exoplanet
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Exoplanet the size of Earth discovered in its star’s habital zone

While discovering a new exoplanet will always be an exciting achievement, few raise quite as much interest as TOI-700 d, which was discovered recently by a team led by Emily Gilbert from the University of Chicago. The discovery was made using NASA’s Transiting Exoplanet Survey Satellite (TESS) which is part of an ongoing mission to scan 200,000 of the brightest stars close to Earth for periodic dimming in their brightness, an indicator of the presence of an exoplanet.

But what makes this particular exoplanet so special?

The discovery was made using NASA’s Transiting Exoplanet Survey Satellite (TESS)

Not only does TOI-700 d sit within its star’s habitable zone (determined by the region around the star where conditions allow for liquid water to exist), it is also near Earth-sized, at about 1.2 times the size of our planet, and is in orbit around a bright star only 31 parsecs from Earth. All of these features led astronomers to be very interested in the object, as it is far more Earth-like than most other exoplanets we know of.

Since their first discovery in 1992, additional research and missions looking for exoplanets have led to the discovery of thousands in the universe, putting to rest the idea that the Solar System is a unique formation. However, with current methods of detection, most of the planets we know of are classed as ‘hot Jupiters’ as they are of a similar size to Jupiter but orbit much closer to their host stars than Jupiter does to the Sun. It is much easier to detect such objects as they pass in front of their star frequently thanks to their small orbits and cause a more significant dimming of the light reaching Earth as they have a large size with which to cast a shadow.

Most of the planets we know of are classed as ‘hot Jupiters’ as they are of a similar size to Jupiter but orbit much closer to their host stars

Hot Jupiters can tell us a lot about the universe and astronomers are grateful for every new discovery but TOI-700 d could offer us much more.

As it orbits a star which is relatively close (from an astronomical perspective) and which is also bright, this new exoplanet is much easier for researchers to study than those around more distant or dimmer stars. It is not the only planet which TESS has discovered around this star either. Two others have been reported but their orbits are much closer to the star, meaning they lie too close and at too high a temperature for liquid water to exist. Astronomers are particularly interested in TOI-700 d because it is further out, meaning that liquid water could exist on its surface or in its atmosphere and this is commonly believed to be a prerequisite for any potential extra-terrestrial life.

Astronomers are particularly interested in TOI-700 d because it is further out, meaning that liquid water could exist on its surface or in its atmosphere and this is commonly believed to be a prerequisite for any potential extra-terrestrial life

It also looks to be similar to Earth in many respects which is an exciting prospect for researchers. While its mass is as yet unknown, and it could turn out to be a gas-based planet more similar to Neptune than Earth, TOI-700 d still has the potential to be rocky and Earth-like. However, it won’t be a mirror image of the Earth around a foreign star as it orbits a red dwarf star, unlike our own Sun. The light it receives at its surface is also much more faint than that which we receive on Earth from the Sun. Astronomers are still eagerly anticipating what new discoveries this exoplanet could bring and hope to continue research of the atmosphere of TOI-700 d with the launch of the James Webb Space Telescope, knowing that it will be a challenge but one well worth the effort.

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