Temperatures on Mars Peak Twice a Day: A Study

Temperatures in the Martian atmosphere regularly rise and fall not just once but twice a day.

The discovery, published in the journal Geophysical Research Letters, was made by NASA scientists using the Mars Reconnaissance Orbiter to sample a range of times of day and night all over the planet, according to a press release from the space agency.

“We see a temperature maximum in the middle of the day, but we also see a temperature maximum a little after midnight,” said Armin Kleinboehl of the NASA’s Jet Propulsion Laboratory and lead author of the report on the findings.

In all, temperatures swing as much as 58 degrees Fahrenheit (32 kelvins) in this twice-a-day pattern all across the planet, according to the new set of the MRO’s Mars Climate Sounder observations.

Global oscillations of wind, temperatures and pressure repeating each day or a fraction of a day are called atmospheric tides. Unlike ocean tides, they are driven by variation in heating between day and night and while Earth boasts atmospheric tides as well, they produce little temperature difference in the lower atmosphere.

On Mars, however, they dominate short-term temperature variations throughout the atmosphere due to its thin nature.

“We were surprised to find this strong twice-a-day structure in the temperatures of the non-dusty Mars atmosphere,” Kleinboehl said. “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.”

Along with four other co-authors, Kleinboehl found the answer was in the planet’s water-ice clouds that are present for most of the year.

Clouds in the equatorial region between 6 and 19 miles (10 to 30 kilometers) above the surface of Mars absorb infrared light emitted from the surface during the daytime. Though relatively transparent, these clouds absorb enough to heat the middle atmosphere each day.

Also unexpected was the semi-diurnal temperature pattern that showed maximum temperature swings occurring away from the tropics, but has since been replicated in Mars climate models when the radiative effects of water-ice clouds are included.

“We think of Mars as a cold and dry world with little water, but there is actually more water vapor in the Martian atmosphere than in the upper layers of Earth’s atmosphere,” Kleinboehl said. “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.”

Going forward, the scientist said, this new information will be used in coming to a better understanding of the Martian atmosphere.

“This is comparable to scientific studies concerning Earth’s atmosphere,” he explained, “Where we have to better understand clouds to estimate their influence on climate.”