The Rocky Worlds DDT Program will use JWST to search for atmospheres around a dozen nearby M-dwarf exoplanets while using HST to characterize activity in the host stars. Over the past month, community members have provided feedback on a provisional set of targets — the Targets Under Consideration (TUC) list. Based on that feedback, the Science Advisory Council (SAC), together with the Leads of the Core Implementation Team (CIT), have identified an initial set of targets for JWST MIRI 15 µm photometry:

• LTT 1445 A c (11 eclipses)
• GJ 3929 b (15 eclipses)

Further targets will be selected after the results of the JWST Cycle 4 Call for Proposals are published in March 2025. Proposers may not apply for Cycle 4 Archival Research programs to analyze these data, as STScI cannot guarantee that all data will be in the archive when Cycle 4 begins. However, the SAC and CIT leads would like to encourage the community to consider JWST Cycle 4 proposals for complementary and supplementary observations of these targets or Theory programs. The standard JWST Duplication Policies apply. Additional exoplanet targets will be selected after the results from the Cycle 4 Telescope Allocation Committee are known. The DD program will be structured to avoid duplicating Cycle 4 General Observers programs.

We also highlight the importance of ancillary observations from ground and space-based facilities to better characterize these stellar systems and help prioritize future target selection. In particular, the following observations are critical for all targets in the TUC, specially those with high Priority Metrics and/or radii < 1.6 R_Earth:

• Precise radial-velocity monitoring: This is crucial to constrain the rocky nature of the planets via their bulk density and the planetary escape velocity (mass), which is required to match targets against the “Cosmic Shoreline” (and to calculate the Priority Metric). In addition, they set important constraints on orbital eccentricities that enable better scheduling of secondary eclipse observations.
• Stellar activity measurements: These include emission line measurements (H-alpha, Ca II H&K) and/or rotation measurements that set constraints on the radiation environment and, in some cases, the likely age of the system.
• Precise X-ray observations: Combined with HST UV observations, X-ray observations characterize the high-energy environment, constraining the integrated XUV instellation for the exoplanet.

For further feedback or questions on the TUC, please use the Rocky Worlds DDT’s TUC Feedback Google form. For general questions and inquiries about the Rocky Worlds DDT program, please use this email.