Accurate Measurement of Protoplanetary Disc Masses

Establish robust, empirically validated methodologies to measure the masses of protoplanetary discs around young stars using molecular gas tracers and submillimetre dust continuum emission, quantifying uncertainties and resolving the current discrepancy between disc mass estimates and exoplanet population requirements.

Background

The paper highlights that protoplanetary discs are central to planet formation studies and that over the last decade ALMA has revolutionized high-resolution disc imaging. Despite this progress, reliably determining disc masses remains difficult, which underpins the so-called “missing mass” problem: disc mass estimates often appear insufficient to form the observed exoplanet population.

The authors note that both gas-tracer-based and dust-continuum-based approaches yield inconsistent or inadequate mass estimates, motivating deeper, systematic multi-line and continuum observations, and improved modeling frameworks to overcome this unresolved issue.

References

Accurately measuring the masses of protostellar discs, whether using molecular gas tracers or dust continuum emission, remains an unsolved problem.

— The UK Submillimetre and Millimetre Astronomy Roadmap 2024  (2408.12975 - Pattle et al., 2024) in Section 3.1 Formation of planets and the potential for life — Subsubsection Protoplanetary Discs

However, although throughout this work we adopt the scale height--disc mass relation using the aspect ratio measured relative to the central star, it remains unclear how the dust and gas surface density distributions, such as the dust rings and gaps observed in J16120, affect the disc emission surface and, consequently, the inferred disc gas mass.

— Dust Substructures and Line Perturbations driven by a Forming Planet in J16120  (2609.05366 - Sierra et al., 4 Sep 2026) in Section 2.5, 'Gas mass'