Neptune-size exoplanet found zooming around nearby young star

A planet about the size of Neptune has been found zipping around a young star about 32 light years away from Earth, according to a new study. This young system, named AU Microscopii, will allow scientists to study planet formation and evolution and learn more about how planets interact with their stars. The planet, named AU Mic b, completes an orbit around the AU Microscopii star every 8.5 Earth days. The star, also called AU Mic, has long intrigued astronomers. It’s located in the Microscopium constellation and part of the Beta Pictoris moving group, a collection of stars. The star named Beta Pictoris has two known exoplanets in orbit around it.

Astronomers have been searching around AU Mic for evidence of an exoplanet, or planet orbiting a star outside of our solar system, for more than a decade. The cool red dwarf star is only around 20 million to 30 million years old, which is very young compared to our sun, which is 150 times older. The star is surrounded by a disk of gas and dust debris, the leftover remnants of when the star formed. Thanks to data from NASA’s retired Spitzer Space Telescope and its current planet-hunting Transiting Exoplanet Survey Satellite, or TESS, astronomers have finally struck gold. They’ve now spotted an exoplanet about 8% larger than the size of Neptune in a quick orbit around AU Mic.

The AU Mic system is fascinating when compared to the Beta Pictoris system. Both are the same age and have debris disks around them. However, the Beta Pictoris star is a bigger and hotter A-type star and its two exoplanets are at least 50 times more massive, with Beta Pictoris b and c taking 21 and 3.3 Earth years to complete orbits of the star, respectively. “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 Thomas Barclay, study coauthor and associate project scientist for TESS at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, in a statement. “By contrast, Beta Pictoris b’s orbit doesn’t appear to have migrated much at all. The differences between these similarly aged systems can tell us a lot about how planets form and migrate.”