Prelims level : Science and Technology Mains level : GS-III Technology, Economic Development, Bio diversity, Environment, Security and Disaster Management
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Why in News?

  • One year after its launch, NASA’s TESS (Transiting Exoplanet Survey Satellite) discovered its first Earth-sized exoplanet.


  • Named HD21749c, the planet orbits a star just 53 light-years from Earth and is likely rocky but uninhabitable.
  • The findings — published in Astrophysical Journal Letters– suggest TESS is capable of fulfilling its mission to catalog thousands of planet candidates, including more than 300 that are expected to be Earth-sized and super-Earth-sized exoplanets.
  • This newly identified planet is the smallest world outside our solar system that TESS has spotted.
  • And the spacecraft’s data shows HD21749c circles its star every 7.8 days, meaning it has a tight orbit that would lead to surface temperatures of up to 800 degrees Fahrenheit.
  • TESS has now found 10 planets smaller than Neptune, and its ability to locate this one is a good indicator that it’s capable of finding other small planets — perhaps even some in the “Goldilocks” zone, close enough to their star to have liquid water but far enough to avoid being roasted.
  • TESS, is eyeing planets much closer to us, so scientists can attempt, for instance, to determine their mass. Next, the team of astronomers behind this discovery, will try to do just that. If they’re successful, we could have the first mass measurement of an Earth-sized planet.


  • Planets that orbit around other stars are called exoplanets.
  • Exoplanets are very hard to see directly with telescopes. They are hidden by the bright glare of the stars they orbit. So, astronomers use other ways to detect and study these distant planets.

Light year

  • A light-year is a unit of distance. It is the distance that light can travel in one year. Light moves at a velocity of about 300,000 kilometers (km) each second. So, in one year, it can travel about 10 trillion km. More precisely, one light-year is equal to 9,500,000,000,000 kilometers.
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