Thirteen years. That is how long NASA’s Opportunity rover has now been exploring Meridiani Planum on Mars; not bad for a robot which was designed with a hoped-for nominal 90-day mission. Today marks the 13th anniversary of the landing of Opportunity, on Jan. 24, 2004 PST (Jan. 25, 2004 UTC). The mission since then has been nothing short of incredible, as Opportunity soon found evidence that Meridiani Planum used to be a much wetter place than it is now. It was a place where microbial life could have existed; whether it actually did or not is still unknown but Opportunity continues to provide more clues as it continues exploring vast sandy plains and mountainous crater rims.
Opportunity began its journey in tiny Eagle crater, which it literally rolled into inside its cushioned airbags like a hole-in-one. The rover was designed to land protected inside these huge airbags where it would then bounce and gradually roll to a stop and then open up. The very first images showed layers of light-colored bedrock inside the crater, which was a jackpot for geologists.
Before long, the rover discovered the famous “blueberries” scattered everywhere on the plains: tiny spheres only a few millimeters across which turned out to be hematite concretions similar to ones seen on Earth. Such concretions form in watery environments on Earth. This was the first big piece of evidence, along with the bedrock, for water in this region a long time ago.
Over the next months and years, Opportunity discovered yet more evidence for past water on these now-dry plains, most likely in the form of salty playa lakes and groundwater. The saltiness meant that it would have been more difficult for life to thrive here, but it was by no means impossible. Hardy microbes on Earth called extremophiles can easily survive in such environments on Earth.
Opportunity then went on to visit the larger Endurance crater to the east, arriving in June 2004, before heading farther south to the much larger Victoria crater, reaching it in late September 2006. Here, the rover examined massive layered rocky cliffs along the crater’s rim, a beautiful sight to behold. There was a lot of geological history recorded in these rocks, documenting changes in the environment over billions of years.
From late April to early June 2005, Opportunity had become stuck in a sand dune, but was freed several weeks later. Its twin rover, Spirit, hadn’t been so lucky after also getting stuck in sand in Gusev crater in 2010.
It was considered to be an incredible accomplishment that Opportunity made it as far as Victoria crater, which was much better than had been hoped for at the beginning of the mission. But later, scientists set their eyes on an even more distant destination: Endeavour crater, farther southeast. Could Opportunity possibly make it that far? Endeavour crater was an enticing target, dwarfing even Victoria crater in size at 14 miles (22 kilometers) in diameter. Opportunity left Victoria crater in August 2008 and arrived at Endeavour crater in August 2011.
The rover climbed to the top of Cape Tribulation, a massive ridge on the western side of Endeavour crater, which is 4,560 feet (1,390 meters) tall. The views out across the floor of the crater were spectacular. Opportunity discovered high levels of sulfur in this location, in a scuff in the soil made by one of the rover’s wheels, another water clue.
“In the scuff, we found one of the highest sulfur contents that’s been seen anywhere on Mars. There’s strong evidence that, among other things, these altered zones have a lot of magnesium sulfate. We don’t think these altered zones are where the clay is, but magnesium sulfate is something you would expect to find precipitating from water,” Squyres added. “Fractures running through the bedrock, forming conduits through which water could flow and transport soluble materials, could alter the rock and create the pattern of red zones that we see.”
Most recently, the rover has been examining Marathon Valley, a large cut through the Endeavour crater wall. Opportunity found clay minerals here, which had been first detected from orbit. These minerals are also evidence for ancient water in this region, and this water would have been less acidic or salty than the water elsewhere in Meridiani Planum. Opportunity found that the clays were most abundant in darker reddish streaks in rocks within the valley. Opportunity has been inspecting these clay deposits with its RAT instrument, which can grind into rocks.
“What we usually do to investigate material that’s captured our interest is find a bedrock exposure of it and use the RAT,” said Principal Investigator Steve Squyres of Cornell University in Ithaca, N.Y.. “What we didn’t realize until we took a close-enough look is that this stuff has been so pervasively altered, it’s not bedrock. There’s no solid bedrock you could grind with the RAT. Fractures running through the bedrock, forming conduits through which water could flow and transport soluble materials, could alter the rock and create the pattern of red zones that we see,” Squyres also noted.
Now, the rover is heading toward a gully on the inside of the rim, a bit farther south from where the rover is now. That gully is thought to have been carved by running water millions or billions of years ago, according to mission scientists, and is about the length of two football fields. Gullies such as this have been seen in many locations on Mars, from orbit, but this is the first time that one will be examined up-close on the ground. It is another significant achievement for the mission.
“We are confident this is a fluid-carved gully, and that water was involved,” Squyres said. “Fluid-carved gullies on Mars have been seen from orbit since the 1970s, but none had been examined up close on the surface before. One of the three main objectives of our new mission extension is to investigate this gully. We hope to learn whether the fluid was a debris flow, with lots of rubble lubricated by water, or a flow with mostly water and less other material.”
As Squyres also noted: “We may find that the sulfate-rich rocks we’ve seen outside the crater are not the same inside. We believe these sulfate-rich rocks formed from a water-related process, and water flows downhill. The watery environment deep inside the crater may have been different from outside on the plain – maybe different timing, maybe different chemistry.”
The trip to the gully is part of a two-year extended mission for the rover, which began last Oct. 1. Opportunity’s prime mission ended in April 2004, and has been extended multiple times since then.
“We have now exceeded the prime-mission duration by a factor of 50,” said Opportunity Project Manager John Callas of NASA’s Jet Propulsion Laboratory, Pasadena, Calif. “Milestones like this are reminders of the historic achievements made possible by the dedicated people entrusted to build and operate this national asset for exploring Mars.”
The fact that Opportunity has lasted as long as it has is a testament to the engineers and designers who built the rover. Even as of last year, it was considered almost miraculous. As previously noted:
“Twelve years is a very long time to have this sort of a continuous presence,” said Matt Golombek, Mars rovers project scientist. “For a science team to be this involved, on a daily basis, for this long on Mars, is pretty much unprecedented.”
And now it’s 13 years. How much longer will Opportunity be able to keep exploring? Nobody knows. Some scientists have started looking at other destinations even farther away than Endeavour crater, but for now the rover will keep busy on the rim of the crater, including a close look at the gully. Opportunity has already outlived its initial planned mission many times over, helping to answer some age-old questions about Mars as well as raising new ones.
More information about the Opportunity mission is available on the NASA website.