Mars is the closest planet from our human currently habiting planet — Earth. This implies the fact that Mars could be the planet where similar physical environmental conditions may be present. Since traces of rivers were captured by cameras, Mars became the planet that scientists question whether there may possibly be any living creatures living on Mars habitat. Despite of the closest distance from Earth, the environment is still very different and can be quite challenging for terrestrial organisms to live on. Microbes are also known for the great ability to adapt to extreme environments rapidly on Earth, and therefore, microbes are the most suitable candidates to test whether a place like Mars will have any chances to sustain any lives. Provided that, I will argue in this essay about how microbes will be able to adapt living on Mars in 3 different ways — physical environment, chemical molecules and evolution.
To begin with, it is very clear that
one of the most significant physical factors is extreme temperatures, which can
greatly affect the survival of microbes. Mars has a range of temperatures over
the seasons, ranged from -140°C in winter to 21°C in summer.[1]
The extremely low temperature shows a huge difference from the room temperature
on Earth, leading to Mars may not be a habitable planet for terrestrial
microbes. It can be
argued that low temperatures can affect the uptake of inorganic nutrients as
the affinity to the mineral ions are reduced. For example, a study on algae and
bacteria suggested that uptake of nitrate ions and ammonium ions were reduced resulting
in limited growth of microbes under cold temperature.[2]
Inefficient uptakes of essential growth ions may not be able to supply
nutrients for the entire colony shadowing the fact of microbes living on Mars
is unlikely to happen. Even though the environment may seem too harsh for
terrestrial microbes to live on Mars, and still, some microbes on Earth are
discovered the ability to withstand freezing temperatures. For example, Panagrolaimus
davidi is a known bacteria on Earth which can stay alive under very cold
temperatures. It is suggested that they can survive when their extracellular
fluid is frozen or by supercooling. In the experiment, Panagrolaimus davidi was
kept at -80°C and the results showed impressive
survival of them under long exposure of cold. Around half of them survived
after 24 hours and more than 10% of them survived after an exposure for a
month.[3]
Although the result may not seem positive since the population of them
decreased, the fact that temperature on Mars will not always be under -80°C and
it also depends on the region they live in. Therefore, it is possible that
microbes like Panagrolaimus can live on planet Mars.
Apart from temperature, another physical
challenge which organisms could experience on Mars will be radiation. It is
measured that the natural radiation level on Mars is around 24-30 rads per year
and that is around 40-50 times of which on Earth.[4]
In fact, the level of radiation on Mars is far less than the level required to
kill bacteria if they were living on Earth conditions —
Earth’s pressure and temperature. However, due to low pressure and
temperature, their ability to resist strong radiation and repair DNA reduces
causing the majority of the population unable to survive. For example,
Deinococcus radiodurans is one of the most successful terrestrial bacteria
which is known to be able to live under exposure of radiation of 5000 Gy. It
was discovered that none of that species survived under the UV radiation
exposure in less than 10 mins due to the effect from desiccation and low
pressure. The paper also concluded the fact that UV radiation is the major
reason leading to death of microbes on Mars.[5]
Although the experiment simulated under Martian conditions seems to be strong
evidence to suggest microbes may not be able to live on Mars, it is unlikely
that microbes will live under the exposure of UV light for long duration like
the experiment. It is possible that the microorganisms can find a more stable
environment as their habitat, such as behind a rock or under the Martian sand.
In the investigation, more than 95% of the UV light can be absorbed by the iron
salts for the depths and concentration on present and past Mars.[6]
Range of mineral ions dissolved in the water in the experiment even showed the
possibility to completely absorb all the UV light, suggesting that the
possibility of habitation of microbes may not be totally impossible.
Indeed, the change in physical environment has
a great impact to the chance of survival of microbes, besides that, the
accessibility to different chemical elements and compounds are also very
important to help maintaining growth. Water is definitely one of the most vital
compounds that all living organisms rely on for living, and range of functions
can be contributed by water to microbes, such as a solvent, a temperature
buffer and a metabolite for reactions. It is widely accepted the fact that
without water, it is nearly impossible for lives to be maintained. However, it
is obvious that the presence of water on Mars is not as rich as that on Earth,
even though traces of rivers with no water were discovered. The reason for Mars
lacking of water was suggested that was because of its crust sucking up 99% of
the water and the evidence from water-containing minerals was used to support.[7]
It is doubtful that the dry surface of Mars would be able to maintain the lives
of microbe colonies. But, in a more recent finding, by the use of
ice-penetrating radar, MARSIS, radar signals were detected under the ice
glacier in the poles of Mars,[8]
suggesting the possibility of the presence of liquid accumulating under the ice
caps. This piece of evidence further supported that the area where microbes may
possibly live can be underground, where more stable conditions are provided, as
stated previously.
Organic compounds are also essential for
microbes as they are oxidized to release energy. It seems wise to use light
energy to convert CO2 to glucose since the supply of CO2
is immensely rich in Martian atmosphere (around 96%).[9]
For example, it was suggested that Cyanobacteria is one of the types of
microorganisms that is able to form a colony on Mars by conducting
photosynthesis. In the experiment, Nostoc sp. HK-01 was able to grow on Mars
regolith and produce polysaccharides successfully.[10]
Nonetheless, it was not a complete explanation to the possibility that
Cyanobacteria is able to live on Mars. The experiment did not simulate the
environment on Mars while strong UV radiation and cold temperatures can
potentially kill the bacteria. Consequently, the possibility of an autotrophic
microbes to live on Mars is relatively low. And still, other ways can be used
for bacteria to obtain organic compounds. Heterotrophic bacteria rely on the
organic materials that planet Mars itself originally contains and oxidize the
organic compounds to release energy. It has always been thought that the soil
on Mars is not very fertile, but in a more recent finding, it stated that it
may not be true. Due to water-rock interactions, complex organic molecules
associated with minerals can be detected in the Martian meteorite Allan Hills
84001 (ALH 84001) by the use of collocated nanoscale analyses.[11]
This piece of evidence gives support to the argument for chemotrophic bacteria
living colonizing on Mars, providing the picture of the abiotic factors in the
habitat for microbes should include both water and rocks.
Lastly, evolution of microbes is also a
crucial factor that affect the likelihood of survival. Physiological
adaptations and also behavioral changes can allow microorganisms live better
under extreme conditions. The evolutionary pressure can be given by the extreme
changes of the environment and challenges provided by strong UV radiation. Bacteria
is able to adapt quickly due to their range of ways to exchange genes to create
variation, such as transformation, to incorporating genome from other
disintegrated bacteria, and conjugation, transferring genome from one to
another by direct contact. Variation in gene encourages more possible
phenotypes to adapt to the changes.[12]
Other than that, chemotactic behaviors allow bacteria to look for chemical
favorable environment efficiently. This behavior can maximise their chance of
survival in areas that are prone to extreme changes so dangers can be
prevented.[13] On
the other hand, using Panagrolaimus as an example again, the more ancient form
of Panagrolaimus was not freezing-tolerant but the recent forms are. It
suggests that it is very likely that this trait is created by evolution,[14]
indicating the power of evolution is able to help the bacteria to adapt to
extreme environments. Under the evolutionary pressure from Mars conditions, there
can be prospects that microbes can derive more effective traits from evolution
to greatly increase their chance of survival.
In conclusion, there are 3 main areas that
microbes are able to adapt to if they were on Mars — physical environment,
chemical molecules and evolution. It is crystal clear from the evidence
presented that the likelihood that microbes can adapt and build a colony on
Mars is very high, even when facing the challenges from freezing-cold
temperatures and powerful UV radiation. Despite the surface of Mars may not be
suitable for lives, the possibility of microbes habiting in more hidden and
resourceful areas like underground or under glacier can be anticipated since
the discovery of water and rocks supported the idea in this essay. And most
importantly, evolution of microbes could happen over time to help microbes
adapting the environment in long term. However, the overall reliability of the
research is not the best because most experiments were unable to give a
complete picture of the Mars condition, even though some experiments were
trying to simulate the Mars environment. Scientists may conduct more
investigations based on different conditions through recreating more accurate
Mars condition or by the use AI modeling.
[1]
NOAA US Department of Commerce, “The Planet Mars,” National Weather Service
(NOAA's National Weather Service, November 29, 2022), https://www.weather.gov/fsd/mars#:~:text=Temperatures%20on%20Mars%20average%20about,lower%20latitudes%20in%20the%20summer.
[2]
David S. Reay et al., “Temperature Dependence of Inorganic Nitrogen Uptake:
Reduced Affinity for Nitrate at Suboptimal Temperatures in Both Algae and
Bacteria,” Applied and Environmental Microbiology 65, no. 6 (1999): pp.
2577-2584, https://doi.org/10.1128/aem.65.6.2577-2584.1999.
[3]
D. A. Wharton and I. M. Brown, “Cold-Tolerance Mechanisms of the Antarctic
Nematode Panagrolaimus Davidi,” Journal of Experimental Biology 155, no. 1
(January 1991): pp. 629-641, https://doi.org/10.1242/jeb.155.1.629.
[4]
“Radiation,” Marspedia, accessed April 21, 2023, https://marspedia.org/Radiation#Exposure_limits.
[5]
Giuseppe Galletta, Giulio Bertoloni, and Maurizio D’Alessandro, “Bacterial
Survival in Martian Conditions,” June 1, 2010, https://arxiv.org/pdf/1002.4077.pdf.
[6]
Paul J. Godin et al., “UV Attenuation by Martian Brines,” Canadian Journal of
Physics 98, no. 6 (2020): pp. 567-570, https://doi.org/10.1139/cjp-2019-0425.
[7]
Leah Crane, “Mars's Crust May Have Sucked up Most of the Planet's Water,” New
Scientist (New Scientist, March 16, 2021), https://www.newscientist.com/article/2271407-marss-crust-may-have-sucked-up-most-of-the-planets-water/.
[8]
Sarah Collins, “Liquid Water beneath Martian Polar Ice Cap,” University of
Cambridge, September 28, 2022, https://www.cam.ac.uk/stories/liquid-water-mars#:~:text=Like%20Earth%2C%20Mars%20has%20thick,to%20the%20Greenland%20Ice%20Sheet.
[9]
“The Five Most Abundant Gases in the Martian Atmosphere – NASA Mars
Exploration,” NASA (NASA), accessed April 22, 2023, https://mars.nasa.gov/resources/4848/the-five-most-abundant-gases-in-the-martian-atmosphere/.
[10]
Inês P. Macário et al., “Cyanobacteria as Candidates to Support Mars
Colonization: Growth and Biofertilization Potential Using Mars Regolith as a
Resource,” Frontiers in Microbiology 13 (May 2022), https://doi.org/10.3389/fmicb.2022.840098.
[11]
A. Steele et al., “Organic Synthesis Associated with Serpentinization and
Carbonation on Early Mars,” Science 375, no. 6577 (2022): pp. 172-177, https://doi.org/10.1126/science.abg7905.
[12]
Nature news (Nature Publishing Group), accessed April 23, 2023, https://www.nature.com/scitable/topicpage/some-organisms-transmit-genetic-material-to-offspring-6524963/.
[13]
Anat Bren and Michael Eisenbach, “How Signals Are Heard during Bacterial
Chemotaxis: Protein-Protein Interactions in Sensory Signal Propagation,”
Journal of Bacteriology 182, no. 24 (2000): pp. 6865-6873, https://doi.org/10.1128/jb.182.24.6865-6873.2000.
[14]
Lorraine M. McGill et al., “Anhydrobiosis and Freezing-Tolerance: Adaptations
That Facilitate the Establishment of Panagrolaimus Nematodes in Polar
Habitats,” PLOS ONE 10, no. 3 (June 2015), https://doi.org/10.1371/journal.pone.0116084.
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