NASA’s Transiting Exoplanet Survey Satellite (TESS) has discovered its first Earth-size planet in its star’s habitable area, the ‘Goldilocks zone’ where conditions are just right to allow the existence of liquid water and therefore life.


Dubbed TOI 700d, the planet is the latest in a handful of potentially habitable Earth-sized worlds found throughout the galaxy.

It is the outermost planet found in orbit around TOI 700 a small, cool dwarf star located just over 100 light-years away in the southern constellation Dorado that is roughly 40 per cent of the Sun’s mass and size and about half its surface temperature.

It is around 20 per cent bigger than Earth, completes its orbit every 37 days and receives 86 per cent of the energy from its star that the Sun provides to Earth.

“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.

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“Discovering TOI 700 d is a key science finding for TESS. Confirming the planet’s size and habitable zone status with Spitzer [Space Telescope] is another win for Spitzer as it approaches the end of science operations this January.”

TESS monitors large swaths of the sky, called sectors, for 27 days at a time. This long period of observation allows the satellite to monitor changes in a star’s brightness caused by an orbiting planet crossing in front of its star from our perspective, an event called a transit.

While the exact conditions on TOI 700 d are unknown, a team of researchers art NASA’s Goodard Space flight Centre used information that is known, such as the planet’s size and the type of star it orbits, to generate a series of computer models and make predictions.

One simulation revealed an ocean-covered world surrounded by a dense, carbon-dioxide-dominated atmosphere similar to what scientists suspect surrounded Mars when it was young. Another model depicts TOI 700 d as a cloudless, all-land version of modern Earth.


“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,” said Gabrielle Englemann-Suissa, who led the computer modelling team.