Numerical modelling of the growth of the dust cloud detected by Mars Express. This is the temporal evolution of the quantity of dust in Mars' atmosphere. In 4 hours, the cloud climbs up to 35 km altitude. The cloud ends by horizontally unravelling in a layer subsisting at high altitude, which lowers during the night but climbs back the next day. © LMD / Aymeric Spiga
One of the most exotic aspects of the Martian atmosphere is the presence of microscopic grains of dust hanging in the air which play a crucial role in the planet's climate. However, the question of the continuous renewal of this dust is still unanswered. A team of researchers from the IPSL has just lifted the curtain on this mystery by discovering an extreme phenomenon called "rocket dust"in the atmosphere of Mars.
Scientists used an inovative approach by resorting to a new numerical model which enables to forecast the weather at very small scale in a particular region of Mars. They studied the evolution of a violent dust storm seen by the Omega instrument of the European mission Mars Express. The scientists from Aymeric Spiga team, first author of the paper, were far from suspecting the surprises that awaited them! If a dust storm begins at first by the uplifting of dust from the Martian soil, the scientists discovered that a column of dust with a spectacularly fast ascencion can appear, a "rocket dust". Then considerable quantities of dust are injected up to 30 or 50 kilometers above the surface of Mars.
The mechanism creating these rocket dusts on Mars is called a deep convection. It is also responsible for the formation of powerful storm clouds on Earth, the cumulonimbus. The energy which powers the vertical movements is nevertheless not the same on the two planets. On Earth, it is the energy released by the condensation of the water vapour on cloud water droplets. On Mars, the dust grains carried by a dust storm heat the thin atmosphere by absorbing the incident Sun radiation. As the Red Planet has no stratosphere, which limits the heigth of the cumulonimbus on Earth, the rocket dust on Mars can reach very high altitudes.
These discoveries enable to propose the first solid explanation for the enigmatic enriched layers of dust observed at high altitude on Mars by Mars Reconnaissance Orbiter. The permanent renewal of dust in Mars' atmosphere is also better understood. Rocket dusts have numerous other implications on atmospheric dynamics, water cycle and chemistry on Mars. Moreover, knowing the potential danger guarantees the success of future robotic and human missions sent to Mars.
Rocket dust storms and detached dust layers in the Martian atmosphere, Aymeric Spiga, Julien Faure, Jean-Baptiste Madeleine, Anni Määttänen, François Forget, Journal of Geophysical Research: Planets 01/2013 doi:10.1002/jgre.20046
Laboratoire de Météorologie Dynamique,
Boîte courrier 99,
Université Pierre et Marie Curie (UPMC),
4 place Jussieu,
75005 Paris, France