Neptune-sized Planet Found Around a Baby Star 32 Light-years Away

AU Mic b
Illustration of AU Mic b (Credit: NASA/Goddard Space Flight Center)

Astronomers using NASA’s Transiting Exoplanet Survey Satellite (TESS) and data from the now-retired Spitzer Space Telescope  have announced the discovery of a Neptune-sized exoplanet orbiting AU Microscopii (AU Mic for short), a red M-dwarf star 31.93 light-years away and only about 20 to 30 million years old. The star is so young that it’s still surrounded by the protoplanetary disk of material within which planets form, and the planet, named AU Mic b, orbits so closely to the star that it completes an orbit every 8.46 Earth days (that’s a 203-hour-long year!)

From a press release from NASA/JPL on June 24, 2020:

“AU Mic is a young, nearby M dwarf star. It’s surrounded by a vast debris disk in which moving clumps of dust have been tracked, and now, thanks to TESS and Spitzer, it has a planet with a direct size measurement,” said Bryson Cale, a doctoral student at George Mason University in Fairfax, Virginia and coauthor of the paper describing the research. “There is no other known system that checks all of these important boxes.”

The planet AU Mic b almost hugs its star, completing an orbit every 8.5 days. It weighs less than 58 times Earth’s mass, placing it in the category of Neptune-like worlds.

The system provides a one-of-kind laboratory for studying how planets and their atmospheres form, evolve and interact with their stars.

“We think AU Mic b formed far from the star and migrated inward to its current orbit, something that can happen as planets interact gravitationally with a gas disk or with other planets,” said coauthor Thomas Barclay, an associate research scientist at the University of Maryland, Baltimore County and an associate project scientist for TESS at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.

The new planet is described in the research team’s paper led by Peter Plavchan, assistant professor of physics and astronomy at George Mason University. The report was published on Wednesday, June 24, in the journal Nature.

Read the full release here.