GAP Workshop

2025-03-15

Captain’s Log: Stardate 60748.5

This week, I embarked on a new scientific voyage, attending the Gas Accretion in Planet Formation (GAP) workshop, held at the Max Planck Institute for Astronomy (MPIA) in Heidelberg, Germany. This marks my first trip abroad for a conference since the COVID-19 pandemic, and given the current flight restrictions over Russia, the journey took nearly 15 hours to Frankfurt Airport, followed by another hour-long train ride to Heidelberg.

Heidelberg is a small yet historic town, renowned for its well-preserved medieval architecture and academic legacy. Among its many landmarks, Heidelberg Castle stands as an iconic symbol, perched majestically on the mountainside—a sight both imposing and inspiring.

Figure 1: The Heidelberg Castle under the full moon

MPIA, situated at the highest point of Heidelberg, is a stunning location for astronomical research. In the heart of the institute, suspended elegantly in the central stairwell, is a striking vertical structure composed of illuminated cubes, each adorned with breathtaking images of the cosmos. I took the liberty of naming it the “Pillar of the Cosmos.” This cascading display of nebulae, galaxies, and celestial phenomena transforms the space into a journey through the universe, an inspiring centerpiece fitting for a place dedicated to unraveling the mysteries of the cosmos.

Figure 2: the “Pillar of the Cosmmos” in MPIA main building

Mission Briefing: Key Research Topics

Over the course of three days, experts gathered to discuss circumplanetary disks (CPDs), accretion processes, and planet formation, delving into observational breakthroughs, theoretical models, and open questions on how planets and moons emerge within protoplanetary environments.

Observing and Detecting Protoplanets & CPDs

Unveiling Embedded Protoplanets:
- C. Swastik presented follow-up observations with the Enhanced Resolution Imaging Spectrograph (ERIS), targeting systems such as HD 143006, J1604, J1842, V4046 Sgr, J1615, and J1852. These systems exhibit highly structured gas distributions, as traced by CO emission in the exoALMA project.
H-alpha Imaging:
- Lillian Jiang discussed deep HST H-alpha imaging surveys to trace accretion signatures in IC 348, utilizing deep learning techniques to distinguish cosmic rays from planetary signals.

Accretion Processes in Planet Formation

Accretion Mechanisms in Young Stars & Planets

A. Thanathibodee reviewed magnetospheric accretion in young stars, raising key questions on how protoplanetary magnetic fields form and interact with their disks.
J. Weber examined the role of MHD wind-driven disk evolution, highlighting its effects on planet migration and accretion.
Nick Choksi discussed the direct imaging of runaway accretion, shedding light on how young gas giants rapidly accumulate mass.

Hydrogen Line Diagnostics

K. Follette explored the use of Balmer lines as tracers for detecting accreting protoplanets, highlighting how these signals distinguish accreting vs. non-accreting objects.
Joshua Blackman presented early results from the RISTRETTO spectrograph, tracking protoplanetary H-alpha emissions.

Planet-Disk Interactions

Yaping Li examined accretion and migration patterns, showing that:
- Highly viscous disks enable outward migration, while
- Low-viscosity disks still favor inward migration.
Mario Flock presented 3D MHD simulations, demonstrating how the inner dead zone edge traps solid material, fostering rocky planet formation.

Chemical Composition of Planets and Disks

Comparing CPD and Protoplanetary Disk Chemistry:
- Gabriele Cugno analyzed chemical signatures of accreting gas giants, detecting C₂H₂, HCN, CO₂, and C₆H₆ in the spectrum of CT Cha B.
- Luna Rampinelli explored HCN fractionation profiles, providing insight into chemical links between planets and their disks.
Planetary Evolution and the HR Diagram Analogy:
- Benedikt Gottstein presented models illustrating planetary luminosity-temperature evolution, establishing an L-T track analogous to the HR diagram used for stellar classification.

Dynamical Influences on Planet Formation

Circumbinary & Multiple Star Systems

Ian Rabago analyzed the dynamics of circum-multiple star disks, revealing how binary truncation can create multiple disk breaks and influence planet formation.

Star Cluster Encounters & Planetary System Evolution

Kai Wu & Francesco Flammini Dotti investigated how stellar encounters within 1000 AU significantly impact planetary orbits, leading to planetary ejections and migration events.

Final Reflections

This conference underscored both the progress and challenges in understanding the formation and evolution of planets and their surrounding disks. While detecting protoplanets remains difficult, advances in hydrogen line imaging, infrared spectroscopy, and numerical simulations are pushing the limits of what we can observe and model.

Despite the wealth of new data, fundamental questions remain, such as:

What determines the final mass of a gas giant?
How strong are the magnetic fields of young protoplanets?
Do planets accrete steadily or undergo episodic accretion events?

One thing is certain—our journey toward understanding planetary origins is far from over. As we refine observational techniques, improve simulations, and deepen our knowledge of planetary chemistry, we will continue to unravel the mysteries of circumplanetary disks and planetary evolution.

Beyond the scientific discussions, this meeting was also a chance to reconnect with many familiar faces in the field. The insights, debates, and collaborations that emerged during this workshop have been invaluable, and I leave with new ideas and perspectives to explore in the coming months.

Captain out.