VocExile To Main Menu/Life on Mars
Speculation by Ed Perley
For most of this century, scientists believed that the one place in the solar system, besides the earth, with a potential to harbor life as we know it is Mars. It was assumed that such life would be most abundant on the planet's surface, as is on Earth. But the first space probes to Mars told us that the surface of Mars is very inhospitable to life. The atmosphere is very thin and dry, and unable to shield the surface from deadly ultraviolet radiation. The consensus of scientists was that we will have to look elswere for extraterrestrial life.
New discoveries in the last two decades indicate that life does not have to live on the surface. Separate ecosystems, independent of the surface, have been found in the deep ocean trenches. The energy source for this life is hydrogen sulfide released from hot water vents on the ocean floor. Other living organisims have been found living quite comfortably within solid rock. So, it is time to again search for signs of life on Mars, this time under the surface.
Certain minimum conditions are needed. Liquid water, a carbon source, and some kind of chemical energy are needed. Early in the history of Mars, living organisims may have been abundant on the surface. Now, the only remnants of this life, if they exist, are probably deep below the surface.
One possible abode for living organisms on Mars is in deep caves under the surface. It would seem that caves on Mars could be much deeper than those on earth bacause Mars has only one third the gravity of the earth, and it's crust appears to be thicker and more stable than that of our planet. Evidence of large eruptions of water from beneath the Martian surface suggests that these underground chambers could be quite extensive. Some might even still contain ice or even liquid water.
The atmospheric pressure at the surface if Mars is between 6 and 10 millibars, or .180 to .300 inches of mercury. The vapor pressure of water at 0 degrees centigrade is about 4.5 inches of mercury. At 10 degrees, it is just over 9 inches. In order for water to stay around for any length of time at each temperature, the atmospheric pressure needs to be higher than this. With a surface pressure of .180 to .300 inches of mercury, it is obvious that liquid water can not exist for long on the Martian surface. It does not, however, preclude the possibility of liquid water deep under the surface.
I performed some rough calculations using the formula of Babinet to see what the atmospheric pressure would be at different depths. These are only rough approximations resulting from a succession of calculations at ever increasing depths. Calculations also were done to account for a Carbon Dioxide atmospheric composition and the lower gravity of the planet.
The values shown below were calculated, assuming a surface pressure of .180 cm of mercury at the mean surface altitude, and a temperature of 0 degrees centigrade. The pressure effects resulting from increase of temperature with depth were not accounted for. Warm air does not compress down as far as cold air. The lowest surface altitude on Mars, on the floor of the Hellas basin, is five miles below the mean surface altitude. You can see that even at the very lowest point on the planet, the atmosphere is still far too thin to allow liquid water to stay around very long.
DEPTH (MILES)...............PRESSURE (INCHES OF MERCURY)
0 ...................................... .18
5 ...................................... .30
20 .................................... 1.50
30 .................................... 4.75
40 ................................... 15.
55 ....................................40.
On the earth, the deepest explered cave is about one mile below the surface in France. The deepest mine is over 11,000 feet deep in South Africa. At that depth, the rock is quite hot. A powerful refrigeration system is needed to keep the air cool enough to allow miners to work.
Mars is believed to have a thicker crust and a cooler interior than Earth. Still, it would seem unlikely that at a depth of 30 miles, it would be cool enough for liquid water to be present. At lesser depths, the atmosphere would just be too thin.
There is another possibility that could provide conditions under the Martian surface conducive to the existance of life. Consider the possibility of an ancient steam vent a mile or so below the surface. What if the mouth of the cave has been plugged up with ice? There is evidence on the surface of outflow from ice melting under the Martian surface. Gasses seeping from below could be trapped inside such a cavern, producing an atmospheric pressure much higher than on the surface. Such an environment could easily contain all of the conditions required for supporting living organisms.
We will never know if there can be life under the surface of Mars until we are able to thoroughly study it's structure and dynamics. That should come in the decades ahead, done either by humans or robots. We should realize that underground ecosystems, if they exist on Mars, could be extremely fragile. For instance, drilling a shaft down to a sealed cave like that described above could destroy an entire ecosystem within minutes.
We must always remember. We wish to seek out life, not destroy it.
Note: An article on the possibility of life under the Martian surface
is in the July 2000 issue of Astronomy Magazine