NASA has announced that its Transiting Exoplanet Survey Satellite (TESS) has discovered a rocky world that is the size of Earth that is orbiting the so-called “habitable zone” of its home star. The habitable zone is the distance from a star where liquid water might exist. The find was confirmed by NASA’s Spitzer Space Telescope.
The planet was detected orbiting a star 100 light-years from Earth designated TOI 700. TOI 700 is an M class dwarf star that is just 40 percent of the Sun’s mass and size. It has 50 percent of the Sun’s surface temperature. The star has at least three planets orbiting it.
“The innermost planet, called TOI 700 b, is almost exactly Earth-size, is probably rocky and completes an orbit every 10 days. The middle planet, TOI 700 c, is 2.6 times larger than Earth — between the sizes of Earth and Neptune — orbits every 16 days and is likely a gas-dominated world. TOI 700 d, the outermost known planet in the system and the only one in the habitable zone, measures 20% larger than Earth, orbits every 37 days and receives from its star 86% of the energy that the Sun provides to Earth. All of the planets are thought to be tidally locked to their star, which means they rotate once per orbit so that one side is constantly bathed in daylight.”
TESS is a space telescope that was launched onboard a SpaceX Falcon 9 in April 2018. Its mission is to discover exoplanets, worlds orbiting other stars, by using the “transit method.” The transit method notes how a star’s light diminishes and then brightens as a planet transits between it and Earth and then calculates the size and number of planets that star has.
The Kepler Space Telescope used the same method to discover over 2600 exoplanets, including a handful that are Earthlike because of their size and distance from their home star, during the life of its mission that ended in October 2018. NASA hopes to find 20,000 exoplanets with the TESS mission.
TESS is in a high elliptical orbit of Earth, with a distance that ranges between the orbit of the moon and 100,000 kilometers. The satellite uses an array of telescopes that images entire sections of the sky at once, examining several stars at once to detect transitioning exoplanets. While Kepler detected mainly huge gas giants about the size or greater than Jupiter, TESS is specifically designed to go after small, rocky worlds that might be other Earths, with at atmosphere and enough water to hold life. TOI 700 d is the first such world to have been confirmed during TESS’s mission.
As TESS detects exoplanet candidates, they are being confirmed by space telescopes such as the Spitzer as well as several ground-based telescopes. When the James Webb Space Telescope is finally launched and deployed in 2021, one of its tasks will be to further characterize the exoplanets that had been detected by TESS, examining them in the infrared range.
The search for exoplanets, especially Earth-like worlds, is an important goal of astronomical science. The more worlds that have the characteristics of Earth that are discovered, the more likely that life may exist elsewhere in the universe. Needless to say, the close examination of such life will have to wait until human civilization develops something akin to Star Trek’s warp drive. Such technology is theoretically possible, but some centuries likely remain before it can be practically developed.
Meanwhile, TOI 700 d and its sister planets have several interesting characteristics.
“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.”
Future space telescopes may be able to determine what sorts of atmospheres and environments exist on exoplanets such as TOI 700 d.