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Once upon a time, the great planet Jupiter, surrounded by a glorious ring of dust, according to astronomers. Now, nothing remains, having merged long ago in the Galilean moons of the planet.
But these discs forming the moon should be found around other planets in extraterrestrial star systems. And for the first time, we have confirmation, because astronomers have found one and they have the images to prove it.
It is PDS 70c, one of two giants of Jupiter's size, gravitating around a young, low-mass star, located about 370 light-years from Earth. Astronomers have used Atacama's Large Millimeter / Subillimeter Array (ALMA) system to detect radio waves emitted by microscopic dust spots surrounding the entire system.
These observations revealed a concentration of dust around the planet in formation, gravitating around the star at a distance of about 5.31 billion kilometers.
Astronomers think that it is nothing more than a circumplanetary disk; Just as the protoplanetary disks surrounding young stars eventually merge into planets, it seems likely that this disk will eventually gather into moons.
"For the first time, we can conclusively see the telltale signs of a circumplanetary disk, which helps support many of the current theories on planet formation," said astronomer Andrea Isella of the Rice University.
"By comparing our observations to high-resolution infrared and optical images, we can clearly see that an otherwise enigmatic concentration of tiny dust particles is actually a dust disk that surrounds the planet, the first characteristic of this type ever observed conclusively. "
Such rings are very different from the rings of Saturn, which are estimated to date back only about 100 million years, compared to the 4.5 billion years of the solar system. . The rings of Saturn consist of ice, dust and rocks. It is thought that these are the debris of comets, asteroids and perhaps even moons that have broken in one way or another around the planet.
In contrast, the ring around the PDS 70c is much older. The star is only 10 million years old, the planets barely formed.
Once their nuclei are formed, the process of accretion seems to be very similar in stars and planets, the matter swirling around them in a disc and falling on the object, increasing its mass. In the case of a star, the material that remains of this process ends up forming planets.
It is therefore believed that the disk around the PDS 70 c is the result of this accretion process; indeed, the brightness of the object in the infrared and hydrogen bands indicates that there is not only one planet in the dust block, but that it is going through a growth spurt , actively growing from this incandescent drive.
(ALMA (ESO / NAOJ / NRAO) Isella, ESO)
But, we mentioned that it was one of the two planets. The other, which revolves around the star around 3.22 billion kilometers, is the PDS 70B. Astronomers are not quite sure because the signal is so weak, but they think that he could also have a ring around him, even if he is weaker.
In addition, there is a strange smear of dust not far from PDS 70b, a dragging mass like the tail of a comet.
"What it is and what it means for this planetary system is not yet known.The only conclusive thing we can say is that it is far enough away from the planet to constitute an independent element, "noted Isella.
It's a mysterious system, and it can have a lot to teach us. It is unlikely that we will show our first exomoons – that dust will probably not form solid pieces for many human lives, and it would be nice to think that we are closer to exomoons than that – but its value in understanding the process planetary formation was shaken a few notches with the discovery of the first circumplanetary disk.
And ALMA's ability to image objects in the dust around the stars means that astronomers will be able to take more observations in the future, by mapping the positions of the planets and changes in the dust, to observe these processes in action.
The search was published in The letters of the astrophysical journal.
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