Life on Mars
Few places inspire the imagination like one of Earth’s closest neighbors when it comes to places where extraterrestrial life could potentially exist. For centuries, humans have imagined Mars as a home for other beings. Various missions to Mars have attempted to determine the likelihood of such an evolution over the last fifty years. However, how likely is life on Mars?
The rover can collect samples in two ways. It can either analyse them with its on-board laboratory or save them for future missions to return to Earth. But what exactly is it looking for, and what would it need to find in order to convince us that there is past or present life?
If the landing goes well, it will be the first mission in decades to actively seek direct evidence of life on Mars. If life exists, it will most likely be in the form of extinct microbes.
We recently discovered some tantalising hints of current life in the form of methane gas in the atmosphere. Biological processes produce a large portion of the methane in the atmosphere on Earth. As a result, methane could be regarded as a biological signature. However, it can also be produced easily by geological processes, so it is not proof of life.
Rock samples from a depth of approximately 5 cm will also be collected and stored in sealed containers for future collection missions. The analysis we can perform on Earth is many orders of magnitude more precise and detailed than the instruments we can send to Mars. Furthermore, we can conduct multiple types of analyses in multiple labs around the world, resulting in better overall results. For example, if we suspect that evidence of extinct life is preserved in a sample, we could use electron microscopy (which probes a sample with electrons rather than light) to see if it contains fossilised microbial cells.
Any proof of life must go through a rigorous scientific process of testing, re-testing, and peer review. Furthermore, Perseverance is only analysing one crater on Mars. Other missions looking for life, such as the European Space Agency’s Rosalind Franklin rover, aren’t far behind. Rosalind Franklin will be the first to drill up to 2 meters beneath Mars’ harsh, freezing surface. If there is current life on Mars, it may be found deeper beneath the surface, which is constantly bombarded with harmful radiation. The possibility of life on Mars has piqued the interest of astrobiologists due to its proximity and similarities to Earth. To date, no evidence of past or present life on Mars has been discovered. The evidence suggests that the surface environment of Mars had liquid water during the ancient Noachian time period and may have been habitable for microorganisms, but habitable conditions do not always indicate life.
Because of its resemblance to the early Earth, Mars is of particular interest for the study of life’s origins. This is especially true because Mars has a cold climate and no plate tectonics or continental drift, so it has remained virtually unchanged since the end of the Hesperian period. At least two-thirds of Mars’ surface is more than 3.5 billion years old, and Mars may thus have the best record of the prebiotic conditions that led to life, even if life does not or has never existed there, which could have begun as early as 4.48 billion years ago.
NASA announced in June 2018 the discovery of seasonal variations in methane levels on Mars. Methane can be produced by microorganisms or geological processes. In April 2018, the European ExoMars Trace Gas Orbiter began mapping atmospheric methane. The 2022 ExoMars rover Rosalind Franklin will drill and analyse subsurface samples, while the NASA Perseverance, the Mars 2020 rover that successfully landed, will store dozens of drill samples for possible transport to Earth laboratories in the late 2020s or 2030s. An updated status of studies involving the possible detection of lifeforms on Venus (via phosphine) and Mars (via methane) was reported on February 8, 2021.
William Herschel demonstrated that they grow and shrink alternately in each hemisphere’s summer and winter. By the mid-nineteenth century, astronomers were aware of other similarities between Mars and Earth, such as the fact that the length of a day on Mars was nearly identical to that on Earth. They also knew that its axial tilt was similar to Earth’s, which meant it had seasons like Earth, but nearly twice as long due to its much longer year. These observations fueled speculation that the darker albedo features were water and the brighter ones were land, which fueled speculation about whether Mars could be inhabited by life.
According to recent models, early Mars was colder than Earth has ever been, even with a dense CO2 atmosphere. Even though the mid-late Noachian global conditions were most likely icy, transiently warm conditions caused by impacts or volcanism could have created conditions favourable to the formation of late Noachian valley networks. Local warming from volcanism and impacts would have been sporadic, but there should have been numerous events of water flowing on Mars’ surface. Both the mineralogical and morphological evidence point to a decline in habitability beginning in the mid Hesperian. The precise causes are unknown, but they may be related to a combination of processes such as early atmosphere loss, impact erosion, or both.
Soil and rock samples examined by NASA’s Curiosity rover’s onboard instruments in 2013 yielded new information on several habitability factors. The rover team identified some of the key chemical ingredients for life in this soil, including sulphur, nitrogen, hydrogen, oxygen, phosphorus, and possibly carbon, as well as clay minerals, indicating a long-ago aqueous environment with neutral acidity and low salinity—possibly a lake or an ancient streambed. On December 9, 2013, NASA reported that Gale Crater contained an ancient freshwater lake that could have been hospitable to microbial life, based on evidence from Curiosity’s study of Aeolis Palus.
If life exists (or existed) on Mars, evidence of life may be found, or is best preserved, in the subsurface, away from the harsh surface conditions of today.
Current life on Mars, or its biosignatures, could exist kilometres beneath the surface, in subsurface geothermal hot spots, or just a few metres beneath the surface. The permafrost layer on Mars is only a few centimetres below the surface, and salty brines can be liquid only a few centimetres below that. Water is close to the boiling point even at the deepest points in the Hellas basin, and thus cannot remain liquid for long on Mars’ surface in its current state, unless there is a sudden release of underground water. So far, NASA has pursued a “follow the water” strategy on Mars, with no direct searches for biosignatures of life since the Viking missions. Astrobiologists agree that access to the Martian subsurface may be required to find habitable environments currently on Mars.
Mars Colonisation by Humans
Economic interests, long-term scientific research best carried out by humans rather than robotic probes, and sheer curiosity are some of the main reasons for colonising Mars. Mars’ surface conditions and the presence of water make it arguably the most hospitable planet in the Solar System, aside from Earth. In situ resource utilisation (ISRU) would be required for human colonisation of Mars; according to a NASA report, “applicable frontier technologies include robotics, machine intelligence, nanotechnology, synthetic biology, 3-D printing/additive manufacturing, and autonomy.” When these technologies are combined with the vast natural resources available, pre-and post-human arrival ISRU should be able to significantly increase reliability and safety while lowering costs. The cost of human colonisation of Mars.