Today marks the 2,000th Martian day (Sol) of operation for NASA’s Mars Science Laboratory – more commonly known as the Curiosity rover. The exploration platform touched down on the surface of the Red Planet after a daring and never-before-used landing sequence on 5 August 2012 (Pacific Daylight Time) and has since well surpassed its initial science goals as its science teams plan for the rover’s future.
The first 2,000 Martian days:
To say Curiosity arrived in style at Mars would be an understatement. The rover’s tenure on the Red Planet began like no other mission before it had, with a daring and highly-complex retrorocket deceleration and hovering above the Martian terrain before Curiosity itself was then sky-crane winch lowered from the retrorocket-stabilize platform onto the Martian surface.
It was a night of anxiety, exhilaration, and tremendous achievement – and it’s one that Ashwin R. Vasavada, Project Scientist on Mars Science Laboratory at NASA’s Jet Propulsion Laboratory, remembers well.
“When we landed successfully, my two thoughts were, ‘Oh my gosh, it worked,’ and ‘Wow, okay, I’m going to be up all night planning the next sol now. And we have a lot of work to do,’” said Mr. Vasavada in an interview with NASASpaceflight.com’s Chris Gebhardt about Curiosity’s Sol 2,000 milestone.
“I didn’t doubt it was going to work; there’s no way I would have invested so much of my life in it. It’s just that no matter what you thought, it was remarkable that it did work. But I thought ‘Oh my god, we have a lot of work to do’ because the entire weeks leading up to landing, and certainly the day of the landing itself, I was just focused on the fact that it was landing.
“I even had some roll, a small role in that, where I was helping lead a team that was understanding the weather at the landing site up until the last few hours in case we had to change any parameters in the landing system to account for a dust storm or something.
“So I was consumed by that. And then we landed at about 10:30 at night, pacific time. And the schedule was that around 1:00 am we were going to start the first science shift, start to plan Sol 1. And I was the lead science role on that first planning day just by virtue of the fact that I helped design a lot of it.”
But there was another thought running through Mr. Vasavada’s mind the night Curiosity landed: Gale Crater might be a bad landing spot. “Gale Crater could have turned out to be a total bust, you know? We, of course, did our best job to work to find the best landing site we could for this mission, one that offered the chance to find a habitable environment and one that even offered the chance to ask that question multiple times as we climbed this mountain and accessed rocks at different ages.
“But there was still the completely reasonable possibility that all of Mount Sharp was formed by wind depositing sand and dust and that the evidence for rivers and streams we’d see in pictures from orbit were maybe just insignificant, transient things.”
But Mount Sharp was anything but a bust. “Fast-forward a year later, we found a single habitable environment. That’s huge. And then fast-forward to now where we’ve found 370 meters of nearly continuously habitable environment. I think it’s hard to say that in our wildest dreams we could have imagined that answer, you know… such a positive answer to the question about habitability,” said Mr. Vasavada.
In the first year after Curiosity’s arrival, the rover actually achieved all of its mission objectives. “We were able to accomplish the goals of the mission in the first year, which was to find and quantitatively investigate a habitable environment in ancient Mars. I’m very satisfied with how things have gone [since then]; we’ve just been building on that and it has continued to be very fruitful.”
Looks like we made it: 2,000 sols on Mars, you guys!
I’m looking back on 2,000 Martian days of exploration, and literally looking forward to climbing higher in those to come. The area ahead contains clays I’m eager to investigate: https://t.co/Uk8dCF0tYV pic.twitter.com/qiUxFsL43F
— Curiosity Rover (@MarsCuriosity) March 22, 2018
While the mission’s objectives were achieved early on, Curiosity’s teams have continued to abide by those guiding objectives over the following four and a half years. “We purposely haven’t spent a lot of time doing things that weren’t in the mission priority list. Even today, that original list of priorities (habitable environment, preservation of organics, understanding the climate and weather, and understanding the radiation environment) are sort of our four guiding scientific threads, themes that we try to pursue.”
But that doesn’t mean Curiosity’s exploration of Mars hasn’t yielded surprises. As Mr. Vasavada explained, one of the nice surprises Curiosity has enabled scientists to examine is Mars’s geochronology – made possible through the use of Curiosity’s SAM (Sample Analysis at Mars) instrument.
“It sort of fits into the original themes, but it wasn’t expected to be possible – using the SAM instrument, which is our mass spectrometer / gas chromatograph system, to actually date the age of rocks on Mars in two different ages: their formation age as well as their surface exposure age, which is how long they’ve been close to the surface; in other words how long have they been unburied.”
The surface exposure age – achieved by drilling a hole into a surface rock and measuring the age of specific chemical isotopes that form near the surface as they’re hit by cosmic rays – yielded intriguing results that allowed scientists to better understand the wind erosion rate occurring on the Martian surface.
“The surface exposure age [was found to be] about 80 million years. That was interesting because it allowed us to compute the present-day erosion rate of the surface which is always something geologists are interested in in terms of understanding the modern environment where Mars is being slowly worn away by wind,” noted Mr. Vasavada.
On its own, understanding the surface age of Mars would not generally help scientists understand Mars’s past habitability; however, one of the samples Curiosity’s team used to determine the surface age did yield information on the Red Planet’s past habitability.
“We drilled a sample that had the mineral jarosite in it, and the jarosite was precipitated out of water, probably through ground water that flowed through the rocks well after the lakes were there,” said Mr. Vasavada. “The age of the jarosite was something like three billion years old.
“When you’re talking about three billion years ago, that’s well after all of Mount Sharp formed. Well after the lakes were gone. So that’s our youngest evidence for continued habitability in Gale Crater. And it’s likely confined to being underground, where liquid water was still being circulated.”
That truly exciting find for the Curiosity team and Mars scientists as a whole came completely by surprise from an experiment that wasn’t specifically searching for such a discovery.
The discovery it was searching for, surface age, is actually well suited to helping NASA better determine where to look for signs of ancient Martian life. “When you look at Curiosity as a mission that is producing results that will inform NASA how to do their search for life, which is really what Curiosity is, the ways that we contribute to that is to understand whether Mars ever had habitable environments,” said Mr. Vasavada.
Part of that search is understanding the locations on Mars that could have preserved ancient life or ancient organic molecules, the building blocks of life. And this is an area of its mission that Curiosity has excelled in, with Mr. Vasavada noting that the results of what Curiosity is finding at Gale Crater and Mount Sharp can be offered up to Mars 2020 and future Mars missions to help better target surface locations that have environments like the one found at Gale Crater – environments that might well have been habitable in the past.
And this leads directly back to the wind-erosion surface age determination. “If you specifically try to sample materials where natural erosion is taking place, you have a better chance of having [organic molecules that were] protected from cosmic radiation. With Curiosity, we were able to put a date on that, and 80 million years was a long time, but it’s still offering some chance that materials would not be completely degraded by that time.”
— Curiosity Rover (@MarsCuriosity) September 19, 2017
Moreso, if missions can use Mars’s natural erosion processes to search for organic molecules that have been preserved in rock for millenia, missions wouldn’t necessarily have to take a drill in order to perform the types of experiments needed to search for organic material.
Those kinds of missions could go to places on Mars where the planet is essentially already doing the drilling needed to expose those organics. “The interesting thing about Mars is that the winds are what’s causing most of the geology these days.
“And those winds have probably been pretty consistent for millions and millions of years, so you can find places even within a landing site where one side of the hill is what’s being eroded over time and the other side of the hill may not be. And so you could drive up to that particular side of the hill and do your drilling and/or take advantage of the fact that that’s where the current erosion is the fastest.”
While the ability to perform geochronology of Mars stemmed from one of the four primary scientific objectives for Curiosity, one of the most important elements of the mission has been its service as a precursor to human flights – most notably in understanding the radiation environment present at the Martian surface.
Curiosity has revealed a wealth of information in that arena, though exactly what that information means to future human Mars missions is a judgment for scientists outside the Curiosity project to make.
“The way I see it, as someone who’s on Curiosity, is we’ve successfully been able to produce that [radiation] data. And we’ve been able to measure that data not only in cruise from Earth to Mars, but we’ve been able to measure radiation now for more than five years on the surface of Mars. And that’s something that Curiosity uniquely has done,” stated Mr. Vasavada.
Measuring the radiation environment on Mars’s surface provides a better understanding for our future exploration and colonization goals than has previously been obtained through the fleet of Mars orbiters. “There have been other spacecraft at Mars that have measured [radiation] above the atmosphere. But only [Curiosity has] been able to measure it at the surface.
“The reason that’s important is because galactic cosmic rays or solar particles, both high energy particles, hit the atmosphere, and as they travel through the atmosphere, they can actually collide with molecules in the atmosphere and form secondary products that are also moving at very high speed. But they’ve slowed down somewhat because of the collision.
“And those slightly slower particles can actually be more damaging to humans than some of the original particles. So knowing the radiation that’s on the surface, the types of particles, the energies that they are, is what NASA needs to understand the risk to astronauts on the Martian surface.”
Darker, cooler areas on the Sun – aka sunspots – have been absent for almost 2 weeks, as of Feb. 1. This spotless period is a prelude to the approaching period of solar minimum next year, when the Sun’s activity will be at the low end of its 11-year cycle: https://t.co/LQB3bDLIU4 pic.twitter.com/UPrcEX6C3r
— NASA (@NASA) February 6, 2018
Curiosity’s prolonged lifetime on Mars’s surface also enables a more complete picture of how the radiation environment changes as the Sun goes through its solar cycle. “The sun has these solar flares that can drastically change the kinds of particles that are coming out,” said Mr. Vasavada.
“And we can measure those events on the surface of Mars when they arrive, as well as the overall 11-year solar cycle. It’s been going from a more active period to a more quiescent period over its normal cycle, and we can watch how the radiation at Mars changes as a result of that.”
Based on the information thus far received by Curiosity, it appears that the radiation dosage astronauts would receive is similar to what NASA considers to be a career acceptable level for an astronaut.
And this ongoing exploration of the radiation environment is in part due to how well Curiosity’s science instruments have held up compared to expectations. Curiosity’s instruments were designed to survive for two Earth years. This year, the rover will mark its sixth Earth year anniversary since landing.
“After five and a half years, we’ve really not lost any major scientific capability. The one hit we’ve taken in terms of the science we’re able to do is the ability to sense wind. Our wind sensors are very delicate, and between getting to Mars and landing we lost a part of that sensor. And in the last two years, we’ve lost the other half of the wind sensors as well.”
The only other complication the team has faced stems from Curiosity’s drill, which while not a scientific instrument is crucial to the operation of the laboratory in examining surface rocks. “For the past year we’ve been working really hard on developing a new way of drilling that doesn’t rely on the feed motor that’s currently not working well,” said Mr. Vasavada.
“So we’re testing that out, and it’s promising. It’s just a long process. And once we successfully deliver samples to our laboratories, we’ll be almost as good as new in terms of the scientific capabilities of the instruments after five and a half years.”
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