Mars has often been compared to deserts on Earth, and for good reason: It is pretty much a barren landscape with a lot of sand and rocks everywhere. Sometimes the similarities can be quite striking, and the terrain in Gale crater where the Curiosity rover is roaming around is a good example. The rover is currently in a region of stunning scenery, consisting of buttes and mesas that are very reminiscent of ones on Earth. This area could easily be mistaken for the American southwest if it weren’t for the dusty, pinkish sky and complete lack of vegetation. Curiosity is now getting a close-up look at these formations, which are not only beautiful but record a long and fascinating geological history.
For the past few weeks, Curiosity has been traveling through the Murray Buttes, a collection of buttes near the base of Mount Sharp. They were one of the prime destinations for the rover as it heads closer to the mountain. The foothills of Mount Sharp are also a maze of buttes, mesas, and canyons, which the rover will be moving toward next.
“Curiosity’s science team has been just thrilled to go on this road trip through a bit of the American desert Southwest on Mars,” said Curiosity Project Scientist Ashwin Vasavada, of NASA’s Jet Propulsion Laboratory in Pasadena, Calif.
These sandstone buttes and mesas are remnants of once larger formations which have been eroded over time; they were first created by sand deposited by winds after the lower part of Mount Sharp had already formed.
“Studying these buttes up close has given us a better understanding of ancient sand dunes that formed and were buried, chemically changed by groundwater, exhumed and eroded to form the landscape that we see today,” Vasavada said.
The rover is now almost ready to leave these buttes behind, but right now it is at the base of one of them, preparing to conduct another drilling session. So far, Curiosity has drilled into the rocks in 13 previous locations. After that, Curiosity will continue south, roving ever closer to the foothills of Mount Sharp.
Studying these formations, which often exhibit many thin layers of rock, will help scientists better understand the geological history of Mars in this region. Apart from the buttes, Curiosity has also found abundant evidence that Gale crater was once a lake or series of lakes earlier in the planet’s history. There are also ancient streambeds cutting through the crater’s walls, where water once emptied into the basin. Indeed, Curiosity has even examined old riverbed gravel up close. While bone dry now, this place used to be very wet, and potentially habitable for at least primitive organisms of some kind.
Prior to reaching Murray Buttes, Curiosity had been traveling across Naukluft Plateau, a remnant plateau of fractured sandstone which used to be more extensive in this area. While on the plateau, the rover completed its 12th drilling campaign, in mudstone bedrock, as well as re-examining its 1oth and 11th drill holes, to repeat an experiment which compared material within and away from pale zones around fractures. Curiosity also took additional “self-portraits” while in this region. Before that, the rover skirted some massive sand dunes, part of the Bagnold Dunes, which partially surround the base of the mountain.
Naukluft Plateau covers part of the Murray Formation of bedrock; it is in this region and others that drilling of rock samples provided the evidence for past lakes and rivers.
“The story that the Murray formation is revealing about the habitability of ancient Mars is one of the mission’s surprises,” Vasavada said. “It wasn’t obvious from pre-mission data that it formed in long-lived lakes and that its diverse composition would tell us about the chemistry of those lakes and later groundwater.”
Now, the rover will leave the buttes behind and keep heading south toward Mount Sharp. The scenery has been incredible so far and should be even better when Curiosity starts ascending the slope into the foothills. Large rounded mesas, buttes, and valleys dominate this landscape.
“Now that we’ve skirted our way around the dunes and crossed the plateau, we’ve turned south to climb the mountain head-on,” said Vasavada. “Since landing, we’ve been aiming for this gap in the terrain and this left turn. It’s a great moment for the mission.”
Curiosity has also recently found evidence for the mineral tridymite as well as much more oxygen in the Martian atmosphere a long time ago. The tridymite discovery was exciting as it was unexpected on Mars. On Earth, it is produced by silicic volcanoes, such as Mount St. Helens in Washington. Volcanoes on Mars, however, tend to be of the basaltic type, like the ones in Hawaii, so it’s not clear yet just how the mineral formed in Gale crater.
“I always tell fellow planetary scientists to expect the unexpected on Mars,” said Doug Ming, ARES chief scientist at Johnson and co-author of the paper. “The discovery of tridymite was completely unexpected. This discovery now begs the question of whether Mars experienced a much more violent and explosive volcanic history during the early evolution of the planet than previously thought.”
The thin atmosphere of Mars only contains a trace amount of oxygen now, so where the previously abundant oxygen came from is also unknown. On Earth, most of it is produced by life, but it can be generated other ways as well, although usually in smaller amounts, such as ultraviolet radiation from the Sun breaking down carbon dioxide, the electrolysis of water, or the photolysis of ozone. While actually being dangerous to some forms of life, it is also produced in abundance by others. As interestingly noted by Damien Loizeau of the University of Lyon in France, “O2 is bad for life as we know it, but we only know life to be able to create large amounts of O2.”
“We found 3 percent of rocks have high manganese oxide content,” said Agnès Cousin of the Research Institute in Astrophysics and Planetology in Toulouse, France, at the European Geophysical Union meeting in Vienna, Austria, last April, and reported in New Scientist. “That requires abundant water and strongly oxidising conditions, so the atmosphere may have contained much more oxygen than we thought.”
The discovery of high amounts of silica in some of the rocks examined by Curiosity as well as the manganese oxides also point to a more life-friendly environment millions or billions of years ago, with more abundant water and oxygen. In some cases, at least on Earth, manganese oxides can even be created directly by microbes. However, making that kind of link with these manganese deposits would require a lot more evidence.
Curiosity technically reached the outermost portion of the mountain in 2014, but once it passes Murray Buttes, it will begin ascending up the lower flanks themselves and into the foothills. The long climb up the mountain itself will have finally begun.
The Murray Buttes, just like their earthly counterparts, are a record of extensive geological history in Gale crater. Along with other evidence they show that Mars has had a complex evolution and in many ways used to be much more like Earth than it is now. Whether the planet was ever inhabited by microbes (although probably not anything much more than that) is still unknown, but Curiosity and other missions are bringing us closer to finding an answer. And the scenery isn’t too bad, either.
More information about Curiosity is available on the mission website.