Mars may present an immense challenge for microorganisms living here on Earth; yet billions of years ago it may have had temperate conditions capable of supporting life.
Scientists have made important discoveries through spacecraft missions and by studying rocks from Mars that have fallen to Earth, suggesting it once supported life. Recent evidence points towards Mars being capable of supporting such forms.
Temperature
Mars is notoriously known for being cold. This is partly because its thin atmosphere allows heat from the sun to easily escape, while plate tectonics and gravity also play a significant role. Together, these factors determine how its atmosphere heats and cools – ultimately impacting whether liquid water exists on Mars.
Mars can reach temperatures as high as 27 degrees Celsius near its equator during the day, while at night they can drop as far as minus 133. These extreme temperature fluctuations means there’s rarely any time when liquid water could exist on its surface.
Mars’ climate may be harsh, yet its thin atmosphere and lack of a global magnetic field makes its surface vulnerable to pressure from solar wind: particles released by our Sun in continuous streams that continuously bombard it. Over time, this pressure stripped away lighter molecules in Mars’s atmosphere resulting in its current drought conditions.
Scientists used to believe that Mars was once wetter, creating models which attempted to explain evidence of water erosion features on its surface. But new research demonstrates that cold climate models perform much better at explaining the data.
Mars is situated on an elliptical orbit which makes its closest approach (perihelion) more often than at any other distance from the Sun (aphelion), thus increasing winter conditions on Mars significantly relative to summer conditions, leading to less sublimation of carbon dioxide from its South Polar Ice Cap and consequently less sublimation of CO2.
Mars could produce geologic methane through processes like serpentinization, radiolysis of water or pyrolysis of mineral olivine. Unfortunately there has been no sign of volcanic activity or hydrothermal hotspots so this source may not be viable.
If life ever does arrive on Mars, it will have to adapt quickly in an environment featuring extreme cold, acidity and radiation – which is why scientists are researching extremeophiles; organisms which thrive under conditions beyond what humans experience on Earth.
Atmosphere
Mars’ atmosphere is thin, making it hard for heat from the Sun to reach its surface, as well as being rich in oxidants that could destroy any organic molecules that made their way there. Furthermore, dust storms and small whirlwinds known as dust devils that periodically appear would likely disperse any molecules present anyway; all this has led many scientists to question its viability for life support systems.
Mars’ outer layer, the “lithosphere,” features irregular contours with large canyons and mountains jutting out high above its surface. These features are the result of tectonic movement – however this phenomenon is less pronounced than on Earth due to it not having major continental plates which move against each other as strongly.
Mars’ lithosphere likely comprises basalt, the same type of volcanic rock found on Earth and some of its moons. Along with tectonics and erosion processes, mars’ surface is also shaped by vast polar ice caps and glaciers in several locations on its surface.
Scientists have long speculated that Mars’ former, wetter environment might have contributed to its current, dry climate. Unfortunately, no conclusive solution has been discovered as to how its climate changed from warm and wet environments to its current cold, arid state; the new study provides several possible scenarios, all requiring water – something which cannot be assumed exists today on Mars.
As well as water, an atmosphere rich in nitrogen and oxygen would be necessary for plant life that could support human life on Mars. Scientists have detected evidence of these gases in craters marking places where lakes once existed as well as occasional methane plumes discovered on its surface.
Nitrogen and oxygen are produced naturally through the decay of organic compounds, with more being produced by living organisms than otherwise. Decomposed products of some organic substances — minerals formed when rocks interact with biological material — known as biosignatures can be used to detect ancient life on Earth; their discovery has led many scientists to assume similar signs exist on Mars as well.
Water
Although Mars is currently a very cold planet and much of its surface remains frozen, scientists believe that conditions once existed that enabled life on this icy world. Scientists speculate that oceans and rivers once flourished on Mars billions of years ago; however, due to drying processes they have since vanished. Evidence of past wetness includes riverbeds carved out of rock by running liquid water as well as carbonate minerals formed when liquid reacts with rock minerals to dissolve into them; currently however the only liquid water source on the planet exists underground.
Scientists have yet to fully understand why and how Earth lost so much water, but one theory suggests asteroids and comets bombarding the planet may have stripped it of its greenhouse atmosphere and allowed its temperature to decrease over time.
Another factor could be that Mars has less gravity than Earth, making it easier for chemicals like water to escape into space – possibly contributing to why its surface is much drier than our own planet’s.
Scientists have detected several indications that water once flowed on Mars’ surface. One such sign is its many valley networks dotted across its surface – branching channels in which tributaries converge downstream – which seem to suggest they were formed by flowing water; according to estimates made by scientists, one hundred times more would flow annually through such channels than is used for annual Mississippi River runoff.
Other evidence of past water includes the existence of gullies carved by flowing water on cliff walls and an underground lake under the south polar ice cap that contains enough volume to equal that of Earth’s Arctic Ocean basin, though most known life would likely have perished long ago; though there could still be organisms capable of living in extremely salty environments that thrive today.
Are these organisms evidence that life once existed on Mars or simply proof that there exists an environment suitable for simple organisms to survive remains to be seen. Meanwhile, questions have also been raised regarding Mars’ atmospheric composition and seasonal variations.
Soil
Soil is the material that holds together other materials, providing water, minerals, organic matter and bacteria for living organisms to thrive in their environments. Earth has similar soil to Mars but with significantly more minerals. Also, Mars is 1000 times drier than most places on Earth so microbial life may no longer have survived there in the past or now either.
Mars’ regolith can be difficult to manage chemically; its regolith is rich in toxic and mineral substances, including perchlorate. At high doses, perchlorate inhibits thyroid iodine production while acting as a decontaminant in hospitals; however, in large amounts it’s toxic both to people and plants, leading to death as a result of exposure.
Perchlorates and other compounds found in Martian soil serve as powerful microbe-killers, as evidenced by research conducted at University of California Berkeley geoscientists using a model of Mars’ surface to test whether these chemicals would eliminate molecular evidence of past life on Earth. They found that acidic fluids flowing across its clay surface would have quickly interacted with and destroyed most organic molecules responsible for life on our planet.
Researchers conducted studies to recreate the chemical environment on Mars by planting both lettuce and Arabidopsis thaliana, an annual weed, in three varieties of fake Martian soil: one composed of minerals mined from Hawaii or Mojave Desert that are similar to its makeup; two created from scratch using volcanic rock, clays, salts and other ingredients observed by NASA’s Curiosity rover on Mars; and a third containing sulfur for maximum Mars-realism. All three samples allowed growth of both plants despite high chlorin content; however only one would work in its most Mars-replicating synthetic soil; its contents mimicking sunlight as well as high chlorine content levels!
However, UCSD graduate student Xiao Qiao has devised an ingenious way of making this type of regolith more conducive for plant growth without using cement or concrete as binder. By pressing layers of replica dry Mars clay under considerable pressure and applying pressure over time, natural alignment occurred between each layer which ultimately created a solid without glue being required.