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NASA’s Transiting Exoplanet Survey Satellite (TESS) has discovered its first Earth-sized exoplanet named HD 21749c. It is the smallest world outside our solar system that has been identified by TESS so far. Moreover, it is the second planet to be identified by TESS after HD 21749b, a warm “sub-Neptune” with 36-day orbit.

HD 21749c

It has about 89% of Earth’s diameter. It orbits HD 21749, a K-type star with about 70% of Sun’s mass. It is located 53 light years away from Earth in southern constellation Reticulum. It does not have good life-hosting potential as it circles its host star very tightly and close to it, completing one orbit every 7.8 Earth days, which probably makes it quite hot.

TESS which was launched just about a year ago is already a game-changer in the planet-hunting business. TESS total tally is likely to end up topping that of Kepler has found about 70% of the 4,000 exoplanets discovered to date.

Transiting Exoplanet Survey Satellite (TESS)

• It is space telescope launched as part of NASA's Explorers program. It was launched in April 2018 for two-year mission atop Space X’s Falcon 9 rocket.
• It is aimed at searching for exoplanets using transit method in an area 400 times larger than that covered by its predecessor Kepler mission.
• Its primary mission objective is to survey brightest stars near Earth for transiting exoplanets. It uses array of wide-field cameras to perform survey of 85% of the sky.
• It finds large number of small planets around nearest stars in sky as compared to previous sky surveys with ground-based telescopes which have mainly detected giant exoplanets

Significance of TESS

• With TESS, it will be possible to study mass, size, density and orbit of large cohort of small planets, including sample of rocky planets in habitable zones (or Goldilocks zone) of their host stars.
• It also provides prime targets for further characterization by James Webb Space Telescope, as well as to other large ground-based and space-based telescopes of the future.