Aktuelle Arbeiten
Doktorarbeiten
Barbara Stracke: Modellierung von Atmosphären terrestrischer extrasolarer Planeten im Hinblick auf Habitabilität
In dieser Arbeit soll die Chemie in Atmosphären von erdähnlichen extrasolaren Planeten untersucht werden unter dem Gesichtspunkt der Habitabilität. Genauer analysiert werden soll der Einfluss biogener Flüsse (Methan, Lachgas, etc.) auf die jeweilige Temperatur und Konzentrationen von Biomarkern (Sauerstoff, Ozone, Methan, Lachgas, Wasser, etc) der terrestrische Atmosphäre. Hierbei sind Biomaker Gase in der Atomsphäre deren Vorkommen oder Häufigkeit mit Leben verbunden ist. Diese können als besonders Merkmal in den Spektren von planetaren Atmosphären nachgewiesen werden, welche Leben beherbergen.Mittels eines gekoppelten eindimensionalen Säulenmodels, welches in einen radiative-konvektiven Teil zur Bestimmung des Temperaturprofils und eines photochemischen Teils der die Konzentrationsprofile der untersuchten Biomarker liefert, können die verschiedenen Wechselwirkungen untersucht werden. Dies alles geschieht unter der Voraussetzung, dass sich der Planet innerhalb der 'Habitablen Zone' befindet, welche definiert ist als der Bereich um einen Stern, wo die Bedingungen für Leben günstig sind. Das Vorhandensein von Wasser wird hierbei als wichtigste Voraussetzung für die Entstehung von Leben verwendet. Um den Einfluss der biogenen Spezies auf die Atmosphäre über die habitable Zone zu bestimmen müssen verschiedene Feedback-Mechanismen und auch der Carbon-Silikat-Zyklus in das verwendete Model eingefügt werden.
Thomas Fruth: Charakterisierung extrasolarer Transitplaneten
CoRoT ist eine frz. Satellitenmission mit internationaler Beteiligung zur Transitsuche sowie der asteroseismologischen Untersuchung von Sternen. Die beiden DLR-Projekte BEST und BEST II (Berlin Exoplanet Search Telescope) dienen der näheren Charakterisierung mit CoRoT entdeckter Planetenkandidaten und variablen Sternen.
Ziel dieser Arbeit ist die Untersuchung von CoRoT-Feldern, sowohl vor als auch nach der jeweiligen Beobachtung des Satelliten: (a) Follow-up von "short-runs": In diesen Feldern, die jeweils nur 30 Tage von CoRoT beobachtet werden, sind die Ephemeriden von entdeckten periodischen Objekten nur sehr ungenau bestimmt. Die Erweiterung der Zeitreihe kann die Ergebnisse deutlich präzisieren. (b) Weitere bodengebundene Charakterisierung mit CoRoT entdeckter Planetensystem, z.B. durch Untersuchung auf weitere Objekte mithilfe der Transit-Timing-Methode.(c) Charakterisierung variabler Sterne vor der Satellitenbeobachtung zur Vermeidung von Fehlalarmen. Bestätigung von Kandidaten in der Datenbank zuvor mit BEST/BEST II beobachteter Felder.
How Earth evolved to be habitable is a central question to understanding our own origins and our place in the Universe. Addressing this question requires knowledge of the complex interplay between many processes - physical, chemical, biological and geological - acting over a vast range of temporal and spatial scales. Also, in terms of exoplanet studies, many stars in our solar neighbourhood are young, so any rocky planets they may have are also likely to be young – this is an important motivation for studying the Early Earth’s atmosphere as a reference to compare with such worlds.To investigate these issues, our goal is to apply a global mean column model with interactive oxygen (O2), carbon dioxide (CO2) and nitrogen (N2) chemistry, coupled radiative transfer and including biogeochemical cycles. We will focus on specific points in time (“snapshots”), such as before, at and after the so-called Great Rise in Oxygen (GOE) which took place around 2.3 Ga (gigayears) ago. Each snapshot can also be interpreted as the atmosphere of a hypothetical extrasolar terrestrial planet, which could be found in the near future by space missions like CoRoT and Kepler.
Mareike Godolt: 3D atmospheric modeling of terrestrial extrasolar planets Column models are commonly applied to model terrestrial extrasolar planetary atmospheres since so far no detailed constraints for the nature of such planets such as surface configurations (e.g. land-mass distribution or topography) can be placed. Even atmospheric mass and composition are unknown for those objects and have to be assumed in atmospheric modeling studies. Also, the first generation of future observations will probably provide us with disk-averaged spectra only. Nevertheless, we know that for the Earth, atmospheric processes are strongly influenced by the general circulation of the atmosphere which transports heat, momentum and trace gases. The atmospheric circulation reduces temperature gradients and influences the abundances of trace gases, causing e.g. ozone accumulation at the winter poles for the Earth. For extreme planetary scenarios atmospheric dynamics may be of even higher importance as suggested for the case of a tidally-locked (i.e. constant day and night-side) terrestrial exoplanet orbiting an M-dwarf star (Joshi et al.1997, Joshi 2003), where the circulation can prevent an atmospheric collapse on the night-side down to very low pressures due to heat transport. Furthermore, it is possible to study the impact of different orbital parameters with 3-dimensional (3D) models, such as length of year, obliquity or eccentricity (e.g. Williams and Pollard 2002, 2003) or albedo feedback due to snowfall. In the framework of the Helmholtz Alliance "Planetary evolution and life" work has begun with EMAC (ECHAM/MESSy Atmospheric Chemistry model, Jöckel et al., 2006), which is a state-of-the-art general circulation and chemistry model for Earth, investigating the influence of different stellar types upon atmospheric properties and planetary surface conditions, since the energy input due to stellar radiation is the prime limiting factor for habitability. For stars of different type the energy flux distribution of the incident radiation and the orbital period, and thereby the length of the year changes. Due to modification of the stellar radiation, atmospheric temperatures and temperature gradients change, hence an alteration of the global circulation can be expected. In addition a change of atmospheric dynamics is expected for e.g. adapting orbital periods, which will lead to changed seasonality. In summary, it will be investigated how the Earth's climate would change, if it were to orbit a star other than the sun.
Alexander Hölscher: Evaluation of Cometary Gas Production Rates
The goal of this thesis is to investigate and extend if possible the current classification of comets based on their chemical composition. This classification is based on the abundances of the radicals CN, C2, C3, NH2, OH etc. in the coma.Since these radicals dissociate from larger parent species the goal is to establish a classification with the parent species. These parent species can be observed in the IR and radio wavelength range. But the radicals can be observed in the UV, even for fainter comets. This is important to gain a significant amount of measurements for statistical investigations.The focus of our work is to investigate the link between the C2 and the C3 radicals and possible parent species. For this purpose a 1D-model of the cometary coma is applied, which was developed in our working group and which is to be upgraded. Additionally an expansion of the data set of production rates of the radicals C2, C3 in the existing database can give constraints on the role of possible C2 and C3 parent species like C2H2.
Daniel Kitzmann: Formation and evolution of clouds in atmospheres of terrestrial extrasolar planets
The climate of terrestrial planets results from the energy balance between absorbed stellar radiation and the loss of thermal radiation emitted from the surface and the atmosphere to space. Cloud particles can have a strong impact on the radiation budget in terrestrial planetary atmospheres and, therefore, also on the planetary climate and the position and the extension of habitable zones around different central stars. They can reflect the stellar radiation back towards space, thereby reducing the stellar energy available for heating the surface (albedo effect), but on the other hand also reduce the loss of thermal radiation to space (greenhouse effect). The effectiveness of the albedo and the greenhouse effect depend on the strongly wavelength dependent optical properties of the clouds in combination with the spectral distribution of the incident stellar and atmospheric thermal radiation. The absorption and scattering characteristics of the cloud particles, on the other hand, are determined by their microphysical properties, such as size distribution and shape.
The aim of this thesis is to study the formation and properties of clouds in atmospheres of terrestrial extrasolar planets and their effect on the planetary climate. Special focus is placed on CO2 clouds which are important for the determination of the outer boundary of the habitable zone.
Joachim Stock: Chemical pathways analysis of CO2-dominated atmospheres: Mars On Mars, the main constituent, CO2 is controlled by trace species via potentially complex chemical pathways. On Earth, key species such as ozone, an atmospheric biomarker, also display complex photochemistry. Understanding such responses requires new diagnostic tools. To address these issues, we apply an algorithm developed by a collaboration colleague, Ralph Lehmann of the Alfred-Wegener Institute. This algorithm, termed the Pathway Analysis Program (PAP) determines all significant pathways in a chemical reaction system, The identification of the important pathways will lead to a better understanding of the chemical system in CO2 dominated atmospheres. Identification of key catalysts can provide input for future space missions searching for trace gases in the atmospheres of solar system planets. This, in turn can be used to improve the atmospheric models. Such work can then be applied to extend our knowledge about extrasolar planets.
Thomas Pasternacki: Homogeneous study of the CoRoT-planets
In exoplanetary science it is essential to determine the planetary parameters with the highest possible precision. These parameters are important for our understanding of the nature of the exoplanets and serve as input parameters for the scientific studies which follow.The French satellite mission CoRoT delivers qualitative high photometric signals of around 100,000 stars and has lead to 17 confirmed planets up to now. The evaluation of the data for these planets has, until now been mostly achieved using a rather non-homogeneous setup in terms of staff, software versions, expertise etc.Therefore, a homogeneous study of all currently known CoRoT planets is desirable. Such a study should ideally be performed by one software in the most possible homogeneous way including all knowledge, e. g., gained during evaluation of the confirmed planets, and new aspects such as improved handling of limb darkening, binning and reflection effects. Another outcome of studying the transit events of a planet is the measurement of a possible transit timing variation. These variations can provide hints for other companions in the examined system.
Diplomarbeiten
Arik Rohloff: Effects of Cosmic Rays on extrasolar planetary terrestrial atmospheres
The thesis deals with the effects of Cosmic Rays (CR) on planetary terrestrial atmospheres. More precisely the impact of CR on chemical processes in the atmosphere is to be analysed. To do this the air showers of secondary Cosmic Ray particles are parameterised and their capability of breaking molecular bonds is calculated. Resulting chemical products are implemented in our 1D photochemical model to investigate further effects like temperature variations or the loss of ozone and other biomarkers.
Falk Dambowsky: Modeling hot Atmospheres of terrestrial ExoplanetsRecent advances in technology imply that the era of atmospheric characterisation of hot, rocky super-Earth planets is already beginning. Several transiting super-Earths have been detected so far, e. g.: CoRoT 7b (Leger et al. 2009), Kepler 10b (Batalha et al. 2010) and GJ 1214b (Charbonneau et al. 2009). GJ 1214b is the first super-Earth for which transmission spectroscopy has been performed (Bean et al. 2010). This is an example of a new possible class of rocky planet which is situated inward of the inner boundary of the habitable zone, where temperatures are likely to be too hot for liquid water. In the solar system we find one planet with a thick CO2-dominated atmosphere at such hot temperatures, namely Venus. Such Venus-like CO2-dominated atmospheres are a possible common scenario assumed for hot terrestrial extrasolar planets. Clearly atmospheric modeling studies are required first to distinguish between different proposed atmospheric scenarios (e.g. gassy or steamy atmospheres etc.) and second to interpret future exoplanet spectra in more detail.The aim of this Thesis is to apply current knowledge from the Venus atmosphere to model chical atmospheric compositions of hot terrestrial exoplanets. We use a 1D radiative-convective model with coupled photochemistry which was so far applied to Earth-like exoplanet scenarios only (Segura et al. 2003, Grenfell et al. 2007, Grenfell et al. 2010, Rauer et al. 2011). We will adapt this model to hot atmospheric scenarios with a focus on modeling the chemical composition and spectra. Therefore we will extend the validity range of the photochemistry module and make use of the radiative-convective module from v. Paris et al. (2010).
Abgeschlossene Arbeiten
Philip von Paris: The atmospheres of hot Super-Earths
1. MotivationDue to the ever increasing precision of space- and ground-based observations, detections of low-mass exoplanets have been announced in recent years, some of them with masses below 10 Earth masses. Such planets are likely to be rocky planets, hence might be classified as terrestrial. Among these so-called Super-Earths, many scientists expect to find the first habitable planets outside our solar system. Due to current observing constraints the first generation of Super-Earths to be discovered are expected to be hot Super-Earths orbiting close to their central star 2. AimDuring this PhD thesis, we want to model the atmospheres of hot Super-Earths. These model simulations will be used to assess the habitability of Super-Earths, i.e. surface conditions, as well as temperature structure, cloud formation and chemical composition.3. MethodsWe will use a 1D radiative-convective climate model coupled with a photochemical model to study the influence of parameters like planetary mass, orbital distance or central star type on surface and atmospheric conditions, i.e. the response of climate and photochemistry to parameter changes.In order to do this, we must extend the validity range (temperature, pressure, chemical composition) of our cur-rently available modeling tools to the conditions likely to be encountered for hot Super-Earths.
Karol Palczynski: Analyse chemischer Reaktionszyklen in atmosphären terrestrischer PlanetenStefan Linz: New analysis of multicolour photometry of planetary transits
The aim of this work is the homogenous analysis of light curves from extra-solar planets which have been observed by the transit method. The main focus is the modelling of the transits and the resulting planet parameters. Common methods for light curve modelling and some optimization processes are discussed. Finally, a set of public light curves in different colours are modelled with the same conditions with the aim to determine a whole set of the planetary parameters and their errors and thus to evaluate the reliability of the tools and approach.
André Bathke: Modeling of light curves of eclipsing binaries in fields of BEST Double stars are of central importance for the understanding of stellar structures and evolutions. Through the observation of eclipsing binaries, which are also called photometric binary stars, one is able to determine the physical parameters of the system such as mass, radius, separation, surface temperature and orbital parameters. Such parameters are essential for constraining stellar models in terms of their internal structure and their evolution. They can not be as easily identified for isolated stars. In the search for extrasolar planets, using the telescope BEST (Berlin Exoplanet Search Telescope) located at Observatoire de Haute-Provence in France, many eclipsing binaries have been discovered in the fields of observation. The aim of this thesis is, to model these observed light curves for eclipsing binaries and determine physical parameters of the systems and to determine the quality of the results with respect to the results of modeled light curves of CoRoT. With this work one will be able to make a statement about the possibility of determining the physical parameters of eclipsing binaries, which have been observed with BEST.
Bachelorarbeiten
Fachreddin Tabataba-Vakili: Effects of Cosmic Rays on Trace Gases in Earth-Like Atmospheres
Long lifetimes, a close-in Habitable Zone (HZ) and a favorable size make M stars an ideal candidate for the search for extrasolar planets. However, M star worlds might be subject to extreme conditions. Aside from the strong differences in their stellar spectrum compared to the sun, the main problems lie in their high stellar variability and unfavorable tidal effects, which might lead to reduced magnetospherical protection. The coronal mass ejections (CME) of the star might make its planet target to severe and permanent bombardment of high energy particles. Particularly the cosmic rays (CR) of the M star might erode the atmosphere of a potentially habitable planet surrounding it. The goal of this work is to determine the potential effect of CR on methane and water. These two atmospheric components are vital for habitability and radiative energy transfer alike. At first we describe the general interaction between cosmic rays and the atmosphere. Then we investigate the dissociation cross sections with the CR-induced secondary electron cascade for methane and water. We compare the resulting destruction rates with photolysis and chemical loss rates in the atmosphere to justify further studies. The results indicate that CRs make a significant contribution the the destruction of the considered chemical species only in the case of a constant stellar proton event (SPE) of the M star.