Life on Mars by David A. Weintraub

Author:David A. Weintraub
Language: eng
Format: epub
Publisher: Princeton University Press
Published: 2020-03-15T00:00:00+00:00

Although Levin’s interpretation of the Viking data is an extreme outlier, some additional support for Levin’s point of view emerged in 2010 when Rafael Navarro-Gonzalez, of the National Autonomous University of Mexico, and Chris McKay, of NASA’s Ames Research Center in California, performed an experiment on a handful of dirt taken from the extremely high (13,000 feet or 4,000 meters) and dry Atacama Desert in Chile. After dosing the dirt with perchlorate (the negative ion ClO4—) salt, a very reactive, oxidizing chemical containing only chlorine and oxygen, and heating the sample, they detected the presence of two compounds—chloromethane (CH3Cl) and dichloromethane (CH2Cl2)—that formed when the perchlorate reacted with and consumed other materials in the dirt.18 Both of these newly formed compounds contain both carbon and hydrogen atoms not present in the perchlorate. The chlorine atoms obviously came from the perchlorate. Where did the carbon come from? The carbon atoms must have come from carbon-bearing molecules that were already present in the soil. That is, the formation of chloromethane and dichloromethane is indirect proof of the presence of organic material in the Atacama Desert dirt. We need to be cautious here. Nearly all, but not all, carbon-bearing molecules are, by definition, organic molecules. (An organic molecule must contain carbon, but not all molecules with carbon are considered organic. To be organic, the carbon-containing compounds must contain carbon bound to hydrogen. SiC (silicon carbide), WC (tungsten carbide), and CO (carbon monoxide) are examples of non-organic, carbon-containing molecules.) But organic molecules are not necessarily evidence for the presence of life, as organic molecules can exist in any environment in which carbon and hydrogen are present. Furthermore, the carbon could have come from atmospheric carbon dioxide or carbon monoxide adsorbed onto minerals in the Atacama Desert dirt.

The connection to Mars and the Viking biology experiments is the following: in 1976, Viking 1 detected chloromethane at a level of 15 parts per billion and Viking 2 detected dichloromethane at levels of between 2 and 40 parts per billion. These are the same two chemicals detected by Navarro-Gonzalez and McKay in their experiment with the Atacama Desert dirt. The Viking teams attributed the detections of both the chloromethane and the dichloromethane to terrestrial contaminants.

Planetary scientists make extraordinary efforts to reduce the amount of terrestrial gases that seep into their detector chambers and hoses before launch, but they cannot completely eliminate molecules from Earth’s atmosphere from traveling to Mars as stowaways. The two Viking landers brought these two compounds with them from Earth, said the Viking scientists. Navarro-Gonzalez and McKay, however, now think their laboratory work with Atacama Desert dirt proves otherwise.

Levin gained one more possible line of support after NASA’s Phoenix mission landed in the far north of Mars on May 25, 2008, where it operated for about five months before succumbing to the Martian winter. Phoenix used its robotic arm to scrape up some icy dirt and subject that dirt to onboard testing. One of the discoveries made by Phoenix is that perchlorates are present in the dissolved salts in the Martian soil at a level of 0.

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