Life on Mars
 
By Lynn Weinberger

Science fiction enthusiasts have always hoped that life exists on other planets. For years, popular culture has bombarded us with stories about aliens and Martians. What if these stories are true? According to Professor Churchwell, who teaches Extraterrestrial Life, an astronomy course at UW-Madison, the probability that life has existed on Mars is “non-zero.” However, this extraterrestrial life would not look like the gray and green aliens you see on TV.
 

 
A photograph showing the barren surface of Mars.  Is it possible  
that this icy planet ever supported life?		 Two main pieces of evidence point to the existence of extraterrestrial life, the being that Mars used to be very wet. Photographic evidence of landforms that look like riverbeds and floodplains support this hypothesis. Geologists believe that water, which is made of common elements available within the universe, is the only substance that could carve out the landscape in such a way. Water facilitated the development of life on Earth, and scientists presume that life would originate the same way on Mars. The other piece of evidence pointing to life on Mars came from meteorites that have crashed into Earth from our planetary neighbor. The meteorites were pieces of Mars that were blasted into space by a meteoroid impact. These meteorite pieces are igneous formed by volcanic activity. Scientists from NASA know that these meteorites are from Mars because the gases trapped inside them match measurements taken by Viking Probe of the Martian atmosphere. 

The meteorites from Mars show evidence of fossilized organisms, which are one-hundred times smaller than terrestrial cyanobacteria. Cyanobacteria are single-celled bacteria that are capable of photosynthesis, and they are microscopic, approximately two microns in diameter. The fossils alone are not the only evidence of life from these Martian meteorites. There are localized deposits of hydrogen cyanide and polycyclic aromatic hydrocarbons (PAHs) within the meteorites as well. According to Professor Churchwell, these chemical substances indicate life. 
All life on Earth is based on hydrogen, carbon, oxygen and nitrogen, all of which are common elements in the universe. In order to form other substances, energy, such as sunlight, lightning or volcanic activity must be present. Then, carbon dioxide, nitrogen gas, methane, hydrogen gas, oxygen gas, ammonia and water—all substances that make up Earth’s atmosphere—can form.
After millions of years and the continued fueling by a natural energy source, molecules that are more complex, such as hydrogen cyanide and aldehydes, can form. Add more time and energy and even more complicated things can form, such as amino acids, purines and pyrimdines. These form the bases for DNA, which happens to be a PAH, similar to what was found in the meteorites. If you have DNA and pre-biotic substances, like hydrogen cyanide, in a rock, then that rock most likely came from a place where life existed.

According to Churchwell, this meteorite evidence, along with the ten to fifteen percent probability that there is life in the universe outside Earth, shows a fairly high probability that life existed on Mars. However, the Martian life forms would be single-celled organisms, such as bacteria. It is unlikely that higher life forms ever lived on Mars because it would have taken an incredibly long time for them to develop.

On Earth, eukaryotic cells took about two billion years to form. An eukaryotic cell is more advanced than a bacterial cell because it has a nucleus. All life forms more complex than bacteria are composed of eukaryotic cells. Although Earth has complex organisms, evolution does not necessarily have to result in more complicated creatures. The reason, as Churchwell explains, is that the more complicated the organism, the lower the chance it has for survival.
 


A closer view of Mars, this time from the eye of a probe. 		 Although Mars may have once supported life, it no longer can because it is frozen. Mars is approximately one half the size of Earth and has a lower mass. Therefore, its gravitational pull is smaller, and it can’t hold onto the atmospheric gases. The loss of an atmosphere made Mars cool down because it could no longer retain heat. The rest of the water on the planet probably froze. This caused a runaway ice age on the planet, so now, it can no longer support life. 

Venus had the opposite problem and had a runaway greenhouse effect, making the planet too hot to support life. This means that Earth is in a very narrow range between too hot and too cold—just the right temperature to support life.

It is not extremely likely that a planet like Mars could support a water-based atmosphere for a long enough period to develop advanced life forms. For this reason, the probability of advanced life elsewhere in the universe is quite low. Nevertheless, scientists are still intrigued by the slight possibility of life on other planets to continue their research.
 

Author Bio: Lynn Weinberger is an English major at UW-Madison.

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