How three iron rings could redefine planet formation

Observations using the European Southern Observatory's (ESO) Very Large Interferometer (VLTI) have found various silicate compounds and possibly iron, materials that we also find in large quantities in rocky planets in the solar system. Credit: © Jinri

A three-ringed structure in the planet-forming region of the circumstellar disk where minerals and metals serve as a repository for planetary building blocks.

A research team, including astronomers from the Max Planck Institute for Astronomy (MPIA), has discovered a three-ringed planetary nursery structure in the inner planet-forming disk of a young star. This configuration suggests two Jupiter– Planets with mass form in the gaps between the rings. Detailed analysis is consistent with abundant solid iron grains that complement the dust composition. As a result, the disk likely contains minerals and metals similar to those found in the terrestrial planets in the solar system. It provides a glimpse into conditions similar to the early solar system more than four billion years ago during the formation of rocky planets such as Mercury. Venusand the earth.

Three iron rings in a planet-forming disk

The origin of the Earth and the solar system inspires scientists and the public alike. By studying the current state of our home planet and other bodies in the solar system, researchers have developed a detailed picture of the conditions under which they evolved from a disk of dust and gas surrounding the infant sun about 4.5 billion years ago.

Three rings indicate two planets

With amazing progress in star and planet formation research targeting distant celestial bodies, we can now explore conditions in the environments surrounding young stars and compare them to those from the early solar system. Using the European Southern Observatory (Eso) Very large telescope VLTI is what an international team of researchers led by Józef Varga of the Konkoli Observatory in Budapest, Hungary, did. They observed the planet-forming disk of the young star HD 144432, about 500 light-years away.

Paranal Observatory

An aerial view of the European Southern Observatory's Very Large Telescope (VLT) atop Cerro Paranal in the Atacama Desert in Chile. The VLT interferometer (VLTI) combines the light of four telescopes, enabling high-resolution imaging of distant celestial objects. Photo credit: G.Hüdepohl (

“By studying the distribution of dust in the inner 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 Bokel. He is a scientist at the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, and co-author of the primary research article published in the journal Astronomy and astrophysics. “This region corresponds to the region where rocky planets formed in the solar system,” Van Bokel adds. Compared to the solar system, the first ring around HD 144432 is within the orbit of Mercury, and the second is close to Marsa path. Moreover, the third ring roughly corresponds to the orbit of Jupiter.

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Until now, astronomers have found such formations mostly on larger scales that correspond to worlds located outside of space Saturn It revolves around the sun. Ring systems found in disks surrounding young stars generally indicate that planets formed within gaps as dust and gas accumulated in their path. However, HD 144432 is the first example of such a complex ring system so close to its host star. It occurs in an area rich in dust, which is the building block of rocky planets like Earth. Assuming that the rings indicate the presence of two planets forming within the gaps, astronomers have estimated that their masses are roughly similar to that of Jupiter.

Conditions may be similar to the early solar system

Astronomers determined the composition of dust across the disk until separation from the central star, which corresponds to Jupiter's distance from the Sun. What they found is very familiar to scientists who study Earth and rocky planets in the solar system: various silicates (silicon-oxygen metal compounds) and other minerals found in Earth's crust and mantle, and perhaps metallic iron as found on Mercury and Earth. Cores. If confirmed, this study will be the first to detect iron in a planet-forming disk.

Disc HD 144432

This illustration is a schematic diagram of HD 144432 as observed with VLTI. The data are consistent with a structure of three concentric rings. The gaps between the rings generally indicate that large planets form by accretion of dust and gas along their orbit around their host star. Silicate minerals exist mainly as crystals in the inner hot zone. VLTI feedback cannot limit the cold external disk. Credit: © J. Varga et al. / MPIA

“So far, astronomers have explained observations of dusty disks with a mixture of carbon and silicate dust, materials we see almost everywhere in the universe,” Van Bokel explains. However, from a chemical perspective, the iron-silicate mixture is more acceptable in hot inner disc regions. Indeed, the chemical model that Varga, the lead author of the original research article, applied to the data produces better results when iron is introduced instead of carbon.

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Furthermore, the temperature of the dust observed in HD 144432 can reach 1,800 K (about 1,500 degrees). Celsius) at the inner edge and a moderate temperature of 300 K (about 25 °C) on the outside. Metals and iron melt and condense again, often into crystals, in hot regions near the star. In contrast, carbon grains will not survive the heat and instead exist as carbon monoxide or carbon dioxide gas. However, carbon may still be an important component of the solid particles in the cold outer disk, which observations for this study cannot track.

Iron-rich, carbon-poor dust is also well suited to conditions in the solar system. Mercury and Earth are iron-rich planets, while Earth contains relatively little carbon. “We think the disk HD 144432 may be very similar to the early solar system that provided much of the iron for the rocky planets we know today,” says van Bokel. “Our study may be another example showing that the formation of our solar system may be quite typical.”

Interferometry resolves small details

Retrieval of the results was only possible through exceptionally high-resolution observations, as provided by the VLTI. By combining the four 8.2-meter VLT telescopes at the European Southern Observatory's Paranal Observatory, they can resolve details as if astronomers were to use a telescope with a 200-meter primary mirror. Varga, van Bokel and their collaborators acquired the data using three instruments to achieve broad wavelength coverage from 1.6 to 13 micrometers, which represents infrared light.

MPIA provided biotechnology elements for two instruments, GRAVITY and the Multi-Aperture Mid-Infrared SpectroScopic Experiment (MATISSE). One of Mattis's primary goals is to study the rocky regions that make up planets around young stars. “By looking at the interiors of protoplanetary disks around stars, we aim to explore the origin of the different minerals contained in the disk – minerals that will later form the solid components of planets like Earth,” says Thomas Henning, MPIA director and researcher. Participant PI of the MATISSE tool.

However, producing interferometer images like the ones we are used to getting from individual telescopes is not easy and time-consuming. The most efficient use of valuable observation time to decipher object structure is to compare sparse data with models of possible target configurations. In the case of HD 144432, the three-ring structure represents the data better.

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How common are iron-rich planet-forming discs?

Besides the solar system, HD 144432 appears to provide another example of planets forming in an iron-rich environment. However, astronomers will not stop there. “We still have a few promising candidates waiting for VLTI to take a closer look,” Van Bokel points out. In previous observations, the team discovered a number of disks around young stars that indicate configurations worth revisiting. However, they will reveal its detailed structure and chemistry using state-of-the-art VLTI devices. Eventually, astronomers may be able to clarify whether planets typically form in iron-rich dust disks near their parent stars.

Reference: “Mid-infrared evidence for iron-rich dust in the inner multiring disk of HD 144432” by J. Varga, LBFM Waters, M. Hogerheijde, R. van Boekel, A. Matter, B. Lopez, K. Perraut, L. Chen, D. Nadella, S. Wolf, C. Dominik, Á. Cosbal, B. Abraham, J.-C. Augereau, P. Polly, J. Bordarot, A. Carati or Jarati, F. Cruz Saenz de Mira, W. C. Danchi, V. Gamez Rosas, Th. Henning, K.-H. Hoffman, M. Holley, J.W. Isbell, W. Jaffe, T. Juhasz, V. Kekskemethy, J. Cobos, E. Kokulina, L. Labadie, F. Leco, F. Mellor, A. Moore, N. Morugao, E. Pantin, D. Schertel, M. Schick, L. Van Haester, J. Weigelt, J. Wells, and B. Woytek, January 8, 2024, Astronomy and astrophysics.
doi: 10.1051/0004-6361/202347535

The MPIA researchers involved in this study are: Roy van Boekel, Marten Scheuck, Thomas Henning, Jacob W. Isbell, Ágnes Kóspál (also HUN-REN Research Center for Astronomy and Earth Sciences, Konkoli Observatory, Budapest, Hungary). [Konkoly]; CSFK, MTA Center of Excellence, Budapest, Hungary [CSFK]; ELTE Eötvös Loránd University, Budapest, Hungary [ELTE]), Alessio Carati or Garatti (also INAF-Osservatorio Astronomico di Capodimonte, Naples, Italy).

Other shareholders are: J. Varga (Concoli; CSFK; Leiden Observatory, Netherlands). [Leiden]), LBFM Waters (Radboud University, Nijmegen, Netherlands; SRON, Leiden, Netherlands), M. Hogerheijde (Leiden; University of Amsterdam, Netherlands) [UVA]), a. Mater (Observatoire de la Côte d'Azur/CNRS, Nice, France [OCA]), B. Lopez (OCA), K. Peru (Université Grenoble Alpes/CNRS/IPAG, France [IPAG]), L. Chen (Konkoly; CSFK), D. Nadella (Leiden), S. Wolf (University of Kiel, Germany [UK]), C. Dominic (UVA), P. Abraham (Konkoli; CSFK; ELTE), J.-C. Augereau (IPAG), P. Boley (OCA), G. Bourdarot (Max Planck Institute for Extraterrestrial Physics, Garching, Germany), F. Cruz-Saénz de Miera (Konkoly; CSFK; University of Toulouse, France), W. C. Danchi (NASA Goddard Space Flight Center, Greenbelt, USA), V. Gámez Rosas (Leiden), K.-H. Hoffmann (Max Planck Institute for Radio Astronomy, Bonn, Germany [MPIfR]), M. Houllé (OCA), W. Jaffe (Leiden), T. Juhász (Konkoly; CSFK; ELTE), V. Kecskeméthy (ELTE), J. Kobus (UK), E. Kokoulina (University of Liège, Belgium ; OCA), L. Labadie (University of Cologne, Germany), F. Lykou (Konkoly; CSFK), F. Millour (OCA), A. Moór (Konkoly; CSFK), N. Morujão (Universidade de Lisboa and Universidade do Porto, Portugal), E. Pantin (AIM, CEA/CNRS, Gif-sur-Yvette, France), D. Schertl (MPIfR), L. van Haastere (Leiden), G. Weigelt (MPIfR), J. Woillez (European Southern Observatory, Garching, Germany ), P. Woitke (Institute for Space Research, Austrian Academy of Sciences, Graz, Austria), MATISSE and GRAVITY Collaborations

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