



In the introduction from the site NASA





NASA’s Transiting Exoplanet Survey Satellite (TESS) has discovered its first Earth-size planet in its star’s habitable zone, the range of distances where conditions may be just right to allow the presence of liquid water on the surface. Scientists confirmed the find, called TOI 700 d, using NASA’s Spitzer Space Telescope and have modeled the planet’s potential environments to help inform future observations.





TOI 700 d is one of only a few Earth-size planets discovered in a star's habitable zone so far. Others include several planets in the TRAPPIST-1 system and other worlds discovered by NASA’s Kepler Space Telescope.





“TESS was designed and launched specifically to find Earth-sized planets orbiting nearby stars,” said Paul Hertz, astrophysics division director at NASA Headquarters in Washington. “Planets around nearby stars are easiest to follow-up with larger telescopes in space and on Earth. Discovering TOI 700 d is a key science finding for TESS. Confirming the planet’s size and habitable zone status with Spitzer is another win for Spitzer as it approaches the end of science operations this January."





In other Article from SPACE





TESS found three different planets circling the star TOI 700 (TOI is short for "Tess Object of Interest"). One of the other planets is a red dwarf about 40% as massive, 40% as wide and 50% as hot as Earth's sun. The innermost world, TOI 700 b, is roughly Earth-sized and completes one orbit every 10 Earth days. The center planet, TOI 700 c, is 2.6 times bigger than our planet, meaning it's likely a gassy "mini-Neptune," and zips around TOI 700 every 16 days.





TOI 700 d, the outermost known planet in the system, is the really intriguing one. It's just 20% larger than Earth and completes one orbit every 37 days. The alien world receives 86% of the stellar energy that Earth gets from the sun, putting TOI 700 d in the habitable zone (at least as it's traditionally defined), discovery team members said.





All three planets may be tidally locked to TOI 700, always showing it the same face just as Earth's moon only ever shows us its near side. But tidal locking doesn't necessarily preclude the possibility of life on an alien world, astronomers say. And there's more good news along these lines regarding TOI 700.









...Because TOI 700 is bright, nearby, and shows no sign of stellar flares, the system is a prime candidate for precise mass measurements by current ground-based observatories. These measurements could confirm scientists’ estimates that the inner and outer planets are rocky and the middle planet is made of gas.





Future missions may be able to identify whether the planets have atmospheres and, if so, even determine their compositions.





While the exact conditions on TOI 700 d are unknown, scientists can use current information, like the planet’s size and the type of star it orbits, to generate computer models and make predictions. Researchers at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, modeled 20 potential environments of TOI 700 d to gauge if any version would result in surface temperatures and pressures suitable for habitability.





Their 3D climate models examined a variety of surface types and atmospheric compositions typically associated with what scientists regard to be potentially habitable worlds. Because TOI 700 d is tidally locked to its star, the planet’s cloud formations and wind patterns may be strikingly different from Earth’s.





One simulation included an ocean-covered TOI 700 d with a dense, carbon-dioxide-dominated atmosphere similar to what scientists suspect surrounded Mars when it was young. The model atmosphere contains a deep layer of clouds on the star-facing side. Another model depicts TOI 700 d as a cloudless, all-land version of modern Earth, where winds flow away from the night side of the planet and converge on the point directly facing the star.





When starlight passes through a planet’s atmosphere, it interacts with molecules like carbon dioxide and nitrogen to produce distinct signals, called spectral lines. The modeling team, led by Gabrielle Engelmann-Suissa, a Universities Space Research Association visiting research assistant at Goddard, produced simulated spectra for the 20 modeled versions of TOI 700 d.





“Someday, when we have real spectra from TOI 700 d, we can backtrack, match them to the closest simulated spectrum, and then match that to a model,” Engelmann-Suissa said. “It’s exciting because no matter what we find out about the planet, it’s going to look completely different from what we have here on Earth.”





TESS is a NASA Astrophysics Explorer mission led and operated by MIT in Cambridge, Massachusetts, and managed by NASA's Goddard Space Flight Center. Additional partners include Northrop Grumman, based in Falls Church, Virginia; NASA’s Ames Research Center in California’s Silicon Valley; the Harvard-Smithsonian Center for Astrophysics in Cambridge, Massachusetts; MIT’s Lincoln Laboratory; and the Space Telescope Science Institute in Baltimore. More than a dozen universities, research institutes and observatories worldwide are participants in the mission.





The Jet Propulsion Laboratory in Pasadena, California, manages the Spitzer Space Telescope mission for NASA's Science Mission Directorate in Washington. Science operations are conducted at the Spitzer Science Center at Caltech in Pasadena. Space operations are based at Lockheed Martin Space in Littleton, Colorado. Data are archived at the Infrared Science Archive housed at IPAC at Caltech. Caltech manages JPL for NASA.





The modeling work was funded through the Sellers Exoplanet Environments Collaboration at Goddard, a multidisciplinary collaboration that brings together experts to build comprehensive and sophisticated computer models to better analyze current and future exoplanet observations.









... TRAPPIST-1 is a dwarf star that lies just 40 light-years away from us and hosts seven Earth-size planets, three of which appear to be in the habitable zone. The system is a prime candidate for observation by NASA's James Webb Space Telescope, which is scheduled to launch in 2021. James Webb should be able to probe the TRAPPIST-1 worlds' atmospheres for potential biosignature gases, such as methane and oxygen, scientists have said.





TOI 700 is a bit farther away, but it's still close enough to be scrutinized in more detail in the future. And scientists do hope to learn more about it via observations by other instruments. For example, they want to pin down TOI 700 d's mass by measuring how much its gravity tugs the host star this way and that. Without knowing the mass, it's unclear how dense TOI 700 d is — and thus if it's a rocky world like Earth.





And in-depth observations of light that has streamed through TOI 700 d's atmosphere on its way to Earth could tell us a great deal about conditions on the alien world's surface, which remain a total mystery at the moment.





A third team of researchers, led by Gabrielle Engelmann-Suissa, a Universities Space Research Association visiting research assistant at NASA's Goddard Space Flight Center in Greenbelt, Maryland, did some modeling work to get at the various possibilities. And those possibilities are vast. For example, one of their simulations depicted TOI 700 d as an ocean-covered world with a carbon-dioxide-dominated atmosphere, whereas another one pictured the planet as a dry, cloudless world.





"Someday, when we have real spectra from TOI 700 d, we can backtrack, match them to the closest simulated spectrum and then match that to a model," Engelmann-Suissa said in the same statement. "It's exciting because no matter what we find out about the planet, it’s going to look completely different from what we have here on Earth."





Gilbert, Rodriguez and Engelmann-Suissa presented their results today in Honolulu at the 235th meeting of the American Astronomical Society (AAS). Their papers have also been submitted to scientific journals.





Other exciting TESS news came out at AAS today as well. For example, mission team members also announced TESS' first circumbinary planet — a world with two suns in its sky — and revealed that the bright star Alpha Draconis and its dimmer companion mutually eclipse each other.



