page_title: Geysers on Mars
section_title: Dry venting
hierarchical_section_title: Geysers on Mars / Geyser mechanism models / Dry venting
caption_attribution_description: English: Mars' seasonal cap of carbon dioxide ice has eroded many beautiful terrains as it sublimates (goes directly from ice to vapor) every spring. In the region where the High Resolution Imaging Science Experiment (HiRISE) camera on NASA's Mars Reconnaissance Orbiter took this image, we see troughs that form a starburst pattern. In other areas these radial troughs have been refered to as spiders, simply because of their shape. In this region the pattern looks more dendritic as channels branch out numerous times as they get further from the center. The troughs are believed to be formed by gas flowing beneath the seasonal ice to openings where the gas escapes, carrying along dust from the surface below. The dust falls to the surface of the ice in fan-shaped deposits. This image, covering an area about 1 kilometer (0.6 mile) across, is a portion of the HiRISE observation cataloguedas ESP_011842_0980, taken on Feb. 4, 2009. The observation is centered at 81.8 degrees south latitude, 76.2 degrees east longitude. The image was taken at a local Mars time of 4:56 PM and the scene is illuminated from the west with a solar incidence angle of 78 degrees, thus the sun was about 12 degrees above the horizon. At a solar longitude of 203.6 degrees, the season on Mars is northern autumn. NASA's Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the Mars Reconnaissance Orbiter for NASA's Science Mission Directorate, Washington. Lockheed Martin Space Systems, Denver, is the prime contractor for the project and built the spacecraft. The High Resolution Imaging Science Experiment is operated by the University of Arizona, Tucson, and the instrument was built by Ball Aerospace &amp; Technologies Corp., Boulder, Colo.
context_page_description: Martian geysers are putative sites of small gas and dust eruptions that occur in the south polar region of Mars during the spring thaw. "Dark dune spots" and "spiders" – or araneiforms – are the two most visible types of features ascribed to these eruptions.
  Martian geysers are distinct from geysers on Earth, which are typically associated with hydrothermal activity. These are unlike any terrestrial geological phenomenon. The reflectance, shapes and unusual spider appearance of these features have stimulated a variety of hypotheses about their origin, ranging from differences in frosting reflectance, to explanations involving biological processes. However, all current geophysical models assume some sort of jet or geyser-like activity on Mars. Their characteristics, and the process of their formation, are still a matter of debate.
  These features are unique to the south polar region of Mars in an area informally called the 'cryptic region', at latitudes 60° to 80° south and longitudes 150°W to 310°W; this 1 meter deep carbon dioxide ice transition area—between the scarps of the thick polar ice layer and the permafrost—is where clusters of the apparent geyser systems are located.
context_section_description: Some teams propose dry venting of carbon dioxide (CO₂) gas and sand, occurring between the ice and the underlying bedrock. It is known that a CO₂ ice slab is virtually transparent to solar radiation where 72% of solar energy incident at 60 degrees off vertical will reach the bottom of a 1 m thick layer. In addition, separate teams from Taiwan and France measured the ice thickness in several target areas, and discovered that the greatest thickness of the CO₂ frost layer in the geysers' area is about 0.76–0.78 m, supporting the geophysical model of dry venting powered by sunlight.  As the southern spring CO₂ ice receives enough solar energy, it starts sublimation of the CO₂ ice from the bottom.  This vapor accumulates under the slab rapidly increasing pressure and erupting. High-pressure gas flows through at speeds of 160 kilometres per hour (99 mph) or more;  under the slab, the gas erodes ground as it rushes toward the vents, snatching up loose particles of sand and carving the spidery network of grooves.  The dark material falls back to the surface and may be taken up slope by wind, creating dark wind streak patterns on the ice cap.  This model is consistent with past observations. The location, size and direction of these fans
  are useful to quantifying seasonal winds and sublimation activity.
  It is clear that sublimation of the base of the seasonal ice cap is more than capable of generating a substantial overpressure, which is four orders of magnitude higher than the ice overburden pressure and five orders of magnitude higher than atmospheric pressure as discussed above.
  The observation that a few dark spots form before sunrise, with significant spot formation occurring immediately following sunrise, supports the notion that the system is powered by solar energy.  Eventually the ice is completely removed and the dark granular material is back on the surface; the cycle repeats many times.
  Laboratory experiments performed in 2016 were able to trigger dust eruptions from a layer of dust inside a CO
  ₂ ice slab under Martian atmospheric conditions, lending support to the CO
  ₂ jet and fan production model.
caption: A large 'spider' feature apparently emanating sediment to give rise to dark dune spots. Image size: 1 km (0.62 mi) across.
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