Nasa probe spots first Earth-sized planet

Artist's conception of HD 21749c the first Earth-sized planet found by NASA's Transiting Exoplanets Survey Satellite, as well as its sibling HD 21749b a warm sub Neptune-sized world. (Credit Robin Dienel courtesy of the Carnegie Institution

Artist's conception of HD 21749c the first Earth-sized planet found by NASA's Transiting Exoplanets Survey Satellite, as well as its sibling HD 21749b a warm sub Neptune-sized world. (Credit Robin Dienel courtesy of the Carnegie Institution

NASA's latest planet-hunting probe has discovered its first Earth-sized exoplanet orbiting a star 53 light-years away. The planet orbits star HD 21749, a respectably short 52 light-years from Earth considering the vastness of the universe.

Compared to the other two sightings-Pi Mensae b, a "super-Earth" with a 6.3-day orbit, and LHS 3844b, a rocky world that speeds around its star in 11 hours-HD 21749b is downright lazy, taking 36 days to complete one rotation.

Artist illustration of HD 21749c, the first Earth-size planet found by the TESS Mission as well as its sibling, HD 21749b, a sub-Neptune-sized world.

Both worlds are detailed in a new paper published by The Astrophysical Journal Letters. Unfortunately, it is unlikely the gaseous planet is habitable. TESS - which stands for Transiting Exoplanet Survey Satellite - is created to detect the telltale signs of exoplanets orbiting the stars it observes by spotting the tiny changes in brightness associated with a planet passing in front of them.

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While this is the second planet discovered in this particular star system, the discovery is TESS' tenth planetary find overall. HD 21749c isn't the kind of place where we'd ever expect to find life as we know it, so alien hunters will need to look elsewhere, but the discovery of any planet outside of our solar system is still undeniably interesting.

The discovery of this Earth-sized world is nevertheless exciting, as it demonstrates TESS' ability to pick out small planets around nearby stars.

In April 2018, NASA's planet-hunting spacecraft was launched into orbit by the SpaceX Falcon 9 rocket. As it circles our own planet, TESS focuses its four cameras outward to monitor the nearest, brightest stars in the sky, looking for any periodic dips in starlight that could indicate the presence of an exoplanet as it passes in front of its host star. This "transit method" was also utilized by its predecessor, the now-deceased Kepler space telescope, which discovered 70 percent of the 4,000 known exoplanets. But, it's still a great discovery for TESS, which has only been in the business for a year. HD 21749b has about 23 times Earth's mass and a radius of about 2.7 times Earth's. The code first identified a possible transit that the team later confirmed as the warm sub-Neptune they announced earlier this year. And we're excited about what that mass could be.

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