Origin of Molecular Gas in Debris Discs

Determine whether molecular gas observed in debris discs is primordial material remaining from the protoplanetary phase or secondary gas generated by the release of ices during collisional cascades among planetesimals.

Background

Debris discs are remnants of protoplanetary systems where collisions among planetesimals produce dust and gas observable at submillimetre/millimetre wavelengths. Recent ALMA observations have detected molecular gas in many young debris discs.

The authors explicitly state that the provenance of this gas is unresolved: it could be a leftover from earlier protoplanetary stages or produced by ongoing collisional processes. Distinguishing these scenarios requires targeted observations and modeling of gas composition, distribution, and dynamics.

References

Questions remain over whether this gas is a remnant from the protoplanetary phase or produced from ices in the collisional cascade.

— 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 Debris Discs

Thus, the main remaining question is whether the adopted primordial-origin disk structure can reproduce the observed distribution.

— Thermochemical constraints on a primordial-origin of gas-rich debris disks  (2608.22781 - Mitani et al., 24 Aug 2026) in Section 5, Conclusions, item 3