The origin of the Earth and the solar system inspires scientists and the public. By studying the current state of our home planet and other objects in the Solar System, researchers have developed a detailed picture of the conditions at the time they evolved from the disk of dust and gas surrounding the newborn sun about 4.5 billion years ago.

With astonishing progress in the study of star and planet formation for distant celestial bodies, we can now examine environmental conditions around young stars and compare them with conditions obtained for the early Solar System. An international team of researchers led by Józef Varga of the Konkoli Observatory in Budapest, Hungary, has achieved just that using the European Southern Observatory’s (ESO) Very Large Telescope Interferometer (VLTI). They observed the planet-forming disk of the young star HD 144432, about 500 light-years away.

“While studying the distribution of dust in the innermost region of the disk, we discovered for the first time a complex structure in which dust accumulates in three concentric rings in such an environment,” says Roy van Boeckel. He is a scientist at the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, and co-author of a research paper to be published in the journal. Astronomy and Astrophysics .

“This region corresponds to the region in the Solar System where rocky planets form,” Van Boeckel adds. Compared to the Solar System, the first ring around HD 144432 is located in the orbit of Mercury, while the second is closer to the orbit of Mars. Also, the third ring roughly corresponds to the orbit of Jupiter.

Until now, astronomers have found such configurations mostly on large scales, corresponding to spheres beyond where Saturn orbits the Sun. Ring systems in disks around young stars often show planets forming in the gaps as they accumulate dust and gas in their paths.

But HD 144432 is the first example of such a complex ring system so close to its host star. This occurs in a region rich in dust, the building material of rocky planets like Earth. Assuming that the rings indicate the presence of two planets forming in voids, astronomers estimated their masses to be roughly similar to those of Jupiter.

Conditions may be similar to those in the early solar system

Astronomers determined the composition of the dust in the disk to a distance from the central star corresponding to Jupiter’s distance from the Sun. What they found sounds familiar to scientists studying the Earth and the Solar System’s rocky planets: various silicates (compounds of metal, silicon, and oxygen) and other minerals found in the Earth’s crust and mantle, and possibly metallic iron. Mercury and Earth. nuclei If confirmed, this study would be the first to detect iron in a planet-forming disk.

“Currently, astronomers attribute the observed dust disks to a mixture of carbon and silicate dust, materials we see almost everywhere in the universe,” van Beckel explains. However, from a chemical perspective, a mixture of iron and silicate is more plausible for the hot inner regions of the disk.

In fact, the chemical model that Varga, the research paper’s lead author, applied to the data gave better results when iron was added instead of carbon.

In addition, the dust observed in HD 144432’s disk may be as hot as 1800 Kelvin (about 1500 degrees Celsius) at the inner edge and as moderately hot as 300 Kelvin (about 25 degrees Celsius) further out. Minerals and iron often melt and recondense into crystals in hot regions near the star.

In contrast, carbon grains will not be able to withstand the heat and will instead exist in the form of carbon monoxide or carbon dioxide. However, carbon may still be an important component of solids in the cold outer disk, which the observations made for this study cannot track.

The iron-rich, carbon-poor dust would also be perfectly adapted to the conditions of the Solar System. Mercury and Earth are iron-rich planets, while Earth is relatively low in carbon. “We think the HD 144432 disk may be very similar to the early solar system, which provided abundant iron for the rocky planets we know today,” Van Boeckel says. “Our study may be another example of how the composition of our solar system may be quite typical.”

Interferometry detects small details

Reconstructing the results was made possible by the exceptionally high-resolution observations provided by the VLTI. By combining four 8.2-metre VLT telescopes at ESO’s Paranal Observatory, they can discern detail as if astronomers were using a telescope with a 200-metre diameter primary mirror. Varga, van Boekel and their collaborators obtained the data using three devices to reach the wide range of wavelengths from 1.6 to 13 micrometers that represent infrared light.

MPIA provided vital technology elements for two instruments: GRAVITY and the Multi AperTure mid-infrared SpectroScopic Experiment (MATISSE). One of the main goals of MATISS is to study rocky regions of planet formation in disks around young stars. “By looking at the interior regions of protoplanetary disks around stars, we aim to investigate the origin of various minerals found in the disk – minerals that will eventually form the solid components of planets such as Earth,” says MPIA director Thomas Henning. Common PI of the MATISSE device.

However, creating images using an interferometer similar to the images we are used to from individual telescopes is not easy and takes a lot of time. A more efficient use of valuable observation time to resolve object structure is to compare sparse data with models of potential target configurations. In the case of HD 144432, the three-ring structure best represents the data.

How common are structured, iron-rich planet-forming disks?

HD 144432 appears to be another example of planet formation in an iron-rich environment outside the Solar System. But astronomers won’t stop there.

“We have many promising candidates waiting for VLTI to take a closer look at them,” Van Boekel said. he states. In previous observations, the team found several disks around young stars that showed configurations worth looking at. But using the latest VLTI equipment, they will reveal their detailed structure and chemical composition. Eventually, astronomers will be able to learn whether planets often form in iron-rich dusty disks near their parent stars.