9 research outputs found
Evaluating the Plausible Range of N2O Biosignatures on Exo-Earths: An Integrated Biogeochemical, Photochemical, and Spectral Modeling Approach
Nitrous oxide (N2O) -- a product of microbial nitrogen metabolism -- is a
compelling exoplanet biosignature gas with distinctive spectral features in the
near- and mid-infrared, and only minor abiotic sources on Earth. Previous
investigations of N2O as a biosignature have examined scenarios using Earthlike
N2O mixing ratios or surface fluxes, or those inferred from Earth's geologic
record. However, biological fluxes of N2O could be substantially higher, due to
a lack of metal catalysts or if the last step of the denitrification metabolism
that yields N2 from N2O had never evolved. Here, we use a global biogeochemical
model coupled with photochemical and spectral models to systematically quantify
the limits of plausible N2O abundances and spectral detectability for Earth
analogs orbiting main-sequence (FGKM) stars. We examine N2O buildup over a
range of oxygen conditions (1%-100% present atmospheric level) and N2O fluxes
(0.01-100 teramole per year; Tmol = 10^12 mole) that are compatible with
Earth's history. We find that N2O fluxes of 10 [100] Tmol yr would lead
to maximum N2O abundances of ~5 [50] ppm for Earth-Sun analogs, 90 [1600] ppm
for Earths around late K dwarfs, and 30 [300] ppm for an Earthlike TRAPPIST-1e.
We simulate emission and transmission spectra for intermediate and maximum N2O
concentrations that are relevant to current and future space-based telescopes.
We calculate the detectability of N2O spectral features for high-flux scenarios
for TRAPPIST-1e with JWST. We review potential false positives, including
chemodenitrification and abiotic production via stellar activity, and identify
key spectral and contextual discriminants to confirm or refute the biogenicity
of the observed N2O.Comment: 22 pages, 17 figures; ApJ, 937, 10
Revising the hygroscopicity of inorganic sea salt particles
This is the final version of the article. Available from Springer Nature via the DOI in this record.Sea spray is one of the largest natural aerosol sources and plays an important role in the Earth's radiative budget. These particles are inherently hygroscopic, that is, they take-up moisture from the air, which affects the extent to which they interact with solar radiation. We demonstrate that the hygroscopic growth of inorganic sea salt is 8-15% lower than pure sodium chloride, most likely due to the presence of hydrates. We observe an increase in hygroscopic growth with decreasing particle size (for particle diameters <150ânm) that is independent of the particle generation method. We vary the hygroscopic growth of the inorganic sea salt within a general circulation model and show that a reduced hygroscopicity leads to a reduction in aerosol-radiation interactions, manifested by a latitudinal-dependent reduction of the aerosol optical depth by up to 15%, while cloud-related parameters are unaffected. We propose that a value of Îșs=1.1 (at RH=90%) is used to represent the hygroscopicity of inorganic sea salt particles in numerical models.P.Z. was partially financed by an Advanced Postdoc.Mobility fellowship of the Swiss National Science Foundation (grant no. P300P2_147776). M.E.S., C.L. and I.R. were financed by the Nordic Center of Excellence on Cryosphere-Atmosphere-Cloud-Climate-Interactions (NCoE CRAICC) and the Swedish Research Council (Vetenskapsradet). O.V. and A.V. were supported by the Academy of Finland Centre of Excellence (grant no. 272041) and The Doctoral School of the University of Eastern Finland. J.C.C. and M.G. received financial support from the European Research Commission via the ERC grant ERC-CoG 615922-BLACARAT. A.N. acknowledges support from a Georgia Power Scholar chair and a Cullen-Peck faculty fellowship. S.B. and M.M.-F. acknowledge funding by the Swiss National Science Foundation (grant no. 200020_146760/1). I. Tegen (TROPOS, Germany) is acknowledged for providing help with the sea spray source functions. We thank D. Eklöf and Z. Bacsik from the Department of Materials and Environmental Chemistry at Stockholm University for their assistance in the pycnometre and Fourier transform infrared spectrometer measurements. The ECHAM-HAMMOZ model is developed by a consortium composed of ETH Zurich, Max Planck Institut fĂŒr Meteorologie, Forschungszentrum JĂŒlich, University of Oxford, the Finnish Meteorological Institute and the Leibniz Institute for Tropospheric Research, and managed by the Center for Climate Systems Modeling (C2SM) at ETH Zurich
The CARMENES search for exoplanets around M dwarfs, Wolf 1069 b: Earth-mass planet in the habitable zone of a nearby, very low-mass star
We present the discovery of an Earth-mass planet () on a 15.6d orbit of a relatively nearby (9.6pc)
and low-mass () M5.0V star, Wolf 1069. Sitting at a
separation of au away from the host star puts Wolf 1069b in
the habitable zone (HZ), receiving an incident flux of
. The planetary signal was detected using
telluric-corrected radial-velocity (RV) data from the CARMENES spectrograph,
amounting to a total of 262 spectroscopic observations covering almost four
years. There are additional long-period signals in the RVs, one of which we
attribute to the stellar rotation period. This is possible thanks to our
photometric analysis including new, well-sampled monitoring campaigns undergone
with the OSN and TJO facilities that supplement archival photometry (i.e., from
MEarth and SuperWASP), and this yielded an updated rotational period range of
d, with a likely value at d. The stellar
activity indicators provided by the CARMENES spectra likewise demonstrate
evidence for the slow rotation period, though not as accurately due to possible
factors such as signal aliasing or spot evolution. Our detectability limits
indicate that additional planets more massive than one Earth mass with orbital
periods of less than 10 days can be ruled out, suggesting that perhaps Wolf
1069 b had a violent formation history. This planet is also the 6th closest
Earth-mass planet situated in the conservative HZ, after Proxima Centauri b, GJ
1061d, Teegarden's Star c, and GJ 1002 b and c. Despite not transiting, Wolf
1069b is nonetheless a very promising target for future three-dimensional
climate models to investigate various habitability cases as well as for
sub-ms RV campaigns to search for potential inner sub-Earth-mass planets
in order to test planet formation theories.Comment: 26 pages, 15 figure
Diffusivity measurements of volatile organics in levitated viscous aerosol particles
Field measurements indicating that atmospheric secondary organic
aerosol (SOA) particles can be present in a highly viscous, glassy state have
spurred numerous studies addressing low diffusivities of water in glassy
aerosols. The focus of these studies is on kinetic limitations of hygroscopic
growth and the plasticizing effect of water. In contrast, much less is known
about diffusion limitations of organic molecules and oxidants in viscous
matrices. These may affect atmospheric chemistry and gasâparticle
partitioning of complex mixtures with constituents of different volatility.
In this study, we quantify the diffusivity of a volatile organic in a viscous
matrix. Evaporation of single particles generated from an aqueous solution of
sucrose and small amounts of volatile tetraethylene glycol (PEG-4) is
investigated in an electrodynamic balance at controlled relative humidity
(RH) and temperature. The evaporative loss of PEG-4 as determined by Mie
resonance spectroscopy is used in conjunction with a radially resolved
diffusion model to retrieve translational diffusion coefficients of PEG-4.
Comparison of the experimentally derived diffusivities with viscosity
estimates for the ternary system reveals a breakdown of the StokesâEinstein
relationship, which has often been invoked to infer diffusivity from
viscosity. The evaporation of PEG-4 shows pronounced RH and temperature
dependencies and is severely depressed for RHâŻâČâŻ30âŻ%,
corresponding to diffusivities <âŻ10â14âŻcm2âsâ1 at
temperatures <âŻ15âŻÂ°C. The temperature dependence is
strong, suggesting a diffusion activation energy of about
300âŻkJâmolâ1. We conclude that atmospheric volatile organic
compounds can be subject to severe diffusion limitations in viscous organic
aerosol particles. This may enable an important long-range transport
mechanism for organic material, including pollutant molecules such as
polycyclic aromatic hydrocarbons (PAHs)
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Evaluating the Plausible Range of N2O Biosignatures on Exo-Earths: An Integrated Biogeochemical, Photochemical, and Spectral Modeling Approach
Abstract
Nitrous oxide (N2O)âa product of microbial nitrogen metabolismâis a compelling exoplanet biosignature gas with distinctive spectral features in the near- and mid-infrared, and only minor abiotic sources on Earth. Previous investigations of N2O as a biosignature have examined scenarios using Earthlike N2O mixing ratios or surface fluxes, or those inferred from Earthâs geologic record. However, biological fluxes of N2O could be substantially higher, due to a lack of metal catalysts or if the last step of the denitrification metabolism that yields N2 from N2O had never evolved. Here, we use a global biogeochemical model coupled with photochemical and spectral models to systematically quantify the limits of plausible N2O abundances and spectral detectability for Earth analogs orbiting main-sequence (FGKM) stars. We examine N2O buildup over a range of oxygen conditions (1%â100% present atmospheric level) and N2O fluxes (0.01â100 teramole per year; Tmol = 1012 mole) that are compatible with Earthâs history. We find that N2O fluxes of 10 [100] Tmol yrâ1 would lead to maximum N2O abundances of âŒ5 [50] ppm for EarthâSun analogs, 90 [1600] ppm for Earths around late K dwarfs, and 30 [300] ppm for an Earthlike TRAPPIST-1e. We simulate emission and transmission spectra for intermediate and maximum N2O concentrations that are relevant to current and future space-based telescopes. We calculate the detectability of N2O spectral features for high-flux scenarios for TRAPPIST-1e with JWST. We review potential false positives, including chemodenitrification and abiotic production via stellar activity, and identify key spectral and contextual discriminants to confirm or refute the biogenicity of the observed N2O