Evidence of liquid water on Mars – Expert reaction

Scientists have found evidence that liquid water is currently present on Mars – but does this mean that there might be, or have been, life on the Red Planet?

Credit: NASA/JPL-Caltech/MSSS
Credit: NASA/JPL-Caltech/MSSS

Using data collected by the Curiosity rover, the researchers have determined that tiny amounts of water vapour condenses as a liquid in the planet’s soil at night and evaporates away in the morning.

The study, published this week in Nature Geoscience, shows that high amounts of salt in the soil lower the melting point of water, allowing it to temporarily pool as a liquid despite the subzero temperatures.

The Science Media Centre has collected the following commentary from astrobiology experts. Feel free to use these quotes in your reporting. If you would like to speak to a New Zealand expert, please contact the SMC (04 499 5476; smc@sciencemediacentre.co.nz).

Professor Steve Pointing, who is Director of the Institute for Applied Ecology at AUT and has worked with NASA for over 10 years on astrobiology projects, comments:

“We already know there is plenty of frozen water (ice) on Mars, but this is the first evidence of liquid water. The key to this was discovery of deposits of calcium perchlorate. When the small amounts of water in Mars’ atmosphere condense as frost, this forms a liquid brine with the calcium perchlorate that remains liquid at the very low temperatures on Mars surface.

“Liquid water is essential to all life as we know it. This is why much of NASA’s search for traces of life on Mars have focused on finding evidence for past and present water. It appears likely that although extant life today on Mars may be only a faint possibility, the conditions for abundant liquid water existed during Mars’ recent history. This means that finding ‘biosignatures’ of past life is a more realistic expectation.

“The presence of water on another planet is not by itself a guarantee that live will evolve there.  On our planet there was also unique confluence of fortuitous events and properties that allowed life to flourish. This was a combination of the time during which the Earth avoided catastrophic asteroid impact due to the protective effect of Jupiter’s gravity (shielding the inner planets of our solar system from incoming asteroids), the presence of a magnetic field and an atmosphere to prevent lethal radiation reaching Earth’s surface, and plate tectonics to recycle carbon and ensure that this essential molecule for life did not all become locked up in rocks.

“[Exploring Mars is important because] it is within human nature to seek to explore the unknown, and to suggest we should not try to answer the question “are we alone” by exploring space is to admit we are a lesser generation than those before us who explored unknown frontiers on earth. A positive discovery that life is multi-planetary could lead to huge positive changes in the way we interact as humans.”

Dr. Duncan Steel, who is Space Scientist at NASA-Ames Research Center, Professor of Astrobiology at the University of Buckingham and Astronomer at Armagh Observatory, comments:

“The essential point here is all about LIQUID water. We have known that there is water on Mars for decades. For example, about one-third of the Martian polar caps is (water) ice; and radar observations from Earth showed in the 1970s-80s that there is extensive sub-surface water ice spread across Mars.

“The thing is, in the low-pressure conditions on Mars, water transforms generally in a direct fashion from solid (ice) to gas (vapour) through sublimation, rather than becoming liquid first. Thus the ‘problem’ is how to have water as a LIQUID on or near the surface of Mars. One mooted possibility has been the high pressures feasible in aquifers (i.e. deep sub-surface water seeping through rocks). The present research indicates the possibility (even likelihood) of water being liquid on or at Mars’ surface through the effect upon the physical properties of water of having salts dissolved in it. The dissolved salts have the effect of dropping the freezing point of water, making it feasible (perhaps) that the water can be liquid even down to minus 70 deg C (it is claimed).

“A terrestrial parallel… People coming to NZ from the UK are amazed by how little rust there is on old cars here. The reason that cars in the UK get rusty is that during cold winter spells there is salt spread on the road so as to melt the ice (and salt promotes rusting of iron-containing alloys like steel). The paradox is that dissolving salt in water actually LOWERS its temperature (dissolving salt is an endothermic process), so that one might imagine that spreading salt on the road would cause more ice to form… but in fact the ice melts because there is another effect of the salt: it lowers the freezing point of the water (now ‘brine’) by a greater amount in deg C than the temperature drop caused! Thus the ice melts, and the resultant brine runs off the road.

“Why is this the best evidence yet of liquid water on Mars? There has been no previous direct detection of liquid water, only surmise based on distant observations such as (a) Apparent layering of rocks indicating sedimentation at some time in the distant past; (b) Apparent fresh flow patterns similar to those seen on Earth, and obviously caused by flowing water on Earth. In the present case there is a bringing-together of information derived from several different instruments on the Curiosity rover (e.g. a sensor that measures the water vapour level at the ground level) that indicates that water is being ‘grabbed’ from out of the atmosphere somehow as it cools at night, and the soil conditions (amounts of salts such as perchlorates) are such that if that vapour drops to the ground – as it surely must – then the resultant salty solution will be liquid, not solid (ice).

“Liquid water is the sine qua non of all life on Earth. We know of no life that can exist without liquid water. Therefore any search for life on Mars (or Europa, or Callisto, or Enceladus) sensibly begins with a search for water: liquid water. We know of no way to have life without liquid water, therefore the first thing we do is to search for it. This is why researchers get excited about e.g. the likelihood of an ocean of liquid water on/in Europa: we know the surface (which we can see directly) contains lots of ice, but other information indicates that deep down the water may well be liquid.

“It is possible to have liquid water without life. In fact, we see water all over the universe – in comets, in interstellar space – but generally in either its solid (ice) or gaseous (vapour) form. Various researchers have suggested in the past, for example, that large comets may have liquid water in their cores, and the reason for the interest in that possibility is that liquid water says to us “possibly life?”

“However, finding liquid water on Mars does NOT imply life. The interest here is that such a discovery says: here is one of the prerequisites of life-as-we-know-it, and so it gives us hope (!?) that microbial life might exist there. If nothing else, it tells us somewhere specific to look.

“If life does exist on Mars, then:
(a) It may be part of a common origination of life (with life on Earth), with microbial life having spread from one planet to the other. Some people have very seriously suggested that initially life may have spread from Mars to Earth – making us all Martians! – because initially Earth was far too hot for life to exist.
(b) If this is a separate origination of life, then an implication would be that life is common in the universe. So long as we are alone (so far as we know), we have NO BASIS for any guesses at whether there is life elsewhere (unless we can explain how life got started on Earth…).
(c) If (b) is the case – that there is life elsewhere – then it would be unlikely that we are the most advanced life, and so we ask: where is everyone else?”