Detecting Exoplanetary Rings with Roman CGI Reflected Light Phase Curve Observations
Abstract
The Nancy Grace Roman Space Telescope's Coronagraph Instrument (CGI) will provide the first opportunity to directly detect mature giant exoplanets in reflected light. However, most known radial-velocity planets lie near CGI's sensitivity limit. In contrast, Saturn-like rings around these planets may be much more accessible: our models show that rings can outshine their host planets by one to two orders of magnitude or more, making them easier to detect than the planets themselves. However, because the planet and rings would be unresolved in reflected light, unrecognized rings could lead to misinterpretation of the planet's intrinsic brightness and physical properties. To disentangle these blended signals, we model reflected-light phase curves of ringed and ringless planets. Ring systems can produce a distinctive phase-curve morphology, often with four extrema rather than the two expected for unringed planets, enabling robust confirmation with multi-epoch CGI observations. We develop an analytical framework for ringed-planet phase curves using a modern, self-consistent coordinate system and use it to illustrate phase curves for a range of ring configurations. We then simulate observations of ε Eridani b (3.5 AU, 1 MJup), a prime initial CGI target, with a Saturn-like ring system. These simulations show that such a configuration would be detectable and suggest that rings may expand the pool of viable CGI targets to planets previously considered beyond reach. We conclude that CGI is poised to provide the first observational constraints on the prevalence of Saturn-like rings around giant exoplanets.
Related
- The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems VIII: patchy forsterite and enstatite clouds in the atmosphere of VHS 1256 b, retrieval lessons learned and outlook to the future
- Probing Exoplanetary Rings with Asterodensity Profiling: A PhotoRing Analysis of Kepler-51
- Detecting White Dwarf Exoplanets in the Roman Era
- The JWST Early Release Science Program for Direct Observations of Exoplanetary Systems IX: A Multi-Wavelength Framework for Source Characterization in JWST Coronagraphic Imaging of the HIP 65426 System
- Ultraviolet Reflected-Light Spectroscopy of Modern Earth Analogs with Starshade Observations
BibTeX
@misc{lane2026detecting,
title = {{Detecting Exoplanetary Rings with Roman CGI Reflected Light Phase Curve Observations}},
author = {Elizabeth Lane and Mary Anne Limbach and Logan Pearce and Samantha Hasler and Alexandra Z. Greenbaum},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.23835},
eprint = {2610.23835},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.23835},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Detecting Exoplanetary Rings with Roman CGI Reflected Light Phase Curve Observations
AU - Elizabeth Lane
AU - Mary Anne Limbach
AU - Logan Pearce
AU - Samantha Hasler
AU - Alexandra Z. Greenbaum
PY - 2026
DA - 2026/10/16
PB - arXiv
DO - 10.48550/arxiv.2610.23835
UR - https://arxiv.org/abs/2610.23835
AB - The Nancy Grace Roman Space Telescope's Coronagraph Instrument (CGI) will provide the first opportunity to directly detect mature giant exoplanets in reflected light. However, most known radial-velocity planets lie near CGI's sensitivity limit. In contrast, Saturn-like rings around these planets may be much more accessible: our models show that rings can outshine their host planets by one to two orders of magnitude or more, making them easier to detect than the planets themselves. However, because the planet and rings would be unresolved in reflected light, unrecognized rings could lead to misinterpretation of the planet's intrinsic brightness and physical properties. To disentangle these blended signals, we model reflected-light phase curves of ringed and ringless planets. Ring systems can produce a distinctive phase-curve morphology, often with four extrema rather than the two expected for unringed planets, enabling robust confirmation with multi-epoch CGI observations. We develop an analytical framework for ringed-planet phase curves using a modern, self-consistent coordinate system and use it to illustrate phase curves for a range of ring configurations. We then simulate observations of ε Eridani b (3.5 AU, 1 M_Jup), a prime initial CGI target, with a Saturn-like ring system. These simulations show that such a configuration would be detectable and suggest that rings may expand the pool of viable CGI targets to planets previously considered beyond reach. We conclude that CGI is poised to provide the first observational constraints on the prevalence of Saturn-like rings around giant exoplanets.
ER -