Perhaps precursors to satellites are already forming there: for the first time, astronomers are presenting clear images of a moon-forming disk of dust around a young exoplanet. According to the data, their mass is sufficient to give the Jupiter-like celestial body three satellites the size of our moon. The observations can now help us understand developments in young planetary systems, say the scientists.
Jupiter and Saturn are teeming with them: in addition to the planets, around 170 moons form the worlds of our solar system. There are really exciting specimens: The moons Enceladus and Europa could have liquid water in their interior and thus come into question as potential extraterrestrial habitats. It can be assumed that many planets of distant star systems are orbited by moons. So far, however, no exomond has been definitively detected and their possible educational histories also appear unclear.
In the case of our Earth’s moon, it is believed to have formed as a result of the Earth’s collision with a Mars-sized protoplanet. In the case of the satellites of the gas giants, however, one proceeds from a different story: According to this, the planets initially formed in the so-called circumstellar disk of dust around the sun by collecting more and more matter. During this growth process, a planet can also produce its own so-called circumplanetary disk, from which the material slowly falls onto the center. At the same time, gas and dust in the circumplanetary disk can also clump together to form larger and larger structures, which ultimately leads to the birth of moons. That’s the theory. But there are still many unanswered questions about when, where and how planets and moons form.
A closer look at a young system
For some years now, two planets of the young PDS 70 star system have been in the sights of an international team of astronomers because of possible insights. “More than 4,000 exoplanets have been found so far, but all of them have been discovered in evolved systems. PDS 70b and PDS 70c, which form a system that is reminiscent of the Jupiter-Saturn pair, are the only two exoplanets discovered so far that are still in the process of formation, ”explains co-author Miriam Keppler from the Max Planck Institute for Astronomy in Heidelberg. As early as 2019, astronomers presented evidence of a possibly moon-forming disk around PDS 70c. Since they could not clearly distinguish the disk from its surroundings, there was no clear evidence so far and no more detailed information was available.
“Our work is now a clear confirmation,” says first author Myriam Benisty from the University of Grenoble. The Atacama Large Millimeter / Submillimeter Array (ALMA) enabled a closer look at the system. “Our data were obtained with such excellent resolution that we could clearly see that the disk is associated with the planet. We are also able to narrow down their size for the first time, ”says Benisty.
Material for three earth’s moons
The ALMA data show that the circumplanetary disk is roughly the same diameter as the distance from our sun to earth. So there is a wide area around the planet: The disk around PDS 70c is about 500 times larger than the rings of Saturn. The astronomers report that it was also possible to draw conclusions about the mass of matter it contained. “We used the emission data from dust grains to estimate how much mass there is in the disk, which results in the potential reservoir for the formation of a lunar system around PDS 70c,” explains co-author of the Harvard-Smithsonian Center for Astrophysics in Cambridge. So there is enough material available to produce up to three celestial bodies the size of our Earth’s moon.
In addition to the proof of the lunar birth zone around PDS 70c, the scientists were now able to clearly demonstrate the lack of a circumplanetary disk in the case of the neighboring planet PDS 70b. This also gives rise to interesting hints: According to the scientists, PDS 70c could have withdrawn the dust from its neighboring planet from where it was born.
They hope to gain an even deeper understanding of the exciting planetary system from future observations with the Extremely Large Telescope (ELT) of the European Southern Observatory ESO, which is currently being built on Cerro Armazones in the Chilean Atacama Desert. Above all, they want to use it to examine the gas movements around the PDS 70c in order to obtain a complete 3D image of the system. “The ELT will be the key to this research because, with its much higher resolution, it will allow us to map the system in great detail,” says co-author Richard Teague of the Harvard-Smithsonian Center for Astrophysics.
Source: ESO, Harvard-Smithsonian Center for Astrophysics, specialist article: The Astrophysical Journal Letters, doi: 10.3847 / 2041-8213 / ac0f83