NASA's specialised planet-hunting spacecraft searching for signs of alien life has spotted an Earth-sized world within its star's habitable zone

NASA's alien-hunting telescope discovers an Earth-size planet orbiting within a star's 'habitable zone' just 100 light years away

TOI 700 d may be a the earth 100 light years away and is 20 per cent larger than Earth

It is one among three planets orbiting a star and therefore the just one within the habitable zone

It is possible the planet has liquid water on its surface but this has not been confirmed yet

NASA's specialised planet-hunting spacecraft checking out signs of alien life has spotted an Earth-sized world within its star's habitable zone.

Dubbed TOI 700 d, the earth is simply 100 light years away and is slightly larger than Earth.

It has a way swifter orbit than Earth, taking just 37 days to finish a visit around its star.

TOI 700 d also receives just 86 per cent of the energy Earth does, thanks to its star being around 40 per cent the mass of our Sun and only half as hot.

Its presence within the habitable zone and its size offers hope that it's going to host liquid water, but this has not yet been confirmed.

The breakthrough from the TESS spacecraft was announced during the annual American Astronomical Society meeting in Honolulu, Hawaii.

Dubbed TOI 700 d, the earth is simply 100 light years away, exceptionally close on the size of space. it's slightly larger than Earth and features a much swifter orbit time of just 37 days

TESS found three planets round the star, with just one inside the habitable zone, where the temperature would leave liquid water to exist on its surface.

'TESS was designed and launched specifically to seek out Earth-sized planets orbiting nearby stars,' said Paul Hertz, NASA astrophysics division director.

The exoplanet - a world orbiting a star that's now our Sun - was almost missed by astronomers after an initial error wrongly categorised the star and its planets.

Scientists wrote the planets off as non-viable for extraterrestrial life as they were thought to be too big and too hot.

But a team of amateur astronomers, including a highschool student, identified the error and corrected it.

'When we corrected the star's parameters, the sizes of its planets dropped, and that we realised the outermost one was about the dimensions of Earth and within the habitable zone,' said Emily Gilbert, a grad student at the University of Chicago.

The discovery was later confirmed by the Spitzer Space Telescope.

Similar planets are identified before, including some spotted by the now defunct Kepler Space Telescope.

But this marks the primary such world spotted by TESS after its 2018 launch.

TESS spots distant planets with a patient approach, it studies the image of stars during a specific region of the night sky and waits for objects to pass ahead of it.

These transits often indicate the presence of an orbiting planet making its way round the star and therefore the drop by the star's luminosity is analysed to supply clues to the world's size, speed and chemical composition of its atmosphere.