Life on mars

from Wikipedia, the free encyclopedia
Artist's impression of the possible surface and atmosphere on Mars after terraforming ( see also: Mars colonization )

For centuries mankind has speculated about the possibility of life on Mars because of the planet's proximity and similarities to Earth . The search for traces of life on Mars began in the 19th century and continues today. While historical work was limited to phenomenological methods and speculation, modern science focuses on the search for water , chemical biomarkers in the soil and the rocks of the rocky planet, and gaseous biomarkers in the atmosphere .

Mars is of particular interest for studying the origin of life because it is very similar to early Earth - specifically the cold climate and the absence of plate tectonics and continental shifts , so Mars has largely remained unchanged since the end of the Hesperian . At least two thirds of the surface of Mars are more than 3.5 billion years old. Therefore, Mars could have prebiotic conditions that lead to abiogenesis , even if life no longer exists or has never existed there. The question of whether life ever existed or still exists on Mars, as well as fictional Martians , is a popular recurring theme in the entertainment industry of the 20th and 21st centuries.

In early 2014, NASA announced that current investigations by the Mars rovers Curiosity and Opportunity were now looking for signs of life on Mars. This includes both the biosphere based on autotrophic , chemotrophic and / or chemolithotrophic microorganisms , as well as water including lake levels (levels that are connected to earlier rivers or lakes) that may have been habitable at one time. Finding evidence of habitability, traces of fossilization and organic carbon is now one of NASA's primary goals .

There are various hypotheses as to whether and how possibly life on Mars that once existed could be related to life on Earth. According to the panspermia hypothesis , life on Mars could have originated and been brought to Earth by asteroid impacts. However, there is also the possibility that large asteroid impacts on Earth could have brought life to other planets in the solar system.

Speculation before the space age

Historical map of Mars by Giovanni Schiaparelli .
Martian channels illustrated by astronomer Percival Lowell , 1898.

The thought of the possibility of life on Mars often fired people's imaginations. In the 18th century it was observed that the dark spots on the surface of Mars changed their color and grew or shrunk. They were thought to be extensive vegetation zones , the extent of which changed with the seasons.

The polar caps of Mars were discovered in the middle of the 17th century. In the late 18th century, William Herschel first described the rising and falling of the polar ice caps with the changing of the seasons in the respective hemisphere . As early as the middle of the 19th century, astronomers recognized that Mars has some similarities to Earth, such as the length of a Martian day (called a sol) being almost the same as a day on Earth. Its axis inclination is also similar to the earth, i.e. H. Mars also has seasons like Earth, but due to the duration of a Mars year of 687 days, they are almost twice as long as the earthly. These observations led to a number of speculations that the larger albedo features were water and the lighter colored land. So it was logical to assume that Mars could harbor some form of life.

In 1854, William Whewell theorized that Mars had oceans, land, and possibly life forms. After telescopic observations of the Mars channels (which later turned out to be an optical illusion), speculations about life on Mars exploded at the end of the 19th century. For example, the American astronomer Percival Lowell published his book Mars in 1895 , followed by Mars and its Canals in 1906, in which he suggested that the canals could be the work of a civilization long ago. Lowell even set up his own observatory , the Lowell Observatory , to study the Martians. For him the canals were the product of extraterrestrial engineers and were created to save the Martian civilization from a great drought. Lowell described his ideas about the Martian world in numerous publications that were widely distributed. This led the British writer HG Wells to write his famous work The War of the Worlds in 1897 , which tells of an alien invasion of Mars.

Spectroscopic analyzes of the Martian atmosphere began in 1894 when the US astronomer William Wallace Campbell showed that neither water nor oxygen existed in the Martian atmosphere. Around 1909, better telescopes and the best perihelic opposition on Mars since 1877 finally led to an end to the Mars Canal hypotheses. However, until 1963, shortly before the start of the first Mars probes ( Mariner ), the existence of mosses and lichens was considered possible.

Today's view

Mars appears today as a dry desert planet. The ecosphere (or habitable zone ) of the solar system ranges from 0.95 to 1.37 AU from the sun, so only the earth is within this zone, but Mars is just outside. The results of the Mars missions available so far, however, allow the conclusion that the Martian atmosphere was much denser in the past (billions of years ago) and that there was abundant liquid water on the surface of the planet.

There is no higher or even intelligent life on Mars, but scientists consider primitive life forms ( microbes ) deeper in the ground, where they would be protected from UV rays , to be conceivable. The focus of today's missions is therefore the search for traces of microbial life in the form of cells such as bacteria, although the possibility of viruses being found cannot be ruled out.

Speculations about intelligent life

The face of Mars in the Cydonia region; Image of the Viking 1 orbiter , 1976

When orbiter 1 of the Viking mission took pictures of the Cydonia region in July 1976 and sent them to Earth, Mars became a topic of public conversation again. One of the recordings showed a formation on the surface of Mars that resembled a human face looking up at the sky. Structures that resemble pyramids on earth and rectangular structures (called “Inca City” by scientists) have also been discovered in the immediate vicinity . It was not until NASA's Mars Global Surveyor mission in April 1998 that many were disillusioned: all the structures discovered were the result of natural erosion . New images with a much higher resolution made it clear that no artificial structures of extraterrestrial intelligence are visible on Mars.

Many pictures of the Mars rovers also cause speculation about extraterrestrial visitors on Mars, but these are mostly optical illusions or changes in the environment caused by the rovers themselves. At the beginning of 2014, for example, an emerging stone called Pinnacle Island , which was not seen on earlier footage by Opportunity , caused a stir. Presumably the stone was thrown there by the wheels of the rover itself.

Speculations about microbiological life

Mars atmosphere

The atmosphere is recognizable as a hazy veil over the Mars horizon. On the left is the Galle crater, which resembles a smiley face . Viking, 1976
Illustration of the methane concentrations in the atmosphere of Mars during the northern summer - NASA

Mars has a very thin atmosphere. As a result, the atmospheric pressure is very low, and water cannot exist in liquid form on the surface of Mars, except for brief periods in the deepest areas.

In 2003, earth-based telescopes and in 2004 the Planetary Fourier Spectrometer (PFS) on the Mars Express spacecraft detected traces of methane (about 10  ppb ) and formaldehyde (130 ppb). Methane remains in the atmosphere of Mars for about 340 years, formaldehyde only 7.5 hours. Methane is broken down by ultraviolet radiation because the thin atmosphere of Mars does not protect against this radiation. In the process, methane oxidizes to water and carbon dioxide.

To explain the amount of methane in the atmosphere, a production of 150 tons per year is sufficient. However, when converting to formaldehyde, 2.5 million tons would have to come from “methane sources”. Active volcanism , cometary impacts or methane-producing microorganisms come into consideration as sources . But it could also be caused by a geothermal reaction, the serpentinization (components involved are water, carbon dioxide and the mineral olivine , which occurs frequently on Mars). Formaldehyde can be produced by cosmic radiation from gases and ice. However, it is doubted that an abiotic process can produce so much methane, as it requires regions with high geological activity. The existence of microorganisms such as methanogens would be a possible explanation, but these would have to exist deep below the surface, where it is warm enough for liquid water.

The methane is not evenly distributed but shows a pattern of slightly increased concentrations. Obviously, the supply of methane is or was temporarily interrupted before it could be evenly distributed in the atmosphere. In the biological production of methane on earth, which is responsible for around 90 to 95% of all methane deposits, ethane is almost always produced as an associated gas. In contrast, sulfur dioxide is released during volcanic formation . The measurement of these gases in the Martian atmosphere could provide some clarification. This could be done through the Mars Science Laboratory . In December 2014, NASA reported the measurement of noticeable fluctuations in methane concentration in the vicinity of the Mars rover Curiosity.

Goro Komatsu from the Gabriele d'Annunzio University in Pescara presented his discovery of geological structures about 1 km in diameter on satellite images of the Chryse Plain , which resemble methane gas producing mud volcanoes on Earth. However, a primary source for the gas has not yet been found.

According to Kevin Zahnle, a planetary scientist at NASA's Ames Research Center , it is also possible that the measured methane deposits in the Martian atmosphere were falsified by the methane in the earth's atmosphere, and that there is no methane on Mars.

The Curiosity rover , which landed on Mars in August 2012, can use its Tunable Laser Spectrometer (TLS) to measure methane concentrations in the atmosphere. Less than 5 ppb was measured at the landing site in Gale Crater . Studies published by NASA in 2013, based on data from the TLS, could also not show any increased methane concentration.

India's Mars Orbiter mission , which has been in orbit since September 24, 2014, will continue to study the atmosphere using its Methane Sensor for Mars (MSM). In 2016, as part of the ExoMars project, ESA sent the Trace Gas Orbiter to Mars to investigate methane, if any.

Martian meteorites

Electron microscope picture showing the bacteria- like structures in the ALH84001 meteorite .

In 1996, David S. McKay and his colleagues found structures in the Martian meteorite ALH 84001 , which they interpreted as traces of fossil bacteria. The chain-like magnetite found in this meteorite is morphologically similar to the bacterial magnetite from Magnetospirillum magnetotacticum . However, the evidential value of the structures found is questioned by many scientists, as these could also be created purely chemically.

Fragment of the Nakhla meteorite, after splitting in 2006

In 1999 NASA discovered possible biomorphic traces and various amino acids in the Nakhla meteorite , but could not rule out terrestrial contamination. In 2006 a fragment of the meteorite was broken open to examine a contamination-free sample. It contained an abundance of complex carbonaceous materials, which contained dendrite-like pores and channels in the rock, similar to the effects of bacteria known from the earth. However, the majority of scientists believe that the presence of shapes similar to those of living organisms is not enough to prove that bacteria once lived on Mars. In 2014, further investigations discovered an oval cell-like microbubble, which consists of nanocrystalline, ferrous saponite and amorphous materials and in many ways resembles fossilized biological cells on earth. However, it was probably not a cell, but was created by a small inclusion of water that was heated when the asteroid impacted on Mars.

Traces of possible biological processes were also discovered in the Martian meteorites Shergotty and Yamato 000593 .

Martian soil

Viking  1 and 2 had, among other things, the task of investigating the question of life on Mars. One chemical and three biological experiments were carried out. The chemical experiment attempted to detect organic substances in the Martian soil. A GC / MS unit developed at MIT (coupling of a gas chromatograph with a mass spectrometer ) was used for this purpose. However, no organic substances based on carbon could be detected.

The first biological experiment was based on the metabolic activities of organisms. A soil sample was wetted with a nutrient solution and the gases produced were recorded. The Martian soil reacted to the experiment by releasing large amounts of oxygen . In the second experiment, a nutrient solution was provided with radioactive carbon atoms and applied to a sample. As a result of a metabolism, they should have been detected among the excreted gases. In fact, radioactive carbon atoms were detected. The third experiment was a photosynthesis experiment. Radiolabelled carbon dioxide was added to the Martian soil. This carbon dioxide should have been assimilated and later detected. This result was also positive. Although the results of the biological experiments were positive, due to the negative result of the GC / MS experiment, they did not provide conclusive evidence of the existence or non-existence of life on Mars.

On January 23, 2004, the European Mars probe Mars Express discovered large amounts of frozen water at the south pole of Mars, and at the end of July 2005 also in a crater near the north pole.

Also at the beginning of 2004, the Mars probe Opportunity discovered rocks that must have been deposited in open water and contain many regularly distributed spherical hematite concretions up to 1 cm in size . Such concretions also occur on earth. Under terrestrial conditions, bacteria are likely to be involved in their formation . Only laboratory tests on Earth could show whether this also applies to Mars.

Further microstructures, which the rovers Spirit and Opportunity had discovered in 2004 and in which part of the interested public had wanted to see signs of life, turned out to be abiotic or artificial on closer examination, for example grinding marks on the rock surfaces or filaments processed by the instruments , which turned out to be the textile fibers of the landing airbags .

Research on earth confirms that life can exist even in extreme conditions. While drilling in the Greenland ice, researchers from the University of California, Berkeley discovered a striking amount of methane at a depth of two miles. This gas is produced by methanogenic bacteria that survive in the ice despite inhospitable living conditions such as cold, darkness and lack of nutrients. In doing so, they only keep themselves alive with great difficulty - they repair genetic damage, but do not increase their population significantly. Methanogenic microbes are a subgroup of archaebacteria that specialize in extreme locations. In 2002, for example, microbes were found in a 15,000 year old hot spring in Idaho . As the name suggests, bacteria are among the oldest microorganisms on earth. The scientists estimate the age of the bacterial colony discovered in Greenland at 100,000 years and assume that the methane detected in the atmosphere of the Red Planet could not only come from chemical processes, but also from such microbes.

The fungus species Cryomyces antarcticus and Cryomyces minteri , which live inside rocks in the Antarctic , survived relatively well an experiment on the International Space Station , in which the environmental conditions on Mars were simulated. After 18 months, 60% of her cells were still intact and the DNA undamaged. The lichen Xanthoria elegans also survived the simulated Martian conditions during the experiment.

Current missions

The Mars Science Laboratory is to try to provide new information about possible life on Mars. It is questionable whether the Mars rover can drill deep enough to find life, or at least the remains of life. But an isotope analysis of the methane can already provide further information. Life, as it is known on Earth, prefers lighter isotopes of hydrogen.

Water resources

Concept art of the former aquasphere of Mars

Liquid water is a necessity for life as we know it. Due to the thin atmosphere of Mars, water cannot permanently exist in liquid form on its surface. However, there are indications that in the polar regions , insolation during the day could cause tiny amounts of liquid water to form beneath the surface. Such an effect is also known from the Antarctic .

About 3.8 billion years ago, Mars had a denser atmosphere and higher temperatures, as well as vast amounts of running water on its surface all the way to oceans. According to calculations, these oceans could once have covered 36% to 75% of the planet's surface. However, the salinity ( salinity ) of the oceans would have been too high for most terrestrial living things. However, the Halobacterium even needs a very high salt content and could have survived in the former Martian oceans.

River valleys

Kasei Vallis , the largest river valley on Mars

River valleys that can be several hundred kilometers long and several kilometers wide run on the surface of Mars. Today's dry valleys begin quite abruptly and have no tributaries. Streamlined islands sometimes rise up in the valleys. They point to a past flood period during which large amounts of water appear to have flowed over a relatively short geological period. It could have been water ice that was under the surface of Mars, then melted by volcanic processes and then flowed off. The dimensions of these primeval water masses are, however, the subject of scientific discussion. The Zasada diagram shows that the erosion processes of Mars differ significantly from those on earth due to the lower gravity. Thus, conclusions by analogy between earthly sedimentation bodies and their formation conditions are not permissible.

In addition, there are traces of erosion on slopes and crater edges , which may also have been caused by liquid water.

On December 6, 2006, NASA called a press conference because they spoke of a unique find : On some NASA photographs, which were taken seven years apart from Mars, changes on the Martian surface can be seen that are somewhat similar to Having changes from running water. NASA is now discussing whether there could be liquid water in addition to water ice.

Delta structures

In ancient Martian landscapes, e.g. For example, in the Eberswalde crater in the southern hemisphere or in the Xanthe Terra plateau near the equator , there are typical deposits of former river deltas.

Tharsis-tholus strip captured with the Hirise camera of the Mars Reconnaissance Orbiter . The stripe can be seen in the center left. On the right are the foothills of Tharsis Tholus .

It has long been assumed that the deeply cut valleys in Xanthe Terra were once formed by rivers. When such a river flowed into a larger basin, for example a crater, it deposited eroded rock material as sediments. The type of deposit depends on the nature of this basin: If it is filled with the water of a lake, a delta is formed. However, if the basin is dry, the river will slow down and slowly seep away. A so-called alluvial cone forms, which is clearly different from the delta.

Recent analyzes of sediment bodies based on orbiter photos point to deltas in numerous places in Xanthe Terra - rivers and lakes were therefore quite common in the early Martian period.

Dark Slope Streaks

Dark streaks on slopes are common on Mars. They appear on steep slopes of craters, troughs, and valleys and get lighter with age. Sometimes they start in a small point-like area and then get progressively wider. They were observed to move around obstacles such as hollows.

The color is believed to come from dark underlying layers exposed by avalanches of light dust. However, other hypotheses have also been made, such as water or even the growth of organisms. The most interesting thing about these dark slope streaks is that they are still forming today.

Carbonate deposits

With the help of the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on board the NASA Mars Reconnaissance Orbiter probe, scientists were able to detect carbonate compounds in rock layers around the almost 1,500-kilometer Isidis impact basin . According to this, the water that existed here more than 3.6 billion years ago would not have been acidic, but rather alkaline or neutral. Carbonate rock is formed when water and carbon dioxide react with calcium , iron or magnesium . During this process, carbon dioxide from the atmosphere is stored in the rock. This local find shows that around 3.5 billion years ago there were not exclusively acidic environmental environments on Mars. At least regionally, there may have been more life-friendly places with regard to the pH value .

With the help of data from the MRO, rocks were discovered in 2010 that had been carried to the surface by cosmic impacts from the depths. On the basis of their specific spectroscopic fingerprints it could be determined that they were changed hydrothermally (under the action of water). In addition to these carbonate minerals, silicates have also been detected, which are believed to have originated in the same way. This new find proves that these are not localized occurrences, but that carbonates formed in a very large region of early Mars.

Carbonate finds represent more environmentally friendly environmental conditions, but at the same time they call into question the hypothesis of a significantly warmer Martian past. With the help of climate models, it was possible to calculate that the Martian atmosphere must once contain up to 4 bar CO 2 in order to guarantee habitable conditions with the help of the greenhouse effect. However, this statement contains a geochemical contradiction. A planet that simultaneously hosts significant amounts of CO 2 and liquid water is thermodynamically unstable. The associated weathering of the rocks would remove enormous amounts of CO 2 from the atmosphere . Such a CO 2 atmosphere could not last long in the presence of liquid water. During the most intense volcanic period on Mars, approx. 980 • 10 12 tons of CO 2 were released within 400 Ma . In comparison, 3.3 • 10 8 tons of CO 2 are withdrawn from the earth's atmosphere every year through the silicate weathering. By analogy, one can assume that under similar environmental conditions, CO 2 removal is up to 80 times faster than input. A dense CO 2 atmosphere could therefore not have developed. This is particularly due to the feldspar weathering:

CaAl 2 Si 2 O 8 + 2NaAlSi 3 O 8 + 3CO 2 + 5H 2 O → 2Al 2 Si 2 O 5 (OH) 4 + 2Ca 2+ + 4SiO 2 + 2HCO 3 - + Na 2 CO 3

In particular, carbonates can arise from the weathering products of the plagioclase, which are present in large quantities within the volcanic Martian rocks: Ca 2+ + 2HCO 3 - → CaCO 3 + H 2 O + CO 2 Although CO 2 is released into the atmosphere again, but only a third of what was originally withdrawn from the atmosphere. The carbonate finds thus represent former CO 2 sinks and thus question the notion of a former greenhouse world. It is more likely that Mars was only slightly warmer in its past than its current counterpart and only hosted seasonal temperatures above freezing on its surface.

Hematite globules

Hematite spheres on the rock "Berry Bowl"

The Mars probe Opportunity found millimeter-sized spheres of the iron mineral hematite in the area of ​​the Meridiani Planum . These could have deposited billions of years ago under the action of water. In addition, minerals were found that are composed of sulfur , iron or bromine compounds , such as jarosite . On the opposite hemisphere of Mars, the Spirit probe found the mineral goethite in the "Columbia Hills" , which can only be formed under the influence of water.

Silica

In 2010, researchers used MRO to discover deposits on a volcanic cone caused by water. They were able to identify the mineral as silicic acid hydrate, which can only have formed in connection with water. The scientists believe that if there was life on Mars, it could have lasted longest in the hydrothermal environment.

Ice deposits at the poles

The South Pole region as captured by Viking Orbiter

Radar measurements with the Mars Express probe revealed layers of deposits with embedded water ice in the southern polar region, the Planum Australe , which are far larger and deeper than the southern polar cap, which consists mainly of carbon dioxide ice. The water ice layers cover an area almost the size of Europe and reach a depth of up to 3.7 kilometers. The volume of water stored in them is estimated to be up to 1.6 million cubic kilometers - around two thirds of the Earth's Greenland ice cream  - which, according to the European Space Agency (ESA), would be enough to cover the surface of Mars with a layer of water around 11 meters thick.

More ice deposits

Observed changes could be signs of running water within the last few years.

The long-held suspicion that there might be water ice beneath the surface of Mars proved to be correct in 2005 through discoveries by the ESA Mars Express probe .

Geologists assume recurring periods of ice on Mars, similar to terrestrial ice ages. In the process, glaciers are said to have penetrated into subtropical latitudes. The researchers conclude this from orbiter photos that show traces of former glaciers in these equatorial areas. In addition, radar measurements from orbit also support the existence of considerable amounts of ground ice in these same areas. These ground ice deposits are interpreted as remnants of such “Mars ice ages”.

On the European Planetologenkonferenz EPSC in September 2008 in Muenster high resolution images of were Mars Reconnaissance Orbiter of NASA presented, showing the recent impact craters. Because of the very thin atmosphere, the meteorites crash onto the surface of Mars with practically no glowing up. The five new craters, which are only three to six meters in diameter and 30 to 60 cm deep, were found in mid-northern latitudes. They show a glistening white material on their bottom. A few months later the white spots had disappeared due to sublimation. This corroborates the evidence that water ice is buried close to the Martian surface even far outside the polar regions.

Liquid water

Because the pressure of the Martian atmosphere is so low, liquid water on the surface cannot exist for long periods of time. In addition, it is usually too cold on the surface for that.

There is evidence that the Phoenix spacecraft discovered water droplets on the surface. Here could perchlorates act (salts of perchloric acid) as an antifreeze. These salts have the property of attracting water. This can also be water vapor from the atmosphere. With sufficient admixture, water would remain liquid even down to −70 ° C. By mixing with perchlorates, water could also be present under the surface in a liquid state. In 2010, researchers at the University of Münster found evidence that liquid water exists on the surface of Mars at least in spring and in craters like the Russell crater. In photos taken by the Mars Reconnaissance Orbiter, they discovered erosion channels that had lengthened between November 2006 and May 2009. The gullies lead downhill; The researchers rate the fact that they are thinner towards the bottom as an indication of seeping liquid water as the trigger for erosion. According to more recent scientific findings (as of July 2014), the erosion channels could have been created by carbon dioxide instead of water, as previously assumed , since water would evaporate very quickly at the prevailing atmospheric pressure of 7 millibars. In the Martian winter, carbon dioxide collects as dry ice at below −100 ° C on the mountain slopes and then “flows” down the slopes as sublimed carbon dioxide gas as the planet warms up, washing out the erosion channels like liquid water.

Large amounts of water are also suspected under the Martian cryosphere . (see extraterrestrial ocean ). In 2018, Science reported on the discovery of an underground water deposit in Planum australe at the south pole of Mars with a base at a depth of around 1.5 km and a length of around 20 km. The discovery was made with the Marsis radar of the Mars Express probe. Since water is normally not liquid at the prevailing temperatures (205 degrees Kelvin), a high salt content (magnesium and calcium perchlorates) is assumed.

See also

Individual evidence

  1. ↑ Michael J. Mumma: The Search for Life on Mars. NASA Goddard Space Flight Center, January 8, 2012, accessed September 19, 2014 .
  2. ↑ Christopher P. McKay, Carol R. Stoker: The early environment and its evolution on Mars: Implication for life . In: Reviews of Geophysics . 27, No. 2, 1989, pp. 189-214. bibcode : 1989RvGeo..27..189M . doi : 10.1029 / RG027i002p00189 .
  3. ↑ Eric Gaidos, Franck Selsis: From Protoplanets to Protolife: The Emergence and Maintenance of Life . In: Proto Stars and Planets V . 2007, pp. 929-44. arxiv : astro-ph / 0602008 . bibcode : 2007prpl.conf..929G .
  4. ^ A b John P. Grotzinger: Introduction to Special Issue - Habitability, Taphonomy, and the Search for Organic Carbon on Mars . In: Science . 343, No. 6169, January 24, 2014, pp. 386-387. bibcode : 2014Sci ... 343..386G . doi : 10.1126 / science.1249944 .
  5. ↑ Different authors: Special Issue - Table of Contents - Exploring Martian Habitability . In: Science . 343, No. 6169, January 24, 2014, pp. 345-452.
  6. ↑ Different authors: Special Collection - Curiosity - Exploring Martian Habitability . In: Science . January 24, 2014.
  7. ↑ John P. Grotzinger, DY Sumner, LC Kah, K. Stack, S. Gupta, L. Edgar, D. Rubin, K. Lewis, et al .: A Habitable Fluvio-Lacustrine Environment at Yellowknife Bay, Gale Crater, Mars . In: Science . 343, No. 6169, January 24, 2014, p. 1242777. doi : 10.1126 / science.1242777 .
  8. ↑ Did Life on Earth Come From Mars? National Geographic, September 5, 2013, accessed October 17, 2014 .
  9. ^ RJ Worth, Steinn Sigurdsson, Christopher H. House: Seeding Life on the Moons of the Outer Planets via Lithopanspermia. In: Astrobiology. 13, 2013, p. 1155, doi : 10.1089 / ast.2013.1028 .
  10. ↑ Alfred Russel Wallace: Is Mars habitable ?: A critical examination of Professor Percival Lowell's book 'Mars and its canals', with an alternative explanation . Macmillan, London 1907, OCLC 263175453 .
  11. ^ Paul Chambers: Life on Mars; The Complete Story . Blandford, London 1999, ISBN 0-7137-2747-0 .
  12. ↑ Jeremy Hsu: Scarce Shelter on Mars. Astrobiology (Journal), June 4, 2009, accessed September 16, 2014 .
  13. ↑ Aleksandar Janjic: The Need for Including Virus Detection Methods in Future Mars Missions. In: Astrobiology . tape 18 , no. 12 , p. 1611–1614 , doi : 10.1089 / ast.2018.1851 .
  14. ^ Rock That Appeared in Front of Opportunity on "Murray Ridge". NASA , accessed October 17, 2014 .
  15. ↑ Mars Express confirms methane in the Martian atmosphere. ESA, March 30, 2004, accessed September 18, 2009 .
  16. ↑ Martin Baucom: Life on Mars? American Scientist, accessed February 26, 2007 .
  17. ^ Richard W. Court, Mark A. Sephton: Investigating the contribution of methane produced by ablating micrometeorites to the atmosphere of Mars . In: Earth and Planetary Science Letters . 288, No. 3-4, December 8, 2009, pp. 382-5. bibcode : 2009E & PSL.288..382C . doi : 10.1016 / j.epsl.2009.09.041 .
  18. ↑ Bill Steigerwald: Martian Methane Reveals the Red Planet is not a Dead Planet . In: NASA's Goddard Space Flight Center , NASA, January 15, 2009. Archived from the original on January 16, 2009. “If microscopic Martian life is producing the methane, it probably resides far below the surface, where it's still warm enough for liquid water to exist " 
  19. ↑ Curiosity Detects Methane Spike on Mars Nasa Science News, December 16, 2014.
  20. ↑ Thorsten Dambeck: Solution to methane riddle. Spiegel Online , September 24, 2010, accessed October 11, 2010 .
  21. ↑ Kevin Zahnle, Richard S. Freedman, David C. Catling: Is there methane on Mars? . In: Icarus . 212, No. 2, 2011, pp. 493-503. bibcode : 2011Icar..212..493Z . doi : 10.1016 / j.icarus.2010.11.027 .
  22. ↑ David Tenenbaum: Making Sense of Mars Methane . In: Astrobiology Magazine . June 9, 2008. Archived from the original on September 23, 2008. Retrieved October 22, 2014.
  23. ^ Richard A. Kerr: Curiosity Finds Methane on Mars, or Not . Science. November 2, 2012. Retrieved October 22, 2014.
  24. ↑ Chris R. Webster, et al .: Isotope Ratios of H, C, and O in CO2 and H2O of the Martian Atmosphere . In: Science . 341, No. 6143, July 19, 2013, pp. 260-263. doi : 10.1126 / science.1237961 . PMID 23869013 .
  25. ^ Paul R. Mahaffy, et al .: Abundance and Isotopic Composition of Gases in the Martian Atmosphere from the Curiosity Rover . In: Science . 341, No. 6143, July 19, 2013, pp. 263-266. doi : 10.1126 / science.1237966 .
  26. ↑ Christopher R. Webster, Paul R. Mahaffy, Sushil K. Atreya, Gregory J. Flesch, Kenneth A. Farley: Low Upper Limit to Methane Abundance on Mars . In: Science . September 19, 2013. doi : 10.1126 / science.1242902 .
  27. ^ Paul Rincon: Agencies outline Mars initiative , BBC News. July 9, 2009. 
  28. ↑ NASA orbiter to hunt for source of Martian methane in 2016 , Thaindian News. March 6, 2009. 
  29. ^ Paul Rincon: Space rock re-opens Mars debate. BBC , February 8, 2006, accessed October 17, 2014 .
  30. ^ Martian meteorite yields more evidence of the possibility of life on Mars. University of Manchester, September 15, 2014, accessed October 17, 2014 .
  31. ↑ Silvano Onofri, Jean-Pierre de Vera, Laura Zucconi, Laura Selbmann, Giuliano Scalzi, Kasthuri J. Venkateswaran, Elke Rabbow, Rosa de la Torre, Gerda Horneck. Survival of Antarctic Cryptoendolithic Fungi in Simulated Martian Conditions On Board the International Space Station. In: Astrobiology , 2015, 15 (12), p. 1052, doi: 10.1089 / ast.2015.1324
  32. ↑ Jennifer L. Heldmann, Owen B. Toon, Wayne H. Pollard, Michael T. Mellon, John Pitlick, Christopher P. McKay, Dale T. Andersen: Formation of Martian gullies by the action of liquid water flowing under current Martian environmental conditions . In: Journal of Geophysical Research . 110, No. E5, 2005, p. E05004. bibcode : 2005JGRE..110.5004H . doi : 10.1029 / 2004JE002261 .
  33. ↑ V.-P. Kostama, MA Kreslavsky, JW Head: Recent high-latitude icy mantle in the northern plains of Mars: Characteristics and ages of emplacement . In: Geophysical Research Letters . 33, No. 11, 2006, p. 11201. bibcode : 2006GeoRL..3311201K . doi : 10.1029 / 2006GL025946 .
  34. ↑ Greenhouse Effect on Mars May Be Allowing for Life. softpedia, December 7, 2009, accessed October 21, 2014 .
  35. ↑ David Shiga: Watery niche may foster life on Mars. New Scientist , December 7, 2009, accessed October 21, 2014 .
  36. ^ VR Baker, RG Strom, VC Gulick, JS Kargel, G. Komatsu, VS Kale: Ancient oceans, ice sheets and the hydrological cycle on Mars . In: Nature . 352, No. 6336, 1991, p. 589. bibcode : 1991Natur.352..589B . doi : 10.1038 / 352589a0 .
  37. ↑ Flashback: Water on Mars Announced 10 Years Ago . SPACE.com. June 22, 2000. Retrieved October 22, 2014.
  38. ^ The Case of the Missing Mars Water . In: Science @ NASA . Retrieved March 7, 2009.
  39. ↑ Mars Rover Opportunity Examines Clay Clues in Rock . In: NASA , Jet Propulsion Laboratory, May 17, 2013. 
  40. ↑ NASA Rover Helps Reveal Possible Secrets of Martian Life . In: NASA , November 29, 2005. 
  41. ↑ PSRD: Ancient Flood Waters and Seas on Mars . Psrd.hawaii.edu. July 16, 2003. Retrieved October 22, 2014.
  42. ↑ Gamma-Ray Evidence Suggests Ancient Mars Had Oceans . SpaceRef. November 17, 2008. Retrieved October 22, 2014.
  43. ↑ Michael H. Carr, James W. Head: Oceans on Mars: An assessment of the observational evidence and possible fate . In: Journal of Geophysical Research (Planets) . 108, 2003, p. 5042. bibcode : 2003JGRE..108.5042C . doi : 10.1029 / 2002JE001963 .
  44. ^ William Harwood: Opportunity rover moves into 10th year of Mars operations . Space Flight Now. January 25, 2013. Retrieved October 22, 2014.
  45. ^ Gaetano Di Achille, Brian M. Hynek: Ancient ocean on Mars supported by global distribution of deltas and valleys . In: Nature Geoscience . 3, No. 7, June 14, 2010, pp. 459-63. bibcode : 2010NatGe ... 3..459D . doi : 10.1038 / ngeo891 .
  46. ↑ DE Smith, WL Sjogren, GL Tyler, G. Balmino, FG Lemoine, AS Konopliv: The gravity field of Mars: Results from Mars Global Surveyor . In: Science . 286, No. 5437, 1999, pp. 94-7. bibcode : 1999Sci ... 286 ... 94S . doi : 10.1126 / science.286.5437.94 . PMID 10506567 .
  47. ^ Nicholas J. Tosca, Andrew H. Knoll, Scott M. McLennan: Water Activity and the Challenge for Life on Early Mars . In: Science . 320, No. 5880, 2008, pp. 1204-7. bibcode : 2008Sci ... 320.1204T . doi : 10.1126 / science.1155432 . PMID 18511686 .
  48. ↑ Shiladitya DasSarma: Extreme Halophiles Are Models for Astrobiology . In: Microbe 1, No. 3, 2006, pp. 120-126.
  49. ↑ Patrick Zasada: Gradation of extraterrestrial fluvial sediments - related to the gravity . In: Z. geol. Knowledge , 41/42 (3), 2013/14, pp. 167-183, abstract (PDF)
  50. ↑ a b Florian Rötzer : Flowing water on Mars? Heise online , December 6, 2006, accessed September 18, 2009 .
  51. ↑ Thorsten Dambeck: Lakes on early Mars. NZZ Online, October 1, 2008, accessed on September 18, 2009 .
  52. ^ Robert Roy Britt: Dark Streaks on Mars Suggest Running Water Still Present ( Memento from April 27, 2008 in the Internet Archive ). SPACE.com, December 11, 2002
  53. ↑ Stefan Deiters: Sometimes more life-friendly than you thought? astronews, December 19, 2008, accessed September 18, 2009 .
  54. ↑ Markus Becker: Mars rocks awaken hope for life in the depths. Spiegel Online , October 13, 2010, accessed November 10, 2010 .
  55. ↑ Patrick Zasada (2015): About the potential discovery of life on Mars, stardate (2/2015): 91-96 ( ISSN  0721-8168 ).
  56. ↑ Note: Spirit and Opportunity are in the southern hemisphere at around 5 ° West (Opportunity) and around 175 ° East (Spirit).
  57. ↑ Researchers hope for a mortuary for Mars microbes. Spiegel Online , November 1, 2010, accessed November 10, 2010 .
  58. ↑ Mars Express radar measures the amount of water at the south pole of Mars. ESA, March 15, 2007, accessed September 18, 2009 .
  59. ↑ Thorsten Dambeck: Geologists are amazed at Mars glaciers. Spiegel Online , April 28, 2008, accessed September 18, 2009 .
  60. ↑ Thorsten Dambeck: Europe's planetary research is establishing itself. NZZ Online, October 29, 2008, accessed on September 18, 2009 (report from the EPSC conference in Münster).
  61. ^ Rainer Kayser: Fresh ice on Mars. astronews, April 1, 2009, accessed September 18, 2009 .
  62. ↑ Rainer Kayser: Discovered liquid water on Mars? astronews, February 18, 2009, accessed September 18, 2009 .
  63. ↑ Liquid water on the surface? astronews, April 28, 2010, accessed October 11, 2010 .
  64. ↑ Erosion channels on Mars are created by carbon dioxide In: Spectrum of Science.
  65. ↑ R. Orosei et al .: Radar evidence of subglacial liquid water on Mars , Science, July 25, 2018, eaar7268, DOI: 10.1126 / science.aar7268