Not two months into its mission NASA’s Mars Science Laboratory rover, Curiosity, has made a finding on the surface of the Red Planet of another sign that Mars was once a wet world. NASA”s Jet Propulsion Laboratory (JPL) in Pasadena, Calif, announced Thursday, Sept. 27 that the rover had discovered an ancient stream bed, long dried and cover in red Martian dust, near the rover’s landing site.
The evidence that Curiosity found would be readily recognizable to anyone that has strolled along a stream here on Earth – gravel. Common here, but this marks the first time it has been found on Mars. These small stones are fixed into the side of this ancient waterway in a sort of Martian concrete.
“From the size of gravels it carried, we can interpret the water was moving about 3 feet per second, with a depth somewhere between ankle and hip deep,” said Curiosity science co-investigator William Dietrich of the University of California, Berkeley. “Plenty of papers have been written about channels on Mars with many different hypotheses about the flows in them. This is the first time we’re actually seeing water-transported gravel on Mars. This is a transition from speculation about the size of streambed material to direct observation of it.”
AmericaSpace spoke with MSL’s Project Scientist, John Grotzinger, shortly after the announcement was made and he detailed how this finding was made as well as how NASA’s Mars program is building on past experiences to achieve the stunning results that Curiosity is beginning to rack up.
AmericaSpace: Dr. Grotzinger, thank you for taking the time to chat with us today regarding this important finding.
Grotzinger: “It’s my pleasure!”
AmericaSpace: Was the discovery of this stream bed just a ‘happy coincidence?’
Grotzinger: “Actually no, if you look at the lay of the land in images say from Google Earth and you’ve looked at images from Death Valley in California, but you will see these fan-shaped deposits that are called Alluvial Fans. If you ever been to that part of the world, what you will see are mountains and then canyons that come out of those mountains and then this wide spread of loose material – those are alluvial fans and that’s what we were seeing in images from the Mars Reconnaissance Orbiter (MRO) and from the Mars Odyssey spacecraft.”
AmericaSpace: So, a lot of loose, small particles and pebbles?
Grotzinger: “Actually they can be anywhere from boulders, to small stones – it really depends on how vigorous the flow was. Perhaps it’s a flash flood that produced these deposits.”
AmericaSpace: So the Mars science team knew that they were going to land at this location and possible discover this?
Grotzinger: “Actually we didn’t think we would have a good chance of landing right on it – but that is practically what happened.”
AmericaSpace: John was it MRO or Odyssey that discovered these features?
Grotzinger: “I would most attribute it to MRO; they certainly had the highest resolution images of what was there, both the HiRISE (High Resolution Image Science Experiment) and the CTX camera (Context Camera). It was Odyssey, however, that had an infrared camera that was able to look at a property we call thermal inertia. A good example of what this is, is you walk past a building in the evening and it is giving off heat – all materials have the ability to gain and lose heat – but they do so at different rates. Well what we saw from orbit, out in front of this alluvial fan that you saw in the images from the Odyssey data that looked like a kind of a rock that kept its heat late into the evening, this is consistent with a type of material that is made up primarily of small sediment particles bound together by a kind of cement. That is probably what we are looking at here.”
AmericaSpace: When you first saw this rock, what was your initial impression?
Grotzinger: “Honestly? – it kind of looked like someone had jack-hammered up a piece of sidewalk!” (laughs) So, you look at that and say, jeez, that kind of looks like concrete.
AmericaSpace: How was the determination made about what the Mars science team found made?
Grotzinger: “We have the orbiter image data that is telling you that you are down slope from an alluvial fan and the thermal inertia data tells you to expect that there might be something that could be rocky and cemented and you put those both together and I think that is pretty well what we have discovered.”
AmericaSpace: It seems almost like you found this right after the landing.
Grotzinger: “You’re not wrong, the thrusters from the Sky Crane jetpack blew the soil away and revealed what looked like rockier material, which appeared to be a type of cemented gravel. Seeing this we came up with a number of different hypotheses for that and then we drove the rover around and found more of that jack hammered sidewalk.” Now in that material we saw these ancient pebbles that were transported in a stream.”
AmericaSpace: So what would you describe the process that lead to this discovery?
Grotzinger: “It would go like this, hunch from on-orbit, land the rover, drive around and test hypotheses until you get to a place where it is really very clear what has happened and then you can trim down the number of hypothesis to one favorite that had a strong science team consensus for.”
AmericaSpace: This stream bed was on Curiosity’s ‘to-do’ list from the outset – correct?
Grotzinger: “To some extent we follow that plan; however, if we would have been unfortunate enough to land on a material that wasn’t formed in water. As it turned out, and this is where the serendipity comes in, we landed on precisely the type of material that we were looking for.”
AmericaSpace: That sounds a lot like the Mars Exploration Rover Opportunity’s landing in Eagle Crater.
Grotzinger: “That’s exactly right, but let me add one thing to that, in the ten-years, almost ten years between when Opportunity landed and when Curiosity landed. The place we sent Opportunity to land, well we had a similar hunch and when we landed? It turned out to be completely different than what we thought. This time around? We’re getting better from interpreting what we are seeing from orbit in predicting what is on the ground. This is really good for Mars science because it means that the synergy between alternating orbiters with rover and lander missions and taking that information and feeding it back – is really starting to pay off.”
AmericaSpace: Who would you most credit for implementing this policy?
Grotzinger: “This is a decision by the Mars program of NASA that has decided to alternate between orbiter and lander and rover. This ultimately comes from the community of scientists that are interested in exploring Mars. We can learn a lot from orbit, but a rover allows us to explore Mars in a level of detail that simply cannot be achieved from orbit alone.”
AmericaSpace: What do you think is the one thing that the public should take away from this discovery?
Grotzinger: “We have discovered evidence for water at Gale Crater and this gives us a very strong foundation to begin our prime mission of exploring for habitable environments.”
AmericaSpace: John, congratulations and thanks for taking the time to speak with us today!
Grotzinger: “You’re more than welcome and thanks!”
The site where Curiosity made its finding is located between the north rim of Gale Crater and the base of Mount Sharp, a mountain that is actually located within Gale Crater.
Two outcrops, called “Hottah” and “Link” were where the discovery was made. This was in large part thanks to the telephoto capabilities of the rover’s mast camera. The rounded shape of the stones in the material that the MSL rover found, points to it being moved over great distances from the top of the crater. There is a channel located there dubbed Peace Vallis feeds the alluvial fan that attracted the program’s scientists.
Another thing that has caught the eye of scientists was the large amount of channels that appeared to flow through the fan. This hints that these flows occurred repeatedly over a long period of time rather than just once or over a few years.
Curiosity launched from Cape Canaveral Air Force Station’s Space Launch Complex-41 (SLC-41) located in Florida on Nov. 26, 2011. The launch vehicle was an Atlas V 541 rocket. The rover traveled between worlds for nearly eight months before setting down on the surface of the Red Planet via its “Buck Rogers” Sky Crane jetpack.
Curiosity’s prime mission is slated to last for two years and the rover boasts a wide array of scientific instruments on the rover’s body, its robotic arm and even the mast that the public associate as the rover’s “face.”
For more about Curiosity, visit: http://www.nasa.gov/msl