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NASA’s TESS detects Earth-sized planet for the first time

Transiting Exoplanet Survey Satellite (TESS), NASA’s space telescope for its Explorer Program has discovered a nearby system which has an Earth-sized planet. Along with it, there is also a warm planet nearly the size of Neptune. The work carried out by a group of astronomers from Carnegie Institution for Science was published in the Astrophysical Journal Letters.

For confirming the planetary nature of the signals from TESS and to calculate the mass of the discovered sub-Neptune planet, the Planet Finder Spectrograph of Magellan II telescope was used which is located at the Las Campanas Observatory, Chile.

The Planet Finder Spectrograph has been built by Shectman and Crane and it functions on the technique known as radial velocity method. Right now, this is the only way of calculating the masses of the planets. Without finding the mass, it is very tough to find out the density of the planet or even the general composition.


This method is advantageous for both influence of gravity of a star orbiting it as well as the planet’s gravity also affects the star in turn. This instrument enables astronomers to find out the tiny wobbles that are reduced because of the planet’s gravity in the star’s orbit.

The newly searched planet, the sub-neptune, HD 21749b, has the orbital period of 36 days to complete an orbit around the sun. It is the longest period among any of the TESS findings. It is predicted that most of the planets which will be discovered by TESS will have an orbital period lesser than 10 days because of the method used.

Its central star has about 80 percent of the mass of the sun and is about 53 light-years away from the earth as per lead author Diana Dragomir of MIT’s Kavli Institute for Astrophysics and Space Research. And the planet has about 23 times mass of Earth as well as its radius is about 2.7 times of earth’s radius. As per its density, one can easily image about its environment to be rocky but there are no such type of things here.

And the long period of the planet is not the only one in this system. The sibling planet, HD 21749c takes almost eight days for completing an orbit around the host star. It is much smaller in size, quite comparable to Earth, hence finding the exact mass and composition is quite a challenge but it is important for comparison to Earth.

Because of TESS, astronomers will be able to calculate the masses, measure atmospheric conditions of many exoplanets and scientists hope this will eventually set the path for finding planets which are potentially habitable.


About the author: Kalpit Veerwal
Kalpit Veerwal is a second year Computer Science undergraduate at IIT Bombay. He is well known for being the only person to score 360/360 in JEE (Main). He is registered in the Limca Book of Records for the same. A blogger in his free time, he has also secured top ranks in various exams held in India and the world.

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