Dynamically determine the mass of candidate planet HR 8799 f

Determine the dynamical mass of candidate planet HR 8799 f using additional astrometric and radial-velocity data, because the available JWST/NIRISS Aperture Masking Interferometry epoch is insufficient for a reliable mass measurement.

Background

The paper reports a tentative candidate fifth planet, HR 8799 f, based primarily on one JWST/NIRISS Aperture Masking Interferometry astrometric measurement. The authors combine this measurement with relative astrometry of the four established planets and absolute Gaia and Hipparcos astrometry, but find that the candidate's mass remains poorly constrained.

The fitted mass is lower than masses suggested by previous dynamical stability analyses, while the authors note that the imminent Gaia DR4 release and continued monitoring could provide stronger constraints. A comprehensive future dynamical analysis should jointly model absolute astrometry, relative astrometry, and radial-velocity measurements.

References

While we were unable to dynamically determine the mass of candidate~f given the data from the \ac{ami} epoch, the imminent release of Gaia DR4 will put significantly better constraints on the stellar reflex motion of the system, thus allowing us to constrain the dynamics of the system to even higher accuracy.

— A Candidate Innermost Fifth Planet In the HR 8799 System Revealed By JWST NIRISS Aperture Masking Interferometry  (2609.10507 - Nguyen et al., 9 Sep 2026) in Section 6, Discussion & Conclusion