NASA’s current rovers, Curiosity and Opportunity, are continuing to explore their respective regions of Mars, with new findings that are providing yet more clues as to the geological history and potential past habitability of this fascinating world. They have also both just completed significant steps in their journeys and are now entering new and exciting phases of their missions. Both missions have found yet more evidence that the Mars we see today – cold and dry – was once much wetter and potentially habitable, at least for microorganisms.
Mars’ atmosphere is thin and cold, composed primarily of carbon dioxide along with other trace gases and some water vapour. Evidence has continued to mount, however, that the rarified atmosphere we see today once used to be much thicker and possibly warmer, making it potentially more life-friendly early on. Just how thick and how warm is still a subject of much debate, but there is also another interesting aspect to all of this: New evidence from the Curiosity rover has shown that the Martian atmosphere also used to have a lot more oxygen in it than it does now. Today, only very small traces of oxygen can be found, as opposed to Earth’s oxygen-rich atmosphere. So what does this mean? Could there be biological implications?
This image from the Curiosity rover on sol 1294 shows some very delicate rock formations on Naukluft Plateau, shaped by blowing Martian sand. The thin atmosphere and lower gravity also help in the formation of such spindly protrusions. Similar ones have also been seen before by the rover.
Since landing in 2012, the Curiosity rover has seen a lot of varied terrain within Gale crater, including ancient riverbed gravel, sandstone and mudstone rock outcrops, sand ripples finely sculpted by the Martian wind, and, of course, Mount Sharp looming above. Now the rover has reached a new type of landform previously only seen from orbit: a field of huge sand dunes.
Mars is often referred to as a desert world, being bone-dry for the most part, with dust and sand blanketing most of the surface. Some regions are covered in vast sand dunes, reminiscent of deserts like the Sahara on Earth, only much colder. Gale crater, where the Curiosity rover landed in 2012, features extensive dune fields around the base of Mount Sharp, and the rover is now approaching some of them for the first time; their dark color makes them stand out starkly against the surrounding terrain. These dunes are also still active, meaning they are still mobile and shaped by the wind, not just old “fossil” (petrified) dunes which are no longer active.
Last week there was the exciting news that Mars still has flows of briny water occurring now, and this week there is more water-related news: additional findings from the Curiosity rover that the huge Gale crater was once a lake or series of lakes a long time ago. Curiosity had already found evidence that there used to be shallow lakes and streams in this area, but the new data confirms this and suggests that the lake(s) once filled Gale crater and were long-lasting, explaining the formation of Mount Sharp in the middle of the crater and also providing a potentially habitable environment for life.
Another beautiful panoramic image of the foothills of Mount Sharp, taken by Curiosity on Sep. 9, 2015. The mesas, buttes and valleys can be seen in greater detail as the rover keeps getting closer. The image has been white-balanced to show the terrain under more Earth-like lighting conditions. The full-size version of the image is available here.
Wind-eroded rocks on Mars can take many different forms, sometimes resembling common earthly objects. Some good new examples include these long, thin slivers of rock which look like “spoons” and “needles,” seen by the Curiosity rover recently on sols 1089 and 1087. These fragile formations are easier to form in Mars’ weaker gravity and thinner atmosphere and can last much longer than they would on Earth – a unique form of Martian “artwork.”
After extensive investigations of rock layers in Marias Pass, a shallow valley near the base of Mount Sharp, the Curiosity rover is now heading southwest again, to continue gradually climbing the lower slopes of the mountain. Marias Pass is a region with rocks and ground which contain high levels of silica and hydrogen, more evidence that there used to be a lot more water here than there is now.