Session M39: Molecular Astrophysics: Hot Corinos and Protoplanetary Disks

The "inherited" organic inventory of (exo)planets

I will review our understanding of the composition of planets that form within the inner few au of their host stars. We focus in particular on the supply of refractory carbon to terrestrial worlds, from Earth-like to super-Earths and sub-Neptunes. This refractory carbon is inherited from the interstellar medium and is supplied with water ice. For many planetary systems, including our Solar System, the water ice line, or ice sublimation front, within the planet-forming disk has long been a key focal point, representing the boundary between where water-rich and water-poor planets would form. We posit that the soot line, the location inside of which solid-state organics are irreversibly destroyed, is also a key location within a planet forming disk. The soot line is closer to the host star than the water snow line and overlaps with the location of the majority of detected exoplanets. Based on this concept we predict a population of planets will form on short-period orbits with significant inventories of organics but low amounts of water. As a result, the mantle of such a planet could be rich in reduced carbon but have relatively low oxygen (water) content. Outgassing would naturally yield the ingredients for haze production, which is widely observed in sub-Neptune-sized exoplanets. Although this type of planet has no solar system counterpart, it should be common in the galaxy.   

An Astronomer's View of Molecules in Protoplanetary Disks

Our view of planet formation has been transformed by state-of-the-art telescopes like ALMA and JWST. This talk will provide an overview of how recent molecular line observations of protoplanetary disks have advanced our understanding of disk chemistry and dynamics. Highlights include measurements of elemental and isotopic abundance ratios enabling us to trace the chemical evolution of disks, possible molecular signposts of hidden protoplanets, detections of increasingly complex and sometimes surprising molecules in disks, and maps unveiling how disks interact with their environments. These observations have also raised a number of new questions that can best be answered through collaborations between observers, theorists, and experimentalists.   

Interstellar Ice and the Organic Inventory of Protoplanetary Disks

To understand the origin of ices in the Solar System, we need to investigate the chemical and physical evolution of ices from where they form in cold molecular clouds through inclusion in the cometary regions of protoplanetary disks. I will give an overview of the latest observational work, in particular those done with the James Webb Space Telescope (JWST), that tracks the ice abundances and physical environment along this evolutionary path. JWST provides the moderate resolution spectra at high spatial resolution and wide field of view across the full 1-30 micron wavelength needed for a complete inventory of ices in dense molecular clouds, embedded protostars, and protoplanetary disks. In addition, the absorption band profiles reveal grain sizes, the degrees of ice porosity and crystallization. Results of a complementary survey of ices with the NASA/IRTF telescope in lines of sight too bright for JWST will also be presented.   

The icy landscape of planet-forming disks: new constraints from combined JWST and laboratory measurements

Planets form by accreting gas, dust, and ice within protoplanetary disks. The composition and distribution of ices across the disk strongly influences the chemical and physical outcomes of planet formation. Excitingly, with JWST it is now possible to probe the composition and mixing status of ices in disks for the first time. I will describe our recent progress retrieving disk ice abundances and mixing conditions using radiative transfer models along with a new library of laboratory spectra of ice mixtures. This is providing new insight into the formation conditions, thermal history, and distribution of icy planet-forming solids in disks.   

The chemical inventory of Hot corinos and protoplanetary disks: An observer's view

Hot corinos are hot (≥100 K), dense (≥10⁶ cm^-3) regions in solar-type protostars enriched of the so-called iCOMs, for interstellar complex organic molecules.

They were discovered at the beginning of 2000s towards the protostar IRAS16293-2422 (Ceccarelli et al. 2000; Cazaux et al. 2003; Ceccarelli 2004). After a decade-long frustrating search for other hot corinos ending up in adding only 3 additional ones, the advent of the IRAM/NOEMA and ALMA millimetre interferometer finally allowed to discover about two dozen hot corino in the last fee years (e.g. see the recent review by Ceccarelli et al. 2023). This has allowed to start studying their molecular content, particularly the iCOM abundances and their interdependence. That said, one has to keep in mind that, with the notable exception of IRAS16293-2422 (see Jorgensen et al. 2016; Manigand et al. 2021), only a bit more than a handful of iCOMs are detected in hot corinos: methanol, acetaldehyde, methyl formate, dimethyl ether, methyl cyanide, glycoaldehyde, ethanol, formamide.

In this talk, I will review what we know from an observational and chemical of view. I will especially discuss what we do not know yet and what is needed to progress in pur understanding of the organic content of hot corinos and possible inheritance from the solar protostellar phase.

REFERENCES

Cazaux S. et al., 2003 ApJL, 593, L51

Ceccarelli C. et al., 2000 A&A, 357, L9

Ceccarelli C., 2004 Star Formation in the ISM, vol. 323 of  Astr.Soc.PacificConf. (D. Johnstone and et al.), p. 195

Ceccarelli C., et al., 2023, in Inutsuka S., Aikawa Y., Muto T., Tomida K., Tamura M., eds, Astronomical Society of the Pacific Conference Series Vol. 534, Astronomical Society of the Pacific Conference Series. p. 379

Jørgensen J. K. et al., 2016 A&A, 595, A117

Manigand S. et al., 2021 A&A, 645, A5   

Modeling the Chemistry of Protoplanetary Disks

Planet-forming disks around young stars exhibit a rich diversity in their chemical content, with observations over the past decade using the Atacama Large Millimeter Array and now the James Webb Space Telescope showing emission signatures of the complex physical, dynamical and chemical processes that occur en route to planet formation. Chemical evolution begins in the cold, interstellar cloud material where species condense onto growing dust particles. Material then falls on to a disk and may get heated during the star formation phase with some or all of the ices being lost. As disks form planets and ultimately disperse, their material is subject to radial and vertical transport processes, impacting the radiation environment and the physical state (vapor or condensed phase) of different chemical species. State-of-the-art models consider irradiation by Ultraviolet and X-ray photons, grain surface chemistry and particle-gas dynamical interactions in a framework that solves for gas and particle evolution with time. Chemical species in the vapor phase and in the condensed phase (as ices on dust particles) are explicitly tracked, with the goal of understanding how the organic inventory available to forming planets is transformed from the cloud to disk. Planet formation may itself result in changes in the bulk chemical composition in disks by preferentially locking C,N,O-bearing species depending on where in the disk planets form. I will summarize recent efforts toward modeling these complex processes as disks form from interstellar cloud material and later evolve, and the implications for the composition of planets and other small bodies that form within, including those in our own Solar System.   

The Mystery Element: Tracing Phosphorus from Stars to Planets

Phosphorus is a key ingredient for the origin of life, being one of the critical six “NCHOPS” elements. It also is thought to play a role in the formation of rocky planets, and is found in solar system bodes as phosphides or phosphates. Phosphorus is thought to originate in supernovae, yet it remains elusive in the interstellar medium (ISM).  Observations of atomic transitions, the basic avenue for studying the elements in stellar photospheres and the general ISM, are problematic for phosphorus, as its lines lie in obscured regions of the electromagnetic spectrum. Consequently, the abundance of this element has only been measured in a small section of the Galaxy, and in 1% of all planet host stars. Observations of molecules containing phosphorus offer an alternative to characterizing the abundance and distribution of the elements. Here we report new measurements of phosphorus-containing molecules in the ISM, including the detection of PO and PN in molecular clouds at the Galaxy’s edge, and in Orion-KL, the best studied star-forming region. We also describe the current state of phosphorus chemistry in circumstellar envelopes, and present new ALMA images of PO and PN in the outflows of the hypergiant star VY CMa. In addition, new studies of phosphorus and its carriers in meteorite samples will be presented, including those from pristine carbonaceous chondrites. These combined data give insight into the history of phosphorus in the ISM and its possible evolution in protostellar disks and delivery to planet surfaces.   

SOFIA/EXES Survey of Gaseous Water in the Binary Hot Core W3 IRS 5

The formation and evolution of massive stars are not well understood because they are deeply embedded. As the disk photosphere of massive protostars serves as a pencil beam mid-infrared (MIR) continuum background, high-resolution absorption spectroscopy at MIR wavelengths provides a unique opportunity to probe the physical conditions and organic inventory of warm, dense gas in the innermost regions of massive star formation, and avoids beam dilution issues that submillimeter observations are subject to.

In this talk, we will present 5–8 μm spectroscopy (R~50,000) toward the hot core region associated with the massive young binary W3 IRS 5 using SOFIA/EXES. Hundreds of individual rovibrational absorption lines of water are identified, and three kinematic components are separated. These components are analyzed with rotation diagrams and curve-of-growth analyses to derive the temperature and the column density: two are over 500 K and one is ~190 K. Each component is linked to a CO component identified in IRTF/iSHELL observations (R=88,100) through their kinematic and temperature characteristics, and we discuss the chemical abundances along the line of sight based on the CO-to-H2O comparison. In the hot gas, all oxygen not locked in CO resides in water.  In the cold gas, we observe a substantial shortfall of oxygen and suggest that the potential carrier could be organics in ices. Finally, we discuss how our high-resolution SOFIA study will help the analysis of low spectral resolution JWST observations.   

Oral: A panel discussion on Hot Corinos and protoplanetary disks

Hot Corinos and the regions of planet formation, protoplanetary disks are reservoirs of organic molecules predicted by chemical models and confirmed by observations. The organic inventory of hot Corinos and protoplanetary disks will be discussed in a panel discussion. The broad topics of the discussion session will be the chemical inventory of Hot corinos and protopanetary disks: An observer’s view, a modelers’ view and an experimentalists’ view.

 

1. How can we enhance our understanding of the chemistry and physics of hot corinos and protoplanetary disks to improve the interpretation of observational data?

2. What are the primary challenges and opportunities in the field of molecular spectroscopic measurements and ab initio studies for hot corinos and protoplanetary disks?

3. How can we create an inclusive workplace environment that encompasses a broad range of perspectives and backgrounds?