A huge planetary nucleus about 40 times the mass of Earth has been discovered around a distant star

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Astronomers have spotted the exposed core of what appears to have been a massive planet: probably an ancient gas giant. This unprecedented discovery could shed considerable light on the formation, evolution and diversity of the planets.

The planetary nucleus, called TOI-849b, is unlike anything scientists have seen so far, and it could hide a wealth of exciting information in its depths, the researchers said. ” The discovery of this planet shows that the formation and evolution of the planets can take place in an unusual way, not foreseen by the study of the Solar System “Said to Space.com David Armstrong, lead author of a new study reporting the discovery of TOI-849b, published July 1 in the journal Nature.

« There is a great variety and diversity of planets, and we discover new ones every week. […] And we shouldn’t be surprised to make amazing new discoveries like this Said Armstrong, a researcher in the Department of Physics at the University of Warwick in England. ” Hopefully, a new understanding of the formation of planets like TOI-849b will help us understand how our own solar system was formed. ».

TOI-849b has been detected by NASA’s TESS exoplanet probing space telescope, which has been in Earth orbit since April 2018 and which has discovered more than 50 extraterrestrial worlds to date, as well as more than 2,000 unconfirmed candidates. TESS hunts planets using the “transit method”, which means it monitors small (but revealing) drops in the brightness of stars, caused by the passage of planets into orbit.

Extreme proximity to its host star

TESS observations revealed that TOI-849b is extremely close to its host star, making a full orbit every 18 hours. This orbital region is known as the “Neptunian Desert” because planets the size of Neptune are very rare.

And according to TESS data, the new object detected is precisely the same size as Neptune, although its properties are very different. Neptune is a cold planet, while the surface temperature of TOI-849b is probably around 1530 degrees Celsius, say Armstrong and his colleagues.

The researchers also studied the object using the High Accuracy Radial velocity Planet Searcher (HARPS), an instrument installed on a telescope at the European Observatory in southern La Silla, Chile. HARPS and other similar spectrographs allow researchers to accurately follow the movements of stars, revealing the disturbances of their movement due to the gravitational pull of planets in orbit. HARPS data suggests that TOI-849b is two to three times more massive than Neptune, which is itself 17 times more massive than Earth.

« YOU 849 b is thus the most massive ‘telluric’ planet – a planet made up essentially of rocks and metal, like the Earth – never discovered “Armstrong said in a statement. ” We would expect such a massive planet to have accumulated large amounts of hydrogen and helium when it formed, becoming similar to Jupiter. The fact that we do not detect these gases proves to us that it is about an exposed planetary nucleus “, he added. ” It is the first time that we discover an intact exposed nucleus of a gas giant around a star ».

On the same subject : Astronomers capture rare images of protoplanetary discs

It is not known how TOI-849b arrived at this mysterious point of evolution. Is it a former gas giant who would have lost its atmosphere after having ventured too close to its host star? Would it have been hit by another planet? These questions seem legitimate, given that the stellar radiation at the orbital location of TOI-849b, although intense, is not powerful enough to completely eliminate the atmosphere of a gas giant, the researchers said. Another hypothesis: would YOU-849b have in fact never accumulated enough gas to become a world similar to Jupiter?

« It’s a mystery and a big question Said Armstrong. ” I think the key clue is that TOI-849b is in the Neptunian desert, which hints at a rare story. But we need more studies to be sure ».

Although TOI-849b is the first object of its kind ever spotted around another star, our own solar system could harbor similar cases: for example, the strange metallic asteroid (16) Psyche, with a diameter of 226 kilometers, according to some astronomers, is the exposed nucleus of an ancient planet the size of Mars. Besides, NASA is currently developing a special mission called Psyche, which should be launched in August 2022 and reach the asteroid in 2026. We will then learn much more about this mysterious object in the relatively near future.

Source : Nature

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