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Transiting exoplanets as the immediate future for population-level atmospheric science

Joanna K. Barstow, Hannah R. Wakeford, Sarah L. Casewell, Vatsal Panwar

TL;DR

This paper argues that population-level atmospheric characterization of transiting exoplanets is the immediate priority for exoplanetary atmospheric science, enabled by the large and diverse transiting planet sample. It outlines a UK-led strategic approach combining broad-wavelength, high-stability observations with laboratory, modeling, and computational infrastructure, and connects these efforts to future ESA and international missions. Key contributions include a concrete vision for UV–IR coverage, the role of phase curves for both transiting and near-edge-on non-transiting planets, and a roadmap that bridges JWST/Ariel with later missions such as HWO. The work underlines the scientific and strategic value of building the capabilities to study hundreds of atmospheres, linking atmospheric properties to formation, evolution, and habitability outcomes, and it highlights international partnerships as essential to realizing this program.

Abstract

The transit method, during which a planet's presence is inferred by measuring the reduction in flux as it passes in front of its parent star, is a highly successful exoplanet detection and characterization technique. During transit, the small fraction of starlight that passes through a planet's atmosphere emerges with the fingerprints of atmospheric gases, aerosols and structure. During eclipse, the relatively small contribution of light from the planet itself may be observed as the planet is occulted by the star. For planets in near-edge-on, short-period orbits, observing the system throughout an entire orbit allows the varying flux from the planet to be extracted as the illuminated `dayside' rotates in and out of view. With spectroscopic observations, we can characterize not only the overall composition of the atmosphere, but also glean insights into atmospheric structure and dynamics. With over 6,000 transiting planets now discovered, such observations are currently our only window into a consistent sample of planetary atmospheres large enough to attempt a population-level study, a critical next step for our understanding of atmospheric science. The vast exoplanet population provides a laboratory for atmospheric physics, including chemistry, dynamics, cloud processes and evolution; extending these results to a larger number of targets will allow us to explore the effects of equilibrium temperature, gravity, mass and parent star type on atmospheric properties, as well as map observable trends to formation scenarios. These findings are critical for addressing STFC's Science Vision Challenge B: how do stars and planetary systems develop and how do they support the existence of life?. Here we outline how the UK must fit within this strategic context, suggest approaches and development for the future, and outline the unique capabilities and leadership of scientists across the UK.

Transiting exoplanets as the immediate future for population-level atmospheric science

TL;DR

This paper argues that population-level atmospheric characterization of transiting exoplanets is the immediate priority for exoplanetary atmospheric science, enabled by the large and diverse transiting planet sample. It outlines a UK-led strategic approach combining broad-wavelength, high-stability observations with laboratory, modeling, and computational infrastructure, and connects these efforts to future ESA and international missions. Key contributions include a concrete vision for UV–IR coverage, the role of phase curves for both transiting and near-edge-on non-transiting planets, and a roadmap that bridges JWST/Ariel with later missions such as HWO. The work underlines the scientific and strategic value of building the capabilities to study hundreds of atmospheres, linking atmospheric properties to formation, evolution, and habitability outcomes, and it highlights international partnerships as essential to realizing this program.

Abstract

The transit method, during which a planet's presence is inferred by measuring the reduction in flux as it passes in front of its parent star, is a highly successful exoplanet detection and characterization technique. During transit, the small fraction of starlight that passes through a planet's atmosphere emerges with the fingerprints of atmospheric gases, aerosols and structure. During eclipse, the relatively small contribution of light from the planet itself may be observed as the planet is occulted by the star. For planets in near-edge-on, short-period orbits, observing the system throughout an entire orbit allows the varying flux from the planet to be extracted as the illuminated `dayside' rotates in and out of view. With spectroscopic observations, we can characterize not only the overall composition of the atmosphere, but also glean insights into atmospheric structure and dynamics. With over 6,000 transiting planets now discovered, such observations are currently our only window into a consistent sample of planetary atmospheres large enough to attempt a population-level study, a critical next step for our understanding of atmospheric science. The vast exoplanet population provides a laboratory for atmospheric physics, including chemistry, dynamics, cloud processes and evolution; extending these results to a larger number of targets will allow us to explore the effects of equilibrium temperature, gravity, mass and parent star type on atmospheric properties, as well as map observable trends to formation scenarios. These findings are critical for addressing STFC's Science Vision Challenge B: how do stars and planetary systems develop and how do they support the existence of life?. Here we outline how the UK must fit within this strategic context, suggest approaches and development for the future, and outline the unique capabilities and leadership of scientists across the UK.
Paper Structure (7 sections, 2 figures)

This paper contains 7 sections, 2 figures.

Table of Contents

  1. Scientific Motivation & Objectives
  2. Strategic Context
  3. Proposed Approach
  4. Proposed Technical Solution and Required Development
  5. UK Leadership and Capability
  6. Suggested Mission Class
  7. Partnership Opportunities

Figures (2)

  • Figure 1: Figure 1: Illustration of the transit method and the measured deviation in flux caused by the transit, eclipse, and phase curve of a tidally locked planet.
  • Figure 2: Figure 2: Top -- the total planetary flux as measured in flux units for cloud-free planetary atmospheres. Bottom -- the percent contribution of reflected light to the total flux as a function of wavelength ($R$ = 300). Colored bands in the top panel show the photometric (hashed) and spectroscopic (solid) coverage from current and future facilities over this wavelength range. Figure updated from Mayorga2019AJ and included with permission of L. C. Mayorga.