Workshop on Young Solar Systems

4th Session of the Sant Cugat Forum on Astrophysics


April 18-22, 2016

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In addition to the Sant Cugat Forum, this Workshop is co-sponsored by:






Brief Outline of Scientific Aims and Scope:


The workshop's inter-disciplinary scope aims at bridging various communities: 1) cosmochemists, who study meteoritic samples from our own solar system, 2) (sub-) millimetre astronomers, who measure the distribution of dust and gas of star-forming regions and planet- forming discs and their physics (density, temperature, kinematics) and chemistry, 3) disc modellers, who describe the complex photo-chemical structure of parametric static discs to fit these to observation, 4) computational astrophysicists, who attempt to decipher the dynamical structure of magnetised gaseous discs, and the effects the resulting internal structure has on the aerodynamic re-distribution of embedded solids, 5) theoreticians in planet formation theory, who aim to piece it all together eventually arriving at a coherent holistic picture of the architectures of planetary systems discovered by 6) the exoplanet observers, who provide us with unprecedented samples of exoplanet worlds. Combining these diverse fields will allow us to shed light onto the riddles that we are currently confronted with, and will pave the way for a comprehensive understanding of the formation, evolution, and dynamics of young solar systems.


Full Scientific Rationale


We will aim at producing a comprehensive book that will provide an unprecedented reference within a rapidly developing interdisciplinary field within the natural sciences. All invited speakers, including SOC members, will be encouraged to contribute in their areas of expertise. The chapters of the book could result from individuals or small groups. The book will be edited by the organizers and published by Springer. Previous publications can be found at http://www.ice.csic.es/research/forum/Publications/Publications.html.


Understanding the formation and early evolution of our Solar System is one of the most fundamental goals within the natural sciences. Elucidating the sequence of events that lead to the formation of Sun-like stars along with their surrounding discs and assessing the circumstances favourable to the emergence of habitable worlds, will ultimately allow us to assess whether planetary system resembling our own are widespread in the Cosmos.


Since the first spectacular discoveries of exoplanets in the early nineties, our knowledge about these distant solar systems has slowly but steadily increased. Then, within a single day in 2014, the database of known extrasolar planets nearly doubled in size with a single data release of the prodigious Kepler space mission. Today, we know of several thousand exoplanet candidates. At the same time, the astrophysical community is becoming increasingly better at characterizing these systems, by measuring their orbital parameters, sizes and masses. Understanding how these exoplanetary systems form and evolve is worldwide one of the most active areas of astrophysics today.


The prolific new discoveries reveal a great diversity of planetary systems, challenging our current understanding of the processes responsible for planet formation. Before the advent of exoplanet discoveries, our knowledge about the assembly of the planets had almost entirely been derived from our own Solar System. Yet the classic dichotomous picture of comparatively inefficient terrestrial planet formation in the dry inner solar system, and the more efficient accumulation of solids into the cores of gas-giant planets outside the so-called ice line, is shaken by the absence of any such dichotomy in the Kepler exoplanet sample.


Planets form in the evolving remnants of the gaseous accretion discs that surround young stars. Therefore, in order to understand the processes that lead to planet formation and evolution, it is crucial to understand the physics that shape the evolution of these discs. In their role as planetary nurseries, such discs are of key importance to planet formation theory. Their dynamical, radiative and thermodynamic properties define in a crucial way the environment for the embedded solids: microscopic dust grains, small pebbles and km-sized planetesimals, in short, the entire inventory of building blocks involved in the formation of rocky planets.


The internal dynamics of the accretion disc, in turn, depends crucially on the influence of magnetic fields that couple to the tenuously ionised and low-density gaseous layers. Magnetic fields with strength of a fraction of a Gauss are known to have threaded the early protosolar nebula. Such fields are by the paleomagnetic record of chondritic material found within meteorites. Polarised dust emission promises to allow us to detect and image the magnetic field geometry of protoplanetary discs in the very near future. From theoretical considerations, we know that, being comparatively cold and dense, the ionisation state of the disc plasma is dominated by external radiation. The nature of these radiation sources, leads to a layered vertical structure. This classic ‘dead-zone’ picture is now turned upside-down by previously ignored microphysical effects. For instance, ambipolar diffusion is predicted to dominate in the tenuous hot corona of the disc. It is expected that parts of the disc will thus be stabilised and a so-called magneto-centrifugal wind will be launched.


These prolific theoretical and computational advances can now be confronted with ground- breaking astronomical observations in the (sub-) millimetre band. The unprecedented resolution and sensitivity of the Atacama Large Millimeter Array (ALMA) is now opening up an entirely new perspective on the formation and early evolution of young solar systems. ALMA images have revealed fascinating structures already: concentric dust rings, lopsided structures, pronounced asymmetries, and even spiral arms. Taken together with data at other wavelengths, for instance in the infrared band, these observations provide a plethora of information about the dynamical processes occurring within protostellar discs. The access to these revolutionary new observational data, in turn, provides fertile grounds for theoretical and numerical developments in this field. The new high-fidelity observations of protostellar discs uncover a fascinating level of details, pointing towards new pathways to overcome long-standing barriers in our understanding of how the solid contaminants of young protostellar discs are ultimately assembled into terrestrial planets, and the rocky cores of gas-giant planets, putting us on the verge of witnessing the earliest evolution of new-born planetary systems.


The workshop's inter-disciplinary scope aims at bridging the various communities: 1) cosmochemists, who study meteoritic samples from our own solar system, 2) (sub-) millimetre astronomers, who measure the distribution of dust and gas of star-forming regions and planet- forming discs and their physics (density, temperature, kinematics) and chemistry, 3) disc modellers, who describe the complex photo-chemical structure of parametric static discs to fit these to observation, 4) computational astrophysicists, who attempt to decipher the dynamical structure of magnetised gaseous discs, and the effects the resulting internal structure has on the aerodynamic re-distribution of embedded solids, 5) theoreticians in planet formation theory, who aim to piece it all together eventually arriving at a coherent holistic picture of the architectures of planetary systems discovered by 6) the exoplanet observers, who provide us with unprecedented samples of exoplanet worlds. Combining these diverse fields will allow us to shed light onto the riddles that we are currently confronted with, and will pave the way for a comprehensive understanding of the formation, evolution, and dynamics of young solar systems.


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