Mars brush with Earth in August - closest in 60,000 years - gave astronomers a peek into the Red Planet s atmosphere that revealed why oxygen levels remain too low for humans to breathe.
The culprit, researchers are reporting today, is hydrogen peroxide - the stuff familiar on Earth as an antiseptic for cuts.
Dr. R. Todd Clancy, who headed the research, in an interview described it as the first detection of hydrogen peroxide in the Martian atmosphere, and a landmark in understanding that thin shroud of gases.
“To a large degree, our measurement of hydrogen peroxide is a confirmation that we understand how the chemistry of the Mars atmosphere behaves,” he said. “Unlike Venus, Mars is hospitable enough to be considered a possible human habitat in the future.”
Dr. Clancy headed a research team from the Space Science Institute in Boulder, Colo., that made the discovery. They used the James Clerk Maxwell Telescope, a radio telescope located near the 14,000-foot summit of Mauna Kea in Hawaii.
“This is the first time that a chemical catalyst of this sort has been found in a planetary atmosphere other than the Earth s,” said Dr. Douglas Pierce-Price. He is with the Joint Astronomy Center in Hilo, Hawaii, which operates the 50-foot-diameter telescope.
The United Kingdom, Canada, and the Netherlands own the Maxwell telescope, which is one of the world s largest.
Dr. Clancy noted that such ground-based instruments – rather than space probes like the rovers now exploring Mars surface - have pieced together most of the knowledge about the planet s atmosphere.
Hydrogen peroxide has been the missing link in that knowledge for almost 30 years.
The big three ingredients in Mars atmosphere are carbon dioxide (95 percent), nitrogen (4 percent), and water vapor (0.02 percent).
Just as on Earth, ultraviolet light from the sun triggers chemical reactions that break those gases apart.
Based on knowledge of Earth s atmospheric chemistry, scientists in the 1960s and 1970s concluded that hydrogen peroxide also must be present on Mars.
That s because Martian chemistry breaks carbon dioxide into carbon monoxide and oxygen. Hydrogen peroxide then acts as a catalyst. It pushes key chemical reactions that reassemble carbon dioxide.
Without the right amount of hydrogen peroxide, oxygen would build up to much higher levels - perhaps 10 percent, Dr. Clancy said. Earth s atmosphere is 21 percent oxygen.
Unable to detect hydrogen peroxide over the years, other scientists proposed complicated schemes to explain how Mars kept a stable atmosphere. The detection of hydrogen peroxide keeps the explanation simple, Dr. Clancy indicated.
What about the possibility of short-circuiting hydrogen peroxide so that oxygen does build up, making Mars more habitable for humans?
Dr. Clancy noted that low oxygen is only part of Mars problem. Low atmospheric pressure is another. Even with more oxygen, Mars atmospheric pressure would be too low for humans to stroll the surface. Pressure would still be about 6 millibars, compared with 1,000 on Earth.
Anyone who ventured outdoors without a pressurized spacesuit would face death, as gases began to bubble out of their blood, he said.