© NASA/JPL-Caltech/Univ. of Arizona
These five images from the HiRISE camera on NASA's Mars Reconnaissance Orbiter show different Martian features of progressively greater size and complexity, all thought to result from thawing of seasonal carbon dioxide ice that covers large areas near Mars' south pole during winter.
These five images from the HiRISE camera on NASA's Mars Reconnaissance Orbiter show different Martian features of progressively greater size and complexity, all thought to result from thawing of seasonal carbon dioxide ice that covers large areas near Mars' south pole during winter.
Researchers using NASA's Mars Reconnaissance Orbiter (MRO) report the first detection of cumulative growth, from one Martian spring to another, of channels resulting from the same thawing-carbon-dioxide process believed to form the spider-like features.
The spiders range in size from tens to hundreds of yards (or meters). Multiple channels typically converge at a central pit, resembling the legs and body of a spider. For the past decade, researchers have checked in vain with MRO's High Resolution Imaging Science Experiment (HiRISE) camera to see year-to-year changes in them.
"We have seen for the first time these smaller features that survive and extend from year to year, and this is how the larger spiders get started," said Ganna Portyankina of the University of Colorado, Boulder. "These are in sand-dune areas, so we don't know whether they will keep getting bigger or will disappear under moving sand."
Dunes appear to be a factor in how the baby spiders form, but they may also keep many from persisting through the centuries needed to become full-scale spiders. The amount of erosion needed to sculpt a typical spider, at the rate determined from observing active growth of these smaller troughs, would require more than a thousand Martian years. That is according to an estimate by Portyankina and co-authors in a recent paper in the journal Icarus. One Martian year lasts about 1.9 Earth years.
"Much of Mars looks like Utah if you stripped away all vegetation, but 'spiders' are a uniquely Martian landform," said Candice Hansen of the Planetary Science Institute, Tucson, Arizona, a co-author of the report.
Comment: Other incredible NASA images from Mars' south pole include these giant 'worm' like features:
The bizarre 'worms of mars': The polar cap is made from carbon dioxide (dry ice), which does not occur naturally on Earth.