively close to Earth, that have the potential to host life. During a Dec. 13, 2022 conference, astronomers reported preliminary findings about the system gathered by the powerful new James Webb Space Telescope (JWST).  

This artist’s illustration shows what the TRAPPIST-1 planetary system may look like. The planetary system has seven planets that rapidly orbit close to the parent star. Three of the planets orbit within the habitable zone of the star where liquid water can exist on a planet’s surface.
Credit: NASA/JPL-Caltech

TRAPPIST-1 is a red dwarf star about 40 light-years from Earth in the constellation Aquarius. One light-year equals the distance light travels in a vacuum in a year, about 5.88 trillion miles (9.46 trillion kilometers). TRAPPIST-1 is notable for having seven orbiting planets. Astronomers classify the planets as terrestrial, meaning they have Earthlike qualities. All of them orbit the star within or near a region that astronomers call the habitable zone. That is, in that region in which liquid water can exist on a planet’s surface. Scientists consider liquid water to be an essential ingredient for life. 

The first three planets in the TRAPPIST-1 system were discovered in 2015. These were discovered by astronomers using the Transiting Planets and Planetesimals Small Telescope (TRAPPIST) robotic telescope pair, located at La Silla Observatory in Chile and Oukaïmeden Observatory in Morocco. Scientists using the Spitzer Space Telescope and the Very Large Telescope in Chile announced in 2017 that they had confirmed the discovery of those three planets and had discovered four more planets. 

The potential of these planets to host conditions favorable for life made the TRAPPIST-1 system a major target for the JWST. This advanced satellite observatory was launched in December of 2021 and began conducting scientific observations in mid-2022. Earlier that year, JWST characterized the atmosphere of the giant exoplanet WASP-96b as a proof-of-concept, setting the stage for TRAPPIST-1 observations.  

The preliminary results from two of the TRAPPIST-1 planets confirm that they do not have hydrogen atmospheres. They may have no atmospheres, or they may have atmospheres composed of other gases, including carbon dioxide, methane, and water vapor. Such atmospheres could make these planets hospitable for life. 

Because these exoplanets are so small, even the powerful JWST needs to view the system for extended periods to gather accurate data. But the system’s diminutive proportions will speed up the observation process. JWST detects minute changes to the star’s light as each planet passes in front of it. The seven planets whirl around TRAPPIST-1 with orbital periods of 1.5 to 18.8 Earth days. In contrast, Earth’s orbital period (also called a year) is about 365 days, and Mercury’s is 88 Earth days. (Because TRAPPIST-1 is a small, cool star, these tight orbits still lie within or near its habitable zone.) Astronomers are confident that they will have a good “family portrait” of the TRAPPIST-1 within a year.  

JWST has already racked up impressive observations after just a half-year of activity. With its study of TRAPPIST-1, it will help bring astronomers closer to answering one of the most fundamental questions in science: are we living things on Earth alone in the universe, or not? 

March 1, 2017

On February 22, astronomers announced the discovery of a remarkable planetary system orbiting a relatively nearby star. Planets outside the solar system are called extrasolar planets or exoplanets. The new system has a whopping seven planets, many of which might host conditions favorable for life. The finding was published in the journal Nature.

This artist’s concept shows what each of the TRAPPIST-1 planets may look like, based on available data about their sizes, masses and orbital distances.
Credit: NASA/JPL-Caltech

The system is located some 40 light-years away in the constellation Aquarius, the Water Bearer. One light-year is the distance that light travels in a vacuum in a year, about 5.88 trillion miles (9.46 trillion kilometers). The planets orbit a star called TRAPPIST-1, named in honor of the telescope used in the discovery. TRAPPIST stands for Transiting Planets and Planetesimals Small Telescope. It is a robotic telescope in Chile funded by Belgium. In May 2016, TRAPPIST detected three planets orbiting a type of small, relatively cool star called a red dwarf. In September, the Spitzer Space Telescope, operated by the United States National Aeronautics and Space Administration (NASA), began monitoring the system. With the help of NASA’s Hubble Space Telescope and other ground-based telescope systems, Spitzer confirmed the existence of two of the planets. But Spitzer determined that the third signal detected by TRAPPIST actually came from four planets, not one. Later, the telescope observed traces of a seventh, even more distant, exoplanet.

Even this farthest exoplanet orbits closer to TRAPPIST-1 than Mercury does to the sun, at a distance of only about 5.6 million miles (9.0 million kilometers). For comparison, Earth orbits about 93 million miles (150 million kilometers) from the sun. Because red dwarfs are much smaller and cooler than the sun, however, three of the planets orbit within a region that should be neither too hot nor too cold for liquid water to exist on their surfaces. Most scientists consider liquid water essential for life, so such a region around a star is known as its habitable zone.

The planetary system’s compact size would provide spectacular views only imagined in science fiction. The star TRAPPIST-1 would appear three times as large as the sun does on Earth, bathing the planets with a dim, pinkish light. Because the exoplanets are so close together, an observer standing on one planet could clearly see the other six. Neighboring planets would sometimes appear larger than does the moon in Earth’s sky.

Follow-up studies are already underway. NASA’s renowned planet-hunting satellite Kepler is currently examining the system. All seven planets are about the size of Earth, but Kepler will more precisely calculate their sizes and possibly find more planets. Spitzer has already confirmed that two of the planets are rocky worlds, rather than gaseous planets like Neptune. But Spitzer will continue to examine the system to learn more about the planets’ masses and compositions. In 2018, NASA plans to launch the James Webb Space Telescope. This powerful satellite should be able to detect if any of the exoplanets have atmospheres and determine their compositions. If the atmosphere contains compounds such as methane, oxygen, and ozone, it would be a strong indication that life exists there.

Other Behind the Headlines posts:

• Ten to 30 Alien Planets for Every Person on Earth? (Jan. 13, 2012)
• Amateur Astronomers Discover a Planet with Four Suns (Oct. 17, 2012)
• New Exoplanet Candidates from Ailing Kepler Spacecraft (June 20, 2013)
• Kepler Space Telescope Goes Dark–For Now (Aug. 16, 2013)
• Exoplanet Bonanza from Kepler (Feb. 27, 2014)
• First “Earth-Cousin” Found by Kepler Space Telescope (May 1, 2014)
• “Hello, Aliens? Are You Out There?” (Feb. 13, 2015)
• New Planetary Neighbors (May 11, 2016)
• The Pale Red Dot: Proxima b (Aug. 31, 2016)