Water under the ice

Ken Tapping, August 15th, 2018

In the sky this week…

  • After dark look for Mars in the southeast, Saturn low in the south and Jupiter in the southwest.
  • The Moon will reach First Quarter on the 19th.

In 1993 a huge lake of liquid water was detected under Earth’s Antarctic ice. It lay some 4 km below the surface of the ice, and 500 m below sea level. The lake is 250 km long, 50 km wide, with a mean depth of about 430 m.  It was named Lake Vostok.  A borehole drilled down to it showed the lake to be fresh water and teeming with microscopic life. Geological studies suggest the lake to have been an isolated ecosystem for 15 to 25 million years.

The lake exists because the pressure of the overlying ice does not allow the water to freeze. When water freezes it expands and becomes less dense, which is why ice floats on water. If the water cannot expand, it cannot freeze. There is also a possibility of some heat coming up from the Earth underneath. Unfortunately, since the lake water is under extremely high pressure, when the borehole broke through the roof of the lake, water surged upwards into the hole, picking up the drill lubricants and other chemicals used to stop the drill equipment freezing in the hole. As soon as we touched the lake, we contaminated it: not a good start. So far, some 400 lakes have been found under the Antarctic ice. Now it looks as though we have found a lake under Mars’ south polar ice cap.

The discovery was made using a ground-penetrating radar mounted on the European Space Agency’s Mars Express Orbiter spacecraft. The lake is 1.5 km under the ice, some 20 km across and a metre or two deep. Unlike Lake Vostok, this lake is believed to be salty. However, since most water creatures on Earth live in salty water, this does not affect the likelihood of finding life.

Mars has always been a tantalizer. Once it looked really inviting. We thought we were seeing waves of darkening due to vegetation growing in the spring, and then there were the “canals”. Mars had to be inhabited by living creatures, some of whom were brilliant engineers. Then, with better telescopes and close examination using spacecraft, the whole illusion came crashing down, and we realized Mars’ surface is a dry, cold, almost airless desert. However, there remained the north and south polar caps, which grew and shrank with the seasons, so there had to be water.

When we put landers and then rovers on the surface of Mars, they showed us the expected desert, but also dustings of frost on the rocks every morning. All around they showed us dry watercourses, lakebeds, rock formations and minerals and sedimentary rocks that were formed in the presence of water – lots of it. Billions of years ago Mars was a warmer, wetter world, where did all that water go?

Spacecraft orbiting Mars occasionally detected streaks of meltwater and sand slurry on steep slopes and cliffs, where avalanches and rockslides had exposed ice, which melted in the sun and flowed down the slopes, and then evaporated.  Liquid water cannot last long on Mars’ surface. One of the rovers scraped away at the surface, exposing white ice. Now we believe there to be huge amounts of ice just below the surface of the planet. However, what we would really like to find is liquid water. On Earth, it seems that all liquid water, hot or cold, fresh or salty, on the surface or deeply buried in the rocks, has little creatures swimming around in it. In some cases big ones

Is this true for Mars too, or for that matter the deep, dark ocean under the icy surface of Europa? If there is liquid water, nutrients and a source of energy, such as sunlight or hydrothermal vents, we have the recipe for life. It will be some time before we drill our way down to subglacial lakes on Mars, or the seas of Europa. The current idea is to melt our way down through the ice, and explore using robot submarines.

Ken Tapping is an astronomer with the National Research Council's Dominion Radio Astrophysical Observatory.

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