Astrochemistry of young Solar-analogs: understanding our chemical origins

The Solar System started from a cold and dense clump in a molecular cloud, and ended up becoming the planetary system that we know, with the Earth as its habitable planet. Indeed, planets are a very common product of the star formation process and there is an incredible variety of planetary systems in the Galaxy ( http://exoplanet.eu/ ). What makes such diversity is quite certainly the history of the star and planetary system formation. Therefore, to comprehend our origins, we need to understand what happened during the earliest phases of the formation of the Solar System.

To this end, we can study, on the one hand, the final products of the formation process of the Solar System, i.e. the planets, comets, and asteroids. On the other hand, we have the possibility to study the formation of Solar-like planetary systems via observations and physical-chemical models and simulations of their earliest stages: prestellar cores, protostars and protoplanetary disks, the three major steps in the Solar-like star formation process. Each step is characterised by a specific chemical composition, which depends on the physical status and previous history of the object. The chemical characterisation of Solar-like young objects, therefore, provide us with a key to unveil the message hidden in the primitive Solar System objects, such as comets and asteroids.

The aim of our astrochemical studies is to chemically characterise prestellar cores, protostars, and protoplanetary disks by observing selected chemical proxies which can be linked to the Solar System primitive objects and interpret them via astrochemical models. In particular, we are focused on the so-called interstellar Complex Organic Molecules (iCOMs, i.e. N-, O-bearing species with at least 6 atoms), which can be considered as the bricks used for an even more complex pre-biotic chemistry.

Figure 1. From Codella et al. (2018): chemical differentiation around a Sun-like protostar: HH212-mm. ALMA observations simultaneously reveal: the flattened envelope (continuum at 0.9mm due to dust), the bipolar fast jet (SiO), the static high-density cavity (C³⁴S), and the chemical enrichment associated with the disk along the equatorial plane (HDO, CH₃CHO).

Participation to large programs and observational campaigns

The world-wide recognized Arcetri group of astrochemistry has been and is actively leading in the last 15 years a number of Large Programs (LP) and observational campaigns (see slides) to obtain observations of young Solar-like star-disk systems at (sub-)millimeter wavelengths using single-dish and interferometers. In detail, these are: the CHESS LP with the Herschel satellite, the CALYPSO LP with the IRAM-PdBI, the ASAI LP (link) with IRAM 30m, the SOLIS LP with IRAM-NOEMA. In addition, we recently obtained the first ALMA Large Program on astrochemistry: FAUST (Fifty AU STudy of the chemistry in the disk/envelope system of Solar-like protostars). The FAUST program is complemented by other campaigns, such as ALMA-DOT, the ALMA chemical survey of Disk-Outflow sources in Taurus, which is aimed to characterise the distribution and formation of simple to complex organic molecules in young planet-forming disks (0.1-1 Myr). This is key to understand the chemical composition inherited by the forming planets and their atmospheres.

Figure 2. From Podio et al. (2019, 2020) and Garufi et al. (2020). The observations taken with the ALMA interferometer in the context of the ALMA-DOT survey show the distribution of dust (in red) and molecules (CS in green, and one of the simplest organic molecules, H2CO, in blue) in the protoplanetary disk of DG Tau, located in Taurus at 121 parsec distance. H2CO is one of the simplest organic molecule, and could be the signature of efficient grain chemistry in the disk, the starting point for the formation of complex organic and prebiotic molecules.

Bridging the chemistry of young Solar-like stars with that of exoplanets and comets: preparatory work for future space missions

The chemistry of protostellar and protoplanetary disks obtained from the FAUST and ALMA-DOT programs will be compared with that of exoplanets atmospheres which will be studied by the JWST and, in the near future, by ARIEL and ELT-HIRES. In this context, the team of Arcetri is involved in the working group on protoplanetary disks and planet formation for the scientific exploitation of ARIEL, the Atmospheric Remote-sensing Infrared Exoplanet Large-survey, which has been selected as the next medium-class science mission, M4, by the European Space Agency. Moreover, we have started to compare the abundances of complex organic molecules in young Solar analogs with what observed on comets, e.g. the comet 67P/Churyumov-Gerasimenko for which in-situ measurements of its chemical content have been obtained thanks to the success of the European Space Agency's mission Rosetta. In this context, we are involved in the white paper to support AMBITION, a mission to return the first-ever cryogenically-stored sample of a cometary nucleus to Earth, for the ESA's Voyage 2050 programme .

The synergy with chemists and laboratory experts

The approach of our team is to interpret astronomical observations in light of up-to-date quantum chemical computations and grain surface laboratory experiments. Therefore, we work in strong synergy with chemistry and laboratory experts in Italy (e.g. the University of Turin and Perugia, the INAF nodes of Catania, Palermo, and Napoli), and in Europe (e.g., University of Grenoble and Barcelona). This kind of synergies are supported by the INAF funded PRIN project called GENESIS-SKA. Moreover, the European Community funded, in the context of the H2020 EC MARIE SKŁODOWSKA-CURIE ACTIONS, the Innovative Training Network ACO (AstroChemical Origins), which involves several European institutes and companies with INAF-Arcetri as an active node funding 2 PhD projects on this topic.