An analysis of Mars Express observations finds that water-ice clouds usually block more light in the morning than in the afternoon. The peer-reviewed study spans roughly eight Martian years and compares the daily cycle with climate models. Uncertainty in cloud particle size and observing times limits how precisely the differences can be interpreted.
Mars water-ice clouds generally appear more opaque in the morning than in the afternoon, according to a peer-reviewed analysis published on October 28. Researchers used roughly eight Martian years of Mars Express observations to examine a daily cycle that is difficult to separate from seasonal change. Stronger opacity means that the clouds block more of the light used in the measurement.[1], [2]
The Planetary Fourier Spectrometer’s short-wavelength channel measured the signal near 3.3 micrometers. Morning-to-afternoon differences were strongest during the season when Mars is farther from the Sun. Higher cloud opacity also appeared over the Tharsis region and other elevated terrain. Comparisons with THEMIS and CRISM showed similar seasonal changes, but different numerical values; observing hours and measurement methods are possible contributors to that gap.[1]
The researchers held ice particle size fixed. Changing that assumption can shift the retrieved opacity by about 20 percent to 30 percent, and the downward view cannot resolve the clouds’ vertical structure. A comparison with climate simulations suggests the actual water cycle may change more slowly than the models predict. That interpretation still needs confirmation from further observations.[1]
