NASA's TESS telescope spots first Earth-sized planet in habitable zone

NASA's TESS telescope spots fi...
Render of TESS observing an M dwarf system
Render of TESS observing an M dwarf system
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Illustration depicting the TOI 700 system
Illustration depicting the TOI 700 system
Render of TESS observing an M dwarf system
Render of TESS observing an M dwarf system

Since being launched into space in April of 2018, NASA's TESS (Transiting Exoplanet Survey Satellite) telescope has notched up a few noteworthy achievements. These include its first detection of an Earth-sized exoplanet, a complete survey of the southern sky and an observation of a comet outburst in our own solar system. Its latest feat, however, is also its most significant, with NASA confirming the space telescope has now identified its first Earth-sized exoplanet that lies in a habitable zone, where conditions could allow for liquid water at the surface.

NASA's trusty Kepler space telescope identified thousands of planets beyond our own solar system, but the agency has especially high hopes for TESS, its successor. The new telescope has the capacity to study stars 30 to 100 times brighter than Kepler, and will observe an area of the sky around 400 times larger.

So the newly discovered exoplanet may be the first of many identified by the orbiting instrument, which circles the Earth every 13.7 days. Called TOI 700 d, the exoplanet joins just a handful that we know to be positioned in their star's habitable zone, including those in the TRAPPIST-1 system that was discovered in 2017.

The exoplanet orbits a cool M dwarf star around 100 light years way called TOI 700. The system features two other exoplanets, one thought to be Earth-sized and rocky and another 2.6 times larger than Earth and probably made of gas. These were discovered by TESS, with NASA confirming the findings with its Spitzer space telescope.

Illustration depicting the TOI 700 system
Illustration depicting the TOI 700 system

TOI 700 d is the outermost of the bunch and the only one in the habitable zone. Scientists believe it to be 20 percent larger than Earth and orbit its star every 37 days. All planets in the TOI 700 system are believed to be tidally locked, meaning one side constantly faces the star and is in continuous daylight. The bright and nearby star has also shown no sign of flaring, which bodes well for follow-up observations of the system using ground-based instruments.

There is no way for scientists to understand exactly what the conditions could be like on TOI 700 d, but they can make some educated guesses. Using the planet's size and characteristics of its parent star as a guide, the researchers generated computer models of 20 potential environments, with one simulation portraying an atmosphere rich in carbon dioxide much like that believed to have blanketed Mars in its early days.

One of the ways scientists will be able to gain a clearer picture of TOI 700 d is through a technique called transit spectroscopy. As the planet passes in front of its star, the starlight collides with the different molecules in its atmosphere, such as carbon dioxide or nitrogen, to create distinctive spectral lines. Studying these signals can therefore shed light on what the conditions on TOI 700 d could be like.

"Someday, when we have real spectra from TOI 700 d, we can backtrack, match them to the closest simulated spectrum, and then match that to a model," says Engelmann-Suissa, who led the modeling team. "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."

The video below provides an overview of the discovery.

TESS Mission's First Earth-size World in Star's Habitable-zone

Source: NASA

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