NASA TESS Discovers Earth Sized Exoplanet

NASA’s Transiting Exoplanet Survey Satellite (TESS) has discovered its first Earth-size exoplanet. The exoplanet, HD 21749c, is about 89% Earth’s diameter. It orbits HD 21749, a K-type star with about 70% of the Sun’s mass located 53 light-years away in the southern constellation Reticulum, and is the second planet TESS has identified in the system. The new world is likely rocky and circles very close to its star, completing one orbit in just under eight days. The planet is likely very hot, with surface temperatures perhaps as high as 800 degrees F (427 degrees C).

Above – This is an artist’s conception of HD 21749c, the first Earth-sized planet found by NASA’s Transiting Exoplanets Survey Satellite (TESS), as well as its sibling, HD 21749b, a warm sub-Neptune-sized world. Credits: Illustration by Robin Dienel, courtesy of the Carnegie Institution for Science

Astrophysical Journal Letters – TESS Delivers Its First Earth-sized Planet and a Warm Sub-Neptune


The future of exoplanet science is bright, as Transiting Exoplanet Survey Satellite (TESS) once again demonstrates with the discovery of its longest-period confirmed planet to date. We hereby present HD 21749b (TOI 186.01), a sub-Neptune in a 36 day orbit around a bright (V = 8.1) nearby (16 pc) K4.5 dwarf. TESS measures HD 21749b to be ${2.61}_{-0.16}^{+0.17}$ R ⊕, and combined archival and follow-up precision radial velocity data put the mass of the planet at ${22.7}_{-1.9}^{+2.2}$ M ⊕. HD 21749b contributes to the TESS Level 1 Science Requirement of providing 50 transiting planets smaller than 4 R ⊕ with measured masses. Furthermore, we report the discovery of HD 21749c (TOI 186.02), the first Earth-sized (${R}_{p}={0.892}_{-0.058}^{+0.064}{R}_{\oplus }$) planet from TESS. The HD 21749 system is a prime target for comparative studies of planetary composition and architecture in multi-planet systems.

SOURCES- NASA, Astrophysical Journal Letters

1 thought on “NASA TESS Discovers Earth Sized Exoplanet”

  1. We’ve seen this headline several times before.
    Each time the planet is a bit closer the size of the Earth, and so each time “Earth sized” gets redefined.

    I expect we’ll see it several times in the future too as we get something 92% of Earth, 103% of Earth, 98% of Earth etc. etc.

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