Science and Exploration

CuriousMars: Curiosity to Drill into ‘Whole Different World’

By Craig Covault
January 17, 2013
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CuriousMars: Curiosity to Drill into ‘Whole Different World’
Curiosity's first drilling ground: This image shows the veined, flat-lying rock selected as the first drilling site for Curiosity. The rover took this with its Mast Camera (Mastcam), equipped with a telephoto lens, from about 16 feet (5 meters) away on its Sol 153 (Jan.10, 2013). The area is defined by fractures and veins, with the intervening rock also containing concretions, which are small spherical concentrations of minerals. The image was white-balanced to show what the rocks would look like if they were on Earth. Image credit: NASA / JPL-Caltech / MSSS
NASA / JPL-Caltech / MSSS

As the Mars Science Laboratory (MSL) science team completes final assessments of the mission’s first drilling target in the bedrock at Yellowknife Bay, Curiosity is roving through “a whole different world,” uncovering evidence for rocks saturated with water and other diverse and unexpected aqueous clues that hint of an ancient and very wet environment at Gale Crater.
It’s a world of conglomerate rocks, sandstones, siltstones, spherules – known as “blueberries” to MER followers – lustrous pebbles, cross-bedding, tiny grains and filled veins, cracks, and fractured rocks – and, it appears, no end of evidence for past water. “We wouldn’t have predicted any of this stuff from orbit,” said John Grotzinger, MSL project scientist, of Caltech during a telebriefing on January 15th. “This is a great example of the occurrence of serendipity in scientific discovery.”

It all serves as evidence that further supports the popular and leading theory that Mars was once warmer and wetter and more like Earth – and that it was capable of providing a habitat for microbial life.

MSL lead scientists also officially announced at that briefing that Curiosity’s first drill target IS in this “different world,” in a richly layered bedrock that lies just ahead for the rover.

They christened the destination bedrock John Klein, in honor of a former project manager who passed away in 2011. “John’s leadership skill played a crucial role in making Curiosity a reality,” noted Richard Cook, deputy project manager, of the Jet Propulsion Laboratory (JPL), home to all the American Mars rovers.

Roving into a whole different world: This image maps the traverse of Curiosity from Bradbury Landing to Yellowknife Bay. Between Sol (Martian day) 120 and Sol 121 of the mission on Mars (Dec. 7 and Dec. 8, 2012), the rover crossed a terrain boundary into lighter-toned rocks that correspond to high thermal inertia values observed by NASA’s Mars Odyssey orbiter. The green dashed line marks the boundary. After the first use of the drill, the rover’s main science destination will be the lower reaches of Mount Sharp. The base image from the map is from the High Resolution Imaging Science Experiment Camera (HiRISE) onboard the Mars Reconnaissance Orbiter.
Image credit: NASA / JPL-Caltech / UA / CAB (CSIC-INTA) / FMI

The team has not yet set a date for the much-anticipated drilling or even chosen the exact spot on the John Klein bedrock, but the event could happen “sometime in the next two weeks,” Cook said Tuesday.

Curiosity is ready and everything is going about as nominally or normally as it could on Mars. The only problem has been “all the interesting things the scientists have been finding,” Cook said. “They have been led into the candy store. It’s delayed the campaign for a few days.”

The robot’s mission objective inside Mars’ Gale Crater is to determine whether the planet ever offered an environment favorable for microbial life. What it has been observing and analyzing during the last month is as confirming as it is puzzling.

Curiosity actually crossed the contact or boundary into this “different world” last December. The contact geologically defines the border between two areas: one of lower thermal inertia terrain, which tends to indicate an area of dust and soil; another area of higher inertia terrain, which tends, on Mars, to indicate rocks.

The contact is clearly visible in an image taken by the HiRISE camera onboard the Mars Reconnaissance Orbiter (MRO) that Grotzinger showed during the briefing and which accompanies this article. In the image, one can see the area of lower thermal inertia terrain on the left which appears darker from orbit. This is the area where the rover landed, near a dry streambed. Toward the right hand side of the image, one can see the lighter area of higher inertia terrain, which is the “different world,” lush with sedimentary rocks and spherules and veins, where the rover is now.

Crossing the contact: On this version of the map, an inset documents the change in the ground’s thermal properties that Curiosity recorded as it crossed the boundary or contact between terrain types on its Sol 120 and Sol 121 (Dec. 7 and Dec. 8, 2012). The inset graphs the range in ground temperature recorded each day by the Rover Environmental Monitoring Station (REMS) on Curiosity. Note that the arrival onto the lighter-toned terrain corresponds with an abrupt shift in the range of daily ground temperatures to a consistently smaller spread in values. This independently signals the same transition seen from orbit, and marks the arrival at well-exposed, stratified bedrock. The base image from the map is from the High Resolution Imaging Science Experiment Camera (HiRISE) in NASA’s Mars Reconnaissance Orbiter. Image credit: NASA / JPL-Caltech / UA / CAB (CSIC-INTA) / FMI

As Curiosity drove across the contact, it recorded the ground temperature, validating the fact that the temperature of materials with low thermal inertia changes significantly during the day, while the temperature of materials with high thermal inertia does not. “Suddenly, the high is not quite as high and the low is not quite as low,” confirmed Grotzinger. “It’s like we entered a whole different world and that’s exactly what’s happened,” he said.

Since then, the scientists have been burning the midnight oil, trying to take as much of this different world in before directing the rover to put drill to stone.

It’s been a little more than five months since Curiosity made its spectacular entry and landing at Gale Crater to begin its two-year prime mission. The team promptly decided to direct the rover to what they called the “triple junction” of three different rock types, an area they quickly dubbed Glenelg.

For the last several months, Curiosity has been slowly descending from its landing area plateau, Bradbury Landing, down the 500 meters or so to Glenelg, and the shallow depression that is Yellowknife Bay. It is here, in the Yellowknife Bay area of Glenelg, that the rover has been taking pictures with all its cameras that show a jaw-dropping range of diverse and unexpected features that have had the scientists marveling.

The MSL scientists have only begun to study the various targets in the area, but already team members have acquired evidence for past water in vein fills, evidence that some of the rocks were once saturated with water, and possibly much, much more. “The orbital signal drew us here, but what we found when we arrived has been a great surprise,” said Grotzinger. “This area had a different type of wet environment than the streambed where we landed, maybe a few different types of wet environments.”

There is a “high diversity of rock types” in this area, noted Michael Malin, of Malin Space Science Systems (MSSS). “Diversity is always a measure of the number of processes and the differently types of materials and this is a very diverse area,” he pointed out. “It’s one reason we are going slow. We want to characterize this diversity.”

On Mars as it is on Earth? This set of images shows the similarity of sulfate-rich veins Curiosity is seeing on Mars to sulfate-rich veins seen on Earth. The view on the left is a mosaic of two shots from the remote micro-imager on Curiosity’s Chemistry and Camera (ChemCam) instrument of Sheepbed rock in the Yellowknife Bay area of Mars. The image on the right is from the Egyptian desert on Earth. On Earth, calcium sulfates like gypsum form frequently in veins when relatively dilute fluid circulates at low to moderate temperatures. Image credit: NASA / JPL-Caltech / LANL / CNES / IRAP / LPGNantes / CNRS / LGLyon / Planet-Terre / Pierre Thomas

Among the outstanding features, science team members have noticed small holes or pits that have developed fracturing in this location. Such holes are “caused by sand infiltrating down into a crack and not being replenished from above,” Malin explained. “So it is likely that this is a relatively recent feature or sand would have filled the hole.” The fact that they have seen these holes in a variety of places in the area, “suggest the area is still undergoing some changes,” he said. That adds a whole other dimension to the history story the MSL team is trying to tell.

Meanwhile, other scientists have been looking at the rocks and soil and veins up close. Vein fills are immediately alluring to geologists because they indicate that water moved through the area. After examining some of the whitish filling in the veins with its laser-pulsing Chemistry and Camera (ChemCam) instrument, Curiosity returned data showing elevated levels of calcium, sulfur and hydrogen.

“These veins are likely composed of hydrated calcium sulfate, such as bassinite or gypsum,” reported Nicolas Mangold, ChemCam team member, of the Laboratoire de Planétologie et Géodynamique de Nantes, in France. “On Earth, forming veins like these requires water circulating in fractures.”

In Yellowknife Bay, the water “percolated through these fractured networks and then minerals precipitated to form the white material,” Grotzinger suggested. “This is first time we’ve seen something that is not just an aqueous environment, but one that also results in precipitation of minerals which is very attractive to us,” he noted.

The John Klein site contains a broad variety of rock textures that are right there for all to see in the pictures from the Mars Hand Lens Imager (MAHLI), “from conglomerate to sandstone to siltstone,” said R. Aileen Yingst, the imager’s deputy principal investigator, of the Planetary Science Institute, Tucson. “MAHLI has been having an absolute field day at this site, acquiring some images at the instrument’s best resolution of about 16 microns per pixel,” she said.

The fact that all the rocks appear to be sedimentary rocks is a significant finding and a big clue. “These rocks are telling us that Mars had environments actively depositing material here,” Yingst informed. “That means that other rocks had to be broken down into fragments and transported elsewhere and then turned into rocks, lithified. And that means Mars, at least in this location, was geologically active enough to have created such rocks.”

Curiosity took this close-up image of diverse grains on the surface of a Martian rock called Gillespie Lake inside Yellowknife Bay with its Mars Hand Lens Imager (MAHLI) on the rover’s Sol 132 (Dec. 19, 2012). The grains highlighted in this annotated version are about 1 to 2 millimeters (0.04 to 0.08 inches) long; the full frame is about 3 to 5 centimeters (1 to 2 inches) across. Some grains look crystal clear in appearance; others are darker and duller. And one, bottom arrow, looks to untrained observers to be a Martian “flower” or face. Image credit: NASA / JPL-Caltech / MSSS

Something that really stands out, Yingst noted, is the difference in grain size in the rocks Curiosity has been looking at in Yellowknife Bay and near the John Klein site. One odd, bud-shaped grain that dared shine with a distinctive gleam garnered Internet buzz as a “Martian flower.” Since then other conspiracy theorists have likened it to the “face on Mars.” But at the risk of bursting the bubble of the uninformed, it’s still but a grain, insofar as the MSL scientists see it.

Grain size, by geologists’ definition can refer to particles as large as “pebbles, cobbles, and larger,” Yingst pointed out and some of the sandstone rocks Curiosity has inspected feature grains up to about the size of peppercorns. Other rocks nearby are siltstone, sedimentary rocks that have a grain size in the silt range, finer than sandstone and coarser than claystones. Or, as Yingst put it, the grains are “finer than powdered sugar,” and differ significantly from pebbly conglomerate rocks that the rover found around Bradbury Landing.

The different grain sizes can tell scientists a lot about different transport conditions. “Grain size tells us is about the strength of the transport mechanism,” Yingst pointed out. “The stronger the transport mechanism, the larger the grains can be transported.”

Size, in other words, matters. Some of the samples that Curiosity and crew have viewed with MAHLI sport grain sizes in the geologists’ larger-than-sand size category, and that, Yingst noted, “usually indicates a fluid that is not air has transported the grains.”

The MAHLI team members have also noticed that some of the larger grains have been “knocked around and busted up,” and “rounded” by some process. “There is a difference in a grain being round and being rounded,” said Yingst. “Because these grains are relatively large on the sand-size spectrum, and even larger than that, starts to indicate to many of us that we’re looking at water,” she said.

In addition to the difference in size of the grains in each of the three main rock types the rover had found and examined, the distribution of the grains tells the scientists that “these three rocks were formed by different conditions,” said Yingst. Mars, therefore, was not only active, “but active in a diverse sense, with one or more transport mechanisms in play, all in all very exciting for drilling,” she concluded.

Curiosity is heading now for a flat-lying rock in the John Klein bedrock to drill. It will become the first target to be drilled for a sample on the MSL mission and the event will complete the last of the instrument check-outs on Curiosity. But the science team members are not quite ready to put the metal to the rock.

Curiosity’s turret: This graphic shows Curiosity’s 60-pound turret and the science instruments that are on it. The rover will soon be making use of its Dust Removal Tool (DRT) and 3-pronged Drill, which are components of the Sample Acquisition/Sample Processing and Handling subsystem, to drill into a rock in the John Klein site. It will be the first time a rover has actually drilled into a rock on Mars. Image Credit: NASA / JPL

Drilling into a rock to collect a sample will be Curiosity’s “most challenging” and “most significant engineering activity” since the rover landed last August. “It has never been done on Mars,” Cook reminded. “The drill hardware interacts energetically with Martian material [that] we don’t control. We’re really excited from engineering point of view, as well as scientifically. But we’re going to take it slow.”

The plan for the next few days calls for Curiosity to do a little more sampling in its current location, and then drive to a spot where the veins “stick up vertically,” said Grotzinger. “Our hope is that we can actually drive around on that surface and break them up and study them in cross-section and study them with ChemCam, APXS, and MAHLI, and get more information before we start drilling,” Grotzinger said.

“This lowest unit that [Curiosity is currently] at, in Yellowknife Bay, the very furthest thing we drove to, turns out to be kind of the jackpot unit here,” Grotzinger noted. “It is literally shot through with these fractures.” Plus, every place the rover has driven so far within this unit exposes other interesting features, like the filled veins. “In most cases, they’re covered with dust, but we’ve learned now even where dust is present to look carefully and [we] can still see fractures going along with these vein fills,” he said.

The spherules, which the team readily recognized from Opportunity’s landing site and elsewhere at Meridiani Planum as “blueberries,” are dispersed and strongly suggestive of being similar sedimentary concretions, according to Grotzinger. The MSL scientists “feel very confident” that these are sedimentary concretions, he said.

Spherules found: Curiosity took this image of the newfound spherules with its right Mast Camera (Mastcam) on its Sol 139 (Dec. 25, 2012). Spherules are common in this stratigraphic unit, called Sheepbed, which defines the lower part of the sequences of strata exposed in Yellowknife Bay. The MSL science team believes they are concretions, implying they formed in water that percolated through pores in the sediment. The image has been white-balanced to show what the rock would look like if it were on Earth. Image credit: NASA / JPL-Caltech / MSSS

“Put that together with the vein fills that look like they’re made out of hydrated calcium sulfate and basically [that tells us] these rocks were saturated with water,” Grotzinger said. “It could be there were several phases of this history of water,” he added. “We still have that to work out.”

The cross-bedding they see in a rock dubbed Shaler, conveniently recorded the passage of sediment in a moving current that created small dunes, Grotzinger said. “As the dunes migrated their avalanche faces [were] preserved in rock record as this cross-bedding.”

Since the grains there are too coarse for the wind to have pushed them along, the team also believes this rock formed in water. “The inclination of this cross-bedding is very divergent,” he added. “That’s another clue that we are looking at an aqueous origin here for these deposits.”

Shaler’s stream? Curiosity took this image of inclined layering, known as cross-bedding, in an outcrop called Shaler with its Mast Camera (Mastcam) on its Sol 120 (Dec. 7, 2012). The crossbedding seen here is indicative of sediment transport in stream flows. Currents mold the sediments into small underwater dunes that migrate downstream. When exposed in cross-section, evidence of this migration is preserved as strata that are steeply inclined relative to the horizontal, thus the term “cross-bedding.” The grain sizes here are coarse enough to exclude wind transport. The image has been white-balanced to show what the rock would look like if it were on Earth. Image credit: NASA / JPL-Caltech / MSSS

As Curiosity has journeyed down the hill over the past several months and into Yellowknife Bay, it has traveled through terrain with coarse conglomerates, into the finer conglomerates and sandstones, and now sits among the finer siltstones shot full of cracks and contain the concretions. “We’re not really sure what kind of environment this was formed in yet,” said Grotzinger. “Regardless of the environment, it’s shot through with these fractures. I think that came as a surprise to all of us, because we’re used to associating these fractures in concretions with what be older time periods in Mars’ history,” he said.

“We’ve entered into a quite different chapter,” Grotzinger said. “We’ve got overprinting diagenesis. We’ve got the evidence for the concretions and they could have formed after the primary depositional environment had long been buried, and the fractures which could possibly be an even later event.”

The task before the MSL scientists now is to arrange these events in relative order and then interpret them. “The relative order would be: primary depositional environment that transports the sediment; and then we have the overprinting diagenesis, and that could be two or three different phases here,” Grotzinger reiterated.

“We still have a lot of work to do. That’s why we’ve selected [John Klein] for drilling Grotzinger added. “There’s a real trend that is emerging here on our tour.”

Somewhere here: Curiosity will drill into a rock somewhere in here, the John Klein site, in Yellowknife Bay in Gale Crater, Mars. Enlargement A shows a high concentration of ridge-like veins protruding above the surface. Enlargement B shows that in some portions of this feature, there is a horizontal discontinuity a few centimeters or inches beneath the surface. The discontinuity may be a bed, a fracture, or potentially a horizontal vein. Enlargement C shows a hole developed in the sand that overlies a fracture, implying infiltration of sand down into the fracture system. The image was white-balanced to show what the rocks would look like if they were on Earth. Image credit: NASA / JPL-Caltech / MSSS

Once the exact spot on John Klein is chosen for drilling, Curiosity will first conduct a percussion test, and then drill a shallow hole and then drill deeper. It will gather powdered samples from inside the rock and use those to scrub the drill. Then, the rover will drill and ingest more samples from this rock, which it will analyze for information about its mineral and chemical composition.

Each sample will be small, equivalent to “about half an aspirin,” said Grotzinger. The scientists plan to sample the vein-filling materials, rocks, and the spherules to “try to assess in very general way,” he said. The rover will also look for organics.

“We’re still in the phase of just really being excited about the fact that we have evidence not just for water but something that precipitates minerals,” said Grotzinger. “We really have to drill into a rock in order to confidently know what the mineralogy but that is our definite goal here.”

If everything goes as planned, the drilling and sampling to come will reveal how the water that was apparently once in Yellowknife Bay, appeared there, because right now they don’t know what form the water took, whether it was pooled or flowing. “This is, I would guess, at least as complex a history for the involvement of water that we’ve seen anywhere on Mars so far,” Grotzinger suggested.

“The summary conclusion of the team is that if the spacecraft had gone long during entry, descent and landing (EDL) and landed on flank from Mount Sharp, and a unit from orbit would have predicted sulfates to have been present, and we would have found this – we would have been absolutely thrilled,” said Grotzinger. “This is something that we waited patiently for, and accepted a little bit of risk in driving to this destination. But this has been really exciting.”

Bring on the rock: Curiosity is ready to rock’n’drill. The Mars Science Laboratory (MSL) team has chosen the site and named it John Klein, after a colleague and former deputy project manager who passed away in 2011. The forthcoming drill will be the first time a rover has actually drilled into a rock on Mars. This is the last of the science instruments on the rover to go through check-out, so this will also be the very first time Curiosity will use her high-tech rock gouger on Mars. Image Credit: NASA / JPL-Caltech / Malin Space Science Systems

Over the longer term, Curiosity’s investigations at John Klein should add critical new pieces to the puzzle of what Mars was really like millions and billions of years ago.

For her part, Curiosity is good to go. The big new rover has been “working great” and hasn’t had any significant issues since landing, or even any more minor issues, Cook reported.

Curiosity would be hunkered down at John Klein for “a fairly extended period of time,’ Cook said. But he declined to define “extended period of time.”

The drilling to come is the last “first time” activity for Curiosity. The fact that the rover is in a “sweet spot” to dig into its first target, offers MSL science team members the opportunity “to make discoveries no one ever thought of before,” mused Grotzinger. “We’re thrilled and we can’t wait to get drilling on this stuff.”