278 research outputs found
Characterizing Habitable Extrasolar Planets using Spectral Fingerprints
The detection and characterization of Earth-like planet is approaching
rapidly thanks to radial velocity surveys (HARPS), transit searches (Corot,
Kepler) and space observatories dedicated to their characterization are already
in development phase (James Webb Space Telescope), large ground based
telescopes (ELT, TNT, GMT), and dedicated space-based missions like Darwin,
Terrestrial Planet Finder, New World Observer). In this paper we discuss how we
can read a planets spectrum to assess its habitability and search for the
signatures of a biosphere. Identifying signs of life implies understanding how
the observed atmosphere physically and chemically works and thus to gather
information on the planet in addition to the observing its spectral
fingerprint.Comment: 14pg, 4 figures, Accepted CRAS (Proceedings of the National Academy
of Science France), Palevol serie
Water Planets in the Habitable Zone: Atmospheric Chemistry, Observable Features, and the case of Kepler-62e and -62f
Planets composed of large quantities of water that reside in the habitable
zone are expected to have distinct geophysics and geochemistry of their
surfaces and atmospheres. We explore these properties motivated by two key
questions: whether such planets could provide habitable conditions and whether
they exhibit discernable spectral features that distinguish a water-planet from
a rocky Earth-like planet. We show that the recently discovered planets
Kepler-62e and -62f are the first viable candidates for habitable zone
water-planet. We use these planets as test cases for discussing those
differences in detail. We generate atmospheric spectral models and find that
potentially habitable water-planets show a distinctive spectral fingerprint in
transit depending on their position in the habitable zone.Comment: 8 pages, 4 figures, ApJ, 775, L4
UV Surface Environment of Earth-like Planets Orbiting FGKM Stars Through Geological Evolution
The UV environment of a host star affects the photochemistry in the
atmosphere, and ultimately the surface UV environment for terrestrial planets
and therefore the conditions for the origin and evolution of life. We model the
surface UV radiation environment for Earth-sized planets orbiting FGKM stars at
the 1AU equivalent distance for Earth through its geological evolution. We
explore four different types of atmospheres corresponding to an early Earth
atmosphere at 3.9 Gyr ago and three atmospheres covering the rise of oxygen to
present day levels at 2.0 Gyr ago, 0.8 Gyr ago and modern Earth (Following
Kaltenegger et al. 2007). In addition to calculating the UV flux on the surface
of the planet, we model the biologically effective irradiance, using DNA damage
as a proxy for biological damage. We find that a pre-biotic Earth (3.9 Gyr ago)
orbiting an F0V star receives 6 times the biologically effective radiation as
around the early Sun and 3520 times the modern Earth-Sun levels. A pre-biotic
Earth orbiting GJ 581 (M3.5V) receives 300 times less biologically effective
radiation, about 2 times modern Earth-Sun levels. The UV fluxes calculated here
provide a grid of model UV environments during the evolution of an Earth-like
planet orbiting a range of stars. These models can be used as inputs into
photo-biological experiments and for pre-biotic chemistry and early life
evolution experiments.Comment: 10 pages, 5 figure
Effect of UV Radiation on the Spectral Fingerprints of Earth-like Planets Orbiting M dwarfs
We model the atmospheres and spectra of Earth-like planets orbiting the
entire grid of M dwarfs for active and inactive stellar models with =
2300K to = 3800K and for six observed MUSCLES M dwarfs with UV
radiation data. We set the Earth-like planets at the 1AU equivalent distance
and show spectra from the VIS to IR (0.4m - 20m) to compare
detectability of features in different wavelength ranges with JWST and other
future ground- and spaced-based missions to characterize exo-Earths. We focus
on the effect of UV activity levels on detectable atmospheric features that
indicate habitability on Earth, namely: HO, O, CH, NO and
CHCl.
To observe signatures of life - O/O in combination with reducing
species like CH, we find that early and active M dwarfs are the best
targets of the M star grid for future telescopes. The O spectral feature at
0.76m is increasingly difficult to detect in reflected light of later M
dwarfs due to low stellar flux in that wavelength region. NO, another
biosignature detectable in the IR, builds up to observable concentrations in
our planetary models around M dwarfs with low UV flux. CHCl could become
detectable, depending on the depth of the overlapping NO feature.
We present a spectral database of Earth-like planets around cool stars for
directly imaged planets as a framework for interpreting future lightcurves,
direct imaging, and secondary eclipse measurements of the atmospheres of
terrestrial planets in the HZ to design and assess future telescope
capabilities.Comment: in press, ApJ (submitted August 18, 2014), 16 pages, 12 figure
Detecting planetary geochemical cycles on exoplanets: Atmospheric signatures and the case of SO2
We study the spectrum of a planetary atmosphere to derive detectable features
in low resolution of different global geochemical cycles on exoplanets - using
the sulphur cycle as our example. We derive low resolution detectable features
for first generation space- and ground- based telescopes as a first step in
comparative planetology. We assume that the surfaces and atmospheres of
terrestrial exoplanets (Earth-like and super-Earths) will most often be
dominated by a specific geochemical cycle. Here we concentrate on the sulphur
cycle driven by outgassing of SO2 and H2S followed by their transformation to
other sulphur-bearing species which is clearly distinguishable from the carbon
cycle which is driven by outgassing of CO2. Due to increased volcanism, the
sulphur cycle is potentially the dominant global geochemical cycle on dry
super-Earths with active tectonics. We calculate planetary emission, reflection
and transmission spectrum from 0.4 to 40 micrometer with high and low
resolution to assess detectable features using current and Archean Earth models
with varying SO2 and H2S concentrations to explore reducing and oxidizing
habitable environments on rocky planets. We find specific spectral signatures
that are observable with low resolution in a planetary atmosphere with high SO2
and H2S concentration. Therefore first generation space and ground based
telescopes can test our understanding of geochemical cycles on rocky planets
and potentially distinguish planetary environments dominated by the carbon and
sulphur cycle.Comment: 9 pages, 6 figures, ApJ accepted - detailed discussion adde
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