Ariel Mission

Maximizing Ariel’s Survey Leverage For Population-Level Studies Of Exoplanets

By Keith Cowing
Status Report
astro-ph.EP
June 10, 2025
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Maximizing Ariel’s Survey Leverage For Population-Level Studies Of Exoplanets
Number of planets observed in a notional 3 year Ariel transit survey. The white star highlights the best overall leverage. The one-room schoolhouse yields the most targets, with other scenarios resulting in 30–60% fewer planets. — astro-ph.EP

ESA’s Ariel mission will be uniquely suited to performing population-level studies of exoplanets. Most of these studies consist of quantifying trends between an Ariel-measured quantity, y, and an a priori planetary property, x; for example, atmospheric metallicity as inferred from Ariel transit spectroscopy vs. planetary radius.

We define the leverage of a survey with N targets as L = sqrt(N)stdev(x) and show that it quantitatively predicts the precision of population-level trends. The target selection challenge of Ariel can therefore be summarized as maximizing L along some axes of diversity for a given cumulative observing time.

To this end, we consider different schemes to select the mission reference sample for a notional three year transit spectroscopy survey with Ariel. We divide the exoplanets in the mission candidate sample into logarithmic classes based on radius, equilibrium temperature, and host star temperature.

We then construct a target list by cyclically choosing the easiest remaining target in each class. We find that in many cases the leverage is greatest for a single class: dividing planets into multiple classes increases the diversity of targets, but reduces their numbers.

The leverage on a single axis of diversity can be increased by dividing that axis into many planet classes, but this sacrifices leverage along other axes of diversity. We conclude that a modest number of classes, possibly only one, should be defined when selecting Ariel targets.

Lastly, we note that the statistical leverage of the Ariel transit survey would be significantly increased if current candidate planets were confirmed. This highlights the urgency of vetting and confirming the easiest transmission and emission spectroscopy targets in the Ariel mission candidate sample.

Nicolas B. Cowan, Ben Coull-Neveu

Comments: 7 pages, 6 figures, submitted to the Open Journal of Astrophysics
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM)
Cite as: arXiv:2506.06429 [astro-ph.EP] (or arXiv:2506.06429v1 [astro-ph.EP] for this version)
https://doi.org/10.48550/arXiv.2506.06429
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Submission history
From: Nicolas Cowan
[v1] Fri, 6 Jun 2025 18:00:02 UTC (3,079 KB)
https://arxiv.org/abs/2506.06429

Astrobiology,

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻