The first known system of seven Earth-size planets orbiting around a single star has been revealed by NASA's Spitzer Space Telescope. It has been observed that three of these planets are firmly positioned in the habitable zone, referring to the area surrounding the parent star where a rocky planet is expected to have liquid water.
This new discovery sets a new record for the greatest number of habitable-zone planets spotted around just one star existing outside the solar system. Liquid water, a vital necessity for life on earth, could be present in all of these seven Earth-size planets under accurate atmospheric conditions. However, the chances of the presence of liquid water seem to be much higher with the three planets in the habitable zone.
This discovery could be a significant piece in the puzzle of finding habitable environments, places that are conducive to life. 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.
Thomas Zurbuchen, Associate Administrator, Science Mission Directorate
This new system is about 40 light-years (235 trillion miles) from Earth, which is considered to be relatively close to earth, in the constellation Aquarius. These seven planets are scientifically known as exoplanets as they are located outside of our solar system.
This new exoplanet system is called TRAPPIST-1, named for The Transiting Planets and Planetesimals Small Telescope (TRAPPIST) in Chile. The discovery of three planets in the system was announced on May 2016 by researchers using TRAPPIST.
Spitzer, together with many ground-based telescopes, including the European Southern Observatory's Very Large Telescope, confirmed the existence of two of these planets and further discovered five additional ones, thus increasing the existing number of known planets in the system to seven.
The new results were recently published in the journal Nature, and an announcement of this discovery was made at a news briefing at NASA Headquarters in Washington. The team used Spitzer data to accurately measure the sizes of the seven planets. This was followed by developing first estimates of the masses of six of the planets, allowing an estimation of their destiny.
All of the TRAPPIST-1 planets are expected to be rocky based on their densities. Additional observations will help to determine whether these planets are rich in water, and will probably reveal whether any of these planets could have liquid water present on their surfaces. The mass of the farthest and seventh exoplanet is yet to be estimated, and scientists assume that it could be an icy, "snowball-like" world, however further observations are required.
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.
Michael Gillon, Principal Investigator of the TRAPPIST exoplanet survey at the University of Liege, Belgium
When compared to the sun, the TRAPPIST-1 star, classified as an ultra-cool dwarf, is extremely cool such that liquid water could survive on planets orbiting very near to it, which indeed is closer than is possible on planets existing in the solar system. It has been observed that all seven of the TRAPPIST-1 planetary orbits are located closer to their host star than Mercury is to the sun.
Even the planets are extremely close to each other. A person standing on the surface of one of the planets will be able to gaze up and potentially view geological features or clouds of neighboring worlds, which could at times appear to be larger than the moon in Earth's sky.
It is possible that the planets could also be tidally locked to their star, which explains the fact that the same side of the planet always faces the star, so each side is either perpetual day or night. This means that the planets could have weather patterns totally different from those on Earth, such as strong winds that blow from the day side to the night side, and also intense temperature changes.
Spitzer is an infrared telescope that traces Earth as it orbits the sun. This telescope was considered ideal for analyzing TRAPPIST-1 because the star is observed to glow brightest in infrared light, whose wavelengths are longer than what can be seen by the eye.
TRAPPIST-1 was observed almost constantly for 500 hours in the fall of 2016. Spitzer has been uniquely positioned in its orbit in order to observe adequate crossing – transits – of the planets in front of the host star to disclose the system’s complex architecture. Spitzer’s ability was optimized by engineers to observe transiting planets during Spitzer’s “warm mission,” which started after the coolant of the spacecraft ran out as planned after the first five years of operations.
This is the most exciting result I have seen in the 14 years of Spitzer operations. 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.
Sean Carey, Manager of NASA's Spitzer Science Center at Caltech/IPAC in Pasadena, California
The screening of four of the planets, including the three present inside the habitable zone, was initiated by NASA's Hubble Space Telescope after Spitzer’s discovery. These observations focus on analyzing the presence of puffy, hydrogen-dominated atmospheres, ideal for gaseous worlds like Neptune, around these planets.
The two innermost planets were observed by the Hubble team in May 2016, and evidence for such puffy atmospheres was not discovered by the team. This resulted in strengthening the case that the planets very close to the star are rocky in nature.
"The TRAPPIST-1 system provides one of the best opportunities in the next decade to study the atmospheres around Earth-size planets," said Nikole Lewis, co-leader of the Hubble study and astronomer at the Space Telescope Science Institute in Baltimore, Maryland.
The planet-hunting Kepler space telescope from NASA is also analyzing the TRAPPIST-1 system, by carrying out measurements of the star's minute changes in brightness due to transiting planets.
Operating as the K2 mission, the observations made by the spacecraft will permit astronomers to improve the properties of the known planets, and also to search for extra planets in the system. The K2 observations will conclude in early March and will also be made available on the public archive.
Kepler, Hubble, and Spitzer will help astronomers plan for follow-up studies by using NASA's upcoming James Webb Space Telescope, which will be launched in 2018. With increased sensitivity, Webb will be able to identify the chemical fingerprints of ozone, oxygen, methane, water, and various other components of a planet's atmosphere. The surface pressures and temperatures of the planets, key factors in studying their habitability, will also be analyzed by Webb.
NASA’s Jet Propulsion Laboratory (JPL) in Pasadena, California, manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate. Science operations are performed at the Spitzer Science Center, at Caltech, in Pasadena, California. 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.
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