Astronomers utilizing NASA’s Mars Reconnaissance Orbiter (MRO) have discovered that temperatures in the Red Planet’s atmosphere rise and fall twice each day.

According to lead author Armin Kleinboehl of the NASA’s JPL, astronomers have detected a temperature maximum both in the middle of the day and shortly after midnight.

The temperature swings are incredible, varying by as much as 58 degrees Fahrenheit in this strange thermal rhythm. The data for these findings was provided by the MRO’s Mars Climate Sounder instrument.

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The instrument discovered that the pattern is consistent all over the planet and year-round.

Global swings of wind, temperature and pressure recurring each day are known as atmospheric tides. As opposed to ocean tides, they are caused by changes in heating between day and night. Earth also has atmospheric tides, but the ones on Earth create very little temperature variation in the lower atmosphere away from the ground. On the Red Planet, which has approximately one percent as much atmosphere as our planet, atmospheric tides are the driving force behind short-term temperature differences throughout the atmosphere.

Tides that rise and fall once per day are known as “diurnal” tides. The twice-a-day tides are called “semi-diurnal” tide. This particular pattern on the Red Planet was first observed in the 1970s, but until recently it had been believed to show up just in dusty seasons, associated with sunlight heating up dust in the Martian atmosphere.

According to Kleinboehl, astronomers were amazed to discover this unusual thermal rhythm in the temperatures of the non-dusty Martian atmosphere. In fact, the finding of a regular semi-diurnal response caused the astronomers to think seriously about what caused this response.

Kleinboehl and his colleagues discovered the answer in the water-ice clouds of Mars. The Red Planet’s atmosphere contains water-ice clouds for much of the Martian year. Clouds in the equatorial region, approximately six to 19 miles above the surface of Mars, take on infrared light emitted from the surface during daytime. According to the astronomers, these are comparatively transparent clouds. However, the absorption of infrared light is just enough to warm up the middle atmosphere each day.

The strange thermal rhythm has been replicated in Mars climate models when the radiative impacts of water-ice clouds are taken into consideration.

Though people tend to think of Mars as a cold and dry world, there is actually more water vapor in the Red Planet’s atmosphere than in the upper layers of our planet’s atmosphere, Kleinboehl posits. He adds that astronomers will have to examine cloud structure if they want to truly learn about the Martian atmosphere.

The study’s findings are described in detail in the journal Geophysical Research Letters.

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