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Exoplanet with the Size of Neptune Discovered. Photo: CNN
The research, published on June 24, 2020, in the journal Nature, suggests that the young star named AU Microscopii will aid scientists in studying the formation and evolution of planets, as well as understanding the interactions between planets and their stars.
The newly discovered planet is called AU Mic b. It completes an orbit around the star AU Microscopii every 8.5 Earth days. AU Mic has long attracted the attention of astronomers and is part of the constellations Microscopium and Beta Pictoris. Beta Pictoris, in particular, hosts two exoplanets in its orbit.
For over a decade, astronomers have been searching around AU Mic for evidence of an exoplanet or a planet outside our solar system.
This young, red, and cool star is only about 20 to 30 million years old, which is approximately 150 times younger than our Sun. It is surrounded by a disk of gas and debris, remnants of its formation.
Thanks to data from NASA’s Spitzer Space Telescope, the Transiting Exoplanet Survey Satellite (TESS), and other telescopes, astronomers have finally detected a planet with a size larger than Neptune in orbit around AU Mic, approximately 8% larger than Neptune.
AU Mic and Beta Pictoris are around the same age. They both share the characteristic of having debris around them. However, Beta Pictoris is a larger and hotter type-A star, hosting two exoplanets. With a mass at least 50 times larger, Beta Pictoris b and Beta Pictoris c take about 21 and 3.3 Earth years, respectively, to complete their orbits around the star.
“We believe AU Mic b formed far from the star and moved inward to its current orbit. On the other hand, Beta Pictoris b’s orbit appears not to have changed much. The difference between two stars with similar ages can provide us with valuable information about the formation and migration of planets,” said Thomas Barclay, co-author of the study and TESS project scientist at NASA’s Goddard Space Flight Center in Greenbelt, Maryland.
Even though AU Mic is a small star, it is very young and active. In July and August 2018, TESS observed the star and witnessed intense stellar flares. In fact, some of the flares were stronger than the most powerful flares our Sun has emitted.
AU Mic is close enough for astronomers to study easily. It is bright, has a circumstellar disk, and currently has at least one planet with a direct size measurement. Astronomers regard AU Mic as a “nearby laboratory” where they can easily study the formation and development of stars and planets.
Typically, astronomers can only observe planets after they have formed and slowly evolved to determine their positions and orbits around stars. It is believed that planets form from gas and dust in disk-shaped clouds around stars. However, observing AU Mic has shed more light on this process.
“One of the things we want to know is when planets form and how they operate in their early days. By studying this planet, we will gain deeper insights into how the Solar System was formed. This star may not have had time to form small or rocky planets. Nevertheless, it gives us additional insight into what happened before terrestrial planets like Earth and Mars were formed,” said Barclay.
Scientists also want to observe more about the star to learn more about the atmospheres of the planet. After that, they will determine if there might be a second planet around this star.