121 research outputs found
Implications of atmospheric non-detections for Trappist-1 inner planets on atmospheric retention prospects for outer planets
JWST secondary eclipse observations of Trappist-1b seemingly disfavor
atmospheres >~1 bar since heat redistribution is expected to yield dayside
emission temperature below the ~500 K observed. Given the similar densities of
Trappist-1 planets, and the theoretical potential for atmospheric erosion
around late M-dwarfs, this observation might be assumed to imply substantial
atmospheres are also unlikely for the outer planets. However, the processes
governing atmosphere erosion and replenishment are fundamentally different for
inner and outer planets. Here, an atmosphere-interior evolution model is used
to show that an airless Trappist-1b (and c) only weakly constrains stellar
evolution, and that the odds of outer planets e and f retaining substantial
atmospheres remain largely unchanged. This is true even if the initial volatile
inventories of planets in the Trappist-1 system are highly correlated. The
reason for this result is that b and c sit unambiguously interior to the
runaway greenhouse limit, and so have potentially experienced ~8 Gyr of
XUV-driven hydrodynamic escape; complete atmospheric erosion in this
environment only weakly constrains stellar evolution and escape
parameterizations. In contrast, e and f reside within the habitable zone, and
likely experienced a comparatively short steam atmosphere during Trappist-1's
pre-main sequence, and consequently complete atmospheric erosion remains
unlikely across a broad swath of parameter space (e and f retain atmospheres in
~98% of model runs). Naturally, it is still possible that all Trappist-1
planets formed volatile-poor and are all airless today. But the airlessness of
b (and c) does not require this, and as such, JWST transit spectroscopy of e
and f remains the best near-term opportunity to characterize the atmospheres of
habitable zone terrestrial planets.Comment: Accepted for publication in ApJL (June 7th 2023). First submitted May
3rd, 2023. 15 pages, 6 figures, 1 tabl
Robert Burns Woodward
This poster for the Natural Sciences Poster Session at Parkland College features chemist Robert Burns Woodward (1917-1979). Woodward was awarded the Nobel Prize in Chemistry in 1965 for his work on organic synthesis. His work on total synthesis includes cholesterol, chlorophyll, colchicine, erythromycin, reserpine, and vitamin B12
Detectability of biosignatures in anoxic atmospheres with the James Webb Space Telescope: A TRAPPIST-1e case study
The James Webb Space Telescope (JWST) may be capable of finding biogenic
gases in the atmospheres of habitable exoplanets around low mass stars.
Considerable attention has been given to the detectability of biogenic oxygen,
which could be found using an ozone proxy, but ozone detection with JWST will
be extremely challenging, even for the most favorable targets. Here, we
investigate the detectability of biosignatures in anoxic atmospheres analogous
to those that likely existed on the early Earth. Arguably, such anoxic
biosignatures could be more prevalent than oxygen biosignatures if life exists
elsewhere. Specifically, we simulate JWST retrievals of TRAPPIST-1e to
determine whether the methane plus carbon dioxide disequilibrium biosignature
pair is detectable in transit transmission. We find that ~10 transits using the
Near InfraRed Spectrograph (NIRSpec) prism instrument may be sufficient to
detect carbon dioxide and constrain methane abundances sufficiently well to
rule out known, non-biological CH production scenarios to ~90%
confidence. Furthermore, it might be possible to put an upper limit on carbon
monoxide abundances that would help rule out non-biological methane-production
scenarios, assuming the surface biosphere would efficiently drawdown
atmospheric CO. Our results are relatively insensitive to high altitude clouds
and instrument noise floor assumptions, although stellar heterogeneity and
variability may present challenges.Comment: 21 pages, 7 figure
Is the Pale Blue Dot unique? Optimized photometric bands for identifying Earth-like exoplanets
The next generation of ground and space-based telescopes will image habitable
planets around nearby stars. A growing literature describes how to characterize
such planets with spectroscopy, but less consideration has been given to the
usefulness of planet colors. Here, we investigate whether potentially
Earth-like exoplanets could be identified using UV-visible-to-NIR wavelength
broadband photometry (350-1000 nm). Specifically, we calculate optimal
photometric bins for identifying an exo-Earth and distinguishing it from
uninhabitable planets including both Solar System objects and model exoplanets.
The color of some hypothetical exoplanets - particularly icy terrestrial worlds
with thick atmospheres - is similar to Earth's because of Rayleigh scattering
in the blue region of the spectrum. Nevertheless, subtle features in Earth's
reflectance spectrum appear to be unique. In particular, Earth's reflectance
spectrum has a 'U-shape' unlike all our hypothetical, uninhabitable planets.
This shape is partly biogenic because O2-rich, oxidizing air is transparent to
sunlight, allowing prominent Rayleigh scattering, while ozone absorbs visible
light, creating the bottom of the 'U'. Whether such uniqueness has practical
utility depends on observational noise. If observations are photon limited or
dominated by astrophysical sources (zodiacal light or imperfect starlight
suppression), then the use of broadband visible wavelength photometry to
identify Earth twins has little practical advantage over obtaining detailed
spectra. However, if observations are dominated by dark current then optimized
photometry could greatly assist preliminary characterization. We also calculate
the optimal photometric bins for identifying extrasolar Archean Earths, and
find that the Archean Earth is more difficult to unambiguously identify than a
modern Earth twin.Comment: 10 figures, 38 page
- …