NASA Mission Discovers the Smallest Planet Yet

NASA has recently found a new planet with a size that lies between the sizes of Earth and Mars. NASA discovered the new planet using Transiting Exoplanet Survey Satellite (TESS) and called it ‘L 98-59b’.

Tiniest Planet discovered so far by TESS

TESS is an Astrophysics Explorer mission led by NASA. It’s operated by MIT in Cambridge, Massachusetts, and managed by Goddard Space Flight Center of NASA.

The new planet, L 98-59b, discovered by TESS, is orbiting a bright, cool star in the nearby known as M Dwarf. There are two other planets orbiting the same star. The scientists named them as L 98-59c and L 98-59d.

NASA's TESS L98-59 Planet
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Credits: NASA’s Goddard Space Flight Center

The scientists have evaluated the sizes of all the three planets. The size of the tiniest planet, L 98-59b, is about 80% of the Earth’s size. It’s about 10% smaller than the previous record holder planet discovered by TESS.

While the other two planets, L 98-59c and L 98-59d, are about 1.4 and 1.6 times the Earth’s size, respectively.

After the discovery of L 98-59, the no. of small exoplanets has got almost doubled the no. of planets beyond our solar system. The scientists, further, intend to study the atmosphere of the planets and the gases present there using other telescopes.

READ MORE: 10 Most Amazing Galaxies In The Universe

An astrophysicist at Goddard Space Flight Center of NASA in Greenbelt, Veselin Kostov, shared his views about the latest discovery by TESS. According to him, it is a great engineering and scientific accomplishment by NASA.

He further added that it’s difficult to detect such small planets. To study the atmosphere of the small planets, short orbits around the star are needed. However, this discovery will lead to fascinating future studies.

The host star of L 98-59, M dwarf, lies about 35 light-years away in the southern constellation Volans. It is about one-third of the mass of the Sun.

Although L 98-59b became the record holder as the tiniest planet discovered by TESS, there are even smaller planets discovered by Kepler satellite of NASA. One of the smallest planets discovered by Kepler is Kepler-37b, which is only 20% larger than the Moon.

How TESS discovers planets using Transits?

TESS discovered all three planets using transits. Transits are the periodic dips in the brightness of the star, which are caused when each planet passes in front of it.

In this process, TESS monitors a 24×96-degree region of the sky for 27 days at a time. That region is known as a sector. When the satellite will finish its first year of observations in July this year, the L 98-59 system will have appeared in 7 out of 13 sectors that make up the southern sky.

This will allow scientists to refine the knowledge about the three planets and look for additional planets in the universe.

Another astrophysicist from Goddard, Jonathan Brande, stated that if there is more than one planet orbiting in a system, it’s possible that they gravitationally interact with each other.

TESS will observe L 98-59 system in a no. of sectors in order to detect planets with orbits around 100 days. And it’s also possible that we might discover the gravitational effects of undiscovered planets on the ones that we currently know.

The host star M dwarfs account for three-quarters of the stellar population of our Milky Way. But they are no larger than about half of the mass of the Sun. Moreover, they are much cooler than the Sun. Their surface temperature is less than 70% of the temperature of the Sun.

Other examples of small stars include TRAPPIST-1 and Proxima Centauri. The former hosts a system of seven Earth-size planets. While the latter has one confirmed planet. Proxima Centauri is also the nearest stellar neighbor to our planet.

Since such small and cool stars are very common in our universe, scientists want to learn more about the planetary systems that form around them.

The tiniest planet, L 98-59b, orbits the star every 2.25 days. It stays so close to the star that it receives as much as 22 times the amount of energy Earth receives from the Sun.

On the other hand, the middle planet, L 98-59c, orbits the star every 3.7 days. It’s about 11 times as much radiation as Earth. While the farthest planet, L 98-59d, orbits the star every 7.5 days. It experiences about four times the radiations as Earth.

None of the three planets lie within the habitable zone of the star. It is the range of distances from the star to the planets where the liquid water could exist on their surfaces. However, all of them lie in the Venus zone. It’s the range of stellar distances where a planet with Earth-like atmosphere could experience a runaway greenhouse effect and transforms it into a Venus-like atmosphere.

The scientists think that the third planet could have either a Venus-like rocky structure or a small, rocky core like a Neptune cocooned beneath a deep atmosphere.


One of the TESS’s mission is to build a catalog of small, rocky planets on short orbits around very bright, nearby stars. This will help in the atmospheric study by the future James Webb Space Telescope by NASA. For this mission, Four TRAPPIST-1 worlds are already the prime candidates, while the scientists are considering the L 98-59 planets are as well.


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