Jan. 8, 2020 7:25 am EST

NASA's TESS Discovers First Earth-Size Planet In The Habitable Zone

By Shane McGlaun

NASA has used the TESS (Transiting Exoplanet Survey Satellite) to find exoplanets since the mission launched. The goal is to discover exoplanets that might be orbiting stars in their habitable zone to search for habitable worlds and potentially extraterrestrial life. TESS has found its first Earth-sized planet that is in a star's habitable zone.

That puts the planet in a range of distances where conditions may allow the presence of liquid water on its surface. The planet is called TOI 700 d, and it has been confirmed using the Spitzer Space Telescope. Researchers have modeled the planet's potential environments to help future observations.

TOI 700 d is one of only a few Earth-size planets discovered so far. Those systems include TRAPPIST-1 and other worlds that were discovered by the Kepler Space Telescope. The discovery of TOI 700 d is a key science finding for TESS, and being able to confirm the size of the planet and habitable zone status with Spitzer is another win for Spitzer, which is set to end science observations this month.

TOI 700 is a small, cool M dwarf star about 100 light-years away in the constellation Dorado. The star is about 40% of the Sun's mass and size and has about half its surface temperature. TESS observed the star and its planets in 11 of the 13 sections it observed in the first year of the mission. The star was originally misclassified as being larger and more like our Sun.

When the smaller, cooler, and dimmer star calculations were used, the team realized that the outermost planet was about the size of Earth and in the star's habitable zone. The innermost planet is TOI 700 b and is almost exactly Earth-size and is thought to be rocky and completes an orbit every 10 days. TOI 700 c sits in the middle and is 2.6 times larger than Earth and is believed to be a gas dominated world. The outermost planet is TOI 700 d and is the only one in the habitable zone. It's about 20% larger than Earth and orbits ever 37 days. If the planets have atmospheres will be studied in future missions.

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