First insights from the Berlin Atmospheric Simulation Experimental Chamber (BASE)
Authors: Hofmann Florence , Rauer Heike , Grenfell John Lee , Taysum Benjamin , Elsaesser Andreas 
Published: July 2024

Ongoing mission such as TESS [1], CHEOPS [2] and JWST [3] as well as forthcoming missions such as PLATO [4] and ARIEL [5] have remarkably expanded our capacity to investigate planetary objects beyond our solar system, revealing new classes of planets, including hot-Jupiters [6, 7, 8, 9], mini-Neptunes [10, 11, 12] and super-Earths. &#160;Excitingly, among these several thousands of detected exoplanets, there are some rocky planets orbiting their star within the habitable zone. As planetary atmospheres likely play a pivotal role in shaping habitability, significant efforts have been made to characterize the physical properties and the complex chemistry occurring in rocky exoplanet atmospheres. As we discover a growing list of Earth-like exoplanets orbiting prevalent later star types, such as K and M dwarfs, discussions about the habitability of exoplanets around these longer-lived stars have been initiated [13]. There is an ongoing debate about the significance of potential biosignature compounds, like e.g. oxygen or ozone under various atmospheric conditions. With most of the oxygen in modern Earth&#8217;s atmosphere thought to be biotically produced through photosynthesis, oxygen and ozone are considered to be possible biomarker compounds [14]. Regarding ongoing discussions about habitability of early-Earth, early life probably evolved in an anoxic, high-UV environment [15]. Under such conditions, it can be shown that molecular oxygen also forms through photolysis of CO2 &#160;and subsequent recombination of O atoms [16]. The question to what extent these potential false positive biosignatures can be produced abiotically is therefore of great potential relevance for the interpretation of data from future missions. Further, biosignature abundances in exoplanet atmospheres may be greatly influenced by high energy particles (HEPs) emitted from stellar flares [17, 18]. Correct interpretation of spectral measurements therefore requires a new generation of photochemical-climate models that consider important factors such as the incoming stellar radiation the atmospheric mass and composition as well as the role of clouds and surface properties. However, as exoplanets often have no counterpart in our solar system, nor can in-situ data be acquired, model parameters are often inferred from limited data sets.Consequently, careful comparisons with laboratory experiments plays a pivotal role in advancing our understanding of atmospheric processes [7]. Atmospheric simulation chambers are controlled laboratory environments that allow researchers to simulate and study complex phenomena that occur in the Earth's atmosphere and beyond. We present the Berlin Atmospheric Simulation Experimental Chamber (BASE) which is a versatile platform designed to replicate various atmospheric conditions representative for Earth-like exoplanet atmospheres. The BASE chamber is capable of simulating a range of atmospheric pressures ranging from 1 bar (e.g. modern Earth surface) down to a few mbar (e.g. Mars surface) and temperatures (293 K - 373K). It is equipped with a sophisticated gas mixing system that allows for precise control of atmospheric composition, including the introduction of trace gases and water vapor. Possible scenarios include primary, steam early-Earth-like, thin, cool Mars-like and thick, hot Venus-like atmospheres. In contrast to many atmospheric simulation chambers that lack simultaneous photon and electron irradiation capabilities, studies using BASE can examine photochemical processes driven by UV and Lyman alpha radiation, and electrons radiation. Experiments conducted at BASE focus on potential alterations of gaseous biomarkers and their distinction from potential abiotic sources [19] in various conditions. The chamber allows continuous spectroscopic real-time monitoring of gas samples across a wide wavelength range, covering VUV/VIS/NIR and simultaneous mass spectrometric analysis, allowing for precise measurements of gas composition, chemical reactions, and optical properties. We present first results on the photochemical formation and destruction processes of ozone in Earth&#8217;s stratosphere and extended experiments under enhanced UV irradiation. As has been recognized very early on, the lifetime of ozone in given atmospheric conditions is very sensitive to minor changes, with ozone production being a highly non-linear process. Therefore, future experiments at BASE aim to investigate ozone chemistry at elevated temperatures, radiation levels and increased amounts of H2O and NOx species in different atmospheric compositions. In combination with atmospheric modelling we envision deeper insight on the role of oxygen and ozone as gaseous biomarkers and the potential formation of ozone layers under atmospheric conditions of rocky exoplanets orbiting distant stars.&#160;AcknowledgementsThis work was supported by Volkswagen Foundation and its Freigeist Program (F.H., A.E.). A.E. also acknowledges support from the Ministry of Economics and Energy (Projektr&#228;ger Deutsches Zentrum f&#252;r Luft- und Raumfahrt, grants 50WB1623 and 50WB2023. Furthermore, funding and support from the Forschungskomission (via TEAMS funding to H.R. and A.E.) of Freie Universitaet Berlin is gratefully acknowledged.&#160;&#160;References R. Ricker et al, AAS/Division for Extreme Solar Systems Abstracts 47 (2015) 503&#8211;01.
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