TESS Discovers Its First Earth-Sized Planet

Iwastheone shares a report from MIT News: NASA's Transiting Exoplanet Survey Satellite, TESS, has discovered its first Earth-sized exoplanet. The planet, named HD 21749c, is the smallest world outside our solar system that TESS has identified yet. In a paper published today in the journal Astrophysical Journal Letters, an MIT-led team of astronomers reports that the new planet orbits the star HD 21749 -- a very nearby star, just 52 light years from Earth. The star also hosts a second planet -- HD 21749b -- a warm 'sub-Neptune' with a longer, 36-day orbit, which the team reported previously and now details further in the current paper.

The new Earth-sized planet is likely a rocky though uninhabitable world, as it circles its star in just 7.8 days -- a relatively tight orbit that would generate surface temperatures on the planet of up to 800 degrees Fahrenheit. The discovery of this Earth-sized world is nevertheless exciting, as it demonstrates TESS' ability to pick out small planets around nearby stars. In the near future, the TESS team expects the probe should reveal even colder planets, with conditions more suitable for hosting life. Slashdot reader RockDoctor shares a link to the paper at Arxiv, adding:

The 'b' object in the system (the largest perturbation on the star's light) is estimated at 2.61*Radius_earth, and 22.7*Mass_earth for a surface gravity of 3.332*littleG_Earth. If it has a 'surface' in any recognizable sense rather than gradual transitions between gas mixtures, liquid mixtures, and the digested remains of any 'metals' (lithium or higher, as the astronomers say).

The 'c' object is more poorly constrained. The authors give a radius (0.892*Radius_earth, derived from the depth of the eclipses), but only put an upper limit on the mass at
The TESS mission has a Science Requirement 'of providing 50 transiting planets smaller than 4*Radius_earth with measured masses,' and the 'b' planet fits that criterion, but the 'c' planet does not, yet, have a well-enough constrained mass. Keep on catching planets!

Read more of this story at Slashdot.