Life is abundant – encompassing every corner on planet Earth we know to exist! Yet, no matter how transparent we think our definition of life is, we can see that it is inadequate in specific situations. For the purpose of this article, we will describe life as ‘a system that has the capacity to undergo self-replication and evolution’[1]. In order to define a habitable planet, it is common to adopt the Earth as a reference, for it is the only habitable terrestrial planet the Human race is aware of that can sustain complex life over a myriad of major climate changes, including but not limited to large scale glaciations and vast volcanic eruptions.
A circumstellar habitable zone determines the distance from a star for which liquid water will stably exist on the planetary surface. Kasting’s habitable model[2] places the inner edge of the Sun’s habitable zone at 1.37 Au, determined where Carbon dioxide starts to condense. The outer edge is estimated at 1.67 Au, where the maximum greenhouse effect can take effect. Mars, at 1.52 Au from the Sun, sits within this domain. Liquid water is a property that is pivotal to support an abundance of life on Earth’s planetary surface, thus it is expected that the search for water is closely linked to the search for life itself. Topography and geological activity of Mars indicate the presence of water locked up in the polar caps of this celestial body, but there is other principal evidence for its existence below the Martian surface:
Analyses of New impact craters reveals exposure of the ice-layer below the Martian soil. High-albedo material (where albedo is a measure of the intensity of light reflected from a surface) from the crater floor or distributed in the eject due to cometary impact is confirmed as water-ice from near-infrared spectroscopic data. This material is seen to disappear relatively in line with that expected for the rate of sublimation given the conditions in this harsh environment.
Ground Penetrating radar works by emitting a string of microwave radiation pulses and then recording the echoes that are reflected back. This technique works because the microwaves can penetrate the surface of ice but be reflected back by layers within the cold block. Both the Mars Express (MARSIS) and the Mars Reconnaissance Orbiters (SHARAD) carried orbital radars and detected layering in places other than the polar caps.
Recurring slope lineae are a narrow streaks that resemble downward sloping features and are seen scattered across the Martian Surface. They are visible during the warmer periods of Mars’ sidereal year, fading away when the effective temperature of the planet starts to fall. However, they are observed to reoccur during several subsequent Mars years. The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM)[3] instrument onboard the Mars Reconnaissance Orbiter has observed some hydrated salts in recurring slope lineae, which suggests they were formed from a water-formation mechanism. Imagery collected by the High-Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter from 2007 clearly demonstrate Recurring slope lineae inside Newton Crater, with sizes ranging from 0.5m to 5m in width, and up to 50m in length[4].
It is hoped that the Radar Imager for Mars’ Subsurface Experiment (RIMFAX) on the perseverance rover can accurately locate underground ice stores that could be accessed and provide drinking water for astronauts.
Key to survival on the red planet is a steady supply of Oxygen – a very costly process if trying to transport the required quantity for a space mission from Earth. The atmosphere of Mars only has trace quantities of Oxygen, but an abundance of Carbon dioxide, composing approximately 96% of the atmosphere. The Mars Oxygen In-Situ Resource Utilization Experiment (MOXIE)[5] is a cube-like structured device developed by NASA to solve this problem. A Carbon dioxide Acquisition and Compression system sucks in the Martian atmosphere feeding it through a filter before pressuring to approximately 1 atmosphere. This pressurised Carbon Dioxide is then directed towards the Solid Oxide Electrolyser (SOXE), where it will be electrochemically split at the cathode to produce pure Oxygen at the anode. MOXIE systems engineer Asad Aboobaker at NASA’s Jet Propulsion Laboratory in Southern California expects ‘Moxie to make about 6 to 10 grams of Oxygen per hour – just about enough for a small dog to breath’[6]. For future Martians, the team at NASA expect a full-scale MOXIE system to be a bit larger than a household stove and weigh somewhere in the region of a metric ton.
An important feature to sustain life here on Earth is its magnetic field. Earth’s magnetosphere mitigates and repels cosmic rays and charged particles in the solar wind, which can have detrimental and dangerous consequences for living organisms. Lymphocytes are susceptible to damage through exposure to high doses of radiation. Lymphocytes are an important type of white blood cell which play a pivotal role in helping to maintain a healthy vertebrate immune system. Investigation into cataracts realises a strong correlation between radiation exposure and incidence of cataracts in astronauts. A cataract causes blurry vision, trouble around bright lights and trouble seeing at night. Shockingly, fifty percent of all cases for blindness and a third of visual impairment problems worldwide are a direct consequence of cataracts. A serious concern of terraforming the Martian surface is that its global magnetic field was lost billions of years ago, with only certain regions of the surface containing smaller remnant magnetic fields today. NASA’s used its Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft to observe Mars’ magnetic field, with the interesting discovery that these fields stream into a magnetic tail on the dark side of the planet. The magnetic tail is offset at a 45-degree angle from a horizontal plane through this celestial body, speculated to arise from the phenomena of magnetic reconnection caused by interaction of Mars’ isolated remnant magnetic fields and the Solar wind.
Researchers are weary about this phenomenon, as it is believed it could play a vital role in the stripping away of Mars’ atmosphere. Magnetic reconnection releases energy, which could accelerate the atmosphere into space via the magnetotail. It is of no surprise that the surface of Mars is cold. At its low altitudes, the mean temperature during a Martian day is −60 °C, with a range from −100 °C to +17 °C.[8] The atmosphere of Mars is also extremely thin with a surface pressure of about 6 mbar, less than one percent of that on Earth. For the Martian surface to be habitable for Human life, we would need to raise both the temperature and pressure. A suggested solution involves releasing the carbon dioxide stored in the ice caps, dust and rocks, but there isn’t sufficient gas to raise the pressure to the target of 1 Bar.
References
https://learn2.open.ac.uk/pluginfile.php/2780714/mod_resource/content/8/s283_bk2_wholebook_lo_res_9781108430838.pdf [1], [2], [3], [4], [8]
MOXIE Could Help Future Rockets Launch Off Mars (nasa.gov) [6]
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