What a liquid water lake reveals and conceals about Mars

The discovery of a 20-km lake a kilometre and a half under the southern polar ice cap of Mars concludes in some ways a decades-old debate over the presence of a persistent body of liquid water on the planet.

Written by Sowmiya Ashok | New Delhi | Updated: August 8, 2018 11:10:53 am
Dark streaks on slopes, captured by ‘HiRISE’ camera on the Mars Reconnaissance Orbiter, are inferred to be formed by seasonal water flows on today’s Mars. (Source: NASA/JPL-Caltech/Arizona Univ)

In The Things that Live on Mars, which appeared in Cosmopolitan in March 1908, H G Wells asked, “Is it probable that evolution has gone upon exactly parallel lines on the two planets (Earth and Mars)?” Intelligent beings could not be present in isolation, he wrote; “they can be but a part of the natural history of Mars in just the same way that man is but a part of the natural history of the earth”.

The discovery by an 11-member Italian team led by Prof Roberto Orosei of the Istituto Nazionale di Astrofisica in Bologna of a 20-km lake a kilometre and a half under the southern polar ice cap of Mars concludes in some ways a decades-old debate over the presence of a persistent body of liquid water on the planet. Does it also make it more likely for life to be present on Mars?

Water of life?

“Life as we know it on Earth is kind of tied up with water. Our definition of life is based on how it is on Earth. But why does that have to be (the same) elsewhere?” said Dr Amitabha Ghosh of NASA’s Mars Exploration Rover Mission. “Our fascination with Mars is partly because there is evidence of water and partly because of popular imagination. For example, some of the satellites of Jupiter and Saturn apparently have underground oceans, which also might have past or present life…”

However, Dr Ghosh said, “We don’t think of Jupiter as a hospitable planet. By chance, the more we explored Mars, the more we found evidence of past water, present water… the more we explore, there does seem there is evidence of water, all over.”

The repeated missions to Mars in search of life coincided with the search for life in extreme environments on Earth, Dr Ghosh said. “A couple of decades back at NASA, we started looking at extreme environments on Earth. We perhaps don’t think life can exist in very hot conditions, in oceans, in the Antarctic. (But) In absolutely unexpected places, in extreme conditions, people find life. It helped broaden our sense of where life can survive.”

Martian salts

Dr Anil Bhardwaj, Director of the Ahmedabad-based Physical Research Laboratory, said atmospheric pressure on the Martian surface is almost a hundred times less than on Earth, ensuring that water will not be in liquid form, but rather, as ice or vapour.

“What this means is that the presence of water is much beneath the surface,” said Dr Bhardwaj, who previously worked on ISRO’s Mars Orbiter Mission (MOM). “Now, this observation (by the Italian scientists) is based on a very large number of datasets collected over a three-year-period which previous researchers had an inkling about, but the finding was not conclusive.”

Dr Bhardwaj said it is possible the water is mixed with other compounds including salt, which reduces the temperature and helps it retain liquid form. Dr Ghosh agreed: “The atmospheric pressure is so low that water doesn’t survive. The perplexing thing here is how does this persistent body of water survive? That we might have to probe. The way we do it on Earth is we add a lot of salt. What is the composition of water? Is it water, is it combined with salts?”

Mission technology

While this isn’t the first time water has been found on Mars (Dr Orosei and his team said evidence of lakes, rivers, and deltas had been reported by the Viking Mission Orbiter 40 years ago, and findings from NASA’s Mars Reconnaissance Orbiter last year provided evidence of intermittent flows of liquid water on present-day Mars), the discovery of the underground lake is still important.

“We have gotten water in different forms, subsurface water, this is perhaps the persistent stagnant lake, but see, it is like, you find water at a lake near Delhi and then you have underground water from a well. Both are equally interesting,” Dr Ghosh said.

The Italian researchers surveyed the Planum Australe region, or the southern polar plains of Mars, using the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) instrument, a low-frequency radar on board the European Space Agency’s Mars Express Orbiter. However, MARSIS could not detect the composition of the water, Dr Orosei said at the press conference where he announced the discovery. There was no technology yet to investigate the discovery, he said.

Dr Ghosh concurred that “All missions start with technology that needs to be developed to an extent, (and) an entire mission cannot be put together by existing technology.” It was “perfectly conceivable”, he said, that the technology would be developed “once a space agency thinks this is a kind of mission they want to do”.

Humans on Mars

Dr Bhardwaj said the discovery was “very significant” because of its implications for human exploration of Mars. India’s MOM, launched in November 2013, has been in orbit around the planet since September 24, 2014, and has picked up its surface features. “Our belief is that there will be more areas where liquid water could be, it so happens it has not be discovered so far,” he said.

Dr Ghosh made the point that while water is important for the journey to Mars and its colonisation, it is also important “to rationalise the cost structure of going to Mars”. Referring to SpaceX founder Elon Musk’s push to get humans to Mars, he said: “One of the core things is the generation of fuel. He (Musk) talks about fuel depots on Mars, and water is a very important part of that story. We have just found evidence of water. (It is a) minute example… (and) it is not economically viable to extract it, so you have to show that Martian water can be extracted, converted… The game of space exploration is also in large part (about) doing things at a rational cost.”

Dr Amitabha Ghosh is Chair of the Science Operations Working Group of the NASA Mars Exploration Rover Mission. Dr Anil Bhardwaj is Director of Physical Research Laboratory, Ahmedabad, and was previously Principal Investigator of ISRO’s Mars Orbiter Mission.

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