Back in 2018 scientist made a discovery on Mars that would change their understanding
of Mars. Radar signals that had bounced just below the surface of Mars revealed
a shiny patch. This patch was consistent with a pool of liquid water.
Based on this finding they started to search for more of these signals and slowly more and
more of them started to turn up revealing what looked like a network of underground lakes.
Up until this stage they had only ever been able to detect frozen water and this was the
first indication that liquid water was still present on Mars. The next step was for them to
explain how these underground lakes could still be liquid and here is where the mystery deepened.
They discovered that some of these patches were in regions that are just too cold for liquid water,
even with salt added which could lower the freezing point.
Lets dive in and find out more…
The scientist admit that they were not certain whether these signals are liquid or not, but
they appear to be much more widespread than they had originally thought. And this means that either
liquid water is common beneath Mars' south pole, or these signals are indicative of something else.
Using the Mars Advanced Radar for Subsurface and Ionosphere Sounding instrument on the Mars
Express orbiter they discovered the first of these features at the Martian south
pole. This triggered a seach of archived data which revealed 3 more of these lakes.
It is believed that the Martian ice cap consists of alternating layers of carbon dioxide and water
ice. From the analysis of this radar technology on Earth we know which signals are indicative
of certain materials. Some materials reflect radar signals better than others,
and liquid water is one of these. This means that when analysing a radar signal
those of liquid water will appear brighter or stronger compared to other materials.
So when they examine the radar signals from Mars they also saw that the signals were strong
coming the suspected lakes compared with the surface but they were very small. This
caused them to expand their search. They went back over 15 years of archived MARSIS data
and found dozens more of these highly reflective patches below the surface.
More interesting was the fact that some of these patches appeared much closer to the surface
some as close as 1km. This close to the surface the temperature would be as low as -63C.
In a previous piece of research, they found that water with salts of calcium and magnesium
could remain liquid at temperature as low as -123C
for very long periods of time. Mars itself it rich in salts of calcium and magnesium.
But in a 2019 paper, they found that no amount of salt is sufficient to melt the ice at the
base of the Martian south pole. This meant that the only way this water could be liquid
is through some form of volcanism. The problem was there is no sign of any volcanism around
the poles of Mars. Therefore at this stage, they think that the signals cannot be caused by water
but the problem is that they have no credible alternative for what the sources might be instead.
So what might cause a super cooled liquid to remain liquid well below its supposed
freezing point? In order to find a potential candidate, we have to look back to 2010
when some researchers from Isreal were conducting experiments on supercooled liquids.
Normally when you cool a liquid it should start to freeze at its freezing point.
If you cool pure water it turns out it will not freeze as the temperature reaches zero.
The reason for this is that freezing has to first nucleate by forming a baby crystal. This
process takes energy which can make this process extremely slow. Due to this, the water can become
much colder than its normal freezing point. This process is called supercooling. If you take this
supercooled water and disturb it by adding an impurity for example it will freeze immediately.
Normal supercooled water can freeze at temperatures as low as -40C. It has been known
for over 150 years that the presence of an electric field
can affect the freezing point. This phenomena is called electrofreezing. Dufour in 1861 stated
that such an electrofreezing phenomena existed but presented no details of his experiments.
Much later Rau demonstrated that a few drops of a few millimetres diameter, supercooled to
temperatures between -4 and -7C froze immediately if a spark passed between them and an electrode.
The main hypothesis for the effect is due to water’s polar nature. Water has
a small negative charge on one end and slight positive charge on the other.
An electric field would align them according to their charge. But studying this phenomena
has been difficult as charged surfaces act as nucleating agents, and therefore trigger freezing.
The scientist managed to solve this problem by creating a charge on a non-nucleating
pyroelectric material surface, to allow the electrical affects alone to be examined.
Their results shows that in the absence of an electric field the water droplets froze at an
average temperature of -12.5C. If the surface was negatively charged the freezing point was -18C
but if the surface was positively charged the droplets froze at -7C. They were very surprise at
the difference between the charges and the exact mechanism which causes the effect is unknown.
They also found that they could freeze liquid supercooled water by heating it.
When the surface was negatively charged, the water was kept liquid at -11 for around ten minutes,
but after the charge dissipated the temperature was increased to induce a positive surface
and they observed that the water started to freeze at the temperature rose to above -8C
Now, these temperatures are obviously well above the temperature on Mars and none of
the experiments were conducted using the brine that they believe is present on Mars.
Is it possible that there are currents flow below the surface on mars
that are enough to lower the freezing point of the brine
keeping it liquid? Or is the surface in these chambers being charged in some other manner?
One other thing that this links to is the frozen mammoth and other mammal carcases we
have discussed in the Earth in Upheaval series. Is it possible that those animals were flash frozen
by super cooled vapour caused by electric field and that a sudden change in the field
triggered an almost instant freezing of that vapour over vast regions?