New Insights into Cosmic Ray induced Biosignature Chemistry in Earth-like Atmospheres

With the recent discoveries of terrestrial planets around active M-dwarfs, destruction processes masking the possible presence of life are receiving increased attention in the exoplanet community. We investigate potential biosignatures of planets having Earth-like (N$_2$-O$_2$) atmospheres orbiting in the habitable zone of the M-dwarf star AD Leo. These are bombarded by high energetic particles which can create showers of secondary particles at the surface. We apply our cloud-free 1D climate-chemistry model to study the influence of key particle shower parameters and chemical efficiencies of NOx and HOx production from cosmic rays. We determine the effect of stellar radiation and cosmic rays upon atmospheric composition, temperature, and spectral appearance. Despite strong stratospheric O$_3$ destruction by cosmic rays, smog O$_3$ can significantly build up in the lower atmosphere of our modeled planet around AD Leo related to low stellar UVB. N$_2$O abundances decrease with increasing flaring energies but a sink reaction for N$_2$O with excited oxygen becomes weaker, stabilizing its abundance. CH$_4$ is removed mainly by Cl in the upper atmosphere for strong flaring cases and not via hydroxyl as is otherwise usually the case. Cosmic rays weaken the role of CH$_4$ in heating the middle atmosphere so that H$_2$O absorption becomes more important. We additionally underline the importance of HNO$_3$ as a possible marker for strong stellar particle showers. In a nutshell, uncertainty in NOx and HOx production from cosmic rays significantly influences biosignature abundances and spectral appearance.Comment: Manuscript version after addressing all referee comments. Published in Ap

Detectability of biosignatures on LHS 1140 b

Terrestrial extrasolar planets around low-mass stars are prime targets when searching for atmospheric biosignatures with current and near-future telescopes. The habitable-zone Super-Earth LHS 1140 b could hold a hydrogen-dominated atmosphere and is an excellent candidate for detecting atmospheric features. In this study, we investigate how the instellation and planetary parameters influence the atmospheric climate, chemistry, and spectral appearance of LHS 1140 b. We study the detectability of selected molecules, in particular potential biosignatures, with the upcoming James Webb Space Telescope (JWST) and Extremely Large Telescope (ELT). In a first step we use the coupled climate-chemistry model, 1D-TERRA, to simulate a range of assumed atmospheric chemical compositions dominated by H$_2$ and CO$_2$. Further, we vary the concentrations of CH$_4$ by several orders of magnitude. In a second step we calculate transmission spectra of the simulated atmospheres and compare them to recent transit observations. Finally, we determine the observation time required to detect spectral bands with low resolution spectroscopy using JWST and the cross-correlation technique using ELT. In H$_2$-dominated and CH$_4$-rich atmospheres O$_2$ has strong chemical sinks, leading to low concentrations of O$_2$ and O$_3$. The potential biosignatures NH$_3$, PH$_3$, CH$_3$Cl and N$_2$O are less sensitive to the concentration of H$_2$, CO$_2$ and CH$_4$ in the atmosphere. In the simulated H$_2$-dominated atmosphere the detection of these gases might be feasible within 20 to 100 observation hours with ELT or JWST, when assuming weak extinction by hazes. If further observations of LHS 1140 b suggest a thin, clear, hydrogen-dominated atmosphere, the planet would be one of the best known targets to detect biosignature gases in the atmosphere of a habitable-zone rocky exoplanet with upcoming telescopes.Comment: 18 pages, 11 figure

Distinguishing between wet and dry atmospheres of TRAPPIST-1 e and f

The nearby TRAPPIST-1 planetary system is an exciting target for characterizing the atmospheres of terrestrial planets. The planets e, f and g lie in the circumstellar habitable zone and could sustain liquid water on their surfaces. During the extended pre-main sequence phase of TRAPPIST-1, however, the planets may have experienced extreme water loss, leading to a desiccated mantle. The presence or absence of an ocean is challenging to determine with current and next generation telescopes. Therefore, we investigate whether indirect evidence of an ocean and/or a biosphere can be inferred from observations of the planetary atmosphere. We introduce a newly developed photochemical model for planetary atmospheres, coupled to a radiative-convective model and validate it against modern Earth, Venus and Mars. The coupled model is applied to the TRAPPIST-1 planets e and f, assuming different surface conditions and varying amounts of CO$_2$ in the atmosphere. As input for the model we use a constructed spectrum of TRAPPIST-1, based on near-simultaneous data from X-ray to optical wavelengths. We compute cloud-free transmission spectra of the planetary atmospheres and determine the detectability of molecular features using the Extremely Large Telescope (ELT) and the James Webb Space Telescope (JWST). We find that under certain conditions, the existence or non-existence of a biosphere and/or an ocean can be inferred by combining 30 transit observations with ELT and JWST within the K-band. A non-detection of CO could suggest the existence of an ocean, whereas significant CH$_4$ hints at the presence of a biosphere.Comment: 37 pages, 18 figures, accepted for publication in Ap

The PAC2MAN mission: A new tool to understand and predict solar energetic events

An accurate forecast of flare and coronal mass ejection (CME) initiation requires precise measurements of the magnetic energy buildup and release in the active regions of the solar atmosphere. We designed a new space weather mission that performs such measurements using new optical instruments based on the Hanle and Zeeman effects. The mission consists of two satellites, one orbiting the L1 Lagrangian point (Spacecraft Earth, SCE) and the second in heliocentric orbit at 1AU trailing the Earth by 80° (Spacecraft 80, SC80). Optical instruments measure the vector magnetic field in multiple layers of the solar atmosphere. The orbits of the spacecraft allow for a continuous imaging of nearly 73% of the total solar surface. In-situ plasma instruments detect solar wind conditions at 1AU and ahead of our planet. Earth-directed CMEs can be tracked using the stereoscopic view of the spacecraft and the strategic placement of the SC80 satellite. Forecasting of geoeffective space weather events is possible thanks to an accurate surveillance of the magnetic energy buildup in the Sun, an optical tracking through the interplanetary space, and in-situ measurements of the near-Earth environment

The PAC2MAN mission: a new tool to understand and predict solar energetic events

An accurate forecast of flare and CME initiation requires precise measurements of the magnetic energy build up and release in the active regions of the solar atmosphere. We designed a new space weather mission that performs such measurements using new optical instruments based on the Hanle and Zeeman effects. The mission consists of two satellites, one orbiting the L1 Lagrangian point (Spacecraft Earth, SCE) and the second in heliocentric orbit at 1AU trailing the Earth by 80$^\circ$ (Spacecraft 80, SC80). Optical instruments measure the vector magnetic field in multiple layers of the solar atmosphere. The orbits of the spacecraft allow for a continuous imaging of nearly 73\% of the total solar surface. In-situ plasma instruments detect solar wind conditions at 1AU and ahead of our planet. Earth directed CMEs can be tracked using the stereoscopic view of the spacecraft and the strategic placement of the SC80 satellite. Forecasting of geoeffective space weather events is possible thanks to an accurate surveillance of the magnetic energy build up in the Sun, an optical tracking through the interplanetary space, and in-situ measurements of the near-Earth environment.Comment: Accepted for publication in the Journal of Space Weather and Space Climate (SWSC

The PAC2MAN mission: A new tool to understand and predict solar energetic events

An accurate forecast of flare and coronal mass ejection (CME) initiation requires precise measurements of the magnetic energy buildup and release in the active regions of the solar atmosphere. We designed a new space weather mission that performs such measurements using new optical instruments based on the Hanle and Zeeman effects. The mission consists of two satellites, one orbiting the L1 Lagrangian point (Spacecraft Earth, SCE) and the second in heliocentric orbit at 1AU trailing the Earth by 80\ub0 (Spacecraft 80, SC80). Optical instruments measure the vector magnetic field in multiple layers of the solar atmosphere. The orbits of the spacecraft allow for a continuous imaging of nearly 73% of the total solar surface. In-situ plasma instruments detect solar wind conditions at 1AU and ahead of our planet. Earth-directed CMEs can be tracked using the stereoscopic view of the spacecraft and the strategic placement of the SC80 satellite. Forecasting of geoeffective space weather events is possible thanks to an accurate surveillance of the magnetic energy buildup in the Sun, an optical tracking through the interplanetary space, and in-situ measurements of the near-Earth environment

A secondary atmosphere on the rocky exoplanet 55 Cancri e

Characterizing rocky exoplanets is a central endeavor of astronomy, and yet the search for atmospheres on rocky exoplanets has hitherto resulted in either tight upper limits on the atmospheric mass or inconclusive results. The 1.95-REarth and 8.8-MEarth planet 55 Cnc e, with a predominantly rocky composition and an equilibrium temperature of ~2000 K, may have a volatile envelope (containing molecules made from a combination of C, H, O, N, S, and P elements) that accounts for up to a few percent of its radius. The planet has been observed extensively with transmission spectroscopy, and its thermal emission has been measured in broad photometric bands. These observations disfavor a primordial H2/He-dominated atmosphere but cannot conclusively determine whether the planet has a secondary atmosphere. Here we report a thermal emission spectrum of the planet obtained by JWST's NIRCam and MIRI instruments from 4 to 12 {\mu}m. The measurements rule out the scenario where the planet is a lava world shrouded by a tenuous atmosphere made of vaporized rock, and indicate a bona fide volatile atmosphere likely rich in CO2 or CO. This atmosphere can be outgassed from and sustained by a magma ocean.Comment: Published online in Nature on May 8, 2024. https://www.nature.com/articles/s41586-024-07432-x. Authors' preprin

Habitabilität terrestrischer Planeten um aktive M-Sterne: Der Einfluss von Sternstrahlung und kosmischer Strahlung auf Klima und Foto-Chemie

Planetary habitability depends strongly on the interaction between the planetary atmosphere and the energy from its host star. Due to both the anticipated diversity of exoplanetary atmospheres as well as the large range of stellar classes and activities, modeling possible planetary climate states and atmospheric conditions is a challenging endeavor. A central aim of this work was to extend the understanding of the effects of stellar radiation upon atmospheric temperatures, and the multitude of cascading effects which Stellar Energetic Particles together with Galactic Cosmic Rays may have upon atmospheric composition. Both these effects are likely to be key factors affecting potential surface habitability. This thesis therefore addressed the following scientific questions for some well-chosen scenarios: • What kind of atmospheres may provide habitable conditions? • Which atmospheres can explain observed spectral features? • How does the host star ́s spectral type affect planetary habitability? • How do energetic particle showers impact atmospheric composition and habitability? To address these questions, a comprehensive one-dimensional coupled climate chemistry model was developed and applied during the course of this cumulative thesis. Part of this thesis are the works published in Scheucher et al. (2018) and Scheucher et al. (2020a) focusing on the effect of energetic particle bombardment onto exoplanetary atmospheres and habitability, and Scheucher et al. (2020b) focusing on the effect of opacities in radiative transfer through a large variety of atmospheric conditions upon planetary climate and atmospheric spectral characteristics.Die Habitabilität eines Planeten hängt stark von der energetischen Strahlung des Zentralsterns und dessen Interaktion mit der Planetenatmosphäre ab. Die zu erwartende Vielfalt an exoplanetaren Atmosphären sowie die breite Spanne an stellaren Spektralklassen und Sternaktivitäten, stellt eine große Herausforderung für die Modellierung des planetaren Klimas und atmosphärischen Bedingungen dar. Ein zentrales Ziel dieser Arbeit war es, den Effekt von Sternstrahlung auf atmosphärische Temperaturen, sowie die Vielzahl an Kaskadeneffekte die Stellare energetische Teilchen zusammen mit Galaktischer kosmischer Strahlung auf die atmosphärische Zusammensetzung haben, besser zu verstehen. Diese Effekte scheinen eine Schlüsselrolle für planetare Habitabilität an der Oberfläche zu spielen. Daraus ergaben sich die folgenden zentralen wissenschaftlichen Fragestellungen für diese Doktorarbeit für ausgewählte Szenarien: • Welche Atmosphären können im allgemeinen für habitable Konditionen sorgen? • Welche Atmosphären können beobachtete spektrale Signaturen erklären? • Wie beeinflusst die Spektralklasse des Zentralsterns mögliche planetare Habitabilität? • Wie beeinflussen energetische Teilchenschauer die atmosphärische Zusammensetzung und Habitabilität? Um diese Fragestellungen gezielt behandeln zu können, wurde im Zuge dieser kumulativen Dissertation ein umfassendes eindimensionales, gekoppeltes Klima-Fotochemie Modell entwickelt und angewandt. Teil dieser Dissertation sind die Arbeiten veröffentlicht in Scheucher et al. (2018) and Scheucher et al. (2020a) mit dem Fokus auf dem Effekt von energetischem Teilchenbeschuss auf exoplanetare Atmosphären und planetare Habitabilität, sowie Scheucher et al. (2020b) welches den Effekt von Opazitäten im Strahlungstransport auf Klima und spektrale Charakteristik von Planeten mit sehr unterschiedlichen atmosphärischen Bedingungen untersucht