AU Mic b: the Neptune-sized planet spotted near the Milky Way

Hyperaxion Jun 24, 2020

The recently discovered planet is about 25 million years old. According to astronomers, observing it can help us better understand how the Solar System evolved.

A team of astronomers from different countries published in the journal Nature on Wednesday (24) the discovery of the planet AU Mic b, which is the size of Neptune. The object orbits the AU Microscopii star, 32 light-years from the Milky Way, and is only 20 or 30 million years old – at least 150 times younger than the Sun.

AU Mic b: the Neptune-sized planet spotted near the Milky Way
An artist’s impression of the young exoplanet. (Credit: NASA’s Goddard Space Flight Center / Chris Smith).

According to scientists, the planet has a mass of 58 Earths and completes one orbit around its host star every 8.5 days, which indicates that it is very close to the star. In addition, astronomers believe it is no more than 25 million years old – and, because it is very young, studying it would be a way of understanding how planets evolve. “Studying this planet, and hopefully others like it, can give us insight into how our own solar system formed,” explained Tom Barclay, one of the researchers, in a statement.

When the AU Microscopii star was found in the 2000s, a disc of debris remaining from its formation was also identified. So, since then, astrophysicists have been looking for planets in that region of space, since it is in dusty disks like these (protoplanetary disks) that they form.

“These stars generally have very strong magnetic fields, which make them very active. That explains in part why it took nearly 15 years to detect the exoplanet, called AU Mic b,” said Jonathan Gagné, co-author of the research, in a statement to the press. “The numerous spots and eruptions on the surface of AU Mic hampered its detection, which was already complicated by the presence of the disc.”

It was thanks to NASA’s TESS satellite that astronomers were able to detect a cosmic object that periodically passed in front of AU Mic, blocking a small fraction of its light. Investigating this region more carefully, and with the help of other NASA equipment, scientists became increasingly sure that they had found a new exoplanet.

However, it was only after observations made with the iSHELL instrument, located in Hawaii, that scientists were able to make accurate measurements of the star’s movement. The analysis revealed a slight oscillation of AU Microscopii in response to the planet’s gravitational attraction – and this confirmed the existence of AU Mic b.

Next steps

Now scientists intend to learn more about the atmosphere of the new planet. As the planet was formed recently, it may be going through the phase when it is losing its atmosphere. Observing this and other phenomena would be particularly interesting because it would allow astronomers to analyze how a planet evolves.

According to the researchers, careful observations can also help determine what AU Mic b’s atmosphere is made up of. “Planets, like people, change as they mature,” said Eric Gaidos, one of the researchers, in a statement. “For planets this means that their orbits can move and the compositions of their atmospheres can change. But we need observations to test these ideas and planets like AU Mic b are an exceptional opportunity.”

Because AU Mic b is very young, it’s probably gaseous, and studying it will allow scientists to better understand what may have happened in the Solar System before rocky planets like Earth and Venus formed. “One of the fun things and one of the most frustrating things about studying stars is that we can never go to them,” said Barclay. “So this discovery is just one more puzzle piece in trying to understand what’s going on.”

Related topics:

exoplanets Milky Way Neptune


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