Mars Temperature Mystery Solved: NASA Discovers Water-Ice Clouds to Blame

NASA's Mars Reconnaissance Orbiter has discovered something else about the Red Planet. While Earth experiences rises and falls in temperatures once a day, it turns out that the Martian atmosphere actually feels these rises and falls twice daily. The findings may reveal a bit more about the reasons behind the weather conditions on the planet's surface.

Global fluctuations of wind, temperature and pressure repeating each day--or a fraction of a day--are called atmospheric tides. In contrast to ocean tides, which are driven by gravity, these changes are driven by variation in heating between night and day. In fact, Earth also possesses atmospheric tides, though the ones on our planet produce little temperature difference in the lower atmosphere away from the ground. On Mars, in contrast, these tides dominate short-term temperatures variations throughout the atmosphere; temperatures can swing by as much as 58 degrees Fahrenheit on the Red Planet.

While tides that go up and down once per day are called diurnal, ones that happen twice per day are called semi-diurnal. While this semi-diurnal pattern was seen on Mars first in the 1970s, it was thought to only occur during the dusty season. Researchers believed that it was related to sunlight warming dust in the atmosphere. New findings, though, suggest otherwise.

"We were surprised to find this strong twice-a-day structure in the temperatures of the non-dusty Mars atmosphere," said Armin Kleinboehl of NASA's Jet Propulsion Laboratory in a news release. "While the diurnal tide as a dominant temperature response to the day-night cycle of solar heating on Mars has been known for decades, the discovery of a persistent semi-diurnal response even outside of major dust storms was quite unexpected, and caused us to wonder what drove this response."

That's why researchers set to find out what was affecting the presence of the semi-diurnal cycle. The answer? Clouds. It turns out that the water-ice clouds of Mars absorb enough heat to warm the middle atmosphere of the Red Planet each day. This, in turn, helps cause the temperature swings.

"Water-ice clouds have been known to form in regions of cold temperatures, but the feedback of these clouds on the Mars temperature structure had not been appreciated," said Kleinboehl in a news release. "We know now that we will have to consider the cloud structure if we want to understand the Martian atmosphere."

The findings reveal a little bit more about the Red Planet, which could be crucial for future space missions. Knowing exactly what conditions affect the atmosphere and surface of Mars is an important step when it comes to conceptualizing a manned mission to the planet.

The findings are published in the journal Geophysical Research Letters.