Why did NASA select Gale Crater for the Mars Curiosity rover? It’s a good question, with an intriguing answer that suggests Curiosity will be spending considerable time in this region.
The image below faces from north to south. Take a good look at Gale Crater. Apart from the dark band of sand dunes, what do you notice?
The most remarkable aspect of Gale Crater is that Aeolis Mons (Mount Sharp) rises up from within it to reach a height greater than the crater walls. And that raises the question, how to you get a massive mountain to form in the middle of a compressed crater floor?
Complex craters can form central mounds similar to this, but those mounds are not higher than the surrounding crater walls. The key to understanding Aeolis Mons is to remember that when dealing with geology we’re not dealing with one, isolated, lone geological feature but rather the sum total of all the geological influences in an area as they’ve accumulated over thousands, millions, hundreds of millions and billions of years.
Rather than thinking of Gale as a crater, we should consider Gale a basin that just happened to originally be a crater. For our purposes, that this overall feature is a crater is incidental. The real interest is around Aeolis Mons which represents the eroded remnants of billions of years worth of sedimentary accumulation. In this regard, the crater walls probably provided some protection from erosion, allowing the Mons to form slowly as the plain around it fell away.
Scientists estimate that the impact that formed Gale Crater happened roughly 3.8 billion years ago. Putting things in perspective, at that time Earth was still in the process of cooling from its initial formation and gave off three times the heat it does today. Our planet had suffered a massive collision that had formed the moon, the late heavy bombardment from space had just finished, and yet, somehow, life had scratched out a niche in an atmosphere largely devoid of oxygen. Bacteria, in a form somewhat similar to modern stromatolites, were in abundance, as were prokaryote, but eukaryotes, of which we are a fine specimen, were yet to evolve for somewhere in the order of a billion years or more.
In the intervening 3.8 billion years, there’s been plenty to talk about on Earth as the planet has been transformed beyond recognition by the proliferation of life. A visit to Gale Crater, to observe strata laid down over almost four billion years, will give us a very good idea about the kind of transformations that have occurred on Mars over the same time period. Gale is a time capsule of planetary development.
Aeolis Mons represents a trip back in time in the same way a journey down the Grand Canyon exposes geological strata over tens of millions of years.
Mars may look pretty boring to the untrained eye, but it is awash in geological features that speak volumes about its history. The first images from Curiosity showed a bleak, barren, featureless plain, with the crater wall somewhere way off in the distance, but look at the features in this image that have been identified for investigation during the Curiosity mission.
The orange squiggle in this image is the proposed path Curiosity will travel over the next couple of months as NASA begins its scientific investigation of past epochs unveiled by the erosion of Aeolis Mons.
NASA has spent considerable energy planning this mission to the finest detail, carefully examining satellite imagery to identify targets for research. Studies have revealed layers of different minerals depending on elevation, exactly as we would expect to find in a sedimentary system. Near the bottom of the mound there’s clay. Above the clay-bearing layers are layers laced with sulfur, followed by layers of oxygen-bearing minerals. Running water appears to have carved channels in both the mound and the crater wall, so Curiosity will examine the evidence for a watery Mars in close detail. To get to the most recent deposits, which may still pre-date complex cellular life on Earth, the Mars Science Laboratory will carefully work its way up the Mons, moving layer by layer. Along the way, the rover will investigate how these layers formed to understand the environments in which they formed, looking for tantalizing clues about the possibility of Martian life.
If you have the time, I highly recommend you check out the interactive demo on Curiosity’s planned exploration of Gale Crater.
An example of stratification within Gale Crater (NASA HiRise)