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A team of researchers has discovered a new planet the size of Neptune, they have called AU Mic b , in the vicinity of a star that is located relatively close to the Milky Way, to 31.9 light-years away. The astro is AU Microscopii, that has “only” 20 or 30 million years, for what turns out to be at least 150 times younger than our Sun.

The discovery, published in “Nature”, is noteworthy because there are only two or three known stars that are nearby and young, and scientists have been searching for planets in its orbit for at least a decade. Now, finally, the world newly discovered can be a great opportunity to learn how to form the star systems, including our own.

AU Mic b was discovered by the mission Satellite to Study Exoplanets in Transit (TESS) NASA. TESS observes the same section of the sky for weeks, collecting data on the brightness of stars in its field of view every two minutes. Thanks to this constant monitoring, the device can detect planets when they transit in front of its star, which causes its brightness to dim. The dips in brightness not only reveal that there is a planet but also its size and year, how much time it takes you to make a full return to the star.

TESS detected two transits of AU Mic b, but the research team needed a third party to be sure of the discovery. Therefore, they requested additional data collected by the satellite Spitzer of NASA and terrestrial instruments in Hawaii and Chile.

A “year” of eight days and a half

Tom Barclay, researcher at the Center for Science and Technology Space of the University of Maryland, analyzed the combined information and was able to confirm that AU Mic b has a mass of no more than 58 Land and completes an orbit every 8.5 days! An orbit as short indicates that the planet is extremely close to its small star, that has only about 50% of the mass of the Sun. This type of stars generally have very strong magnetic fields, which makes them very active. This explains in part why it took almost 15 years to detect the exoplanet. The numerous spots and rashes on the surface of Au Microscopii difficult its detection, which was already complicated by the presence of a large disc of debris around it.

The next step to Barclay and his colleagues was to learn more about the atmosphere of the new planet. Because it was formed recently, “could well be losing its atmosphere at a rate that we can see,” says Barclay. “You might even have a teardrop shape, as the planet is moving and leaving a part of his atmosphere in his way. So we’re going to find that.”

Domino planetarium

careful Observations can also help to determine what it’s made of the planet’s atmosphere, which in turn could help the team discover where they are formed, since certain substances can only exist at a known distance of the star. And this is like a domino effect because his time, knowing where it formed the planet would provide clues about how it has moved since its creation. And knowing that would go up to the scientists to understand more generally how they are formed and migrate the planets in a new solar system.

AU Mic b is composed mainly of gases. “It is likely that this star has not yet had time to form planets small and rocky,” says Barclay. “It gives us the opportunity to have an idea of what could have happened before we formed our own terrestrial planets like Earth and Venus”.

But the work is not easy, say the authors. “To understand the migration of the planets is a really hard problem. One of the fun things and one of the most frustrating things about studying the stars is that we can never go to them,” says Barclay. “So this discovery is just one more piece of the puzzle when trying to understand what is happening.”