Exoplanets & Exomoons

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

By Keith Cowing
Press Release
September 27, 2022
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A New Method for Finding Nearby White Dwarf Exoplanets and Detecting Biosignatures
Left: Minimum detectable radius of a habitable-zone exoplanet (𝑇eq = 287 K) for each WD in our sample. This figure demonstrates that the size of HZ planet that can be detected depends primarily on the distance to the system. The small amount of scatter in this dependency is due to variations in the temperature and radius of the WD—a fit for hot (𝑇eff = 20,000 K) WDs (top dotted line) and cold (𝑇eff = 6,000 K) WDs (bottom dotted line) is shown here, and an equation for this fit is given in the text. The magnitude of the WD is not a driving factor when determining the minimum detectable planet radius Right: Minimum detectable exoplanets of a given temperature-radius around WDs at four different distances (2.7 − 13 pc). Earth-analogs can be detected around WDs within 6 pc of Earth and hot, rocky planets with tenuous atmospheres (Mercury-analogs) within 10 pc. Habitable-zone exoplanets orbiting WDs are detectable via IR excess out to 8 − 10 pc (e.g. Kepler-62e). Jupiters and Saturns are detectable with MRS out to 10 − 20 pc, but can more efficiently be detected with 21 𝜇m MIRI imaging. For both plots, we determine detectability based on the amount of IR excess measured from the exoplanet with 10 hrs of observation in the JWST MIRI/MRS sub-band C channels (see Section 5.1.4).

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; Teq=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 CO2-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 λ=21μm 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 O3+CH4 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).

Mary Anne Limbach, Andrew Vanderburg, Kevin B. Stevenson, Simon Blouin, Caroline Morley, Jacob Lustig-Yaeger, Melinda Soares-Furtado, Markus Janson

Comments: Accepted to MNRAS
Subjects: Earth and Planetary Astrophysics (astro-ph.EP); Instrumentation and Methods for Astrophysics (astro-ph.IM); Solar and Stellar Astrophysics (astro-ph.SR)
Cite as: arXiv:2209.12914 [astro-ph.EP] (or arXiv:2209.12914v1 [astro-ph.EP] for this version)
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Submission history
From: Mary Anne Limbach
[v1] Mon, 26 Sep 2022 18:00:09 UTC (5,349 KB)

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) 🖖🏻