A three-ring structure in the planetary formation zone of the periplanetary disk, where metals and minerals serve as repositories for planetary building blocks.
A team of researchers, including astronomers at the Max Planck Institute for Astronomy (MPIA), has discovered a three-ring structure in the planetary nursery of a young star's inner planet-forming disk. This configuration suggests that two planets of Jupiter's mass are forming in the gap between the rings. The detailed analysis is consistent with the abundance of solid iron particles and complements the dust composition. As a result, the disk may contain metals and minerals similar to those found in the terrestrial planets of the solar system. It gives us a glimpse into conditions similar to those of the early solar system during the formation of rocky planets such as Mercury, Venus, and Earth more than 4 billion years ago.
The origins of the Earth and the solar system have inspired scientists and the public. By studying the current state of our parent star and other objects in the solar system, researchers have learned in detail about the conditions under which they evolved from a disk of dust and gas surrounding the baby sun about 4.5 billion years ago.
With the astonishing progress made in the study of star and planet formation for distant objects, we can now study the conditions of the surroundings of young stars and compare them with those of the early solar system. Using the Very Large Telescope Interferometer (VLTI) from the European Southern Observatory (ESO), an international team led by József Varga of the Konkoly Observatory in Budapest, Hungary, did just that. They observed the planetary forming disk of the young star HD 144432 about 500 light-years away.
When studying the distribution of dust in the innermost region of the disk, we detected for the first time a complex structure in which dust accumulates in three concentric rings in such an environment," says Roy van Boekel. He is a scientist at the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany, and co-author of a basic research article published in the journal Astronomy & Astrophysics. "This area corresponds to the area in the solar system where rocky planets are formed," Van Boekel added. In contrast to the solar system, the first ring around the HD 144432 is within the orbit of Mercury, and the second ring is close to the orbit of Mars. In addition, the third ring roughly corresponds to Jupiter's orbit.
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So far, astronomers have found this configuration mainly on larger scales corresponding to the field where Saturn revolves around the Sun. The ring system in the disk around the young star usually points to the planets forming in the void as they accumulate dust and gas along the way. However, the 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 a component of rocky planets such as Earth. Assuming that the rings indicate that two planets formed in the gaps, astronomers estimate that their masses are roughly similar to those of Jupiter.
Astronomers determined the dust composition of the entire disk until its separation from the central star, corresponding to the distance of Jupiter from the Sun. Their findings are very familiar to scientists studying the rocky planets of the Earth and the solar system: various silicates (metal-silicon-oxygen) and other minerals present in the Earth's crust and mantle, and possibly metallic iron, such as Mercury and the Earth's core. If confirmed, this study would be the first to discover iron in a planet-forming disk.
This image is a sketch of an HD 144432 disk observed using VLTI. The data is consistent with the structure of the three concentric rings. The gaps between the rings usually indicate that large planets were formed by accumulating dust and gas along their orbits around the host star. Silicate minerals are mainly found in crystalline form in the internal hot zone. VLTI observations cannot constrain the cold outer disk. **j. varga et al. / mpia
So far, astronomers have explained the observations of the dust disk with a mixture of carbon and silicate dust, which we can find almost everywhere in the universe," explains van Boekel. However, from a chemical point of view, a mixture of iron and silicate is more reasonable for the hot inner disk area. In fact, the chemical model that varga, the lead author of the basic research article, applied to the data, produced better fitting results when iron was introduced instead of carbon.
In addition, the temperature of the dust observed in the HD 144432 disc at the inner edge can be as high as 1800 Kelvin (about 1500 degrees Celsius), while at further distances it can reach 300 Kelvin (about 25 degrees Celsius). Minerals and iron melt and re-condense in hot regions near stars, often in the form of crystals. Carbon particles, in turn, do not survive at high temperatures, but in the form of carbon monoxide or carbon dioxide gas. However, carbon may still be an important component of solid particles in the cold outer disk, which cannot be tracked by the observations made in this study.
Iron-rich and carbon-poor dust is also well suited to the conditions of the solar system. Mercury and Earth are iron-rich planets, while Earth has comparatively less carbon. "We think the HD 144432 disk may be very similar to the early solar system, which provided a lot of iron to the rocky planets we know today," Van Boekel said. "Our study could be another example of how the composition of our solar system may be very typical.
Results can only be retrieved through very high-resolution observations provided by VLTI. By combining the four VLT 8 of the ESO Paranal ObservatoryWith a 2-meter telescope, they can parse the details in the same way that astronomers use a primary mirror with a diameter of 200 meters. Varga, Van Boekel, and their collaborators obtained data using three instruments to achieve data from 1A wide wavelength coverage of 6 to 13 microns, representing infrared light.
The MPIA provides important technical elements for the Gr**ity and Multi Aperture mid-infrared spectroscopy experiments (MATISSE). One of Matisse's main purposes was to study the rocky planet-forming regions of the disk around the young star.
By looking at the inner regions of the protoplanetary disk around the star, our goal is to explore the origin of the various minerals contained in the disk – which would later form the solid composition of planets such as Earth," said Thomas Henning, director of the MPIA and co-PI of the Matisse Instrument.
However, making an image with an interferometer, like the one we are used to getting from a single telescope, is not simple and very time-consuming. A more efficient use of valuable observation time to decipher the structure of an object is to compare sparse data with a model of potential target configurations. For HD 144432 disks, the three-ring structure best represents the data.
In addition to the solar system, HD 144432 seems to provide another example of planets forming in an iron-rich environment. However, astronomers don't stop there. "We still have a number of promising candidates waiting for VLTI to take a closer look," Van Boekel noted. In earlier observations, the team found a number of disks around the young star that indicated configurations worth revisiting. However, they will use the latest VLTI instruments to reveal their detailed structure and chemistry. Eventually, astronomers may be able to clarify whether planets typically form in iron-rich dust disks close to their parent stars.
Reference: "Mid-infrared evidence of iron dust in the multi-ring inner disk of the HD 144432", by J varga， l. b. f. m. waters， m. hogerheijde， r. van boekel， a. matter， b. lopez， k. perraut， l. chen， d. nadella， s. wolf， c. dominik， ákóspál， p. ábrahám， j.-c.augereau， p. boley， g. bourdarot， a. caratti o garatti， f. cruz-sáenz de miera， w. c. danchi， v. gámez rosas， th. henning， k.-h.hofmann， m. houllé， j. w. isbell， w. jaffe， t. juhász， v. kecskeméthy， j. kobus， e. kokoulina， l. labadie， f. lykou， f. millour， a. moór， n. morujão， e. pantin， d. schertl， m. scheuck， l. van haastere， g. weigelt， j. woillez and p.Woitke, January 8, 2024, Astronomy and Astrophysics.
doi： 10.1051/0004-6361/202347535
The MPIA researchers involved in this study were Roy van Boekel, Marten Scheuck, Thomas Henning, Jacob WIsbell, Ágnes Kóspál (also the Konkoly Observatory in Budapest, Hungary Hun-Ren Center for Astronomical and Earth Science Research [Konkoly]; CSFK, MTA Center of Excellence, Budapest, Hungary [CSFK]; ELTE University, Budapest, Hungary [ELTE]), Alessio Caratti o Garatti (also Capodimonte Observatory in Naples, Italy).