An international team of researchers has observed, for the first time, the early stages of planet formation around a star. The relevant data were collected using ESO’s ALMA radio telescope array, as well as the James Webb Space Telescope, and analysis of the data shows that the formation of the first grains of matter—from which planets are formed—has already begun. This discovery marks the first time a planetary system has been detected at such an early stage of its formation, and further study of it will open a new “window” into the origins of our own Solar System.
“For the first time, we’ve identified the earliest moment that marks the trigger for the formation of planets around a star,”, explains Melissa McClure, a professor at Leiden University in the Netherlands and lead author of the new study, which was published on July 16 in the scientific journal Nature. This newborn planetary system is forming around the protostar HOPS-315, which is located about 1,300 light-years away.
The gases and dust swirling around such protostars form what are called protoplanetary disks around them, discs of matter, within which planets eventually form over time. The primary material—that is, the “building blocks”—from which planets form are precisely these microscopic dust grains in the protoplanetary disk. In a way that is not yet fully understood, these microscopic particles begin to stick together, increasing their size and mass more and more. Due to the complex gravitational interactions within the protoplanetary disk, these pieces of matter become distributed asymmetrically and irregularly, as most of them accumulate in specific orbits.
Within each such orbit, and with the help of gravity, these space debris particles accumulate more and more matter from the disk in which they were formed, while collisions among them lead to the formation of a large number of increasingly larger clumps of matter, known as planetesimals. Collisions between asteroids are more violent, which is why many of them break apart. Other planetary embryos, however, survive these collisions and merge with one another, continuously increasing their mass and gradually forming protoplanets and, ultimately, planets.
In fact, in our Solar System, we have already detected such primordial solid materials inside primitive meteorites. These materials had condensed at relatively short distances from the newborn Sun, and analyzing them helps astronomers pinpoint the early stages of its formation. More specifically, these meteorites contain crystalline silicon monoxide (SiO) minerals, which have a high melting point and can therefore be further condensed.
In fact, the high temperatures prevailing in the inner regions of protoplanetary disks typically do not allow for the condensation and solidification of various volatile compounds. This, however, does not apply to compounds with a high melting point, such as metals and silicon-based minerals.
By analyzing the data from the two telescopes, astronomers found that these superheated silicon-based minerals in the protoplanetary disk of HOPS-315, which were initially in gaseous form, have already begun to condense, which means that the early stages of planetesimal formation have already begun. Specifically, they found that SiO is present around the protostar, both in its gaseous state and in its crystalline form, a fact that suggests it has only just begun to solidify. This process had never been observed before in a protoplanetary disk.
Photo: The image shows the primary star HOPS-315. The orange color corresponds to the distribution of CO gas emitted by the protostar, while the blue color corresponds to a narrow jet of SiO, also in gaseous form. These gas outflows are common in protostars, such as HOPS-315. However, the combined observations from ALMA and JWST indicate that, in addition to these features, HOPS-315 is surrounded by a gaseous SiO disk, which has already begun to condense into solid silicate minerals. This means that the initial stage of planetary formation has already begun (Credit: ALMA (ESO/NAOJ/NRAO)/M. (McClure et al.).
Source: For the first time, astronomers witness the dawn of a new solar system | ESO