2,606 research outputs found
Exploring the Climate of Exoplanets with OASIS
No full textIn the last two decades, the astrophysical community discovered a multitude of planets orbiting other stars. The variety of planetary environments that these exoplanets may harbour is still unknown. Most importantly it propels the fundamental scientific and philosophical quest of searching for the first detection of life beyond our own planet. As more observational data become available, models of exoplanetary atmospheres are essential, at a first level to interpret the data and more importantly to reproduce and explain the physical and chemical processes that generate the climate of planets. My poster presents the new planet simulator, OASIS, that I have developed from scratch to study planet's habitability and search for life in exoplanets. Our new planetary virtual lab includes a new state-of-the-art 3D atmospheric model (THOR) coupled self-consistently with other modules that represent the main physical and chemical processes that shape planetary climates and their evolution. We have recently submitted a manuscript presenting our first results using OASIS. Using our new platform, we successfully performed challenging simulations of Venus-like environments and compared the model's results to Venus observations. We will present our new results and describe the main advantages of using OASIS compared with other models. The new results show that OASIS is a robust and efficient tool to simulate a large diversity of planet's environments. ..
Modelling the 3D Climate of Venus with OASIS
No full textFlexible 3D models to explore the vast diversity of terrestrial planets and interpret observational data are still in their early stages. In this work, we present OASIS: a novel and flexible 3D virtual planet laboratory. With OASIS we envision a platform that couples self-consistently seven individual modules representing the main physical and chemical processes that shape planetary environments. Additionally, OASIS is capable of producing simulated spectra from different instruments and observational techniques. In this work we focus on the benchmark test of coupling four of the physical modules: fluid dynamics, radiation, turbulence and surface/soil. To test the OASIS platform, we produced 3D simulations of the Venus climate and its atmospheric circulation and study how the modelled atmosphere changes with various cloud covers, atmospheric heat capacity, and surface friction. 3D simulations of Venus are challenging because they require long integration times with a computationally expensive radiative transfer code. By comparing OASIS results with observational data, we verify that the new model is able to successfully simulate Venus. With simulated spectra produced directly from the 3D simulations, we explore the capabilities of future missions, like LUVOIR, to observe Venus analogues located at a distance of 10 pc. With OASIS, we have taken the first steps to build a sophisticated and very flexible platform capable of studying the environment of terrestrial planets, which will be an essential tool to characterize observed terrestrial planets and plan future observation
Is ozone a reliable proxy for molecular oxygen?
No full textMolecular oxygen (O2) paired with a reducing gas is regarded as a promising biosignature pair for the atmospheric characterization of terrestrial exoplanets. In circumstances when O2 may not be detectable in a planetary atmosphere (e.g., at mid-IR wavelengths) it has been suggested that ozone (O3), the photochemical product of O2, could be used as a proxy to infer the presence of O2. However, O3 production has a nonlinear dependence on O2 and is strongly influenced by the UV spectrum of the host star. To evaluate the reliability of O3 as a proxy for O2, we used Atmos, a 1D coupled climate and photochemistry code, to study the O2–O3 relationship for “Earth-like” habitable zone planets around a variety of stellar hosts (G0V-M5V) and O2 abundances. Overall, we found that the O2–O3 relationship differed significantly with stellar hosts and resulted in different trends for hotter stars (G0V-K2V) versus cooler stars (K5V-M5V). Planets orbiting hotter host stars counter-intuitively experience an increase in O3 when O2 levels are initially decreased from 100% Earth’s present atmospheric level (PAL), with a maximum O3 abundance occurring at 25–55% PAL O2. As O2 abundance initially decreases, larger amounts of UV photons capable of O2 photolysis reach the lower (denser) regions of the atmosphere where O3 production is more efficient, thus resulting in these increased O3 levels. This effect does not occur for cooler host stars (K5V-M5V), since the weaker incident UV flux does not allow O3 formation to occur at dense enough regions of the atmosphere where the faster O3 production can outweigh a smaller source of O2 from which to create O3. Thus, planets experiencing higher amounts of incident UV possessed larger stratospheric temperature inversions, leading to shallower O3 features in planetary emission spectra. Overall it will be extremely difficult (or impossible) to infer precise O2 levels from an O3 measurement, however, with information about the UV spectrum of the host star and context clues, O3 will provide valuable information about potential surface habitability of an exoplanet
Exoplanet atmospheres at high resolution through a modest-size telescope. Fe II in MASCARA-2b and KELT-9b with FIES on the Nordic Optical Telescope
No full textGround-based, high-resolution spectrographs are providing us with an
unprecedented view of the dynamics and chemistry of the atmospheres of planets
outside the Solar System. While there is a large number of stable and precise
high-resolution spectrographs on modest-size telescopes, it is the
spectrographs at observatories with apertures larger than 3.5 metres that
dominate the atmospheric follow-up of exoplanets. In this work, we explore the
potential of characterising exoplanetary atmospheres with FIES, a
high-resolution spectrograph at the 2.56 metre Nordic Optical Telescope. We
observed two transits of MASCARA-2 b (also known as KELT-20 b) and one transit
of KELT-9 b to search for atomic iron, a species that has been recently
discovered in both neutral and ionised forms in the atmospheres of these
ultra-hot Jupiters using large telescopes. Using a cross-correlation method, we
detect a signal of Fe II at the and level in the
transits of MASCARA-2 b. We also detect Fe II in the transit of KELT-9 b at the
level. Although we do not find any significant Doppler shift in the
signal of MASCARA-2 b, we do measure a moderate blueshift (3-6 km/s) of the
feature in KELT-9 b, which might be a manifestation of high-velocity winds
transporting Fe II from the planetary dayside to the nightside. Our work
demonstrates the feasibility of investigating exoplanet atmospheres with FIES,
potentially unlocking a wealth of additional atmosphere detections with this
and other high-resolution spectrographs mounted on similar-size telescopes.Comment: 9 pages, 6 figures, accepted to A&
Is ozone a reliable proxy for molecular oxygen?
No full textMolecular oxygen (O2) paired with a reducing gas is regarded as a promising biosignature pair for atmospheric characterization of terrestrial exoplanets. In circumstances when O2 may not be detectable in a planetary atmosphere (for instance, at mid-IR wavelengths) it has been suggested that O3, the photochemical product of O2, could be used as a proxy to infer the presence of O2. While O3 is not directly produced by life, it plays an important role in habitability as the ozone layer is the primary source of UV shielding for surface life on modern Earth. However, O3 production is known to have a nonlinear dependence on O2, as well as being strongly influenced by the UV spectrum of the host star. To evaluate the reliability of O3 as a proxy for O2 we used Atmos, a 1D coupled climate/photochemistry code, to study the O2-O3 relationship for "Earth-like'' habitable zone planets around a variety of stellar hosts (G0V-M5V) for O2 abundances from 0.01%-150% of the Present Atmospheric Level (PAL) on modern Earth. We studied how O3 emission features for these planetary atmospheres varied for different O2 and O3 abundances using the radiative transfer code PICASO. Overall we found that the O2-O3 relationship differed significantly around different stellar hosts, with different trends for hotter stars (G0V-K2V) than cooler stars (K5V-M5V). Planets orbiting hotter host stars experience an increase in O3 when O2 levels are initially decreased from the present atmospheric level, with maximum O3 abundance occurring at 25-55% PAL O2. Although this effect may seem counterintuitive, it is due to the pressure dependency on O3 production, as with less atmospheric O2 incoming UV photons capable of O2 photolysis are able to reach lower (denser) regions of the atmosphere to spark O3 formation. This effect is not present for planets orbiting our cooler host stars (K5V-M5V), as the weaker incident UV flux (especially FUV flux) does not allow O3 formation to occur at dense enough regions of the atmosphere such that the faster O3 production outweighs a smaller source of O2 from which to create O3. As a result, for cooler host stars the O3 abundance decreases as O2 decreases, albeit nonlinearly. Interpretation of O3 emission spectral features was found to require knowledge of the atmosphere’s temperature profiles -particularly the temperature differences between the planetary surface and stratospheric temperature- which are highly influenced by the amount of stratospheric O3. Planets experiencing higher amounts of incident UV have more efficient O3 production and UV absorption leading to larger stratospheric temperature inversions, and therefore shallower emission features. Overall it will be extremely difficult (or impossible) to infer precise O2 levels from an O3 measurement, however, with information about the UV spectrum of the host star and context clues, O3 will provide valuable information about potential surface habitability of an exoplanet
Ozone as a Proxy for Molecular Oxygen
No full textMolecular oxygen (O2) paired with a reducing gas is regarded as a promising biosignature pair for atmospheric characterization of exoplanets. In circumstances when O2 may not be detectable in a planetary atmosphere (for instance, in the IR wavelength region) it has been suggested that ozone (O3), the photochemical product of O2, could be used as a proxy to infer the presence of O2. While O3 is not directly produced by life, it plays an important role in habitability as the ozone layer is the primary source of UV shielding for surface life on Earth. However, O3 production is known to have a nonlinear dependence on O2, along with being strongly influenced by the UV spectrum of the planet's host star. To further evaluate the reliability of O3 as a proxy for O2 we used Atmos, a coupled 1D climate/photochemistry code, to model Earth-like atmospheres of habitable zone planets around a variety of stellar hosts (from G0V-M5V), along with modeling emission spectra of these model atmospheres with the radiative transfer code PICASO. Our models explore the O2-O3 relationship under a range of O2 abundances, along with varying amounts of biologically produced gases that contribute to the destruction of O3. We find that the O2-O3 relationship varies significantly around different stellar hosts, with planets orbiting hotter stars (G0V-K2V) reaching peak O3 levels at O2 abundances of less than 50% present atmospheric levels, while planets orbiting cooler hosts have O3 levels that decrease nonlinearly with O2 levels. Understanding both the chemistry and resulting temperature profiles of a planet's atmosphere will be key for interpreting emission spectral features of O3 as a biosignature gase...
Reptricket. Förord till Lars Gustafsson: Mot noll
No full textIntroduction to a collection of philosophical essays by Swedish author Lars Gustafsson (b. 1936)
Author Functions in Lars Kepler\u27s The Hypnotist: An Analysis
No full textThis paper examines Foucault\u27s notion of the author function as it pertains to Lars Kepler\u27s bestselling 2011 crime thriller, The Hypnotist. Lars Kepler is the pseudonym of a Swedish husband-wife writing duo, making him the perfect subject for analysis centering on illusory notion of the author. This paper will answer these questions: Who is the true author of The Hypnotist? What factors influence the author function of this bestelling novel? And what can The Hypnotist phenomenon tell us about the relationships between authors and their readers? This paper will demonstrate that no literary works may be ascribed to an individual person, and that authors hold no privileged knowledge of the works they produce, because authors cease to be authors the moment pen is lifted from page
Ground-based Optical Transmission Spectroscopy of the Nearby Terrestrial Exoplanet LTT 1445Ab
No full textNearby M-dwarf systems currently offer the most favorable opportunities for spectroscopic investigations of terrestrial exoplanet atmospheres. The LTT 1445 system is a hierarchical triple of M dwarfs with two known planets orbiting the primary star, LTT 1445A. We observe four transits of the terrestrial world LTT 1445Ab ( R = 1.3 R _⊕ , M = 2.9 M _⊕ ) at low resolution with Magellan II/LDSS3C. We use the combined flux of the LTT 1445BC pair as a comparison star, marking the first time that an M dwarf is used to remove telluric variability from time-series observations of another M dwarf. We find H α in emission from both LTT 1445B and C, as well as a flare in one of the data sets from LTT 1445C. These contaminated data are removed from the analysis. We construct a broadband transit light curve of LTT 1445Ab from 620 to 1020 nm. Binned to 3 minute time bins, we achieve an rms of 49 ppm for the combined broadband light curve. We construct a transmission spectrum with 20 spectrophotometric bins each spanning 20 nm and compare it to models of clear, 1× solar composition atmospheres. We rule out this atmospheric case with a surface pressure of 10 bars to 3.2 σ confidence, and with a surface pressure of 1 bar to 3.1 σ confidence. Upcoming secondary eclipse observations of LTT 1445Ab with the James Webb Space Telescope will further probe the cases of a high-mean-molecular-weight atmosphere, a hazy or cloudy atmosphere, or no atmosphere at all on this terrestrial world
Is ozone a reliable proxy for molecular oxygen? II. The impact of N2O on the O2-O3 relationship for Earth-like atmospheres
No full textMolecular oxygen (O2) will be an important molecule in the search for biosignatures in terrestrial planetary atmospheres in the coming decades. In particular, O2 combined with a reducing gas is thought to be strong evidence for disequilibrium caused by surface life. However, there are circumstances where it would be very difficult or impossible to detect O2, in which cases it has been suggested that ozone (O3), the photochemical product of O2, could be used instead. Unfortunately, the O2-O3 relationship is highly nonlinear and dependent on the host star, as shown in detail in the first paper in this series. We explore the O2-O3 relationship around G0V-M5V host stars, using climate/photochemistry modeling to simulate atmospheres while varying abundances of O2 and nitrous oxide (N2O). N2O is of particular importance to the O2-O3 relationship not just because it is produced biologically, but because it is the primary source of nitrogen oxides (NOx), which fuel the NOx catalytic cycle which destroys O3, and the smog mechanism that produces O3. We vary the O2 mixing ratio from 0.01-150% present atmospheric level (PAL), and N2O abundances of 10% and 1000% PAL. We find that varying N2O impacts the O2-O3 relationship differently depending strongly on both the host star and the amount of atmospheric O2. Planets orbiting hotter hosts with strong UV fluxes efficiently convert N2O into NOx, often depleting a significant amount of O3 via faster NOx catalytic cycles. However, for cooler hosts and low O2 levels we find that increasing N2O can lead to an increase of overall O3 due to the smog mechanism producing O3 in the lower atmosphere. Variations in O3 result in significant changes in the amount of harmful UV reaching the surfaces of the model planets as well as the strength of the 9.6 µm O3 emission spectral feature, demonstrating potential impacts on habitability and future observations
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