At the Astrobiology department within the LISA, an Atmospheric Systems Laboratory. (LISA – Laboratoire Inter-universitaire des Systèmes Atmosphériques) Créteil, France. The end of my internship is fast approaching and I have some ideas of future improvement for this program. However, I would maybe not have time to set up these new ideas. Let me introduce some articles which can bring new informations.
1. Polycyclic aromatic hydrocarbon - Polycyclic aromatic hydrocarbon processing by cosmic rays (Micelotta, Jones and Tielens, 2010) Actually, any radiolysis destruction constant under GCRs radiation was determined. This article presents the lifetime of PAHs under GCRs radiation. A theoritical model determine that the lifetime of PAHs under GCR radiation depends of the molecule size, on the electronic excitation energy E0 and on the amount of energy available for dissociation. According to their estimation, the lifetime of PAHs under GCR radiation is between 107 years for the smallest molecules (~10 C-atoms) and 109 years for the larger molecules (~1000 C-atoms). However, our program simulate the survival of molecules during few years and could not take into account a destruction during 107 years. We are, thus, waiting for an experimental radiolysis constant which might be determined thanks to the return of the spatial mission “EXPOSE” which exposes organic matter to a galactic environment on the International Space Station or wainting for a laboratory experiment which can give us this radiolysis constant. 2. Mars sedimentary rock erosion rates - Mars sedimentary rock erosion rates constrained using crater counts, with applications to organic-matter preservation and to the global dust cycle (Kite and Mayer, 2017) This article presents the Mars sedimentary rock erosion rates and the consequences on the preservation of organic matter. Their conclusion were that the radiolysis is less of a threat to the preservation of ancient, complex organic matter. Therefore, the exhumation rate at the paleolake deposits in SW Melas Chasma is relatively high. Whereas, radiolysis is more of a threat to the preservation of ancient, complex organic matter when the exhumation rate is relatively low such as at the Oxia Planum and Aram Dorsum. However, the mean value of their exhumation rate was equal to 100 nm/yr, which is too low to have an impact on our model. 3. “Solar Energetic Particles” (SEPs) or called also “Solar Cosmic Rays” (SCRs) - Degradation of the organic molecules in the shallow subsurface of Mars due to irradiation by cosmic rays (Pavlov et al., 2012) - Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology (Dartnell et al., 2007) These articles discuss about impact of “Solar Energetic Particles” (SEPs) or called also “Solar Cosmic Rays” (SCRs) . (Pavlov et al., 2012) estimated the SEPs flux at the Mars orbit was assumed to be 33 protons/cm2/sec. SCRs particles were assumed to have energies in the range of 1 MeV – 1GeV. SCRs particles with energies below 1 MeV would be absorbed in the atmosphere and would not reach the Martian surface. There are very few SCRs particles with energies above 1 GeV. However, the SEPs flux is dependent on the 11-year solar activity cycle. Then, the impact of SEPs on organics could be almost easly model at the surface of Mars. 4. Adenine on the Martian Surface under secondary particles - Degradation of Adenine on the Martian Surface in the presence of Perchlorates and Ionizing Radiation: A Reflection Time-of-flight Mass Spectrometric Study (Gobi, Bergantini and kaiser, 2017) This article describe the radiolysis decomposition of adenine (C5H5N5) under Martian conditions irradiated with energetic electrons that simulate the secondary particles originating from the interaction of the galactic cosmic rays (GCRs) with the Martian surface. Neat adenine and adenine-magnesium perchlorate mixtures were experimentaly irradiated. Then, the destruction of Adenine under secondary particles on Mars could be added to the model with a new type of radiation. Moreover, thanks to the set-up MOMIE (Mars Organic Matter Irradiation and Evolution) developed at the LISA laboratory, the photodestruction constant of Adenine caused by UV radiation was already determined and during my previous internship in this lab, I was involved in the experiment to study the chemical evolution of Adenine under UV radiation in martian conditions (temperature and pressure).
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At the Astrobiology department within the LISA, an Atmospheric Systems Laboratory. (LISA – Laboratoire Inter-universitaire des Systèmes Atmosphériques) Créteil, France My goal : Model the impact of Galactic Cosmic Rays (GCRs) on organics in the Martian environment. GCRs consist of 98% atomic nuclei (divided into 87% of protons, 12% of alpha particles, 1% of heavier nuclei) and 2% electrons (Ehresmann et al, 2014). (Wilson et al, 2016) and (Pavlov et al, 2012) affirmed that GCRs radiation can penetrate down to few meters in the martian soil. (Dartnell et al, 2007) gives us the evolution of protons and electrons fluxes which compose GCRs radiation according to the depth. Firstly, I assumed that GCRs is composed entirely of protons. Then, I added electrons particles in the GCRs flux to be more realistic. Figure 1 : Attenuation with depth for (top) hadronic core, and (bottom) muons and electromagnetic cascade. Surface model indicated as follows: Dry Homogenous (solid), Pure Ice (dashed), and Wet Heterogeneous (dot-dash). (Dartnell et al, 2007) Bibliography : Dartnell, L., Desorgher, L., Ward, J. and Coates, A. (2007). Modelling the surface and subsurface Martian radiation environment: Implications for astrobiology. Geophysical Research Letters, 34(2). Ehresmann, B., Zeitlin, C., Hassler, D., Wimmer-Schweingruber, R., Böhm, E., Böttcher, S., Brinza, D., Burmeister, S., Guo, J., Köhler, J., Martin, C., Posner, A., Rafkin, S. and Reitz, G. (2014). Charged particle spectra obtained with the Mars Science Laboratory Radiation Assessment Detector (MSL/RAD) on the surface of Mars. Journal of Geophysical Research: Planets, 119(3), pp.468-479. Pavlov, A., Vasilyev, G., Ostryakov, V., Pavlov, A. and Mahaffy, P. (2012). Degradation of the organic molecules in the shallow subsurface of Mars due to irradiation by cosmic rays. Geophysical Research Letters, 39(13), p.n/a-n/a. Wilson, E., Atreya, S., Kaiser, R. and Mahaffy, P. (2016). Perchlorate formation on Mars through surface radiolysis-initiated atmospheric chemistry: A potential mechanism. Journal of Geophysical Research: Planets, 121(8), pp.1472-1487. Posted by Alexandra Perron on April 05, 2017
At the Astrobiology department within the LISA, an Atmospheric Systems Laboratory. (LISA – Laboratoire Inter-universitaire des Systèmes Atmosphériques) Créteil, France During my internship, I have to improve a computing program which simulates the abundance of organics at the surface and in the subsurface of Mars. I explained previously how the “ModelMars” program works to calculate the abundance of organics at the Martian surface under UV radiation. My next step is obviously to explain how the “ModelMars” program works to calculate the abundance of organics in depth under UV radiation. I - “DepthCalculation.f90” file functioning Aim of the file : Determine the organic abundance of Glycine or Polycyclic aromatic hydrocarbon (PAHs) in the subsurface of Mars. Hypothesis : All organic matter is destroyed on the Martian surface because the destruction rate of organics is higher than the supply of organics thanks to micrometeorites. However, there is a possibility that a small quantity of organic matter can be preserved in the subsurface of Mars. - Reason 1. Micrometeorites, containing organic matter, arrive at the surface of Mars with a speed which allows them to bury themselves under the Martian surface. - Reason 2. The Martian surface is composed of regolith*. Due to storms, regolith dust can be found in suspension in the atmosphere and then accumulates on the surface. These events may allow to bury and protect organic matter contained in micrometeorites. * Regolith : “Regolith is a layer of loose, heterogeneous superficial material covering solid rock. It includes dust, soil, broken rock, and other related materials and is present on Earth, the Moon, Mars, some asteroids, and other terrestrial planets and moons.” (En.wikipedia.org, 2017) To determine the photons flux at different depth in the regolith soil, we used the Beer-Lambert law : Instead of Intensity, we replace it by Flux. (KHALFALLAH, B., 2016) UV(Z) = I0*exp(- α *Z) (1) UV(Z) : UV Flux according to the depth Z (protons/km2/yrm) Z : Depth under the surface in micrometers (µm) I0 : UV Flux arriving at the Martian surface which depends on the latitude (protons/km2/yrm) α : The absorption constant of UV by the regolith [equal to 0,027 µm-1 (Caro, Mateo-Martí and Martínez-Frías, 2006) ] Thus, to model the evolution of the organic matter concentration, we used the program to simulate the degradation of organic matter during few years on Mars. Thanks to these simulations, we obtained pictures that show us if the organic matter resists or if it is destroyed by UV radiation. It gives us also indications about the destruction rate of organics according to their species and at which depth it is possible to detect them. II – My contribution to this part of the program I will not resume all modifications that I have made during the first part of my internship. For every problem met since the beginning of my internship, I was able to find solutions and improve this part of the program. If you want more details, just ask ! Now, let’s see the first results ! III – Destruction of organics by UV radiation after 1 year This is our hypothesis before any simulation : Hypothesis : PAHs will be more difficult to destroy than Glycine. Explanation : A molecule containing many atomic bonds requires more energy to break all of these bonds and thus destroy the molecule. As PAHs contain more atomic bonds than Glycine, It seems logical that PAHs take more energy and thus more time to be destroyed. After some simulations, this hypothesis came true ! However, I am not allowed to give you more details. I just will show you which kind of results we can obtain. On the Figure 1, you can observed the initialization of the computer program. At the beginning of the simulation, the abundance of organic matter is equal to 2e+18 molecules/km^2/yrm at any depth (where yrm is a Martian year). This represents hypothetic sources of organic matter in the past, exogenous or endogenous. On the Figure 2, you can observe how organics may be destroyed in depth, based on the equation (1) above. IV – Destruction of organics by UV radiation during 10 years The simulation is divided in several steps : 1. Add Sources (Add the flux of organics brought by micrometeorites) 2. Subtract Losses (Subtract the flux of organics destroyed by UV radiation) 3. Add the burying factor (Add the burying of the organic matter under 400 microns of regolith dust, every year, to simulate the uprising of dust created by storms.) On the Figure 3, you can observe that the organic matter is buried under 400 microns each year and thus, the organic matter is pushed deeper in the soil each year. V – What you have to remember !
Bibliography Caro, G., Mateo-Martí, E. and Martínez-Frías, J. (2006). Near-UV Transmittance of Basalt Dust as an Analog of the Martian Regolith: Implications for Sensor Calibration and Astrobiology. Sensors, 6(6), pp.688-696. En.wikipedia.org. (2017). Regolith. [online] Available at: https://en.wikipedia.org/wiki/Regolith [Accessed 27 Mar. 2017]. KHALFALLAH, B. (2016). Modélisation de l’abondance des molécules organiques sur Mars. Stage effectué au Laboratoire Inter-universitaire des Systèmes Atmosphériques (LISA). pp.9-10. Posted by Alexandra Perron on April 03, 2017 At the Astrobiology department within the LISA (Laboratoire Inter-Universitaire des Systèmes Atmosphériques), Créteil, France In my previous blog-post, I explained the objective of the computer program named "ModelMars". Today, I am going to explain how this program is structured with some details about files composing it. I - “ModelMars” program structure As you can see on the picture below, the “ModelMars” program is composed of several Fortran90 files. The most important file is the “Main.f90” which is the centralization of all information contained in all other files. “ModelMars” program structure Legend : Purple arrows indicate the chronological order in which files are used in the "Main.f90". Blue arrows indicate that a file is used in an other one. Files description Main.f90 : Calls all other files to centralize information and execute the “ModelMars” program. Complementary.f90 : Contains some functions that will be called in the “Main.f90”. UvGeometric.f90 : Performs computations of the UV flux on Mars. DepthCalculation.f90 : Performs computations of the abundance of organics in the subsurface of Mars. gnufor2.f90 : Library GnuFor2 to plot graphs. Sources.f90, PertesUV.f90 & Controller.f90 : Explained below. (Khalfallah, 2016) II - File "Sources.f90" Aim : Annual quantity of organic molecules brought by exogenous sources on the surface of Mars in (molecules/km2/yr). Micrometeorites contain organic molecules as amino acids (ex : glycine, alanine), Polycyclic Aromatic Hydrocarbons (noted PAHs; ex : chrysene, pyrene) or Nucleobases (ex : uracil). During this internship, we are only interested in Glycine and in PAHs, but this program can be adapted for other species with the same approach. Thanks to (Flynn, 1996), we determined that the mass flow of undamaged micrometeorites arriving on Mars is approximately: FMicrometeoritesMars = [7 ; 112] g/km^2/yr (1) Glycine Micrometeorites contain between 0,25 and 21,65 parts per million (ppm) of Glycine (Glavin, Matrajt and Bada, 2004), (Matrajt et al., 2004) : GlycineMicrometeorites = [0,25 ; 21,65] ppm (2) We can thus determine the Glycine flux on Mars FGlycineMars : FGlycineMars = FMicrometeoritesMars * GlycineMicrometeorites FGlycineMars = [1,75 ; 2424,8] * 10-6 g/km^2/yr (3) To obtain finally data in “molecules/km2/yrm” instead of “ g/km2/yr”, we have to multiply FGlycineMars by the Avogadro constant and divide by the molar mass of Glycine (MGlycine = 75,07 g/mol). And finally, you have to multiply by 1,881 to obtain values in “Martian year” (yrm) and not in “Terrestrial year” (yr). FGlycineMars = [2,64 ; 3658,80] * 10^16 molecules/km2/yrm (4) PAHs (Polycyclic aromatic hydrocarbons) Measurements of their contents in micrometeorites were not realized. However, supposing that they represent 10 % in the mass of micrometeorites (Thomas et al., 1993), and by taking their molar mass equal to 228,29 g/mol (Molar mass of the chrysene which is the most abounding PAH in micrometeorites), we obtain: FPAHsMars = [0,7 ; 11,2] g/km^2/yr (5) With the same method as above : FPAHsMars = [1,85 ; 29,54] * 10^21 molecules/km2/yr (6) FPAHsMars = [3,47 ; 55,57] * 10^21 molecules/km2/yrm (7) III - File "PertesUV.f90" Aim : This part consists in studying the influence of the flux of solar ultraviolet photons on the quantity of organic molecules on the surface of Mars. Photons with a wavelength lower than 200 nm are absorbed by CO2 in the Martian atmosphere. Moreover, UV absorption spectra of Glycine and PAHs show that the absorption is strong over 200 nm, but quickly falls in higher wavelengths to become negligible over 250 nm (Poch, 2013). This is why in our study, we are interested only in wavelengths between 200 nm and 250 nm. Calculations of the losses in organic molecules engendered by the ultraviolet photons consist in multiplying the flux of ultraviolet rays arriving on Mars by the photodestruction yield of the chosen species, which is determined experimentally. (Poch et al., 2013), (Poch et al., 2014) LossUV (molecules/km^2/yrm) = Photodestruction Yield (molecules/photons) * Martian UV Flux (photons/km^2/yrm) IV - File "Controller.f90" Thanks to these both informations (Sources & Losses), we could obtain the abundance of organics at the surface affected by UV radiation. (same equation as in my previous blog-post) Abundance of organics (molecules/km^2/yrm) = FglycineMars or FPAHsMars (molecules/km^2/yrm) – LossUV (molecules/km^2/yrm) V - Home Message ! The “ModelMars” program is composed of several Fortran90 files which execute various part necessary for the final execution of the program. i) All information from other files are centralized in the Main.f90 file. ii) Source.f90 file computes the Flux of (Glycine or PAH) falling on Mars through micrometeorites. iii) PertesUV.f90 file computes the Flux of (Glycine or PAH) destroyed by UV radiation between 200 and 250 nm. iv) Controller.f90 file computes the final Flux of (Glycine or PAH) at the surface of Mars. Bibliography Chrysene molecule. (2011). [image] Available at: https://en.wikipedia.org/wiki/Chrysene#/media/File:Chrysene_molecule_ball.png [Accessed 27 Feb. 2017]. Flynn, G. (1996). The delivery of organic matter from asteroids and comets to the early surface of Mars. Earth, Moon and Planets, 72(1-3), pp.469-474. Futura-Sciences, (2017). Alanine. [image] Available at: http://www.futura-sciences.com/sante/definitions/biologie-alanine-8477/ [Accessed 27 Feb. 2017]. Glavin, D., Matrajt, G. and Bada, J. (2004). Re-examination of amino acids in Antarctic micrometeorites. Advances in Space Research, 33(1), pp.106-113. Glycine. (2007). [image] Available at: http://www.wikiwand.com/fr/Glycine_(acide_amin%C3%A9) [Accessed 27 Feb. 2017]. KHALFALLAH, B. (2016). Modélisation de l’abondance des molécules organiques sur Mars. Stage effectué au Laboratoire Inter-universitaire des Systèmes Atmosphériques (LISA). pp.6-9. Love, S., Joswiak, D. and Brownlee, D. (1994). Densities of Stratospheric Micrometeorites.Icarus, 111(1), pp.227-236. MATRAJT, G., PIZZARELLO, S., TAYLOR, S. and BROWNLEE, D. (2004). Concentration and variability of the AIB amino acid in polar micrometeorites: Implications for the exogenous delivery of amino acids to the primitive Earth. Meteoritics & Planetary Science, 39(11), pp.1849-1858. NASA/JPL-Caltech/MSSS, (2014). Curiosity's Color View of Martian Dune After Crossing It. [image] Available at: http://photojournal.jpl.nasa.gov/jpeg/PIA17944.jpg [Accessed 17 Feb. 2017]. NASA/JPL-Caltech/Cornell Univ./Arizona State Univ., (2014). Opportunity's Northward View of 'Wdowiak Ridge'. [image] Available at: http://photojournal.jpl.nasa.gov/catalog/PIA18614 [Accessed 27 Feb. 2017]. Poch O., Recherche d’indices de vie ou d’habitabilité sur Mars : Simulation en laboratoire des processus d’évolution de molécules organiques à la surface de Mars, Thèse de doctorat de l’Université Paris 7 - Denis Diderot (2013) Poch, O., Noblet, A., Stalport, F., Correia, J., Grand, N., Szopa, C. and Coll, P. (2013). Chemical evolution of organic molecules under Mars-like UV radiation conditions simulated in the laboratory with the “Mars organic molecule irradiation and evolution” (MOMIE) setup. Planetary and Space Science, 85, pp.188-197. Poch, O., Kaci, S., Stalport, F., Szopa, C. and Coll, P. (2014). Laboratory insights into the chemical and kinetic evolution of several organic molecules under simulated Mars surface UV radiation conditions. Icarus, 242, pp.50-63. Pyrene molecule. (2012). [image] Available at: https://commons.wikimedia.org/wiki/File:Pyrene_3D_ball.png [Accessed 27 Feb. 2017]. Thomas, K., Blanford, G., Keller, L., Klöck, W. and McKay, D. (1993). Carbon abundance and silicate mineralogy of anhydrous interplanetary dust particles. Geochimica et Cosmochimica Acta, 57(7), pp.1551-1566. Uracil molecule. (2009). [image] Available at: https://commons.wikimedia.org/wiki/File:Uracil-3D-balls.png [Accessed 27 Feb. 2017]. Posted by Alexandra Perron on February 17, 2017
For the second semester of my bachelor's degree, I realize an internship in the Astrobiology department within the LISA, an Atmospheric Systems Laboratory. (LISA – Laboratoire Inter-universitaire des Systèmes Atmosphériques) Créteil, France Astrobiology is an interdisciplinary research domain which studies the apparition and the evolution of living organisms on Earth and potentially in the Universe. Exobiology and Astrobiology are they synonyms? Exobiology is considered to have a narrow scope limited to search of life external to Earth, whereas Astrobiology is wider and investigates the link between life and the universe, including obviously the search for extraterrestrial life, but also the study of life on Earth, its origin, evolution and limits. Within this Astrobiology department, a computer program was created to model the evolution of the organic matter at the surface and in the subsurface of Mars. This program was created by Jérôme Lasne in Fortran90 which is a computational language currently used in scientific laboratories. Fortran90 is relatively easy to learn, but his biggest advantage is that it is an informatics language designed to execute high-speed calculations with precision. Actually, rovers, such as Mars Science Laboratory (MSL) launched in November 2011 (Pavlov et al., 2012), have some difficulties to detect organic compounds on the surface of Mars and can drill into the Martian soil down to only 5 cm. The question which results from these informations is why organics are so difficult to find? Therefore, the goal of this computer program is to understand why some Martian factors would explain the lack of organic compounds on Mars. Actually, the computer program is already functional and the abundance of organics obtained at the end of the simulation is a result of a simple difference between input and output(losses) of organics each year. More precisely, the program take into account both micrometeorites* as an input of organic matter and UV radiation as a factor leading to a loss of these compounds. Abundance of organics = Input (micrometeorites) – output (UV radiation) * Micrometeorites : Micrometeorites (also known as Interplanetary Dust Particles, IDPs) are fragments of objects from the main asteroid belt and comets. (Glavin, Matrajt and Bada, 2004) analyzed the organic content, more precisely amino acid content, of 50-100 μm and 100-400 microns size micrometeorites collected in Antarctic ice. Thus, micrometeorites are sources of organic matter. UV radiation have a huge destructive impact on organic compounds at the surface of Mars but have an impact of only few microns in the subsurface of Mars. Nowadays, only UV radiation is considered as a destructive factor in the program. However, SCR (Solar Cosmic Rays) are destructive radiation that can penetrate several centimeters into the Martian soil (Kminek and Bada, 2006) and GCR (Galactic Cosmic Rays) are destructive radiation that can penetrate to a depth of about 2 meters. (Wilson et al., 2016) Therefore, my goal in the next few months will be, essentially, to model the impact of GCR (Galactic Cosmic Rays) and SCR (Solar Cosmic Rays) on organic molecules embedded in the subsurface of Mars. This improvement could potentially give an idea of where and how deep the next spatial mission ExoMars, planned for 2020, could find organic molecules on Mars. Abundance of organics = Input (micrometeorites) – output (UV radiation + GCR + SCR) Bibliography
Glavin, D., Matrajt, G. and Bada, J. (2004). Re-examination of amino acids in Antarctic micrometeorites. Advances in Space Research, 33(1), pp.106-113. Kminek, G. and Bada, J. (2006). The effect of ionizing radiation on the preservation of amino acids on Mars. Earth and Planetary Science Letters, 245(1-2), pp.1-5. NASA-JPL-CALTECH-D.Bouic, (2013). Une vue de Mars prise par la caméra optique du rover Curiosity. [image] Available at: http://wanderingspace.net/wp-content/uploads/2013/01/20121009_sol49_pano2_postcard_colorized_web.jpg [Accessed 17 Feb. 2017]. Pavlov, A., Vasilyev, G., Ostryakov, V., Pavlov, A. and Mahaffy, P. (2012). Degradation of the organic molecules in the shallow subsurface of Mars due to irradiation by cosmic rays. Geophysical Research Letters, 39(13), p.n/a-n/a. Wilson, E., Atreya, S., Kaiser, R. and Mahaffy, P. (2016). Perchlorate formation on Mars through surface radiolysis-initiated atmospheric chemistry: A potential mechanism. Journal of Geophysical Research: Planets, 121(8), pp.1472-1487. Posted by Alexandra Perron on February 17, 2017 |