Astronomers Detect Three Iron Rings within a Disk Forming Planets

The study of the origin of Earth and the solar system is a subject that captivates both scientists and the general public. Through the examination of our planet and other celestial bodies within the solar system, researchers have been able to develop a comprehensive understanding of the conditions that existed during their formation from a disk composed of dust and gas surrounding the young sun approximately 4.5 billion years ago.

With the remarkable advancements in research on star and planet formation, which focuses on distant celestial objects, we now have the ability to investigate the conditions present in the environments surrounding young stars and compare them to those that existed in the early solar system. A team of international researchers, led by József Varga from the Konkoly Observatory in Budapest, Hungary, utilized the European Southern Observatory’s Very Large Telescope Interferometer (VLTI) to accomplish just that. Their observations were focused on the planet-forming disk of the young star HD 144432, which is located approximately 500 light-years away.

Roy van Boekel, a scientist at the Max Planck Institute for Astronomy in Heidelberg, Germany, and a co-author of the research article that will be published in the journal Astronomy & Astrophysics, explains, “When examining the distribution of dust in the innermost region of the disk, we have discovered a complex structure for the first time. This structure consists of three concentric rings where dust accumulates within this environment.”

Van Boekel further adds, “This particular region corresponds to the zone where rocky planets formed in our own solar system.” In comparison to our solar system, the first ring around HD 144432 is located within the orbit of Mercury, while the second ring is close to the trajectory of Mars. Additionally, the third ring roughly aligns with Jupiter’s orbit.

Until now, astronomers have primarily observed such configurations on larger scales, which are found in the regions beyond where Saturn orbits the sun. The presence of ring systems in the disks surrounding young stars typically indicates the formation of planets within the gaps as they gather dust and gas during their development.

Nevertheless, HD 144432 stands as a pioneering instance of a intricate ring structure situated in such close proximity to its parent star. This phenomenon takes place within a region abundant in dust particles, which serve as the fundamental components for the creation of terrestrial planets akin to Earth. By hypothesizing that the rings signify the emergence of two planets evolving within the gaps, the astronomers approximated their masses to be similar to that of Jupiter.

Conditions may be similar to the early solar system

The composition of dust across the disk, as determined by the astronomers, extends up to a distance from the central star equivalent to the distance between Jupiter and the sun. The findings are reminiscent of what scientists studying Earth and the rocky planets in our solar system have observed: a variety of silicates (compounds of metal, silicon, and oxygen) and other minerals found in Earth’s crust and mantle, along with the possibility of metallic iron, similar to what is found in the cores of Mercury and Earth. If confirmed, this study would mark the first discovery of iron in a planet-forming disk.

According to van Boekel, the current explanation for dusty disks among astronomers involves a combination of carbon and silicate dust, which are materials commonly found throughout the universe. However, from a chemical standpoint, an iron and silicate mixture seems more plausible for the hotter regions of the inner disk.

The chemical model used by Varga, the primary author of the research article, produces more accurate results when iron is introduced instead of carbon.

Additionally, the dust observed in the HD 144432 disk can reach temperatures as high as 1800 Kelvin (approximately 1500 degrees Celsius) near the inner edge, while it is relatively cooler at around 300 Kelvin (approximately 25 degrees Celsius) farther out. In these hot regions near the star, minerals and iron can melt and recondense, often forming crystals.

On the other hand, carbon grains would not survive the intense heat and would instead exist as carbon monoxide or carbon dioxide gas. However, carbon may still play a significant role in the solid particles present in the colder outer disk, which cannot be traced by the observations conducted for this study.

Iron-rich and carbon-deficient particles would also align well with the circumstances within the solar system. Mercury and Earth are both characterized by an abundance of iron, whereas carbon is relatively scarce on Earth. According to van Boekel, “We believe that the HD 144432 disk could closely resemble the early solar system, which supplied substantial amounts of iron to the rocky planets we are familiar with today. Our research serves as yet another instance highlighting the likelihood that the composition of our solar system is quite representative.”

Interferometry resolves tiny details

Exceptionally high-resolution observations provided by the VLTI were necessary to retrieve the results. The VLTI combines the four VLT 8.2-meter telescopes at ESO’s Paranal Observatory, allowing astronomers to resolve details as if they were using a telescope with a primary mirror of 200 meters in diameter. Varga, van Boekel, and their collaborators used three instruments to obtain data across a broad range of wavelengths, from 1.6 to 13 micrometers, which represents infrared light.

MPIA played a crucial role in providing technological elements for two devices, GRAVITY and MATISSE. MATISSE, in particular, focuses on investigating the rocky planet-forming zones of disks around young stars. Thomas Henning, the director of MPIA and co-PI of the MATISSE instrument, explains that by studying the inner regions of protoplanetary disks, they aim to understand the origin of the minerals that will eventually form the solid components of planets like Earth.

However, generating images with an interferometer, unlike single telescopes, is not a straightforward process and requires a significant amount of time. To make more efficient use of precious observing time and decipher the structure of the object, researchers compare the sparse data to models of potential target configurations. In the case of the HD 144432 disk, a three-ringed structure best represents the data.

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

In addition to the solar system, HD 144432 presents another instance of planets emerging in an environment abundant in iron. Nevertheless, the astronomers are not halting their efforts at this point.

“Several promising candidates are still awaiting examination by the VLTI,” van Boekel highlights. In previous observations, the team identified numerous disks encircling young stars that suggest configurations worth reevaluating. However, they intend to disclose the intricate structure and chemical composition of these disks by utilizing the latest VLTI instrumentation. Ultimately, astronomers may gain the ability to ascertain whether planets commonly form in dusty disks rich in iron near their parent stars.

This article is republished from PhysORG under a Creative Commons license. Read the original article.

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