NASA's new planet-hunter TESS finds its first Earth-sized world

NASA's new planet-hunter — the Transiting Exoplanet Survey Satellite (TESS) — has found its first confirmed Earth-sized world after launching to space in April 2018.

Background: TESS is designed to detect the small dips in a star's light created when a planet passes in front of its sun. The telescope uses that "transit" to piece together how large (or small) the planet might be.

The big picture: TESS is currently on a two-year mission to hunt for Earth-sized worlds orbiting small, relatively dim stars not far from our planet, furthering the quest to find habitable worlds with possible life out there in the universe.

Details: The planet, named HD 21749c, takes about 8 Earth days to orbit its star, is around the size of our planet and is located about 53 light-years from Earth, researchers report in the journal The Astrophysical Journal Letters.

• However, learning more about the world isn't easy because it's so small by cosmic standards.
• “Measuring the exact mass and composition of such a small planet will be challenging, but important for comparing HD 21749c to Earth,” Sharon Wang, one of the authors of the new study, said in a statement.

The planet has company when orbiting its star. TESS also found a world, named HD 21749b, that's about 23 times Earth's mass orbiting the star every 36 days.

• Both were confirmed as true signals by the Planet Finder Spectrograph in Chile, which detects slight wobbles in the star as its planets orbit, allowing scientists to measure a planet's mass.

What to watch: This discovery is likely to be followed up by many others as scientists believe that almost every star has at least one planet in its orbit.