Curiosity Finds Mars May Have Lost Much Of Its (h)air

On Halloween, Curiosity used its hand lens imager to shoot 55 high-resolution pictures that were stitched together for this self-portrait. You can see the four scoops in the sand (left) and the base of Mt. Sharp in the background. Click to explore a large, hi-res image. Credit: NASA/JPL-Caltech/Malin Space Science Systems

Mars’ atmosphere is 100 times thinner than Earth’s and composed mostly of choking carbon dioxide. The second most common gas found is argon which is also present in Earth’s atmosphere. The Mars Curiosity Rover recently took a sniff of Martian air and analyzed the contents. In the current early spring season in Gale Crater, CO2 comprises 95.6% of the air, argon and nitrogen 2% each and oxygen a mere 0.14%.  Curiosity also made a most interesting discovery. It seems that the heavier versions of carbon in the carbon dioxide as well as its argon are more common than their lighter cousins.

Each element in the periodic table from hydrogen to carbon to lead has an certain weight, called its atomic weight, based on the number of protons and neutrons in the atom’s nucleus. Nearly all the oxygen we breathe has 8 protons and 8 neutrons for an atomic weight of 16. Oxygen-16, as it’s known, comprises 99.762% of all the oxygen found in nature.

Table showing the five most abundant gases in Mars’ atmosphere measured by the Sample Analysis at Mars Instrument Suite (SAM) last week. Researchers will use SAM to check on seasonal changes in the atmosphere. Credit: NASA/JPL-Caltech, SAM/GSFC

Variants or isotopes of oxygen exist in nature that have the same number of protons but a different number of neutrons. Oxygen-17 has 9 neutrons and oxygen-18 has 10. Both are stable isotopes with properties that differ slightly from the common form of the element.

Curiosity found a 5% enrichment of heavier isotopes of carbon and 2,000 times as much argon-40 as argon-36 compared to isotope ratios when Mars and the other planets formed 4.5 billion years ago. The results suggest the top of Mars’ atmosphere may have been lost to space as the lighter versions of carbon and argon escaped or were picked off by solar radiation, leaving more of the heavier isotopes behind.

It’s been suspected for some time that Mars was once wetter with a much thicker atmosphere. Otherwise how could water have flowed as a liquid on its surface? The isotope ratios are a clue that Mars lost much of that early atmosphere, evolving from a wet world to a dry, cold planet with the thinnest of air.

The Martian soil examined by the Chemistry and Mineralogy (CheMin) instrument shows the “fingerprint” of the mineral olivine, shown here on Earth as tumbled crystals about 1/4-inch in size. The semi-precious gem peridot is a variety of olivine. Credit: Caltech

Also this week, Curiosity blasted a tiny sample of the Martian soil with X-rays and learned its composition is similar to volcanic soils in Hawaii. The X-ray diffraction technique reads minerals’ internal structure by recording how their crystals distinctively interact with X-rays. Scientists found olivine, feldspar, pyroxene and weathered volcanic glasses. None was unexpected based on previous examinations by other rovers and probes.

Mauna Kea in Hawaii shows an area of volcanic soils that contain minerals similar to those identified in the “Rocknest” region on Mars by NASA’s Curiosity rover. Credit: NASA/JSC

The soil and windblown dust sampled and analyzed represent more recent processing of materials on Mars compared to the outcrop of compacted pebbles that settled into place several billion years ago when water likely flowed across the floor of Gale Crater.

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