First Earth-size planet in a ‘habitable zone’ found by NASA’s TESS

Space Science
TOI 700 d planet

NASA’s Goddard Space Flight Center/Chris Smith

MYSTERY WIRE — In NASA’s hunt for planets, there’s a high interest in planets like Earth. Scientists have had their eye on TOI 700 d for awhile, using TESS — which stands for Transiting Exoplanet Survey Satellite — and also the Spitzer space telescope.

This week, they announced that TOI 700 d is TESS’s first discovery of an Earth-size planet in its star’s “habitable zone.” Scientists called it a landmark discovery.

The planet, which is 100 light years away, has the potential for liquid water on its surface. It orbits TOI 700, a red dwarf star.

A statement from NASA’s Goddard Space Flight Center reports:

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.

See more information about TESS and this week’s discovery on

habitable zone
An illustration of the habitable zone around TOI 700, a red dwarf star 100 light years away. (NASA’s Goddard Space Flight Center)

Two more announcements made Monday on TESS discoveries:

‘Old’ North Star part of mutual eclipses

Polaris is the North Star we know today. But in ancient history, when Egyptians were building the earliest pyramids, another star was known as the North Star: Alpha Draconis, also known as Thuban. Astronomers using data from TESS have shown that Alpha Draconis and its fainter companion star regularly eclipse each other. While astronomers previously knew this was a binary system, the mutual eclipses came as a complete surprise.

World orbiting two stars

TESS has discovered a world orbiting two stars. TOI 1338 b is TESS’s first “circumbinary planet.” The discovery was featured in a panel discussion on Monday, Jan. 6, at the 235th American Astronomical Society meeting in Honolulu. It lies 1,300 light-years away in the constellation Pictor. The two stars orbit each other every 15 days. One is about 10% more massive than our Sun, while the other is cooler, dimmer and only one-third the Sun’s mass. It is the only known planet in the system. It’s around 6.9 times larger than Earth, or between the sizes of Neptune and Saturn. The planet orbits in almost exactly the same plane as the stars, so it experiences regular stellar eclipses

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