Rocky planet formation zone rings discovered around young star

Delving into the celestial history of our solar system and Earth’s origins fuels the imagination of both scientists and the public. The ongoing exploration of our planet’s current state and the surrounding cosmic entities provides a profound understanding of their evolution from the primordial dust and gas disk encircling the nascent sun about 4.5 billion years ago.

Advancements in star and planet formation research have propelled us to investigate distant celestial bodies, enabling a comparative analysis between the conditions around young stars and those prevalent during the early stages of our solar system. Leveraging the capabilities of the European Southern Observatory’s (ESO) Very Large Telescope Interferometer (VLTI), an international team led by József Varga from the Konkoly Observatory in Budapest, Hungary, scrutinized the planet-forming disk of the youthful star HD 144432, positioned approximately 500 light-years away.

Roy van Boekel, a scientist at the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, and co-author of the forthcoming research article in the journal Astronomy & Astrophysics, shares insights into their findings. “When exploring the dust distribution in the innermost region of the disk, we identified, for the first time, a complex structure featuring dust accumulation in three concentric rings,” van Boekel explains.

Significantly, this region aligns with where the rocky planets in our solar system, including Earth, took shape. Intriguingly, the first ring around HD 144432 exists within the orbit of Mercury, the second closely aligns with Mars’s trajectory, and the third corresponds roughly to the orbit of Jupiter.

Traditionally, astronomers have observed such configurations on larger scales, typically beyond Saturn’s orbit. Ring systems in the disks surrounding young stars often signal the formation of planets within the gaps as they gather dust and gas in their formative journey.

However, HD 144432 presents a groundbreaking revelation—a complex ring system in close proximity to its host star. This occurrence unfolds in a zone abundant with dust, the fundamental building block for rocky planets akin to Earth. Assuming these rings signify the presence of two developing planets within the gaps, astronomers estimate their masses to resemble that of Jupiter.

This discovery not only expands our comprehension of planetary formation but also challenges preconceived notions by showcasing a unique and intricate ring system in the proximity of a young star, shedding light on the diverse processes shaping planetary systems throughout the cosmos.

Conditions may be similar to the early solar system

The scrutiny of the planet-forming disk around the young star HD 144432 has not only revealed a complex ring structure but also exposed a composition intriguingly reminiscent of our own solar system. Astronomers meticulously analyzed the dust composition across the disk, extending to a distance from the central star equivalent to Jupiter’s orbit in our solar system. The findings, akin to the makeup of Earth and other rocky planets, include various silicates—compounds of metal, silicon, and oxygen—along with minerals found in Earth’s crust and mantle. Remarkably, the potential presence of metallic iron, a key component of Mercury’s and Earth’s cores, could mark a groundbreaking discovery if confirmed.

Roy van Boekel emphasizes the departure from conventional explanations, stating, “Astronomers have thus far explained the observations of dusty disks with a mixture of carbon and silicate dust, materials that we see almost everywhere in the universe.” From a chemical standpoint, the introduction of an iron and silicate combination appears more plausible for the hot, inner regions of the disk.

József Varga, the lead author of the research article, applied a chemical model to the data, revealing that incorporating iron instead of carbon yielded more accurate results. The implications extend beyond theoretical frameworks, challenging established norms in understanding the chemical dynamics of such planetary nurseries.

Moreover, the observed dust in the HD 144432 disk exhibits a wide temperature range, reaching scorching temperatures of 1800 Kelvin (approximately 1500 degrees Celsius) near the inner edge and more moderate temperatures of 300 Kelvin (approximately 25 degrees Celsius) farther out. This environment prompts minerals and iron to undergo phases of melting and recondensation, often forming crystalline structures.

In contrast, carbon grains, under such intense heat, would not endure and would instead manifest as carbon monoxide or carbon dioxide gas. However, the study acknowledges the possibility of carbon playing a substantial role in the solid particles of the cold outer disk, a facet beyond the scope of the current observations.

The juxtaposition of an iron-rich and carbon-poor dust composition aligns intriguingly with the conditions observed in our solar system. Both Mercury and Earth are recognized as iron-rich planets, while Earth, in particular, contains relatively little carbon. “We think that the HD 144432 disk may be very similar to the early solar system that provided lots of iron to the rocky planets we know today,” suggests van Boekel, raising the prospect that this study could offer another instance of our solar system’s composition being representative of broader cosmic patterns.

Interferometry resolves tiny details

The unveiling of these groundbreaking results hinged on the unparalleled resolution afforded by the VLTI, a testament to its capability in pushing the boundaries of observational astronomy. Through the synchronized efforts of the four VLT 8.2-meter telescopes at ESO’s Paranal Observatory, the researchers achieved a level of detail akin to employing a colossal telescope with a primary mirror boasting a staggering 200-meter diameter.

József Varga, Roy van Boekel, and their collaborative team leveraged three instruments to amass data spanning a broad wavelength spectrum, ranging from 1.6 to 13 micrometers, capturing the essence of infrared light. The indispensable technological contributions from the Max Planck Institute for Astronomy (MPIA) played a pivotal role, particularly in enhancing GRAVITY and the Multi AperTure mid-Infrared SpectroScopic Experiment (MATISSE). MATISSE, in particular, stands out for its primary focus on delving into the rocky planet-forming zones within disks surrounding nascent stars.

Thomas Henning, the MPIA director and co-PI of the MATISSE instrument, sheds light on the mission: “By scrutinizing the inner regions of protoplanetary disks around stars, we aim to unravel the origin of the diverse minerals contained in the disk—minerals destined to shape the solid components of planets like Earth.”

Yet, the process of generating images using an interferometer, unlike the conventional approach with single telescopes, poses challenges and demands significant time investment. To optimize the use of invaluable observation time and dissect the structural intricacies of celestial objects, researchers employ a strategy involving the comparison of sparse data with models representing potential configurations. In the case of the HD 144432 disk, the most fitting representation emerged as a three-ringed structure, emphasizing the efficiency of this approach in decoding the enigmatic features within our cosmic neighborhood.

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

Beyond the confines of our solar system, HD 144432 emerges as a compelling case, presenting a scenario where planets seem to be taking shape in an environment rich in iron—a phenomenon not dissimilar to our own cosmic neighborhood. Yet, this revelation is merely a stepping stone for the astronomers involved.

Roy van Boekel emphasizes their ongoing exploration, stating, “We still have a few promising candidates waiting for the VLTI to take a closer look at.” The team, building on earlier observations, has identified several disks surrounding young stars that beckon for closer scrutiny. Their intricate structures and chemical compositions remain undisclosed, awaiting the precision of the latest VLTI instrumentation to unravel the mysteries they hold. This relentless pursuit aims to shed light on whether the prevalence of planets forming in iron-rich, dusty disks near their parent stars is a common cosmic occurrence.

The journey into the cosmos continues, fueled by the curiosity to unveil the diverse mechanisms underlying planetary formation and to discern the patterns that shape the multitude of celestial bodies scattered throughout the vast expanse of the universe.

Source: Max Planck Society

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