Biosignature
A biosignature (sometimes called a “chemical fossil” or “molecular fossil”) is an element , molecule , isotope, or natural phenomenon that provides scientific evidence of the existence of life in the present or past. Measurable properties of life include the complex physical and chemical structures using thermodynamic free energy and the production of biomass and cellular waste products. Because of its unique character, a biosignature can be interpreted to mean that it was produced by a living organism. It is important, however, not to take it as definitive evidence, for one cannot know in advance which quality is true of life in general and which is specific to life on earth. Nonetheless, there are life forms that are known to require certain unique structures, for example DNA in a certain environment is evidence of life.
Molecules in organisms that provide information about their ancestry and evolutionary development are also named as “molecular fossils”, “chemical fossils” or “chemofossils”, especially when - as with microbes ( prokaryotes and protists ) - there are no ordinary fossils (fossils, petrofacts) ) gives. The expression is then analogous to “living fossils”. Examples are telomerase (with a reverse transcriptase as a subunit) and all natural ribozyme , as well as DNA of mitochondrial origin in the cell nucleus of organisms with DNA-free hydrogenosomes or mitosomes , as well as DNA of plastid origin in eukaryotes with DNA-less chloroplasts or after complete loss of the plastids (Explanation: endosymbiotic gene transfer).
In geomicrobiology
Early traces on Earth provide us with the opportunity to find geochemical signatures produced by microbial life and see how these have been preserved over geological time. Some related disciplines such as geochemistry , geobiology, and geomicrobiology often use biosignatures to determine if there are living organisms in the sample at hand. The possible biosignatures include: (a) microfossils and stromatolites , (b) molecular structures ( biomarkers ) and isotopes of carbon, nitrogen and hydrogen in organic material, (c) sulfur and oxygen isotope ratios in minerals and the proportions and isotopic composition of redox sensitive metals (like iron, molybdenum, chromium and rare earth metals ).
For example, fatty acids found in a sample suggest bacteria and archaea that live in a particular environment. Another example is long-chain fatty alcohols with more than 23 atoms, which are produced by plankton bacteria. Geochemists often prefer the term biomarker . Yet another example is the presence of long-chain lipid fragments in the form of alkanes , alcohols and fatty acids with 20-36 carbon atoms in soils and deposits (sediments). Peat deposits are a sign of an epicuticular wax from a higher plant. Life processes can produce a number of biosignatures such as nucleic acids , proteins , amino acids , enzymes and kerogen-like materials with different morphological appearances that can be read in rocks and sediments . Microbes often interact with geochemical processes by leaving structures in the rock and suggesting a biosignature. For example, bacterial micrometer-sized pores in carbonate rock resemble inclusions in transmitted light, but differ in size, shape and pattern, and are distributed differently than traces of a liquid. A potential biosignature is a phenomenon that can have been produced by life, but can also have other, abiotic origins.
In astrobiology
The astrobiology is based on the assumption that Biosignatures, encounters the one in space, on extraterrestrial life point. The benefit of a biosignature is based on the fact that the probability that it was produced by living things is high and, above all, that it is unlikely that it was produced by abiotic processes. In summary, it can be said that in order to prove extraterrestrial life there must be a biosignature that was produced by living beings. As with all scientific discoveries, the biosignature will be held as required evidence until there is another explanation.
Possible examples of biosignatures may be complex organic compounds or structures that are practically impossible to produce without life. Examples are cellular and extracellular morphologies , biomolecules in rock, bio- organic molecular structures, chirality , biogenic minerals, biogenic stable isotope patterns in minerals and organic compounds, atmospheric gases, changeable detectable features on the planet's surface , ...
Categories
- Isotope patterns that presuppose biological processes.
- Chemistry: chemical structures that indicate biological activity.
- Organic material formed through biological processes.
- Minerals whose composition or surface structure is based on a biological activity.
- Biologically formed microscopic structures , microfossils or films.
- Macroscopic physical structures and patterns : Structures that indicate a microbial ecosystem (stromatolites or fossils of larger organisms).
- Change over time : changes in the atmospheric gas composition over a period of time or macroscopic phenomena that indicate life.
- Surface structures: structures of biological pigments that could be detected.
- Atmospheric gases : gaseous substances that are formed in metabolic processes or in aqueous solutions that can be measured on a global scale.
- Technology signatures: Signatures that show the technical progress of a civilization.
Chemically
A single molecule will not be able to prove that life once existed. But there will be different structures in every organic compound that illustrate the selection process of evolution . For example, membrane lipids left by cells are concentrated, of limited size, and of an even number of carbon atoms. Likewise, almost only levorotatory amino acids occur in living organisms . Biosignatures are not necessarily of a chemical nature, but can also have different magnetic properties .
On Mars, oxidants and UV radiation changed or destroyed organic molecules on the surface. One fact makes research more difficult, namely that abiotic organic-rich chondritic meteorites rained on the surface of Mars. At the same time, strong oxidizing agents in the Martian soil together with ionizing radiation destroy the molecular signatures of meteorites or organisms. An alternative approach would be to study layers of crystalline minerals such as clays , which protect the organic material from destruction by ionizing radiation and strong oxidizing agents. The search for biosignatures on Mars has become promising after the discovery that watery areas were discovered on and near the surface, as it was discovered at the same time that biological organic material is preserved in ancient watery sediments on Earth.
Morphologically
Another possible biosignature can be morphology , as the shape and size of certain objects could indicate the presence of present or past life. For example, microscopic magnetite crystals in the Martian meteorite have long been discussed as potential biosignatures in the sample because it is believed that only bacteria form crystals of the specific shape. An example of a possible biomineral is a sample of the Martian meteorite ALH84001 , a microbial biofossil with stone-like structures, the shape of which is a potential biosignature because it resembles known bacteria. Most scientists concluded that the structures are far too small to be fossil living cells . A match emerged and is now viewed as a requirement that one need additional evidence in addition to the morphological data to support the extraordinary claim. The current scientific agreement is that “morphology cannot be viewed as an unrestricted means of proving primitive life.” The interpretation of morphology is often subjective and its use alone has led to multiple misinterpretations.
Properties and compositions of the atmosphere
Atmospheric properties of exoplanets are of particular importance because, from scientific observations, the atmospheres are most likely to provide predictions for the near future, including habitability and biosignatures. For billions of years, the life process on a planet would end up in a mixture of chemicals, unless something provided a normal chemical balance. For example, life on earth produces large amounts of oxygen and small amounts of methane.
In addition, the color - or the reflected spectrum - of an exoplanet can provide information about the presence of life forms on its surface.
The evidence of methane in the Martian atmosphere shows that there must be an active source there, since methane is an unstable gas. Photochemical models can not explain the presence of methane in the Martian atmosphere and its recorded rapid transformation into space and time. Neither the appearance nor the disappearance can be explained so far. In order to rule out a biogenic origin for the methane, a sampling or a mass spectrometer on site will be necessary, since the isotope ratios 12 C / 14 C in methane could differentiate between biogenic and non-biogenic origin, similar to the use of the δ 13 C standard detection for the detection of biogenic methane on earth. In June 2012, scientists reported that measuring the proportions of hydrogen and methane can provide information about whether life exists or is possible on Mars. Scientists claim: "... low hydrogen / methane ratios (<40) show that life is present and active." The ExoMars Trace Gas Orbiter (TGO) aims to examine the Martian atmosphere for trace gases and potential biochemical and geochemical ones Characterize processes. The first results, which are based on measurements of about six months, show no evidence of methane in the atmosphere, although the TGO instruments have a significantly better detection sensitivity than the previous probes.
Other scientists recently reported methods of detecting hydrogen and methane in the extraterrestrial atmosphere. Habitability indicators and biosignatures need to be interpreted in the context of the planetary setting and the environment. For example, the coexistence of oxygen and methane would suggest that some kind of extreme thermodynamic imbalance, created by life, exists. Two of the 14,000 proposed biosignatures are dimethyl sulfoxide and chloromethane (CH 3 Cl). Another biosignature is the combination of methane and carbon dioxide.
Indirect evidence
Scientific observations do not rule out the possible identification of biosignatures through indirect evidence. For example, electromagnetic radiation is recorded by infrared telescopes, radio telescopes or space telescopes. There is a hypothetical radiomagnetic radiation signature from this area, so that SETI scans would be a biosignature or proof of the existence of extraterrestrial life.
Surface robotic missions
The Viking Missions to Mars
The Viking Lander to Mars 1970 carried out the first experiments specifically designed to look for biosignatures on another planet. Each of the two Viking Landers performed three detection experiments to look for signs of metabolism , but the results were not considered conclusive.
Mars science laboratory
The “ Curiosity rover ” from the Mars Science Mission is investigating the potential possibility of Mars being habitable and trying to find biosignatures on the Martian surface. If you look at the Martian science laboratory and its instrument package, you have the option of finding the following biosignatures: morphologies of organisms (cells, fossil structures), microbial mats, organic molecules, isotope signatures, evidence of biominerals and biogenic gases. The “Curiosity Rover” aims to find fossil organic structures in the sediment.
ExoMars Rover
The ExoMars Orbiter Trace Gas Orbiter (TGO) is a telecommunications spaceship and an investigation station for analyzing atmospheric gas. It was supposed to drop the Schiaparelli Mars lander and begin to record methane deposits in the Martian atmosphere and to choose other gases and thus a landing site for the EXoMars rover, which is supposed to start in 2020. The primary task of the ExoMars mission is to find biosignatures below the surface and to take samples from the subsurface that have not been destroyed by the radiation that prevails on the surface.
Mars 2020 rover
The Mars 2020 rover is scheduled to start in 2020 to study the astrobiologically relevant environment of Mars, its geology and history, including the habitability and probability of existing life on Mars, and the ability to preserve the biosignatures that are accessible in the geological material can be found. In addition, samples of material of interest that are to be transported to earth will be taken.
Titan Dragonfly
In the mid-2030s, the Dragonfly space probe will attempt to detect biosignatures on the surface and in the atmosphere of Titan and find possible traces of the primeval soup.
literature
- Barbara Cavalazzi et al. : Biosignatures for Astrobiology. Springer, Cham 2018, ISBN 978-3-319-96174-3 .
See also
Individual evidence
- ↑ a b c Beaty, Steele: The Astrobiology Field Laboratory . In: the Mars Exploration Program Analysis Group [MEPAG] - NASA (ed.): Final report of the MEPAG Astrobiology Field Laboratory Science Steering Group (AFL-SSG) . September 26, 2006, p. 72 ( nasa.gov ).
- ^ Biosignature - definition . In: Science Dictionary . 2011. Archived from the original on May 26, 2011. Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. Retrieved January 12, 2011.
- ↑ a b c d e f g Roger E. Summons, Jan P. Amend, David Bish, Roger Buick, George D. Cody, David J. Des Marais, G Dromart, JL Eigenbrode, AH Knoll, DY Sumner: Preservation of Martian Organic and Environmental Records: Final Report of the Mars Biosignature Working Group . In: Astrobiology . 11, No. 2, February 23, 2011, pp. 157-181. doi : 10.1089 / ast.2010.0506 . PMID 21417945 .
- ↑ Carol Cleland: Philosophical Issues in Astrobiology . NASA Astrobiology Institute. 2003. Archived from the original on July 21, 2011. Retrieved April 15, 2011.
- ^ Carl Zimmer : Even Elusive Animals Leave DNA, and Clues, Behind . In: The New York Times , January 22, 2015. Retrieved January 23, 2015.
- ↑ SIGNATURES OF LIFE FROM EARTH AND BEYOND . In: Penn State Astrobiology Research Center (PSARC) . Penn State. 2009. Retrieved January 14, 2011.
- ↑ David Tenenbaum: Reading Archaean Biosignatures . NASA. July 30, 2008. Archived from the original on November 29, 2014. Retrieved on November 23, 2014.
- ↑ Fatty alcohols ( Memento of the original from June 25, 2012 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Luther Beegle, Michael G. Wilson, Fernando Abilleira, James F. Jordan, Gregory R. Wilson: A Concept for NASA's Mars 2016 Astrobiology Field Laboratory . In: Mary Ann Liebert, Inc. (Ed.): Astrobiology. Research papers . 7, No. 4, August 27, 2007, pp. 545-577. doi : 10.1089 / ast.2007.0153 . PMID 17723090 . Retrieved July 20, 2009.
- ↑ Tanja Bosak, Virginia Souza-Egipsy, Frank A. Corsetti, Dianne K. Newman: Micrometer-scale porosity as a biosignature in carbonate crusts . In: Geology . 32, No. 9, May 18, 2004, pp. 781-784. doi : 10.1130 / G20681.1 .
- ↑ a b Lynn Rothschild: Understand the evolutionary mechanisms and environmental limits of life . NASA. September 2003. Archived from the original on January 26, 2011. Retrieved on July 13, 2009.
- ↑ a b NASA Astrobiology Strategy 2015 ( memento of the original from December 22, 2016 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. . (PDF), NASA
- ↑ a b Rover could discover life on Mars - here's what it would take to prove it . Claire Cousins, PhysOrg . 5 January 2018.
- ↑ Mike Wall: Mars Life Hunt Could Look for Magnetic Clues . Space.com . December 13, 2011. Retrieved December 15, 2011.
- ↑ Matt Crenson: After 10 years, few believe life on Mars . Associated Press (on usatoday.com). August 6, 2006. Retrieved December 6, 2009.
- ↑ David S. McKay, Everett K. Gibson Jr, Kathie L. Thomas-Keprta, Hojatollah Vali, Christopher S. Romanek, Simon J. Clemett, Xavier DF Chillier, Claude R. Maechling, Richard N. Zare: Search for Past Life on Mars: Possible Relic Biogenic Activity in Martian Meteorite ALH84001 . In: Science . 273, No. 5277, 1996, pp. 924-930. doi : 10.1126 / science.273.5277.924 . PMID 8688069 .
- ↑ a b Garcia-Ruiz: Morphological behavior of inorganic precipitation systems - Instruments, Methods, and Missions for Astrobiology II . In: SPIE Proceedings . Proc. SPIE 3755, No. Instruments, Methods, and Missions for Astrobiology II, December 30, 1999, p. 74. doi : 10.1117 / 12.375088 . "It is concluded that" morphology cannot be used unambiguously as a tool for primitive life detection. ""
- ^ Agresti: Detection and geochemical characterization of Earth's earliest life . In: NASA Astrobiology Institute , NASA, December 3, 2008. Archived from the original on January 23, 2013. Retrieved January 15, 2013.
- ↑ J. William Schopf, Anatoliy B. Kudryavtsev, Andrew D. Czaja, Abhishek B. Tripathi: Evidence of Archean life: Stromatolites and microfossils Archived from the original on December 24, 2012. Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. (PDF) In: Precambrian Research . 158, No. 3-4, April 28, 2007, pp. 141-155. doi : 10.1016 / j.precamres.2007.04.009 . Retrieved January 15, 2013.
- ^ Artificial Life Shares Biosignature With Terrestrial Cousins . In: The Physics arXiv Blog . WITH. January 10, 2011. Retrieved January 14, 2011.
- ^ A b Sara Seager, William Bains, Janusz Petkowski: Toward a List of Molecules as Potential Biosignature Gases for the Search for Life on Exoplanets and Applications to Terrestrial Biochemistry . In: Astrobiology . 16, No. 6, April 20, 2016, pp. 465-85. bibcode : 2016AsBio..16..465S . doi : 10.1089 / ast.2015.1404 . PMID 27096351 . Retrieved May 7, 2016.
- ↑ Svetlana V. Berdyugina, Jeff Kuhn, David Harrington, Tina Santl-Temkiv, E. John Messersmith: Remote sensing of life: polarimetric signatures of photosynthetic pigments as sensitive biomarkers . In: International Journal of Astrobiology . 15, No. 1, January 2016, pp. 45–56. bibcode : 2016IJAsB..15 ... 45B . doi : 10.1017 / S1473550415000129 .
- ↑ Siddharth Hegde, Ivan G. Paulino-Lima, Ryan Kent, Lisa Kaltenegger, Lynn Rothschild: Surface biosignatures of exo-Earths: Remote detection of extraterrestrial life . In: PNAS . 112, No. 13, March 31, 2015, pp. 3886–3891. bibcode : 2015PNAS..112.3886H . doi : 10.1073 / pnas.1421237112 . PMID 25775594 . PMC 4386386 (free full text). Retrieved May 11, 2015.
- ↑ Calla Cofield: Catalog of Earth Microbes Could Help Find Alien Life . In: Space.com , March 30, 2015. Retrieved May 11, 2015.
- ↑ R. Claudi, MS Erculiani: Simulating SUPER EARTH ATMOSPHERES IN THE LABORATORY (PDF) in January 2015. Retrieved on May 7, 2016th
- ↑ a b Christopher Oze, Camille Jones, Jonas I. Goldsmith, Robert J. Rosenbauer: Differentiating biotic from abiotic methane genesis in hydrothermally active planetary surfaces . In: PNAS . 109, No. 25, June 7, 2012, pp. 9750-9754. bibcode : 2012PNAS..109.9750O . doi : 10.1073 / pnas.1205223109 . PMID 22679287 . PMC 3382529 (free full text). Retrieved June 27, 2012.
- ↑ Staff: Mars Life Could Leave Traces in Red Planet's Air: Study . Space.com . June 25, 2012. Retrieved June 27, 2012.
- ↑ Mark Allen, Olivier Witasse: MEPAG June 2011 . Ed .: 2016 ESA / NASA ExoMars Trace Gas Orbiter. Jet Propulsion Laboratory, June 16, 2011 ( nasa.gov [PDF]). MEPAG June 2011 ( Memento of the original from September 29, 2011 in the Internet Archive ) Info: The archive link was inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice.
- ↑ Nadja Podbregar: New measurements no longer find methane in the Martian atmosphere Mars: mystery about disappeared methane. In: Scinexx - The Knowledge Magazine. December 18, 2018, accessed January 9, 2019 .
- ↑ Andreas Müller: Researchers are puzzling over disappeared Martian methane. In: Grenzwissenschaft-aktuell.de. December 17, 2018, accessed on January 9, 2019 (German).
- ↑ Matteo Brogi, Ignas AG Snellen, Remco J. de Krok, Simon Albrecht, Jayne Birkby, Ernest JW de Mooij: The signature of orbital motion from the dayside of the planet t Boötis b . In: Nature . 486, No. 7404, June 28, 2012, pp. 502-504. arxiv : 1206.6109 . bibcode : 2012Natur.486..502B . doi : 10.1038 / nature11161 . PMID 22739313 . Retrieved June 28, 2012.
- ^ Adam Mann: New View of Exoplanets Will Aid Search for ET . Wired . June 27, 2012. Retrieved June 28, 2012.
- ↑ Where are they? (PDF) Mario Livio and Joseph Silk. Physics Today , March 2017.
- ↑ Mike Wall: Alien Life Hunt: Oxygen Isn't the Only Possible Sign of Life . In: Space.com . January 24, 2018. Accessed January 24, 2018.
- ↑ Joshua Krissansen-Totton, Stephanie Olson, David Catlig: Disequilibrium biosignatures over Earth history and implications for detecting exoplanet life . In: ScienceAdvances . 4, No. 1, January 24, 2018. doi : 10.1126 / sciadv.aao5747 .
- ↑ James N. Gardner: The Physical Constants as Biosignature: An anthropic retrodiction of the Selfish Biocosm Hypothesis . Amusement. February 28, 2006. Retrieved January 14, 2011.
- ↑ Astrobiology . Biology Cabinet. September 26, 2006. Retrieved January 17, 2011.
- ↑ Levin, G and P. Straaf. 1976. Viking Labeled Release Biology Experiment: Interim Results. Science: vol: 194. pp: 1322-1329.
- ^ Chambers: Life on Mars; The Complete Story . Blandford, London 1999, ISBN 0-7137-2747-0 .
- ↑ Harold P. Klein, Gilbert V. Levin, Gilbert V. Levin, Vance I. Oyama, Joshua Lederberg, Alexander Rich, Jerry S. Hubbard, George L. Hobby, Patricia A. Straat, Bonnie J. Berdahl, Glenn C. Carle, Frederick S. Brown, Richard D. Johnson: The Viking Biological Investigation: Preliminary Results . In: Science . 194, No. 4260, October 1, 1976, pp. 99-105. doi : 10.1126 / science.194.4260.99 . PMID 17793090 . Retrieved August 15, 2008.
- ↑ a b ExoMars rover
- ↑ Boris Pavlishchev: ExoMars program gathers strength . In: The Voice of Russia , July 15, 2012. Archived from the original on August 6, 2012 Info: The archive link has been inserted automatically and has not yet been checked. Please check the original and archive link according to the instructions and then remove this notice. .
- ^ Mars Science Laboratory: Mission . NASA / JPL. Retrieved March 12, 2010.
- ↑ Alicia Chang: Panel: Next Mars rover should gather rocks, soil . July 9, 2013. Retrieved July 12, 2013.
- ↑ Mitch Schulte: Call for Letters of Application for Membership on the Science Definition Team for the 2020 Mars Science Rover . NASA. December 20, 2012. NNH13ZDA003L.
- ↑ Dragonfly: Exploring Titan's Prebiotic Organic Chemistry and Habitability (PDF). EP Turtle, JW Barnes, MG Trainer, RD Lorenz, SM MacKenzie, KE Hibbard, D. Adams, P. Bedini, JW Langelaan, K. Zacny, and the Dragonfly Team. Lunar and Planetary Science Conference 2017 .
