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Exploring Synergies between Twinkle and Ariel: a Pilot Study

Andrea Bocchieri, Luke Booth, Lorenzo V. Mugnai

TL;DR

This study probes potential synergies between the Twinkle and Ariel exoplanet atmosphere missions by simulating a small, Twinkle-selected set of cool gaseous planets and performing TauREx 3-based retrievals across four forward-model scenarios. It uses representative radiometric noise budgets, Tiered observing strategies, and self-retrievals to assess whether Twinkle data can inform Ariel's target prioritization and observing plans. Across fixed- and equilibrium-chemistry models, atmospheric parameters are recovered within $1-\\sigma$ of the inputs, with Ariel typically yielding tighter constraints, demonstrating robust cross-mission consistency and a viable precursor role for Twinkle. The findings suggest that leveraging Twinkle as a precursor could optimize Ariel's survey efficiency and expand the exoplanet atmospheric catalog, while emphasizing the need to account for systematics and final target lists in future work.

Abstract

Launching in 2027 and 2029, respectively, Twinkle and Ariel will conduct the first large-scale homogeneous spectroscopic surveys of the atmospheres of hundreds of diverse exoplanets. This will fundamentally transition the field to an era of population-level characterisation. In this pilot study, we aim to explore possible synergies between Twinkle and Ariel to determine for instance whether prior Twinkle observations can substantially inform the target selection and observing strategy of Ariel. This study primarily aims to encourage further investigation by both consortium communities by showing what a potential scientific synergy would look like on a promising scientific case that requires further exploration. For this aim, we select a small subset of "cool" planets that are also particularly well-suited to be observed by Twinkle and therefore Ariel. By using representative noise estimates for both missions, we compute the number of visits required for an observation. Then, we simulate and retrieve transmission spectra of each target, assuming gaseous, H2/He-dominated atmospheres and various atmospheric models. For all candidates, we find that atmospheric parameters are generally retrieved well within 1-sigma to input values, with Ariel typically achieving tighter constraints. We demonstrate that for a small subset of cool gaseous planets, exploitable synergies exist between Twinkle and Ariel observations and Twinkle may very well provide a vantage point to plan Ariel observations. The true extent of the potential synergies, far beyond our considered sample, will be determined by the final target lists. Once Twinkle is operational and its performance is known, it could reliably inform Ariel's target prioritization and Ariel's capabilities which are already well-established can help define optimal targets and observational approaches for Twinkle.

Exploring Synergies between Twinkle and Ariel: a Pilot Study

TL;DR

This study probes potential synergies between the Twinkle and Ariel exoplanet atmosphere missions by simulating a small, Twinkle-selected set of cool gaseous planets and performing TauREx 3-based retrievals across four forward-model scenarios. It uses representative radiometric noise budgets, Tiered observing strategies, and self-retrievals to assess whether Twinkle data can inform Ariel's target prioritization and observing plans. Across fixed- and equilibrium-chemistry models, atmospheric parameters are recovered within of the inputs, with Ariel typically yielding tighter constraints, demonstrating robust cross-mission consistency and a viable precursor role for Twinkle. The findings suggest that leveraging Twinkle as a precursor could optimize Ariel's survey efficiency and expand the exoplanet atmospheric catalog, while emphasizing the need to account for systematics and final target lists in future work.

Abstract

Launching in 2027 and 2029, respectively, Twinkle and Ariel will conduct the first large-scale homogeneous spectroscopic surveys of the atmospheres of hundreds of diverse exoplanets. This will fundamentally transition the field to an era of population-level characterisation. In this pilot study, we aim to explore possible synergies between Twinkle and Ariel to determine for instance whether prior Twinkle observations can substantially inform the target selection and observing strategy of Ariel. This study primarily aims to encourage further investigation by both consortium communities by showing what a potential scientific synergy would look like on a promising scientific case that requires further exploration. For this aim, we select a small subset of "cool" planets that are also particularly well-suited to be observed by Twinkle and therefore Ariel. By using representative noise estimates for both missions, we compute the number of visits required for an observation. Then, we simulate and retrieve transmission spectra of each target, assuming gaseous, H2/He-dominated atmospheres and various atmospheric models. For all candidates, we find that atmospheric parameters are generally retrieved well within 1-sigma to input values, with Ariel typically achieving tighter constraints. We demonstrate that for a small subset of cool gaseous planets, exploitable synergies exist between Twinkle and Ariel observations and Twinkle may very well provide a vantage point to plan Ariel observations. The true extent of the potential synergies, far beyond our considered sample, will be determined by the final target lists. Once Twinkle is operational and its performance is known, it could reliably inform Ariel's target prioritization and Ariel's capabilities which are already well-established can help define optimal targets and observational approaches for Twinkle.
Paper Structure (14 sections, 5 figures, 6 tables)

This paper contains 14 sections, 5 figures, 6 tables.

Table of Contents

  1. Introduction
  2. Ariel
  3. Twinkle
  4. Science Case
  5. Methods
  6. Target Selection
  7. Noise estimates
  8. Forward Models
  9. Retrievals
  10. Results
  11. Fixed Chemistry Models
  12. Equilibrium Chemistry Models
  13. Discussion
  14. Conclusions

Figures (5)

  • Figure 1: Expected noise estimates for a transit observation (an observation is the combined set of visits required to achieve the S/N threshold, see text) conducted with Twinkle (blue) and Ariel (orange: Tier 2; green: Tier 3). The data are binned to the corresponding spectral grids on the horizontal axis.
  • Figure 2: O-C results for the retrieved parameters w.r.t. their ground truths in model 1, which consists of a constant-with-altitude chemistry and isothermal T-P profile. Values for each planet are displayed as the retrieved median value minus forward-model input value, with errorbars spanning 16th-84th quantiles shown. The lower right panel shows CO posterior distributions for WASP-69 b (left) and WASP-107 b (right), singled out from the rest of the sample for visual purposes. This showcases an example of different results between Ariel and Twinkle: in Twinkle's case, only upper-limits can be obtained due to the unconstrained posterior distribution for both planets, while Ariel is able to constrain the abundance of CO within 1 dex only for WASP-107 b.
  • Figure 3: Retrieved spectra (solid lines with shaded 1- and 2-$\sigma$ confidence intervals) obtained from fitting the observed spectra (data points with errorbars) given each simulated instrument mode (blue: Twinkle, orange: Ariel Tier 2, and green: Ariel Tier 3). The results for all planets in this study are shown, in model 1: cloud-free atmosphere with constant-with-altitude chemistry and isothermal T-P profile. Note: an arbitrary vertical offset between each spectrum is imposed for better visual representation.
  • Figure 4: O-C results for the retrieved parameters w.r.t. their ground truths in model 3, a cloud-free atmosphere under equilibrium chemistry. Values are displayed for each planet as retrieved median value minus forward-model input value, with errorbars spanning 16th-84th quantiles ranges.
  • Figure 5: WASP-69 b corner plot for cloud-free, equilibrium chemistry atmospheric retrievals with an isothermal T-P profile (model 3). Contour plots and posterior distributions are shown for each simulated instrument mode (blue: Twinkle, orange: Ariel Tier 2 and green: Ariel Tier 3), with black lines showing forward-model input truth values.