Mars Annually Pops Its Polar Cork

A unique geological phenomenon has been found on Mars.  Every year, when the southern polar cap heats up, carbon dioxide gas forms underneath a layer of translucent ice.  This gas levitates large portions of the ice cap until it finds weaknesses, and bursts out at over a hundred miles an hour in spectacular fumaroles (see artist’s rendition at Jet Propulsion Laboratory).  The escaping gas carries fine particles of soil and sand upward, that get splayed outward in fan-shaped deposits hundreds of meters long, all pointing in the direction of the prevailing wind.
    Planetary scientists studying the images from the THEMIS infrared camera aboard the 2001 Mars Odyssey had long been puzzled by the dark spots, fans and spider-shaped markings around the vents till they came up with this model.  The findings were published in Nature this week.¹  The authors noted that this model will have an impact on the way polar cap deposits are interpreted:

The erosion and vertical stirring of surface materials under seasonal slab ice may have significantly altered the metre-scale sedimentary structures in the polar-layered deposits in a manner similar to bioturbation on the Earth.  This erosion and redeposition of the surface material on vertical scales of a few metres may have produced sedimentary structures that reflect this modification process, rather than the initial depositional environment.  If so, this process may present major complications to the interpretation of the sedimentary record observed in upcoming Polar Lander observations, and must be considered in relating this record to the climate history of Mars.

What this means is that in this case, layering does not represent a time sequence.  Since every year the same layers are eroded and redeposited, they cannot be used to infer either geological or atmospheric history.

¹Kieffer, Christensen and Titus, “CO2 jets formed by sublimation beneath translucent slab ice in Mars’ seasonal south polar ice cap,” Nature 442, 793-796(17 August 2006) | doi:10.1038/nature04945; Received 4 April 2006; Accepted 30 May 2006.

Yellowstone, eat your heart out.  What a sight it must be to look out over the south polar cap and see jets of dirty gas roaring upward hundreds of feet into the atmosphere every few hundred yards.  It might be even more dramatic to see the geysers of Enceladus, discovered last year (see 11/28/2005).
    Imagine if scientists for the upcoming polar lander mission measured these layers carefully, correlated them with other Martian strata, and came up with a detailed model of the climate history of Mars.  They would be wrong, according to this model.  Interpretations of data are not the same as data.  Sometimes, weird processes can be at work to scramble the data, misleading humans that were not present when the formations were made.  These authors mentioned bioturbation on earth, wherein underground organisms, with their burrowing and tunneling, carry fossil material upward or downward from its initial location (see 05/21/2004).
    Many times, scientists can recognize these effects and account for them in their models.  This new Martian process, apparently unique in the solar system, however, was unrecognized till now.  In this case, the effects take place in the present and can be observed.  (One wonders, offhand, whether this process could continue for billions of years.)  On Earth, much of the history cannot be reconstructed except by fallible inference from complicated data.  Peter Sadler said in the aforementioned 2004 article that cryptic signatures of bioturbation or reworking can go unrecognized by scientists, yet have significant effects on deposits – and by extension, on their interpretations.
    Undoubtedly different physical effects take place on Earth deposits used to infer past geological and climate history.  But by definition, one cannot know all the unknowns.  Let this instance be a lesson that new discoveries can blow holes in the best of scientific models.