New missions to Mars reveal abundant water hidden inside

Each new investigation reveals that Mars harbors large amounts of water in the subsoil, and now we have just learned that its interior is hot and molten.

We have multiple evidences of the importance of water in its evolution obtained in recent decades, thanks to exhaustive monitoring with various devices in orbit and rovers on the surface of any slight change that occurs on the planet. A recent study led by Eva L. Scheller of the California Institute of Technology (Caltech) indicates that the aqueous alteration of many of its minerals made it possible to sequester a good part of that water in the crust, in quantities that could vary between 30 and 99%. of the water initially present.

The evidence is accumulating: the discovery of brine flows on Mars, the existence of subsoil permafrost regions, and even the possible existence of subterranean lakes point to the possibility that it may or may have harbored microorganisms. All this is revealed as an exciting excuse to tackle human exploration of the red planet very soon.

From its superficial exploration we could deduce that water can only be in the polar caps. However, much of it remains in the form of permafrost in the Martian subsoil, as recently revealed by craters excavated by small asteroid impacts in certain regions. Some regions can even harbor large masses of liquid water.

Since 2018, an Italian team, using the MARSIS radar of the European Space Agency’s (ESA) Mars Express probe, has discovered multiple subglacial lakes beneath the subsoil near the southern polar cap. Among them a deep lake about 20 km wide.

The origin of water on Mars

The red planet formed, to a large extent, from the aggregation of hydrated planetesimals. So it should come as no surprise that it ended up hosting plenty of water. Not without reason, it has recently been agreed to call philosophical to that first era that covers the first 500 million years in the evolution of the planet, based on the presence of phyllosilicates (clays) in those ancient terrains.

In fact, some Martian meteorites that have reached Earth, such as the famous Allan Hills 84001, reveal that water flowed over extensive regions of Mars. We studied precisely this meteorite at the Institute of Space Sciences (CSIC-IEEC) and it has carbonates in its fractures that grew in different phases, supporting the existence of various hydration periods while they were part of the Martian surface. Possibly these phases were a consequence of the volcanic activity in successive episodes of floods that occurred in that rocky environment from which that meteorite came.

But, after that golden stage, everything indicates that Mars suffered a gradual cooling, losing its magnetic field and its dense primordial atmosphere. Thus, liquid water on the surface ceased to be stable, as atmospheric pressure and temperature dropped. The degradative flow of UV radiation that, since then, has inexorably reached the surface of the planet also increased.

The loss of its dense atmosphere

Some Martian meteorites, the only samples we currently have from the red planet, support that early Mars had appreciable igneous activity that led to significant outgassing on a global scale, giving rise to a dense atmosphere in its remote past. That atmosphere gradually disappeared because as it cooled it lost its magnetic field and, with it, the ability to retain it and shield ultraviolet radiation. This probably occurred during the Teicican era so called to refer to the sulfate-type minerals formed then, between 3.5 and 4.0 billion years ago.

As the planet lost that atmosphere and volcanic activity decreased, the greenhouse effect ceased and the temperature decreased. The water gradually withdrew underground, where it is now present in the form of permafrost and hydrated minerals. This can be seen in recent impacts that have exposed the frozen subsoil in the coldest regions and the poles.

The mysterious dark flows

A decade ago, the Mars Global Surveyor orbiter discovered a kind of runoff advancing along some crater slopes and slopes of the planet Mars. Such dark flows seem to undergo seasonal changes. During the Martian summer they grow, and retract or disappear in winter.

Since their discovery, these flows have been monitored from space, and are known as recurring slope lines (RSL). The best explanation available so far for these observations is that they are brine flows mixed with sand.

Brine flows and water retained in the subsoil

NASA’s Mars Reconnaissance Orbiter (MRO) has spent years monitoring subtle variations in these dark flows that preferentially propagate during warm seasons. Equipped with high-resolution cameras and spectrometers, the MRO has revealed that these elongated currents are several meters wide and tens of meters long. Its extent and albedo vary during warm periods.

The saline flows seem to be formed by hydrated brines in which magnesium and sodium chlorate and perchlorate abound. In the right proportions, these salts could lower the freezing point of water to 80 K (-193 ºC) and, therefore, would give these hydrated brines the possibility of flowing at the very low temperatures of present-day Mars.

The interest in understanding them is such that rovers are being guided to these regions to characterize their specific nature on a microscopic scale.

The most interesting thing is that the discovery supports that this water stored in the subsoil is capable of flowing in episodes of hydrothermalism and, therefore, an underground hydrological cycle could occur, at least locally. Not only that, detailed studies by the Perseverance rover in the Jezero crater environment reveal the presence of aromatic organic compounds that would have arisen in the stages in which the crater was a hydrothermal environment.

Possible Martian Niches for Extremophile Bacteria

We look at those environments altered by water with a magnifying glass because, if life also arose on Mars, extremophile bacteria could have appeared, microorganisms that are characterized by a higher level of adaptability than conventional ones, capable of moving to the last habitable niches.

We certainly don’t know if those niches existed. But if knowledge is the result of curiosity, these hypotheses arouse the interest of future manned missions and make us focus our efforts on finding the most promising places for future landings.

Brines, evaporites and the origin of life…also on Mars?

Could the evidence of water flowing into the interior of Mars, even punctually today thanks to remaining internal heat, have implications for the search for Martian life? Definitely.

Decades ago, Caltech’s Joseph Kirschvink suggested that life on Earth may have originated from ribose formed on Mars and transported to Earth via meteorites. Kirschvink’s hypothesis is usually considered as bold as it is improbable, given that the transport mechanism to Earth would have been aboard meteorites that would take millions of years to reach our planet. However, certain areas of the surface of Mars appear to have seen the formation of evaporites and other aqueous alteration minerals.

Perhaps future studies suggest that Kirschvink was not so wrong in proposing evaporites as potential catalysts for life.

Despite our current ignorance of the exact scenario required for the origin of life, the discovery of such aqueous environments on Mars is an exciting reason to drive exploration of the red planet.

Josep M. Trigo Rodríguez, Principal Investigator of the Meteorites, Minor Bodies and Planetary Sciences Group, Institute of Space Sciences (ICE – CSIC)

This article was originally published on The Conversation. Read the original.