In a first, NASA scientists have discovered how erosion-carved troughs grow on Mars. The researchers have said that these troughs may actually be the infant versions of Martian ‘spiders’. Scientists have images this for the very first time using data from NASA’s Mars orbiter.
The radially patterned surface features are found in the south polar region of Mars. A report from the NASA’s Mars Reconnaissance Orbiter (MRO) established 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 have different sizes from tens to hundreds of metres. Multiple channels typically converge at a central pit and resemble the legs and body of a spider.
“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 in the US.
“These are in sand-dune areas, so we don’t know whether they will keep getting bigger or will disappear under moving sand,” Ganna said.
The formation of baby spiders may be due to the dunes. But they may also keep many from persisting through the centuries needed to become full-scale spiders.
More than a thousand Martian years would be needed for the amount of erosion required to sculpt a typical spider at the rate determined from observing active growth of these smaller troughs. One Martian year is equivalent to 1.9 Earth years.
Dry ice or carbon-dioxide ice does not naturally take place on Earth.
During winter on Mars, its sheets cover the ground in areas near both poles including the south-polar regions with spidery terrain. Each spring, dark fans are visible in these areas.
In 2007, Hugh Kieffer from the Space Science Institute in the US brought those factors together. This was done in order to deduce the process linking them: Spring sunshine penetrates the ice to warm the ground underneath, causing some carbon dioxide on the bottom of the sheet to thaw into gas.
Pressure is built by the trapped gas until a crack is formed in the ice sheet. The gas that is emitted and the gas beneath the ice rush toward the vent. It then picks up the sand and dust particles.
The ground is eroded by this process, while the geyser is supplied with the particles which fall back to the surface, downwind and appear as the dark spring fans.
This explanation has been well accepted, but actually seeing a ground-erosion process that could eventually yield the spider shapes proved elusive. Six years ago, researchers using MRO’s High Resolution Imaging Science Experiment (HiRISE) camera reported small furrows appearing on sand dunes near Mars’ north pole at sites where eruptions through dry ice had deposited spring fans.
However, those furrows in the far north disappear within a year, apparently refilled with sand.
The newly reported troughs near the south pole are also at spring-fan sites. They have not only persisted and grown through three Martian years so far, but they also formed branches as they extended. The branching pattern resembles the spidery terrain.
(With inputs from PTI)