Far back in Mars’ history, the red planet may have had all the right conditions to support life underground.
A new study has found that enough chemical energy likely flowed through the subsurface region to allow microbial colonies, like those that exist on Earth, to thrive on Mars.
While sunlight may not reach this area, the new research suggests it was home to an abundance of dissolved hydrogen, which would act as an ‘electron donor’ to sustain subterranean microbes.
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Far back in Mars’ history, the red planet may have had all the right conditions to support life underground. According to the new study published in Earth and Planetary Science Letters, the process of radiolysis could have created hydrogen beneath the surface of ancient Mars
‘We showed, based on basic physics and chemistry calculations, that the ancient Martian subsurface likely had enough dissolved hydrogen to power a global subsurface biosphere,’ said Jesse Tarnas, a graduate student at Brown University.
‘Conditions in this habitable zone would have been similar to places on Earth where underground life exists.’
On Earth, areas in which microbes thrive underground are known as SLiMES – subsurface lithotrophic microbial ecosystems.
The microbes living in these colonies don’t get their energy from the sun, instead ‘peeling’ electrons from the molecules in their environment.
In many cases, dissolved molecular hydrogen provides this fuel.
According to the new study published in Earth and Planetary Science Letters, the process of radiolysis could have created hydrogen beneath the surface of ancient Mars.
About 4 billion years ago, Mars’ crust may even have been home to a range of hydrogen concentrations known to support microbial life on Earth today.
While it doesn’t mean life definitely existed on Mars, it is promising for what the past may have held.
‘The question then becomes: What was the nature of that subsurface life, if it existed, and where did it get its energy,’ said Jack Mustard, a professor in Brown’s Department of Earth, Environmental, and Planetary Sciences.
‘We know that radiolysis helps to provide energy for underground microbes on Earth, so what Jesse did here was to pursue the radiolysis story on Mars.’
While sunlight may not reach this area, the new research suggests it was home to an abundance of dissolved hydrogen, which would act as an ‘electron donor’ to sustain subterranean microbes
In the study, the researchers analyzed data from the gamma ray spectrometer on NASA’s Mars Odyssey spacecraft.
After mapping out abundances of the radioactive elements thorium and potassium, the researchers were able to infer a third: uranium.
The decay of these elements drives the radiolytic breakdown of water, the researchers explain.
The team also estimated how much water would have been available, revealing there likely would have been an abundance running through the crust’s porous rocks.
They also used geothermal and climate models to see where life may have thrived.
WHAT PROOF HAS BEEN FOUND OF LIQUID WATER ON MARS? How important is the presence of liquid water? It is now widely believed that Mars holds a reasonably large volume of water. However, the surface of the planet is so cold, this water exists only as ice. In order for life to exist on a planet, many scientists believe it is essential for the world to possess liquid water. Ever since technology has enabled mankind to gaze at Mars in detail, humans have been looking for indications that there was water on the red planet. Did water used to flow on the surface of Mars? The Mariner 9 mission revealed clues of water erosion in river beds and canyons, as well as evidence of weather fronts and fogs on Mars in 1971. Later missions from the Viking orbiters, which first launched in 1975, revealed yet more details about how water flowed on the surface and carved valleys. Several studies investigated the presence of liquid water for decades. In 2000, the first proof of liquid water on Mars was discovered. It was claimed the gullies seen on the surface of the planet had to have been formed by flowing water. Scientists cited the debris and mud deposits left behind as evidence for moving water existing at some point in the history of the red planet. However, the formation of these gullies has been hotly debated throughout the ensuing years. Proof of ice in geological samples from Mars Spirit and Opportunity, the twin rovers, found evidence of the presence of water enclosed in rock in 2007, when one of Spirit's wheels broke and gorged a piece of stone. Analysis of the silica-rich layer discovered in the scratch suggested it formed in the presence of liquid water. In 2008, the Phoenix lander was gathering geological samples, and they disappeared after a few days. Scientists thought these were pieces of ice. This assessment was confirmed when the lander later detected water vapour in a sample. In 2012, Curiosity was meandering over an ancient martian seabed when it examined a number of rocks that were exposed to liquid water billions of years ago. In 2012, Curiosity (pictured) was meandering over an ancient martian seabed when it examined a number of rocks that were exposed to liquid water billions of years ago Recurring slope lineae and debate causes it Features known as recurring slope lineae (RSL) were first identified in 2011. These dark streaks populate the areas of Mars with a sharp incline. Researchers speculated that these may have been caused by the intermittent flow of liquid water down steep banks on the planet. In June 2013, Curiosity found powerful evidence that water good enough to drink once flowed on Mars. In September of the same year, the first scoop of soil analysed by Curiosity revealed that fine materials on the surface of the planet contain two per cent water by weight. In 2015, Nasa claimed to have discovered the first evidence of liquid water on Mars in the present day. The space agency said that its Mars Reconnaissance Orbiter (MRO) provided the strongest evidence yet that liquid water flows intermittently on present-day Mars. In 2017, Nasa issued another statement rebuking its initial findings. Features known as recurring slope lineae (RSL) were first identified in 2011 (pictured). These dark streaks populate the areas of Mars with a sharp incline. Researchers speculated that these may have been caused by the intermittent flow of liquid water It said the dark features that run down steep inclines on the red planet were actually granular flows, where grains of sand and dust slip downhill to make dark streaks, rather than the ground being darkened by seeping water. Images from the MRO revealed the streaks only exist on slopes steep enough for dry grains to descend the way they do on faces of active dunes. Also in 2017, scientists provided the best estimates for water on Mars, claiming it once had more liquid H2O than the Arctic Ocean - and the planet kept these oceans for more than 1.5 billion years. The findings suggest there was ample time and water for life on Mars to thrive, but over the last 3.7 billion years the red planet has lost 87 per cent of its water - leaving the surface barren and dry. A subterranean lake In a study published in the journal Science, ESO researchers have now discovered the first concrete evidence for liquid water on Mars. Using radar imagery from the Mars Express probe, the ESO team have found a 12-mile long underground lake filled with liquid water.
And, they found the habitable zone was likely several kilometers thick.
The team modeled different climate scenarios, and found that a colder environment may even have been better for hosting life.
‘People have a conception that a cold early Mars climate is bad for life, but what we show is that there’s actually more chemical energy for life underground in a cold climate,’ Tarnas said.
‘That’s something we think could change people’s perception of the relationship between climate and past life on Mars.’
The researchers say the findings could help guide the search for ancient life on the red planet.
WHAT IS NASA'S MARS 2020 MISSION? The Mars 2020 mission is part of Nasa's Mars Exploration Program, a long-term effort of robotic exploration of the red planet. Nasa hopes the mission will help to answer key questions about the potential for life on Mars. The mission also provides opportunities to gather knowledge and demonstrate technologies that address the challenges of future human expeditions to Mars, including producing oxygen from the Martian atmosphere, and identifying water. The mission is timed for a launch in July/August 2020 when Earth and Mars are in good positions relative to each other for landing on Mars. According to NASA, the new rover will have 23 cameras (artist's impression pictured)
‘One of the most interesting options for exploration is looking at megabreccia blocks – chunks of rocks that were excavated from underground via meteorite impacts,’ Tarnas said.
‘Many of them would have come from the depth of this habitable zone, and now they’re just sitting, often relatively unaltered, on the surface.’
Among the promising sites where these blocks are present include Northeast Syrtis Major and Midway, both of which are being considered for upcoming missions.
‘The mission of the 2020 rover is to look for the signs of past life,’ Mustard said.
‘Areas where you may have remnants of this underground habitable zone – which may have been the largest habitable zone on the planet – seem like a good place to target.’
Mosaico de  visto por la , 22 de febrero de 1980. 
En un nuevo estudio anunciado el lunes pasado y disponible en el volumen actual de ''Earth and Planetary Science Letters'', un equipo internacional liderado por investigadores de la  de Estados Unidos afirmó que  tuvo alguna vez la cantidad adecuada de  y la temperatura correcta para dar sustento a formas simples de vida, aunque no en su superficie. Hace tiempo, la capa subterránea y rocosa de Marte poseyó suficiente agua y  para mantener los mismos tipos de comunidades microbianas observadas en la .

"Con base en cálculos químicos y de física básica, demostramos que la antigua subsuperficie marciana probablemente tuvo suficiente hidrógeno disuelto para proporcionar una  global en el subsuelo", reportó Jesse Tarnas, autor principal y estudiante de posgrado en Brown. El artículo no afirma que existió , sino que es muy probable que las condiciones adecuadas para la vida hayan perdurado por un tiempo prolongado. Esta zona habitable, localizada por debajo de la entonces congelada superficie marciana, habría alcanzado varios kilómetros dentro de la superficie, potencialmente protegida por el hielo.

El estudio mostró que, durante el periodo Noachiano (entre 4100 y 3700 millones de años atrás), la radiólisis, proceso por el que la radiación rompe las moléculas del agua, produjo suficiente  (H2) para permitir la vida de organismos microbianos mientras permanecieran dentro del área justo debajo de la . La concentración de hidrógeno en el agua subterránea podría haber variado entre aproximadamente 35 y 55  por litro, dependiendo de si el agua del antiguo Marte era caliente o fría, respectivamente. Incluso podría haber sido mayor si el medio de la subsuperficie contuvo suficiente sal. Los investigadores llegaron a este cálculo al establecer tres factores. 

Primero, revisaron los datos obtenidos por el espectrómetro de  abordo de la nave  de la . A partir de ellos dedujeron la cantidad de elementos radioactivos que habrían estado presentes en la corteza de Marte durante el periodo Noachiano y, por tanto, cuánta radiación habría estado disponible para separar las moléculas de agua y producir hidrógeno. Posteriormente, con base en los , determinaron cuánta agua subterránea habría existido. En tercer lugar, emplearon modelos climáticos y geotérmicos para precisar la cantidad de agua en estado líquido y a una temperatura adecuada para los seres vivos.

En ambientes subterráneos de la Tierra, los ecosistemas microbianos litoacutotróficos del subsuelo (SLiMEs, por sus siglas en inglés), los ecosistemas se sustentan en microbios que obtienen electrones de moléculas circundantes y no de plantas que aprovechan la luz solar por medio de la . El hidrógeno molecular es un  especialmente bueno. John Mustard, profesor en la Universidad Brown y uno de los autores del artículo, pertenece a un equipo que diseña la próxima misión del , programada para 2020. Mustard y Tarnas recomiendan que el rover estudie los sitios de colisión de meteoros, que podrían contener rocas excavadas de esta posible profundidad probablemente habitable y que podrían contener rastros de vida antigua.