January 24, 2013

Rocket dust storms on Mars

One of the most exotic aspect of Mars atmosphere is the presence of microscopic grains of dust hanging in the air which play a crucial role in the climate of the planet. However, the question of the continuous renewal of this dust is still unanswered. A team of searchers from the IPSL just lifted the curtain on this mystery by discovering in Mars atmosphere an extreme phenomenon called "rocket dust".

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

Scientists used an inovative approach by using a new numerical model which forecasts the weather at very small scale in a particular region of Mars. They studied the evolution of a violent dust storm seen by the instrument Omega 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 dust on Mars is called a deep convection. It is also responsible of the formation of powerful storm clouds on Earth, the cumulonimbus. The energy which powers the vertical movements is nevertheless the same on the two planets. On Earth, it is the energy released by the condensation of the water vapour in cloud water droplets. On Mars, the dust grains carried by a dust storm heat the thin atmosphere by absorbing the incident Sun radiation. The red planet being without stratosphere, which limit the heigth of the cumulonimbus on Earth, the rocket dust on Mars can then 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 the dust in Mars atmosphere is also better understood. The rocket dust have numerous other implications on the atmospheric dynamics, the water cycle and the chemistry on Mars. Moreover, to know the potential danger enables to prepare the arrival on Mars of the future robotic and human mission.

Article references

Rocket dust storms and detached dust layers in the Martian atmosphere, Aymeric Spiga1, Julien Faure1, Jean-Baptiste Madeleine1,3, Anni Määttänen2, François Forget1, Journal of Geophysical Research: Planets 01/2013

1 Laboratoire de Météorologie Dynamique (LMD), Université Pierre et Marie Curie (UPMC), Institut Pierre Simon Laplace (IPSL), Paris, France
2 Laboratoire ATmosphre, Milieux et Observations Spatiales (LATMOS), Centre National de la Recherche Scientifique (CNRS), Guyancourt, France
3 Brown University, Providence, Rhode Island, USA

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