The Prehistory Of The Red Planet Part Four

On the 6th of August, the NASA probe Curiosity, the 900 kilogram, smart car sized rover, with six wheels, a robotic arm and a complete miniature laboratory on board, entered the thin, toxic atmosphere of Mars at over 1000 metres a second. Soon after, the strongest parachute ever created was deployed, cutting its speed by almost half. Yet it was still travelling far too fast.

The Curiosity probe during its testing phase on Earth

As a result, the NASA scientists used a daring and ingenious solution. Four rocket thrusts blasted the probe out from under the parachute at a 45 degree angle and continued to burn, slowing the descent ever more. Yet the dust thrown up by the thrusts would have damaged Curiosity's systems irrevocably. To get around this, the engineers finished with a risky, but spectacular coup de gras.

The unit hovered 20 metres above the barren red plain as the rover itself was lowered down from a crane. Curiosity was now ready to start its mission: analysing the geology of the Gale Crater to ascertain whether the Red Planet was once capable of supporting life. While no indisputable evidence of past life has been found, less than two months into its two year mission Curiosity has found something incredible.

Images taken of Mars from various telescopes have indicated the presence of geological formations which bear distinct similarities to landforms sculpted by flowing water. Of course one of the major differences between Earth and Mars is that we have rivers and streams, while the Red Planet has ice caps. Therefore if the landforms seen through the telescopes are the work of water, then it must have occurred deep in Mars' geological past.

The Hottah conglomerate formation

Some of the pictures sent back by the rover are of conglomerate rocks composed of large grained sediments such as compacted grit and pebbles. The overall formation itself is probably the remains of a network of streams. What was interesting was that one 15 centimetre thick slab of rock, named Hottah, did not match the bedding plain of the rest of the formation, lying instead at an angle to it.

'To us it just looked like somebody came along the surface of Mars with a jackhammer and lifted up the sidewalk that you might see in downtown LA at a construction site,' said John Grotzinger, a scientist on the rover team. Curiosity is currently examining the size and shape of the conglomerates to try and reconstruct the speed and flow of the streams. Yet an overall picture is beginning to emerge: the current theory is that the rover is sitting at the head of an alluvial fan.

A single river, which the bed Hottah was originally part of, trickled down the sides of the Gale Crater, spreading out into smaller channels like the roots of a tree. As the network dried out, material was deposited into the streams, creating the beds of conglomerates which Curiosity has stumbled upon. When the survey is complete, we will have a clear picture of the environment billions a years ago. Mars was then a warm, mildly volcanic planet, troubled occasionally by the odd asteroid. A place where life may have dwelt under the rocks and in the streams of its ancient craters.