NASA Spots Exoplanet Sized Right Between Earth and Mars

A NASA illustration compares the newly-discovered planet to Earth and Mars. (Image credit: NASA)

NASA's new exoplanet-hunting telescope has discovered its smallest planet yet: a world somewhere between the sizes of Earth and its smaller sister Mars.

The planet is called L 98-59b because it sits in a nearby star system called L 98-59 that's 35 light-years from our solar system in the southern constellation Volans. L 98-59b is not the smallest exoplanet ever discovered — that record belongs to a tiny rock called Kepler-37b, which is just one-fifth larger than Earth's moon. But ever since NASA's more advanced Transiting Exoplanet Survey Satellite (TESS) space telescope came online, replacing the old Kepler telescope, this is the smallest planet NASA has managed to see.

These planets add to humanity's still-small catalog of exoplanets similar in size to Earth. Most exoplanets that astronomers can detect are much larger than our planet.

To make these detections, TESS didn't observe the planets directly; they're much too small and dim for that, especially sitting next to their bright star. Instead, the telescope spotted their shadows as the orbs passed between their star and the telescope.

The planets orbit a star much smaller than our sun, but they're much closer to it. L 98-59b has the smallest orbit, completing a full circuit of its star every two days and 6 hours, and receiving 22 times the energy Earth absorbs from the sun. That almost certainly renders it uninhabitable (i.e. too hot), just like its detected sister worlds.

However, the researchers wrote that this system is especially interesting because the planets are orbiting such a bright star that it will allow TESS to gather an unusual amount of data from them. Close measurements of their orbits might enable scientists to figure out whether there are other planets in the system tugging on them with gravity — perhaps even planets in that star's habitable zone. That could offer valuable data about how small, rocky planets like ours form. Researchers also hope to learn whether the planets have atmospheres, based on how they add color to the light coming from the star as they pass in front of it.

Originally published on Live Science.

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Rafi joined Live Science in 2017. He has a bachelor's degree in journalism from Northwestern University’s Medill School of journalism. You can find his past science reporting at Inverse, Business Insider and Popular Science, and his past photojournalism on the Flash90 wire service and in the pages of The Courier Post of southern New Jersey.