Planetesimals -- asteroids and comets -- form in dust- and gas-rich protoplanetary discs. These planetesimals are the building blocks of planets, and are believed to form in belts close to ice lines within protoplanetary discs. The protoplanetary disc eventually dissipates, but the planetesimal belts remain around their host star for its entire lifespan. Collisions between planetesimals produce detectable dust, and in some cases gas, hence these long lived planetesimal belts are called "debris discs".

Observations of both planetary and planetesimal (disc) components around nearby stars have revealed a diverse range of architectures. The vast majority of these systems are quite unlike the Solar system, and much evidence points to the continuation, or aftermath, of violent dynamical processes. The pathways by which these systems evolve and the information encoded in the composition and dynamics of small bodies are both poorly understood. To better comprehend the formation and evolution of planetary systems, understanding disc-planet interactions is essential.

A multi-wavelength, multi-instrument approach is necessary to characterize these systems and address the outstanding issues. At optical and near-infrared wavelengths, using HST, GPI and SPHERE, we trace the smallest dust grains through scattered light (both total intensity and polarization), revealing dust grain size and composition. At mid-to-far infrared wavelengths, with Spitzer, SOFIA and JWST, we trace micrometre-sized grains affected by transport processes. At radio wavelengths, with ALMA and JCMT, we observe millimetre-sized grains which trace the location of the dust-producing planetesimals and detect gaseous species (e.g. CO, neutral carbon).

Recent results have challenged both the modelling methods used to interpret available observations and our understanding of disc evolution as a steady-state process. Current models struggle to self-consistently replicate both the scattered light and continuum emission from debris discs; this problem has only been exacerbated with the addition of polarimetric information. High cadence photometry and high resolution spectroscopy tracing actively colliding debris and evaporating exocomets has expanded the study of debris discs into a time-dependent phenomenon.

Molecular gas originating from planetesimals (rather than being primordial) is ubiquitous in bright debris disc systems. Understanding its generation and the implications for the planetary system as a whole is of prime importance. For instance, it has recently been suggested that this gas influences atmospheres of planets and their habitability. It may also be used to find relatively low mass planets by tracing deviations from Keplerian motion of the gas disc. Furthermore, it can help determine the abundances of volatiles in planetesimals; this would reveal the compositions of the building blocks of planets, and therefore of the planets themselves.

Now is the right time to bring together experts in theory and modelling (both radiative transfer and dynamics/collisions) within the context of available (and expected) observations to promote collaborative efforts and address the questions outlined above. Expanding our capabilities as a community to meaningfully interpret new results can best be addressed in the forum provided by EAS. Here we will benefit from the broad audience the EAS attracts, and interact with researchers from related fields such as exoplanets and protoplanetary discs.

Programme

Times are CEST (UTC +2)

Monday 28th June:

Tuesday 29th June:

Invited speakers

• Jessica Rigley University of Cambridge
• Virginie Faramaz NASA Jet Propulsion Laboratory
• Florian Kirchschlager University College London
• Johan Olofsson Universidad de Valparaíso
• Isabel Rebollido Space Telescope Science Institute
• Bin Ren Caltech

Scientific organisers

• Élodie Choquet (co-Chair, elodie.choquet "at" lam.fr) AMU - LAM, Marseille, France
• Quentin Kral (quentin.kral "at" obspm.fr) LESIA - Paris Observatory, France
• Jonathan Marshall (Chair, jmarshall "at" asiaa.sinica.edu.tw) ASIAA, Taipei, Taiwan
• Luca Matrà (co-Chair, luca.matra "at "nuigalway.ie) National University of Ireland Galway
• Julien Milli (julien.milli "at" univ-grenoble-alpes.fr) IPAG, Université Grenoble Alpes, France
• Nicole Pawellek (pawellek "at" ast.cam.ac.uk) IoA, University of Cambridge, Cambridge, UK
• Sascha Zeegers (szeegers "at" asiaa.sinica.edu.tw) ASIAA, Taipei, Taiwan

Contact