The Red Planet is a rich source of perchlorates—chemical compounds used in fertilizer and rocket fuel that are rarely formed naturally on Earth. Now, lab experiments suggest how the unusual compounds are created on Mars: from the electrical fields formed by global dust storms, as well as whirlwinds known as dust devils.
For more than 5 years, scientists have surmised that perchlorates are relatively common on Mars, thanks to evidence from the Phoenix Mars lander and the Curiosity rover. On Earth, the chemical reactions that generate these compounds are typically powered by sunlight. But models of atmospheric chemistry suggest mere sunlight isn’t enough to do the trick on Mars. Instead, they indicate that strong electric fields, such as those created by static electricity in global dust storms, could break down gases in the martian atmosphere and thus drive perchlorate-generating reactions.
To test that notion in the lab, researchers put a gas mixture representing the martian atmosphere—95% carbon dioxide, 2% nitrogen, 2% argon, and 1% oxygen—in a large chamber, along with a source of chlorine, table salt. The researchers decreased temperature and pressure in the chamber until they matched Mars-like conditions. They then exposed the mixture to electric fields of the magnitude likely present inside martian dust storms and dust devils (seen from orbit, above).
Almost immediately, some of the gases in the chamber broke down to form highly reactive, positively charged versions of carbon dioxide, carbon monoxide, and nitrogen molecules. Over time, reactions generated substantial amounts of chlorates (ions that contain one chlorine atom and three oxygen atoms) and perchlorates. The team estimates rates of perchlorate formation inside martian dust storms could be as much as 10 million times higher than those driven by sunlight, the researchers report in Earth and Planetary Science Letters.
To astrobiologists, perchlorates are intriguing. Although these substances are toxic to humans—and thus could endanger potential human settlements on Mars—some microbes can to use perchlorates to fuel their metabolism.