A New Method for Finding Nearby White Dwarf Exoplanets and Detecting Biosignatures

Abstract

We demonstrate that the James Webb Space Telescope (JWST) can detect infrared (IR) excess from the blended light spectral energy distribution of spatially unresolved terrestrial exoplanets orbiting nearby white dwarfs. We find that JWST is capable of detecting warm (habitable-zone; T${}_{\mathrm{eq}}$=287 K) Earths or super-Earths and hot (400-1000 K) Mercury analogs in the blended light spectrum around the nearest 15 isolated white dwarfs with 10 hrs of integration per target using MIRI's Medium Resolution Spectrograph (MRS). Further, these observations constrain the presence of a CO${}_2$-dominated atmosphere on these planets. The technique is nearly insensitive to system inclination, and thus observation of even a small sample of white dwarfs could place strong limits on the occurrence rates of warm terrestrial exoplanets around white dwarfs in the solar neighborhood. We find that JWST can also detect exceptionally cold (100-150 K) Jupiter-sized exoplanets via MIRI broadband imaging at $\lambda =21\mu \mathrm{m}$ for the 34 nearest ($<13$ pc) solitary white dwarfs with 2 hrs of integration time per target. Using IR excess to detect thermal variations with orbital phase or spectral absorption features within the atmosphere, both of which are possible with long-baseline MRS observations, would confirm candidates as actual exoplanets. Assuming an Earth-like atmospheric composition, we find that the detection of the biosignature pair O${}_3$+CH${}_4$ is possible for all habitable-zone Earths (within 6.5 pc; six white dwarf systems) or super-Earths (within 10 pc; 17 systems) orbiting white dwarfs with only 5-36 hrs of integration using MIRI's Low Resolution Spectrometer (LRS).

Accepted to MNRAS

References in corpus (38)

• The Evolution of L and T Dwarfs in Color-Magnitude Diagrams
• Astrometric exoplanet detection with Gaia
• A catalogue of white dwarfs in Gaia EDR3
• Precise Radial Velocities of Giant Stars VII. Occurrence Rate of Giant Extrasolar Planets as a Function of Mass and Metallicity
• The Detectability and Characterization of the TRAPPIST-1 Exoplanet Atmospheres with JWST
• Tidal Locking of Habitable Exoplanets
• Techniques and Review of Absolute Flux Calibration from the Ultraviolet to the Mid-Infrared
• Water Clouds in Y Dwarfs and Exoplanets
• A Giant Planet Candidate Transiting a White Dwarf
• Accretion of a giant planet onto a white dwarf
• The 100 pc White Dwarf Sample in the SDSS Footprint
• The frequency and infrared brightness of circumstellar discs at white dwarfs
• The chemical diversity of exo-terrestrial planetary debris around white dwarfs
• $Gaia$ white dwarfs within 40 pc II: the volume-limited northern hemisphere sample
• Tidal Limits to Planetary Habitability
• Transit surveys for Earths in the habitable zones of white dwarfs
• Spitzer IRAC Observations of White Dwarfs. II. Massive Planetary and Cold Brown Dwarf Companions to Young and Old Degenerates
• Prospects for Characterizing the Atmosphere of Proxima Centauri b
• A New Generation of Cool White Dwarf Atmosphere Models. IV. Revisiting the Spectral Evolution of Cool White Dwarfs
• A Jovian analogue orbiting a white dwarf star
• Kepler and the seven dwarfs: detection of low-level day-timescale periodic photometric variations in white dwarfs
• A white dwarf accreting planetary material determined from X-ray observations
• The White Dwarf Opportunity: Robust Detections of Molecules in Earth-like Exoplanet Atmospheres with the James Webb Space Telescope
• Cold giant planets evaporated by hot white dwarfs
• Differentiating Modern and Prebiotic Earth Scenarios for TRAPPIST-1e: High-resolution Transmission Spectra and Predictions for JWST
• Infrared Excesses around Bright White Dwarfs from Gaia and unWISE. II
• Pressure Distortion of the H${}_2$-He Collision-Induced Absorption at the Photosphere of Cool White Dwarf Stars
• Cool Customers in the Stellar Graveyard IV: Spitzer Search for Mid-IR excesses Around Five DAs
• Cool white dwarfs as standards for infrared observations
• An Extreme-AO Search for Giant Planets around a White Dwarf --VLT/SPHERE performance on a faint target GD 50
• A New Method For Studying Exoplanet Atmospheres Using Planetary Infrared Excess
• Infrared absorption of dense helium and its importance in the atmospheres of cool white dwarfs
• A Young White Dwarf with an Infrared Excess
• Search for giant planets around seven white dwarfs in the Hyades cluster with the Hubble Space Telescope
• Confirming new white dwarf-ultracool dwarf binary candidates
• Retrieving Exoplanet Atmospheres using Planetary Infrared Excess: Prospects for the Nightside of WASP-43 b and other Hot Jupiters
• Finding rocky asteroids around white dwarfs by their periodic thermal emission
• An Imaging Search for Post-Main-Sequence Planets of Sirius B

Cited by in corpus (1)

• TTV Constraints on Additional Planets in the WD 1856+534 system