The White Dwarf Opportunity: Robust Detections of Molecules in Earth-like Exoplanet Atmospheres with the James Webb Space Telescope

Abstract

The near-term search for life beyond the solar system currently focuses on transiting planets orbiting small M dwarfs, and the challenges of detecting signs of life in their atmospheres. However, planets orbiting white dwarfs (WDs) would provide a unique opportunity to characterize rocky worlds. The discovery of the first transiting giant planet orbiting a white dwarf, WD 1856+534b, showed that planetary-mass objects can survive close-in orbits around WDs. The large radius ratio between WD planets and their host renders them exceptional targets for transmission spectroscopy. Here, we explore the molecular detectability and atmospheric characterization potential for a notional Earth-like planet, evolving in the habitable zone of WD 1856+534, with the James Webb Space Telescope (JWST). We establish that the atmospheric composition of such Earth-like planets orbiting WDs can be precisely retrieved with JWST. We demonstrate that robust > 5$\sigma$ detections of H${}_2$O and CO${}_2$ can be achieved in a 5 transit reconnaissance program, while the biosignatures O${}_3$ + CH${}_4$, and O${}_3$ + N${}_2$O can be detected to > 4$\sigma$ in as few as 25 transits. N${}_2$ and O${}_2$ can be detected to > 5$\sigma$ within 100 transits. Given the short transit duration of WD habitable zone planets (~ 2 minutes for WD 1856+534), conclusive molecular detections can be achieved in a small or medium JWST transmission spectroscopy program. Rocky planets in the WD habitable zone therefore represent a promising opportunity to characterize terrestrial planet atmospheres and explore the possibility of a second genesis on these worlds.

12 pages, 4 figures. Published in ApJL

References in corpus (23)

• The K2 Mission: Characterization and Early results
• Seven temperate terrestrial planets around the nearby ultracool dwarf star TRAPPIST-1
• A terrestrial planet candidate in a temperate orbit around Proxima Centauri
• The frequency of planetary debris around young white dwarfs
• How to Characterize Habitable Worlds and Signs of Life
• Observing the Atmospheres of Known Temperate Earth-sized Planets with JWST
• A Sub-Neptune Exoplanet with a Low-Metallicity Methane-Depleted Atmosphere and Mie-Scattering Clouds
• The Detectability and Characterization of the TRAPPIST-1 Exoplanet Atmospheres with JWST
• The Solar Neighborhood XLV. The Stellar Multiplicity Rate of M Dwarfs Within 25 pc
• Detection of titanium oxide in the atmosphere of a hot Jupiter
• Accretion of a giant planet onto a white dwarf
• Transit surveys for Earths in the habitable zones of white dwarfs
• Detectable close-in planets around white dwarfs through late unpacking
• Are exoplanetesimals differentiated?
• The occurrence of planets and other substellar bodies around white dwarfs using K2
• The Metal-Rich Atmosphere of the Neptune HAT-P-26b
• A search for planetary eclipses of white dwarfs in the Pan-STARRS1 medium-deep fields
• Analytic Scattering and Refraction Models for Exoplanet Transit Spectra
• Orbital relaxation and excitation of planets tidally interacting with white dwarfs
• The Detectability and Constraints of Biosignature Gases in the Near & Mid-Infrared from Transit Transmission Spectroscopy
• An Extreme-AO Search for Giant Planets around a White Dwarf --VLT/SPHERE performance on a faint target GD 50
• Investigation of X-ray timing and spectral properties of ESO 243-49 HLX-1 with long-term Swift Monitoring
• Near-UV absorption in very cool DA white dwarfs

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• Validation of 13 Hot and Potentially Terrestrial TESS Planets
• Evaluating the Plausible Range of N2O Biosignatures on Exo-Earths: An Integrated Biogeochemical, Photochemical, and Spectral Modeling Approach
• A New Method for Finding Nearby White Dwarf Exoplanets and Detecting Biosignatures
• Atmosphere Models of Brown Dwarfs Irradiated by White Dwarfs: Analogues for Hot and Ultra-Hot Jupiters
• Past, Present and Future Stars that can see Earth as a Transiting Exoplanet
• Alternative Methylated Biosignatures I: Methyl Bromide, A Capstone Biosignature
• H${}_2$-dominated Atmosphere as an Indicator of Second-generation Rocky White Dwarf Exoplanets
• Follow the Water: Finding Water, Snow and Clouds on Terrestrial Exoplanets with Photometry and Machine Learning
• Stratospheric Clouds Do Not Impede JWST Transit Spectroscopy for Exoplanets with Earth-Like Atmospheres