| Author(s) and Co-Author(s) with Affiliation: Parashmoni Kashyap(National Institute of Science Educaiton and Research Bhubaneswar, Jatni-752050, India), Liton Majumdar(National Institute of Science Educaiton and Research Bhubaneswar, Jatni-752050, India), Anne Dutrey(Laboratoire d'Astrophysique de Bordeaux, Universite de Bordeaux, CNRS, B18N, Allee Geoffroy Saint-Hilaire, F-33615 Pessac Frnace), Stephane Guilloteau(Laboratoire d'Astrophysique de Bordeaux, Universite de Bordeaux, CNRS, B18N, Allee Geoffroy Saint-Hilaire, F-33615 Pessac Frnace), Karen Willacy(Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr. Pasadena, CA, 91109, USA), Edwige Chapillon(Institut de Radioastronomie Millimétrique (IRAM), 300 rue de la Piscine, F-38406 Saint-Martin d’Héres, France), Richard Teague(Department of Earth, Atmospheric, and Planetary Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139, USA), Dmitry Semenov(Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany), Thomas Henning(Max Planck Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany), Neal Turner(Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr. Pasadena, CA, 91109, USA), Raghvendra Sahai(Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Dr. Pasadena, CA, 91109, USA) |
| Abstract: Exoplanets inherit their chemical compositions from the protoplanetary disks in which they are born. While the disk midplane is the primary site of planetesimal growth, tracing this region remains a significant challenge due to extreme densities and optical opacity. Leveraging high-resolution and high-sensitivity observations from the Atacama Large Millimeter/submillimeter Array (ALMA), we present the first resolved molecular emissions from the midplane region of the GG Tau A protoplanetary disk—a system famous for its massive ring of dust and gas. By analysing ALMA Band 7 molecular line observations of N2H+ and DCO+, coupled with advanced disk modelling, we have constrained the physical and chemical properties of the midplane where indirect evidence suggests ongoing planet formation. Our findings reveal, a) Unprecedentedly low temperatures, with midplane values reaching as low as 12 K, significantly reshaping our understanding of planet-forming environments beyond major ice lines; (b) Very low ionisation rates, with important implications for the disk’s magnetic coupling and accretion processes; and (c) Constraints on the elemental C/O ratio, a critical tracer linking the chemical evolution of the disk to the eventual atmospheric compositions of mature exoplanets. These results provide vital new constraints on the properties of ringworlds and offer a clearer window into the cold, dense environment where the next generation of planets is currently taking shape. |
