Illustration of planet development around a Sun-like star, with the foundation of the worlds– rocks and iron particles– in the foreground. Credit: © Tania Cunha (Planetário do Porto– Centro Ciência Viva & & Instituto de Astrofísica e Ciências do Espaço).
A compositional link between planets and their particular host star has long been presumed in astronomy. For the very first time now, a team of researchers, with the involvement of researchers of the National Centre of Competence in Research (NCCR) PlanetS from the University of Bern and the University of Zürich, provide empirical proof to support the assumption– and partially contradict it at the exact same time.
Stars and worlds are formed from the exact same cosmic gas and dust. In the course of the formation process, some of the product condenses and forms rocky planets, the rest is either accumulated by the star or becomes part of gaseous planets. The presumption of a connection between the structure of stars and their planets is for that reason sensible and is confirmed, for example, in the solar system by a lot of rocky planets (Mercury being the exception). Nevertheless, assumptions, especially in astrophysics, do not constantly show to be real. A study led by the Instituto de Astrofísica e Ciências do Espaço (IA) in Portugal, which likewise involves researchers from the NCCR PlanetS at the University of Bern and the University of Zürich, published on October 15, 2021, in the journal Science, supplies the very first empirical evidence for this assumption– and at the exact same time partly opposes it.
Condensed star vs rocky world.
To figure out whether the compositions of stars and their worlds are related, the group compared very accurate measurements of both. The composition of the rocky planets was determined indirectly: Their density and composition were obtained from their measured mass and radius.
The assumption of a connection in between the composition of stars and their planets is for that reason sensible and is validated, for example, in the solar system by most rocky planets (Mercury being the exception).” But since stars and rocky worlds are quite various in nature, the comparison of their composition is not simple,” as Christoph Mordasini, co-author of the study, speaker of astrophysics at the University of Bern and member of the NCCR PlanetS starts to discuss.” Our outcomes show that our assumptions concerning star and planet compositions were not basically incorrect: the structure of rocky worlds is indeed intimately tied to the structure of their host star. “Yet for some of the worlds, the iron abundance in the world is even greater than in the star” as Caroline Dorn, who co-authored the study and is a member of the NCCR PlanetS as well as Ambizione Fellow at the University of Zurich, discusses. These are, for example, submodels of accretion (development of a worlds core) or of how planets communicate gravitationally and affect each other, and of processes in the protoplanetary disks in which worlds are formed.
” But given that stars and rocky planets are rather different in nature, the comparison of their structure is not straightforward,” as Christoph Mordasini, co-author of the study, lecturer of astrophysics at the University of Bern and member of the NCCR PlanetS starts to describe. “Instead, we compared the composition of the planets with a theoretical, cooled-down version of their star. While many of the stars material– generally hydrogen and helium– remains as a gas when it cools, a tiny fraction condenses, including rock-forming product such as iron and silicate,” explains Christoph Mordasini.
At the University of Bern, the “Bern Model of Planet Formation and Evolution” has actually been continually established since 2003 (see infobox). Christoph Mordasini says: “Insights into the manifold processes involved in the formation and evolution of planets are integrated into the model.” Using this Bern design the researchers were able to calculate the composition of this rock-forming material of the cooled-down star. “We then compared that with the rocky planets,” Christoph Mordasini states.
Signs of the habitability of worlds.
” Our results show that our presumptions concerning star and planet compositions were not fundamentally incorrect: the composition of rocky planets is certainly intimately tied to the structure of their host star. “Yet for some of the planets, the iron abundance in the world is even greater than in the star” as Caroline Dorn, who co-authored the study and is a member of the NCCR PlanetS as well as Ambizione Fellow at the University of Zurich, describes. “This might be due to giant effects on these planets that break off some of the outer, lighter products, while the dense iron core stays,” according to the researcher.
” The outcomes of this research study are likewise really helpful to constrain planetary structures that are presumed based upon the determined density from mass and radius measurements,” Christoph Mordasini explains. “Since more than one composition can fit a specific density, the results of our research study inform us that we can narrow potential compositions down, based upon the host stars composition,” Mordasini says. And because the specific structure of a planet affects, for example, just how much radioactive material it contains or how strong its electromagnetic field is, it can identify whether the planet is life-friendly or not.
” Bern Model of Planet Formation and Evolution”.
Insights into the manifold processes included in the formation and evolution of planets are incorporated into the design. These are, for example, submodels of accretion (growth of a planets core) or of how worlds connect gravitationally and influence each other, and of procedures in the protoplanetary disks in which worlds are formed.
Recommendation: “A compositional link in between rocky exoplanets and their host stars” by Vardan Adibekyan, Caroline Dorn, Sérgio G. Sousa, Nuno C. Santos, Bertram Bitsch, Garik Israelian, Christoph Mordasini, Susana C. C. Barros, Elisa Delgado Mena, Olivier D. S. Demangeon, João P. Faria, Pedro Figueira, Artur A. Hakobyan, Mahmoudreza Oshagh, Bárbara M. T. B. Soares, Masanobu Kunitomo, Yoichi Takeda, Emiliano Jofré, Romina Petrucci and Eder Martioli, 15 October 2021, Science.DOI: 10.1126/ science.abg8794.