In August 2014, the Mars Curiosity Rover celebrated the two-year anniversary of its landing, and this week it celebrated its two year anniversary – again. This time though, we're talking two Mars years, as opposed to Earth years, and with that milestone, NASA has been able to gather and analyze data on seasonal patterns in the Martian atmosphere.

From the dramatic landing to selfies, triumphs to tribulations, signs of water and other elements key to life, it's been an exciting two or four years (depending on which planet you live on).

A Mars year clocks in at 687 Earth days, or a bit under two Earth years. And with the red planet spinning on a tilt very close to that of our big blue ball, Mars has similar seasons, which NASA can now study in more detail. With two full Mars years under its belt, the agency can compare the data gathered in each and determine which events are cyclical with the seasons and which are one-off anomalies.

The findings have been interesting. One such anomaly is the tenfold spike in methane levels detected in the atmosphere over a few weeks in Curiosity's first autumn, after initially finding this key byproduct of life to be almost non-existent. When the increase didn't repeat the following year, NASA could determine it was an "episodic event" and not a recurring seasonal one.

Other measurements, including temperature, humidity and air pressure are more cyclical. The temperature ranges vary wildly but follow a strong seasonal trend, which is especially clear when mapped alongside those of a location like Los Angeles. As observed by Curiosity, a summer afternoon can be as warm as 60.5° F (15.9° C), while winter nights can plummet to minus 148° F (minus 100° C).

Air pressure variations are also extreme. Millions of tons of carbon dioxide freeze solid at the polar caps during winter, and are released back into the atmosphere in spring, which NASA says leads to seasonal variations in the air pressure of about 25 percent – a huge amount, compared to Earth.

Clarity of the local atmosphere also appears to be dictated by the seasons, with Curiosity recording fluctuations in visibility in Gale Crater from as low as 20 miles (30 km) in summer, up to 80 miles (130 km) in winter.

Learning to differentiate between seasonal variations and one-off anomalies is instrumental in understanding the atmosphere of Mars, both past and present.

Project scientist Ashwin Vasavada explains the findings in the video below.

Source: NASA JPL

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