NASA’s Transiting Exoplanet Survey Satellite (TESS) has been scanning the sky for more than a year, and it’s spotted numerous potential exoplanets. The latest discovery might be the most exciting yet, though. NASA reports that TESS has identified a planet about 100 light-years away that appears to be Earth-sized and in its star’s habitable zone.
The planet in question, TOI 700 d, is one of three that orbit the star TOI 700. This is a red dwarf, the most common type of star in the galaxy. It’s 40 percent smaller than our sun and only half as warm. All three of its planets orbit very close, but TOI 700 d is just barely far enough away to be in the habitable zone. That’s not a judgment of its actual surface conditions — we don’t know that yet. However, it could be capable of supporting liquid water on the surface.
TESS is a followup to the Kepler Space Telescope, using the transit method to scan for possible exoplanets. It observes large patches of the sky for several weeks at a time, recording any momentary dip in luminance that could indicate a planet passed in front of the star. Through repeated observation, scientists can confirm the approximate size and orbit of a planet.
The problem with TIO 700 was that astronomers initially had the star’s parameters wrong. We thought it was more like our sun. However, after correcting that error, the size and temperature of its planets dropped considerably. The TESS team now believes TOI 700 d only 20 larger than Earth. The innermost planet (TOI 700 b) is almost precisely the same size as Earth, but it’s blazing hot. The middle world is a gas giant between Earth and Neptune-size. All three planets are most likely tidally locked to the star, so the same face is always pointing sun-ward.
NASA turned to the Spitzer Space Telescope to confirm the TESS readings on TOI 700 d. The follow-up observations with Spitzer showed the exact transits predicted by TESS, and the team then confirmed again with the ground-based Las Cumbres Observatory network. TOI 700 d completes an orbit of TOI 700 every 37 Earth days, and it gets about 86 percent as much sunlight as Earth because of the dimmer red dwarf.
TOI 700 d is one of precious few Earth-sized exoplanets in habitable zones. Its nearness could make it an excellent target for future studies using ground-based telescopes. The upcoming (but chronically delayed) James Webb Space Telescope could also reveal important new details about this potentially Earth-like exoplanet.
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