- Scientists build a consistent, accurate numeral model of the yearly water cycle on Mars.
- They’ve included all minor parameters that affect Mars hydrological circulation.
- They’ve also measured the atmospheric distribution and density of clouds formed by tiny ice crystals.
Water on Mars was detected more than 50 years ago. Later, it was scrutinized by several space missions, including ExoMars, Mariner 9, and MarsExpress. They all studied the Martian atmosphere and collected important data, which was later used by researchers to create a model of the Martian atmosphere.
Today, almost all water on the red planet exists in the form of ice. A very small portion is present in vapor form in the atmosphere. If you were to gather all the water of the atmosphere and put it evenly on the Mars surface, the layer would be only 0.02 millimeter thick.
Atmospheric water greatly affects the Mars climate, despite the fact it’s present in such a low volume. It is responsible for cloud scattering and re-emitting incident infrared radiation, and atmospheric dust is removed by ice condensed on aerosol particles.
To understand the behavior of water on Mars, it’s quite important to study how ice particles and water vapor transport and redistribute between seasonal polar caps. For more than last 10 years, scientists have been focusing on water condensation nuclei formed due to large-scale airborne dust particle on Mars.
Now scientists at Moscow Institute of Physics and Technology have developed a consistent, accurate numeral model of the yearly water cycle on Mars. This time, they’ve considered all minor parameters that affect Mars hydrological circulation, including three dimensional motion of air masses, water phase transitions, infrared and solar radiation transfer, and microphysics of clouds on Mars.
Particle Size Distribution
Calculations and modeling results are mostly based on aerosol’s particle size distribution. According to the research done in 2014, 2 peaks in the particle distribution (named bimodal) are possible specific seasons.
Courtesy of researchers
The graph represents the probability density function of bimodal aerosol particles’ distribution – particles with nearly 0.025 micrometers radii have more peaks than particle with 0.4 micrometers radii.
The dust bimodality was reliably seen only in certain seasons. Thus, these assumptions of bimodality throughout the Martian year should be validated with measurements. The simulation done at that time shows the sensitivity of water cycle and noticeable improvements in bimodality.
Theoretical Model Of Water Phase Transitions
The team used this bimodal size distribution to develop a model of hydrological cycle on Mars. They also took help of a reliable 3D simulation of Martian Atmosphere built at Max Planck Institute, which enabled them to develop a theoretical model demonstrating water transition phase.
Water vapor density distribution over Mars surface during summer | Arrows show wind direction
They found that the concentration level of water is higher in the North Pole during summers. The airborne vapor particle-density decreases, as winter approaches. During this period, water on Mars condenses and drops on the ground as precipitation.
Furthermore, the researchers applied the same technique to measure the atmospheric distribution and density of clouds created by tiny ice crystals. They discovered that the most of the ice was placed above the equator during summer when the density of water vapor achieved its highest level in the North Pole.
The simulation of bimodal particle size demonstrated that the latter scenario mostly affects the modeled ice clouds’ mass, number density, opacity and particle radii brining them closer to observations. It showed much weaker effect of the excess-of-small-aerosol-particles on water vapor distributions.
The number of particles nucleated in the Martian atmosphere contributes to the growth of ice mass, increases the ice particles’ concentrations and decreases their radii. This enhances the simulated opacity of the clouds.
Overall, these outcomes highlight the importance of distribution of dust size with the peak of tiny particles for modeling water ice in the Martian atmosphere. These distributions throughout all locations and seasons aren’t perfectly bimodal but have more complex shapes.
Also, Martian general circulation mode (MGCM) simulations and more measurements that self-consistently account for dust transport can further improve this and shed the light on the modality of distribution of dust size.