European Space Agency (Mars)

The Underground Lakes of Mars The European Space Agency (ESA) announced in February, they had found the first geological proof of a system of interconnected lakes under the surface of Mars, five of which may contain minerals crucial to life.

By Richard Forsyth

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s our planetary neighbour, Mars has long tantalised us with its mysteries. With successions of sophisticated hardware deployed on the surface and in orbit around the Red Planet we are finding out new astounding facts about this world on a regular basis.

In total there are currently six active satellites orbiting Mars, and the 15 year long exploration of the NASA rover Opportunity, has only recently come to its end in February – but all the time we are planning new missions and machines to ‘take the baton’ for pioneering research.

Scientists are confident that Mars once had substantial, large bodies of surface water and may have had opportunities for sustaining life.

Features on the surface that look like they were shorelines have been identified.

However, it is the underground water systems that have been under scrutiny of late.

Climate models for early Mars reveal temperatures that rarely rise above freezing, so wet periods may not have been prolonged (relatively speaking), which is not the ideal environmental scenario for surface life. The subsurface is more promising a proposition for the hosting of some form of Martian life.

Incredibly, there is evidence that water under Mars remains today.

In 2018, a pool of liquid brine (about 1.5 kilometres below the surface, measuring in length about 20 kilometres) was detected beneath the Red Planet’s South Pole.

Models had suggested an underground, connected system would exist but hard proof was missing, as was the understanding of the mechanics of such as system.

Therefore, European Space Agency’s latest discovery around underground water systems of ancient Mars provided a welcome revelation with fresh insights and confirmed what scientists had been suspecting.

Beneath the Martian Surface Seeing beneath the surface of another planet is, in its own merit, a feat of human ingenuity that deserves being celebrated.

It was all thanks to ESA’s Mars Express orbiter, which has been circling the planet since 2003, using a radar instrument called MARSIS (Mars Advanced Radar for Subsurface and Ionosphere Sounding). The orbiter is able to help find answers to all sorts of questions relating to geology, atmospheric conditions, the surface and the history of water on Mars. It relies on three radar booms, two of which are 20 metres long, to gather data, as it circles the planet from above.

The latest research, now published in the Journal of Geophysical

Research, indicates that there was a groundwater system on Mars that fed into the lakes. By examining imagery sent back from the orbiter, researchers looked at 24 deep, enclosed craters in the Northern Hemisphere, that had floors around 4,000 metres below the estimated sea level at the time.

The features in these craters, that could only be caused by water, consisted of channels etched in crater walls and valleys carved out by sapping groundwater and various other physical indicators. These features showed that some of the craters once had pools and flows of water that changed and receded over periods of time.

“Early Mars was a watery world, but as the planet’s climate changed this water retreated below the surface to form pools and ‘groundwater’,” said lead author Francesco Salese of Utrecht University, the Netherlands. “We traced this water in our study, as its scale and role is a matter of debate, and we found the first geological evidence of a planet-wide groundwater system on Mars.”

“Findings like this are hugely important; they help us to identify the regions of Mars that are the most promising for finding signs of past life.”

This image from ESA’s Mars Express shows a network of dried-up valleys on Mars, and comprises data gathered on 19 November 2018 during Mars Express orbit 18831. The ground resolution is approximately 14 m/pixel and the images are centered at 66°E/17°S. This image was created using data from the nadir and colour channels of the High Resolution Stereo Camera (HRSC). The nadir channel is aligned perpendicular to the surface of Mars, as if looking straight down at the surface. North is to the right. ©ESA/DLR/FU Berlin

This is the ExoMars2020 Rover which will soon be deployed to drill into the Martian surface for sample. ©Mars_ESAATG medialab

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Evolution of water filled basins over time. This diagram shows a model of how crater basins on Mars evolved over time and how they once held water. This model forms the basis of a new study into groundwater on Mars, which found that a number of deep basins – with floors sitting over 4,000 m deep – show signs of having once contained pools of water.

There are three main stages: in the first (top), the crater basin is flooded with water and water-related features – deltas, sapping valleys, channels, shorelines, and so on – form within. In the second stage (middle), the planet-wide water level drops and new landforms emerge as a result. In the final stage (bottom), the crater dries out and becomes eroded, and features formed over the previous few billions of years are revealed. ©NASA/JPL-Caltech/MSSS; Diagram adapted from F. Salese et al. (2019)

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This colour-coded topographic view shows the relative heights of the terrain in and around a network of dried-up valleys on Mars. Lower parts of the surface are shown in blues and purples, while higher altitude regions show up in whites, yellows, and reds, as indicated on the scale to the top right. This view is based on a digital terrain model of the region, from which the topography of the landscape can be derived. It comprises data obtained by the High Resolution Stereo Camera on Mars Express on 19 November 2018 during Mars Express orbit 18831. The ground resolution is approximately 14 m/pixel and the images are centered at 66°E/17°S. North is to the right. ©ESA/DLR/FU Berlin

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The Search for Signs of Life The water levels seem to align with shorelines of a Martian ocean that’s been proposed to have existed three to four billion years ago.

It’s speculated by the researchers that the ocean may have connected to the system of underground lakes around Mars. In addition, signs of minerals were found in five craters that are linked to the emergence of life on Earth such as clays, carbonates, and silicates. This is exciting new evidence that Mars may have supported life, as the ingredients to support it were in place.

Zones beneath the Martian surface have been a promising focus for some scientists who suspect life could have been prevalent on the

planet. For example, a study by researchers at Brown University in the USA, published in Earth and Planetary Science Letters, suggested that ancient underground subsurface areas could have been home for substantial amounts of microbial life over long periods of Martian history.

The idea was that within these habitable zones, microbes could take hydrogen electrons from water for energy. This idea was taken from a study of underground microbes on Earth that were deprived on sunlight, whose source of energy proved to be hydrogen electrons from water molecules that had drained into the subsurface. These communities of microbes thrived in this unusual way. In theory, with flowing water,

Express Delivery Mars Express gained its name from being put together quicker than any other comparative planetary mission.

It arrived at Mars at the same time as Beagle 2 – a lander that made it to the Martian surface but sustained damage that rendered it unable to transmit data.

The orbiter was tasked with imaging the entire surface of Mars at a high resolution (10 metres per pixel) and

there could have been the same system for microbial life on Mars. The researchers concluded that 4 billion years ago, the Martian subsurface was absorbing enough hydrogen to energise microbes for hundreds of millions of years.

The underground lakes prove an exciting find for the basis of future Mars missions. The findings can aid other machines currently investigating Mars, for example another Mars orbiter, the ExoMars Trace Gas Orbiter, is analysing the atmosphere in great detail, looking for gases related to biological or geological activity, and to identify subsurface locations where water-ice or hydrated minerals are present.

The orbiter will be working in tandem with research relayed to it by

an ExoMars rover on the surface. This rover is a joint venture between ESA and Russian Space Corporation, Roscosmos, and is named Rosalind Franklin after the scientist who discovered the structure of DNA. It is to begin research in 2021. It will be capable of drilling down into the surface to around two metres depth to analyse composition of the soil.

The confirmation of the interconnected subsurface lakes has created headlines in both tabloid newspapers and scientific publications, as a milestone development in understanding Mars.

As Dmitri Titov, ESA’s Mars Express project scientist puts it: “Findings like this are hugely important; they help us to identify the regions of Mars that are the most promising for finding signs of past life.”

What ancient mars may have looked like billions of years ago, based on MOLA data. © Ittiz

some parts of the surface at very high resolution (2 metres per pixel). It was also tasked with understanding how the atmosphere interacts with the solar wind, mapping the composition of the atmosphere, as well as the atmosphere’s effect on the surface. Finally, as it has now aptly demonstrated, its mission involved determining the structure of the sub surface to a depth of a few kilometres.

Mars Express discovered water buried under the South Pole of Mars. Copyright Context map: © NASA/Viking; THEMIS background: © NASA/JPL-Caltech/Arizona State University; MARSIS data: © ESA/NASA/JPL/ASI/Univ. Rome; R. Orosei et al 2018.

ESA’s Mars Express has used radar signals bounced through underground layers of ice to find evidence of a pond of water buried below the south polar cap.

Twenty-nine dedicated observations were made between 2012 and 2015 in the Planum Australe region at the south pole using the Mars Advanced Radar for Subsurface and Ionosphere Sounding instrument, MARSIS. A new mode of operations established in this period enabled a higher quality of data to be retrieved than earlier in the mission.

The 200 km square study area is indicated in the left-hand image and the radar footprints on the surface are indicated in the middle image for multiple orbits. The greyscale background image is a Thermal Emission Imaging System image from NASA’s Mars Odyssey, and highlights the underlying topography: a mostly featureless plain with icy scarps in the lower right (south is up).

The footprints are colour-coded corresponding to the ‘power’ of the radar signal reflected from features below the surface. The large blue area close to the centre corresponds to the main radar-bright area, detected on many overlapping orbits of the spacecraft.

A subsurface radar profile is shown in the right hand panel for one of the Mars orbits. The bright horizontal feature at the top represents the icy surface of Mars in this region. The south polar layered deposits – layers of ice and dust – are seen to a depth of about 1.5 km. Below is a base layer that in some areas is even much brighter than the surface reflections, highlighted in blue, while in other places is rather diffuse. Analysing the details of the reflected signals from the base layer yields properties that correspond to liquid water.

The brightest reflections are centred around 193°E/81°S in the intersecting orbits, outlining a well-defined, 20 km-wide zone.

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