
© NASA/JPL/MSSS/Justin Cowart/Seán DoranClouds on Mars
Atmospheric gases on Mars sure provide us with plenty of mystery. First, there was that business with the
disappearing, reappearing methane. Now, oxygen levels have been observed rising and falling over the Gale Crater, by amounts that just don't fit any known chemical processes.
The data comes from
Curiosity, the Mars rover that's been making its slow and methodical trek across the crater floor and
up the foot of Mount Sharp in the centre of it.
The robot isn't just looking down at the rocks beneath its treads;
Curiosity also takes readings of the Martian atmosphere to measure the seasonal atmospheric changes. It's been up there for three Mars years now (that's six Earth years), and scientists poring over the measurements have noticed that oxygen in the planet's atmosphere isn't behaving entirely as expected.
There actually isn't all that much oxygen on Mars. Most of its thin atmosphere (95 percent by volume) is carbon dioxide, or CO2. The rest is made up of 2.6 percent molecular nitrogen (N2), 1.9 percent argon (Ar), 0.16 percent molecular oxygen (O2), and 0.06 percent carbon monoxide (CO).
(
Earth's atmosphere, by contrast, is mostly nitrogen, at 78.09 percent by volume, and 20.95 percent oxygen.)
On Mars, atmospheric pressure changes over the course of the year. On the winter hemisphere, CO2 freezes over the pole, which causes the pressure to drop across the hemisphere. This results in a hemisphere-to-hemisphere redistribution of gases to equalise atmospheric pressure planet-wide.
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- "Mindblowing" haul of fossils over 500 million years old unearthed in China
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