JPL Offers Download Poster of New Exoplanet Discovery

Scientists working at the Infrared Processing and Analysis Center (IPAC) at Caltech in Pasadena were part of an international science team that recently discovered the first known system of seven Earth-size planets around a single star. Three of these planets are firmly located in the habitable zone, the area around the parent star where a rocky planet is most likely to have liquid water.

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Located about 40 light years or 235 trillion miles from Earth, the system of planets is now called TRAPPIST-1, named for The Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile. In May last year, researchers using TRAPPIST announced they had discovered three planets in the system.

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.

The new results were published Wednesday in the journal Nature, and announced at a news briefing at NASA Headquarters in Washington.

To illustrate the newly discovered planetary system, IPAC’s Communications and Education team developed graphics and multimedia that were used at the NASA press conference, including the visualization of the TRAPPIST-1 system featured on the cover of the journal Nature, and a poster advertising a “planet hop” from one of the planets in the system: TRAPPIST 1e, “voted best ‘hab zone’ vacation within 12 parsecs of Earth.”

The discovery sets a new record for greatest number of habitable-zone planets found around a single star outside our solar system. All of the seven planets could have liquid water – the key to life – under the right atmospheric conditions, but the chances are highest with the three in the habitable zone.

“This discovery could be a significant piece in the puzzle of finding habitable environments, places that are conducive to life,” said Thomas Zurbuchen, associate administrator of the agency’s Science Mission Directorate in Washington. “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.”

Using Spitzer data, the team precisely measured the sizes of the seven planets and developed first estimates of the masses of six of them, allowing their density to be estimated.

Based on their densities, all of the TRAPPIST-1 planets are likely to be rocky. Further observations will not only help determine whether they are rich in water, but also possibly reveal whether any could have liquid water on their surfaces. The mass of the seventh and farthest exoplanet has not yet been estimated — scientists believe it could be an icy, “snowball-like” world, but further observations are needed.

“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. “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.”

Michael Gillon, lead author of the paper and principal investigator of the TRAPPIST exoplanet survey at the University of Liege in Belgium, said 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,” Gillon said.

In contrast to the Sun, the TRAPPIST-1 star – classified as an ultra-cool dwarf – is so cool that liquid water could survive on planets orbiting very close to it, closer than is possible on planets in the solar system. All seven of the TRAPPIST-1 planetary orbits are closer to their host star than Mercury is to the sun. The planets also are very close to each other. If a person were 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 planets may also be tidally locked to their star, which 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.

Spitzer, an infrared telescope that trails Earth as it orbits the sun, was well-suited for studying TRAPPIST-1 because the star glows brightest in infrared light, whose wavelengths are longer than the eye can see.

In the fall of 2016, Spitzer observed TRAPPIST-1 nearly continuously for 500 hours. Spitzer is uniquely positioned in its orbit to observe enough crossings, or transits, of the planets in front of the host star to reveal the complex architecture of the system.

Engineers optimized Spitzer’s ability to observe transiting planets during Spitzer’s “warm mission,” which began after the spacecraft’s helium coolant ran out as planned after the first five years of operations.

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.

Spitzer, Hubble, and Kepler will help astronomers plan for follow-up studies using NASA’s upcoming James Webb Space Telescope, launching in 2018. With much greater sensitivity, Webb will be able to detect the chemical fingerprints of water, methane, oxygen, ozone, and other components of a planet’s atmosphere. Webb also will analyze planets’ temperatures and surface pressures – key factors in assessing their habitability.

Aside from Carey, IPAC scientist Jim Ingalls was also part of the science team which used Spitzer to study the system around TRAPPIST-1. Analysis of over 300 light curves at 4.5 micron from Spitzer’s IRAC instrument captured the planets transiting TRAPPIST-1, and allowed the team to precisely measure the sizes of the seven planets, and estimate the masses of six.

Spitzer did not always have the capability to carry out exoplanet observations with such precision. In 2011, Ingalls and Jessica Krick, another member of the IPAC team, together with spacecraft engineers at Lockheed Martin Space Systems, worked on three innovations in the space telescope – modified heater cycling, repurposed peak-up camera for staring observations, and in-depth characterization of individual pixels in the camera – that more than doubled Spitzer’s stability, enabling photometry at remarkable precision.

“Spitzer is a real survivor,” said Carey. “Initially designed for a five-year mission, it has delivered high quality data and transformative science for 14 years now. Its extended life has offered room to imagine and enable new capabilities. With TRAPPIST-1 we see how this really pays off.”