Remnants of Ancient Streambed on Mars discovered by Mars Science Laboratory “Curiosity” rover. Photo credit: NASA/JPL-Caltech/MSSS
In the first of what we hope will be many blockbuster discoveries, the Mars Science Laboratory’s “Curiosity” rover science team, after less than 2 months on the surface of Mars, has announced that they have discovered an outcrop of conglomerate rock that proves that water once flowed “vigorous[ly]” on the surface of the Red Planet. They describe it as an “ancient streambed”. Not only that, but at the end of the press conference, Dr. John Grotzinger, the Project Scientist for the Curiosity rover programme stated that “we have now discovered evidence for water, and what we’d like to do is to begin to characterize habitable environments” [our emphasis – IWPCHI] that might have existed on Mars while this water was flowing over what appears to the NASA team to have been an as yet unquantified but extended period of time – definitely more than just “thousands of years”!
In the press conference held today (Thursday, Sept. 27), a team of NASA scientists made the announcement. Dr. Grotzinger, made the initial presentation:
“As we were driving along on the way to Glenelg, we encountered some really interesting outcrops that were surprising to the team. And in the first graphic, [see photo above] what you’ll be able to see are these outcrops. And this is one of them [shows PIA16156]. It’s named “Hottah”… and to us it just looked like somebody came along the surface of Mars with a jackhammer and lifted up a sidewalk, uh, that you might see in downtown L.A., uh, in sort of a construction site. So you can see this rock unit; and it’s about 10-15 centimeters thick, so it’s sorta on that scale [holds up thumb and index fingers to indicate what 10-15 cm looks like], and it’s tilted: in the perspective you’re looking at it’s tilted off to the right; and what it does is it exposes the materials that, that make up this slab of rock. And there’s a couple of these; and what we’re gonna be presenting today, my colleagues here will show you, what represents the consensus opinion of the science team: that this is a rock that was formed in the presence of water. And we can characterize that water as being a “vigorous flow”, on the surface of Mars. And we, we’re really excited about this because this is one of the reasons that we were interested in coming to this landing site was because it presented from orbit quite a strong case that we would find evidence for water on the ground. Turns out, that in fact we landed on this unit. And this makes a great starting point for us to do more sophisticated studies using the rover payload.”[Source: USTREAM.TV, “NASA Mars Rover News: Ancient River Streambed” Recorded live on September 27, 2012 12:46pm CST]
Over the past 6 years, the Mars Reconnaissance Orbiter has taken numerous spectacular high-resolution photos of Mars which showed what appeared to be unmistakeable evidence that liquid water once flowed – and possibly still today in some form flows, on Mars. Features were spotted that showed what looked like traces of water seeping out of cliffs; stream and river beds were found, and many other geological features indicated that it was a near-certainty that water has flowed on Mars and may still be flowing. Later, the 2 earlier martian rovers, “Spirit” and “Opportunity” also took photos and made observations of regions on Mars that contained rock formations and mineral forms that most likely were created in the presence of water. Now, we have clear evidence that small grains of sand and larger pebbles and even what are described as “cobbles” contained in a slurry of what is similar to very coarse concrete were moved and brought together in a matrix in a form extremely common, seen on Earth in stream and river beds all over our planet.
When NASA scientists were looking for a landing site for “Curiosity”, they sought out locations to land that would place the rover within a short driving distance from these water features. The selection of the apron of what appeared to be an alluvial fan at the foot of Mt. Sharp on Mars seemed well-suited for finding water features such as the one announced today. But most surprisingly, Curiosity, it turns out, landed RIGHT ON TOP of an ancient stream bed! The rockets that were used to gently land the rover on Mars blew away the surface dust from the top of the landing site, revealing the first stream bed outcrop practically under the rover! To say that this is a wonderful surprise is a vast understatement. It’s an extraordinarily lucky occurrence that just continues the incredible success of the MSL project so far.
Dr. Mike Malin of Malin Space Science Systems, San Diego, the designers of the magnificent cameras on both the Mars Reconnaissance Orbiter and the “Curiosity” rover, made a presentation at today’s news conference as well, in which he compared rock outcroppings found here on Earth that were created by flowing water and compared them to the rock outcrops discovered by Curiosity.
“I’m going to show you how we had anticipated, with the design of the cameras, this type of outcrop; and how, when I briefed the media at the launch briefing for science on the 23rd of November, I actually used as an example, this would be the type of rock that the [mast] cameras would excel on.”
First, Dr. Malin showed a slide depicting a rock outcrop that is composed of conglomerate. “This is a conglomerate bedrock outcrop in central Utah. It’s about 100 million years old… and it’s really a rock made out of a bunch of pieces of gravel. […] The white squares are enlarged at the bottom of this [image]… if you look at the [close-up] on the [lower] right, you can see there are a few bands of light-toned intermixed with a sort of speckly texture… the speckly texture is the conglomerate. It has lots of little pebbles in it. The lighter toned things are sandstone. So there was sand moving down along a stream, along with cobbles [and] little pebbles…”
- Images of rock outcrop just south of Green River, Utah, of ancient (Jurassic Period, around 150 Million years old) rocks exposed by erosion of a large amount of sedimentary rock in the area. Credit: NASA/JPL-Caltech/MSSS
Close-up of Green River, Utah rock formation showing areas of deposition of fine-grained sediment and areas of gravelly deposits. Image credit: NASA/JPL-Caltech/MSSS
Describing the photo above, which is an extreme close-up of the same Utah outcrop of conglomerate taken from 10 meters away, Dr. Malin said: “these are water-lain sediments that were then turned into a rock. And then that rock has been eroded away, showing us this large outcrop. The next slide shows a feature on Mars…
Curiosity rover photo showing the blast scour left by it’s descent stage’s rocket engines. This was one of the first photos taken by Curiosity of its landing site.
“…our first view of this similar type of rock came where the landing engines blew away the dirt and unveiled this layer beneath the surface debris; and you can see in the upper left corner of the enlargement of that white box that shows that there’s a layer there that seems to have rocks embedded in it. We have a higher resolution view of that in the next slide, which was taken with the MASTCAM-100;
Close-up of blast scour from Curiosity’s descent engines which revealed conglomerate rock formation from ancient stream bed. Credit: NASA/JPL-Caltech/MSSS
“…and you can see, in the lower left now, that the gravelly surface and the gravel at the edge of this layer. This is a relatively thin layer of this outcrop of the material that you’re gonna see in a few minutes. But, basically, we had anticipated and discussed – both before the launch and right after landing – that where we were going should have these “water-lain” sediments that had been turned into rock.”
Next up was Rebecca Williams, Senior Scientist at the Planetary Science Institute:
View of ancient Martian stream bed, dubbed “Hottah” by NASA’s Mars Science Laboratory team. Image credit: NASA/JPL-Caltech
“…This is the “Hottah” exposure that John introduced you to… we were really just extremely fortunate to have such an ideal viewing geometry of this material. This is a fractured rock outcrop that has been naturally tilted… we acquired these images on Sol 39 [the 39th Martian day that Curiosity has been on the surface of Mars]… and I’m going to zoom in on the lower left-hand portion of this [image].
Close-up of “Hottah” outcrop, an ancient stream bed discovered by NASA’s “Curiosity” rover, showing varied size of materials in this layer of conglomerate. The circled portion is of a large pebble encased in the layer. Image credit: NASA/JPL-Caltech/MSSS
“…what you see is: this rock is made up of rounded gravels – there’s one circled for you at upper right – and a matrix that’s very sand-rich… these attributes are consistent with a common sedimentary rock type called a “conglomerate”. Now, the clast that is circled is about 3 centimeters across… and you’ll see that the perimeter has a very rounded shape; it’s been worn by abrasion in a sediment transport process. And you’ll also notice the gravels sticking out from the rock; and over time, erosion is working on that rock face and liberating some of the gravels, and they’re falling down and accumulating on a pile at the base of the outcrop.
“A second exposure of this very same material we saw on Sol 26, and imaged it with the MASTCAM-100 (the narrow-angle) on Sol 27…
- Second outcrop of ancient Martian streambed (dubbed “Link” by the science team working on NASA’a Mars Science Laboratory) shows clean exposed cross-section of the conglomerate layer indicating clearly that the small pebbles and larger rocks in the layer had been transported by “vigorously flowing” water. Image credit: NASA/JPL-Caltech/MSSS
“… and this outcrop’s name is “Link”. You see the very similar textural properties that we saw at “Hottah”; again, very rounded gravels in a light-toned sandy matrix. And, again, we have that gravel pile that’s adjacent to the rock outcrop. So, by looking at the size and shape distribution of the gravels that are not only in the rock outcrop but those that we infer were liberated from the rock outcrop there on the surface, we can get a good idea of the range of gravel size and shape properties that you see there.
“On the next slide, we’ll zoom in…
This set of images compares the Link outcrop of rocks on Mars (left) with similar rocks seen on Earth (right). A typical Earth example of sedimentary conglomerate formed of gravel fragments in a stream is shown on the right. Rounded grains (of any size) occur by abrasion in sediment transport, by wind or water, when the grains bounce against each other. Gravel fragments are too large to be transported by wind. At this size, scientists know the rounding occurred in water transport in a stream. Image/caption credit: NASA/JPL-Caltech/MSSS and PSI
“…and there’s another one of these rounded gravels that’s about 1 centimeter across (that’s roughly the size of a plain M&M [Nice comparison! – IWPCHI]); and geologists are interested in rounded gravels because they tell you that those particles have been subjected to a sediment transport process, either by water or by wind. And, so, typically, you start off with a very angular rock fragment, and as it’s transported it’s bouncing along, interacting with other grains and the surface, and that wears away the edges until you have a very smooth surface such as you see here in this pebble [she holds up a small, rounded stone taken from a streambed here on Earth]. And the key components of these gravels that we’re seeing here are: one, the rounded shape, but also the size [emphasis in voice – IWP]. These are too large to be transported by wind: the consensus of the science team is that these are water-transported gravels in a vigorous stream.
“On the right of the graphic, you can see a typical streambed deposit: it’s a gravel conglomerate that has gravels of the same size and roughly the same roundness as we see on Mars. And so this is just wonderful “ground truth confirmation” of water-transported material that was predicted based on analysis of orbital images.” [!!! – IWPCHI]
The next scientist up to speak at this amazing news conference was Dr. William Dietrich, (Dept. of Earth and Planetary Science, University of California, Berkeley):
“So, I’m going to ask the question: ‘Where did these gravels come from, and what was the environment like at the time of deposition of the deposits that we now see at the rover site?’ And to do that, I’m going to use a term called ‘fan’, and, specifically ‘alluvial fan’; and to explain that, I’m going to take you on an aerial tour: first through Death Valley [desert in California, USA – IWP] and then back to Gale [Crater, where the “Curiosity” rover is situated -IWP], and connect the dots between the fan and the deposits we see. So, if I could have the first video… [MPEG-4. Additional videos are available here: http://mars.jpl.nasa.gov/msl/multimedia/videoarchive/– IWP]
“… I introduce you to an area you’re familiar with: there’s Los Angeles, and there’s Las Vegas, I-15 [Interstate Highway 15 – IWP] in between. And we’re going to take a flight just to the right of Zzyzx [desert town in California – IWP], and where there are six fans (outlined in white) that illustrate the form and process that I want to talk about. [Video starts and he narrates] So we’ll zoom in… and you’ll see the four [alluvial fans – IWP] that are facing us: the white lines delineating the lateral boundaries of sediment deposition that has occurred as a consequence of sediment and water rushing out of the canyons that are on the hills there. And we’ll now go up to the headwaters… and we see the stream confine the canyon. And then it reaches the front of the mountain; and as water and sediment rushes out, it spills. And as it spills it forms a sheet of water or it runs out as discrete channels. And you can see them there: shifting right, shifting left. As it deposits, it elevates and shifts right, left, back and forth, building the fan structure that’s so characteristic and so identifiable.
“We rotated it across this white-toned fan; and now we’re settling down and looking back. So now you see the fan shape, just like a fan that you would use to cool yourself off on a hot day. You see the white outlines of the structure; and you see how it’s a result of water and sediment pouring out of the canyon.
“So if I could now go to the next video, [this “next video” is edited together with the first video in the link above – IWP] we’re going to go to Gale Crater [on Mars – IWP]. And we’re flying from north to south; and you see (in red lines) the lateral boundaries of a fan just like we saw in Death Valley. And we’re looking down at a canyon: a canyon that is about 11 miles [18 kilometers – IWP] long, 2000 feet [600 meters – IWP] wide and about 100 feet [30 meters – IWP] deep. And that canyon was cut by stream flows. And that stream and sediment then entered the crater rim wall and spilled out left and right; and the blue lines delineate distinct channels that we can recognize. Fossil [stream – IWP] beds if you like. We look at these channels and we see that they cut across the fan system. And to us they suggest that this fan did not form in a single instance but this records some duration of a process.
“Now, we find… we settle down, and there’s “Curiosity”: it’s about a two to four-mile [3 – 6 kilometer – IWP] hike from the nearest channel to Curiosity – all downhill. So we think it’s reasonable to suggest that the water and sediment came down that fan that we see now… [referring to video – IWP] […] And, looking back [referring to the video’s aerial view showing the alluvial fan system on Mars – IWP], you see a watershed: you see a canyon; you saw a fan; you see channels.
“Now: what was it like then, if you were standing at, exactly, Curiosity’s site at the time of the sediment deposition? And the next video will show that. [Shows a video taken with an underwater camera in a fast-moving stream on Earth, which is part of this video here] So, here is water moving sand and gravel. It’s a vigorous sediment transport process: bursts and sweeps of turbulence mobilizing, together, sand and gravel. And, of course, the consequence of that motion is collision, breakage and rounding of particles. And in a flow that we can estimate for the rover site, that might have been from ankle- to hip-deep and maybe moving a few feet a second.
“And we arrive now…
This image shows a dry streambed on an alluvial fan in the Atacama Desert, Chile, revealing the typical patchy, heterogeneous mixture of grain sizes deposited together. On Mars, Curiosity has seen two rock outcrops close to its Bradbury Landing site that also record a mixture of sand and pebbles transported by water that were most likely deposited along an ancient streambed. Image/caption credit: NASA/JPL-Caltech/UC Berkeley
“… at what the bed of the rover site might have looked like after the last flow (of course, visited by a few Earthlings). That was the Atacama Desert [in Chile – he refers to the photo above – IWP]. You see the heterogeneous bed; you see the patches of sediment. And what we can think about, then, is that we were in a watershed. We saw… going from an uplands to a lowlands. And we would start with a rock [places large, heavy, angular piece of stone on desk in view of cameras – IWP] that would be big and broken, like this. And it would travel something like 20 to 25 miles [32 to 40 kilometers] and end up something small and rounded like this [indicating much smaller rounded stone on desk – IWP].
Going from this [indicating large angular stone] to this [indicating small rounded stone] is direct visual evidence of the wear by what we call “bed-load transport”: of the wear, particle collision and the transport by water to the site of interest.”
Dr. Grotzinger wrapped up the news conference with some interesting information regarding the upcoming experiments that will be conducted by the Curiosity rover:
“First of all, this represents a great collaboration between the Curiosity rover and the orbiters that are routinely mapping Mars. Now, in the case of looking at the alluvial fan, we see that that’s provided by both the “HiRISE” imager, the CTX imager [one of the instruments on the Mars Reconnaissance Orbiter] , previous generations of imagers… [the imagers – IWP] look at these features that geologists have long thought of as alluvial fans. But now that we’re down on the ground with Curiosity we can see the textural evidence that Becky and Mike talked about where you see the individual pebbles, the rounding, the geometric relationship that they have to each other that gives us a sense for that. So if we just go back one, please…
This map shows the path on Mars of NASA’s Curiosity rover toward Glenelg, an area where three terrains of scientific interest converge. Arrows mark geological features encountered so far that led to the discovery of what appears to be an ancient Martian streambed. The first site, dubbed Goulburn, is an area where the thrusters from the rover’s descent stage blasted away a layer of loose material, exposing bedrock underneath. The second feature, a naturally exposed rock outcrop named Link, stood out to the science team for its embedded, rounded gravel pieces. The final feature, another naturally exposed rock outcrop named Hottah, offered the most compelling evidence yet of an ancient stream, as it contains abundant rounded pebbles. The grain sizes are also an important part of the evidence for water: the rounded pebbles, which are up to 1.6 inches (4 centimeters) in size, are too large to have been transported by wind. The image used for the map is from an observation of the landing site by the High Resolution Imaging Science Experiment (HiRISE) instrument on NASA’s Mars Reconnaissance Orbiter. Image/caption credit: NASA/JPL-Caltech/Univ. of Arizona
“… we should be able to see where these different features occur on our route to “Glenelg”. And so, “Golburn” was the outcrop that Mike talked about, the one that we got for free way back when when the thrusters blew the soil away. And at that time, the team came up with a number of hypotheses to potentially account for this. And then we had a lot of discussion about it; and then we worked our way to “Link”, where we were able to see the first of the outcrops that Becky talked about, and we began to wonder about the streamflow option as being the most likely candidate. And it was really when we got to “Hottah” where we saw this again, most clearly, that it was very easy to reach team consensus to come to you and present the story about where we are.
“Now the rover is about 3/4 of the way between “Hottah” and “Glenelg”; and we’re working our way down into that key area where these three terrain types come together. So if we can go to the next one…
This image shows the topography, with shading added, around the area where NASA’s Curiosity rover landed on Aug. 5 PDT (Aug. 6 EDT). Higher elevations are colored in red, with cooler colors indicating transitions downslope to lower elevations. The black oval indicates the targeted landing area for the rover known as the “landing ellipse,” and the cross shows where the rover actually landed. An alluvial fan, or fan-shaped deposit where debris spreads out downslope, has been highlighted in lighter colors for better viewing. Elevation data were obtained from stereo processing of images from the High Resolution Imaging Science Experiment (HiRISE) camera on NASA’s Mars Reconnaissance Orbiter. Image/caption Credit: NASA/JPL-Caltech/UofA
“… again, just to remind you, something that we showed you before we landed – in the press conference before then – we see the alluvial fan and “Peace Vallis” – which is now an official name that the IAU [International Astronomical Union – IWP] has approved as the entry point for water into this feature… what we were uncertain of at the time of landing was whether or not this alluvial fan extended all the way down into the landing ellipse. And you see where we landed is quite a bit away from where you would identify – as Bill said, it’d be a few miles’ hike to get to the base of the alluvial fan. So it looks like – at least intermittently – that that fan extended down to where the rover was. That’s our most popular hypothesis right now for the team.
“The other part of the story that we talked about is in the last slide…
This false-color map shows the area within Gale Crater on Mars, where NASA’s Curiosity rover landed. It merges topographic data with thermal inertia data that record the ability of the surface to hold onto heat. Red indicates a surface material that retains its heat longer into the evening, suggesting differences relative to its surroundings. One possibility is that the materials that make up these soils and rocks have been more tightly bound together by mineral cements. The black oval indicates the targeted landing area for the rover, known as the “landing ellipse,” and the cross shows where the rover actually touched down at the Bradbury Landing site. An alluvial fan, or fan-shaped deposit where debris spread out downslope, has been highlighted in lighter colors for better viewing. This image was obtained by the Thermal Emission Imaging System on NASA’s Odyssey orbiter. Image/caption credit: NASA/JPL-Caltech/ASU
“… where you now see the map of this feature called “thermal inertia”. So we’re beginning to get a sense of what that might mean now, because – you see the “X” where Curiosity landed. And you see high values of thermal inertia but not the highest values. So we wonder what might cause this greater retention of heat. And it could be because you’re dealing with materials that are consolidated. [Emphasis in voice – IWP]
“And what we haven’t told you today is anything about the rest of the payload – what we might measure in terms of the chemistry; what we might measure in terms of the mineralogy. What we do know is: we go down towards Glenelg; we’re gonna go down towards that red patch, which is where the thermal inertia becomes the highest. And so, our plan as we go forward now is to study the chemical and mineralogical attributes of these rocks, and see how water may relate to the cementation of these gravels to form a rock.
“And that’s really where it brings us, is to really the beginning of the science mission, where we have now discovered evidence for water, and what we’d like to do is to begin to characterize habitable environments [!!! EMPHASIS ADDED – IWPCHI]. And that requires using all of our payload, including the instruments that measure the chemistry and the mineralogy. So we’ll keep you updated as we go along with those measurements as well.”
[Sources: USTREAM.TV, “NASA Mars Rover News: Ancient River Streambed” Recorded live on September 27, 2012 12:46pm CST; NASA’s Mars Science Laboratory website. All transcriptions of the Sept. 27th press conference were done by IWPCHI].