Targets Under Consideration (TUC)

The following Targets Under Consideration (TUC) have been selected, based on the criteria outlined by the Strategic Exoplanet Initiatives Working Group, as a starting point for collecting community input on the potential target list for the Rocky Worlds DDT program. These are objects that are believed to be rocky orbiting small, M-dwarf stars. The Core Implementation Team and the Science Advisory Committee are soliciting feedback on this target list — for more information on this feedback, please provide this feedback by April 4th, 2025 in this Google Form.

A graphical depiction of the current TUC in the context of Zahnle & Catling (2017)'s "Cosmic Shoreline" is presented below in Figure 1; the same targets are presented below in Table 1, which in turn contains details about possible rankings of the table. Note this is a dynamic table and can be re-ordered using any of the properties in the table. Previous versions of the TUC can be found below for comparison.

The overall parameters of the targets of the most up-to-date TUC (TUC v.1.0) below correspond to publicly available properties. However, the Priority Metrics have been calculated for some targets using input from precise RV characterization performed by teams around the world. Among these targets are:

• TOI-771 b — THIRSTEE team in prep., for questions, contact Rafael Luque (rluque@uchicago.edu) and Palle (epalle@iac.es).
• TOI-198 b — mass in the TUC is the mass measured by the MAROON-X team; for questions, contact Madison Brady & Jacob Bean (mtbrady@uchicago.edu, jacobbean@uchicago.edu). 
• GJ 3929 b — mass in the TUC is the mass measured by the MAROON-X team; for questions, contact Madison Brady & Jacob Bean (mtbrady@uchicago.edu, jacobbean@uchicago.edu). 

1.1. TUC Version 1.0 (September 2024)

Figure 1. Targets Under Consideration (TUC) in the escape velocity (in km/s) versus the estimated relative cummulative XUV irradiation (in units of Earth's estimated value; estimated following Zahnle & Catling (2017)) are represented as grey points. Orange points represent selected Rocky Worlds DDT targets for which 15 um MIRI secondary eclipse photometry will be obtained. Values with added markers represent planets with precise mass constraints (better than 20% mass measurement errors)— see below for the actual table. Note the axes are logarithmic. The "Cosmic Shoreline", which in the Solar System seems to divide atmosphere from atmosphereless bodies and as described in Zahnle & Catling (2017) follows a I ~ V_esc⁴  relationship is presented as the blue line. Note this latter does not account for the fact that the objects plotted in grey orbit M-dwarf stars with different inherent properties — something that is expected to be taken into account when selecting a final target list. A "Priority Metric" is graphically shown, and represents the distance from a planet to the Cosmic Shoreline. Colored circles with black edges represent the Earth (blue), Venus (orange), Mars (red) and Mercury (yellow) in this diagram.

Table 1. Targets Under Consideration (TUC) for the Rocky Worlds DDT program (actual targets marked in bold orange below).

*: The Priority Metric calculated here is used to provide an initial ranking to each target in the TUC. Targets towards the top of this list (with a higher Priority Metric) are the top targets being considered for now. Rankings based on calculated equilibrium temperature and/or orbital period are also being considered; details such as the quality of orbital and physical parameters will also be taken into account for the final ranking. The Priority Metric is estimated by first calculating the Escape Velocity (V_esc) and Relative Cummulative XUV Irradiation (I_XUV; following Zahnle & Catling, 2017) of each exoplanet in the list, and then estimating the distance from this point to the Cosmic Shoreline I ~ V_esc⁴ presented in Zahnle & Catling (2017). Values to the left of the Cosmic Shoreline are given negative distances.

**: Exoplanet has no mass constraint or poor mass constraint; mass has been estimated with the spright formalism following Parviainen, Luque, and Palle, 2023.

^Ψ: Target already in at least one JWST program; observing mode(s) may or may not include emission photometry at 15 um.

1.2. TUC Version 0.0 (August 2024)

The below plots and table correspond to the first TUC version published by the Rocky Worlds CIT Leads in August 2024. Through community input, this plot and tables have been updated on TUC versions > 1.0. The most important change refers to the change in the definition of the Priority Metric from a linear scale in the current instellation observed on the planet (plot and table below, i.e., TUC v.0.0) to the estimated, cummulative integrated XUV irradiation (TUC v.1.0 and up). 

Figure 2. Targets Under Consideration (TUC) in the escape velocity (in km/s) versus planetary instellation (in units of Earth's instellation) are represented as grey points with added name markers — see below for the actual table. Note the axes are logarithmic. The "Cosmic Shoreline", which in the Solar System seems to divide atmosphere from atmosphereless bodies and as described in Zahnle & Catling (2017) follows a I ~ V_esc⁴  relationship is presented as the blue line. Note this latter does not account for the fact that the objects plotted in grey orbit M-dwarf stars with different inherent properties — something that is expected to be taken into account when selecting a final target list. A "Priority Metric" is graphically shown for TOI-1634 b, and represents the distance from a planet to the Cosmic Shoreline (see below for details). Colored circles with black edges represent the Earth (blue), Venus (orange), Mars (red) and Mercury (yellow) in this diagram.  

Table 2. Targets Under Consideration (TUC) for the Rocky Worlds DDT program.

*: The Priority Metric calculated here is used to provide an initial ranking to each target in the TUC. Targets towards the top of this list (with a higher Priority Metric) are the top targets being considered for now. Rankings based on calculated equilibrium temperature and/or orbital period are also being considered; details such as the quality of orbital and physical parameters will also be taken into account for the final ranking. The Priority Metric is estimated by first calculating the Escape Velocity (V_esc) and Instellation (I) of each exoplanet in the list, and then estimating the distance from this point to the Cosmic Shoreline I ~ V_esc⁴ presented in Zahnle & Catling (2017). Values to the left of the Cosmic Shoreline are given negative distances.

**: Exoplanet has no mass constraint or poor mass constraint; mass has been estimated via the Chen & Kipping (2017) formalism.

^Ψ: Target already in at least one JWST program; observing mode(s) may or may not include emission photometry at 15 um.