NASA’s Mars Science Laboratory landed Curiosity, the latest Mars rover, on the surface of Mars on Aug. 6. Although the rover has yet to start the research central to its mission, after two months on the Red Planet it has already found some new evidence for the existence of water on Earth’s planetary cousin.
Finding Fluvial Conglomerates
According to Prof. Steve Squyres ’81, astronomy, the Mars rover Curiosity found evidence of ancient flowing water on the surface of Mars last month. What make Curiosity’s finding different from previous findings of water on Mars are the type of rock from which the rover obtained its evidence, as well as the implications of the finding.
Curiosity discovered a piece of fluvial conglomerate, a substance synthesized from a river. The bed of a rapidly flowing stream has pebbles and other stones rounded by the water and sand. When these materials solidify into a rock, they form a fluvial conglomerate. Scientists do not need to perform intensive analysis to identify this type of stone; the examination from Mars for instance, was done entirely with cameras.
“It’s a form of rock that’s so distinctive. You just need eyes to see this in the field,” Squyres said.
The most identifiable characteristic of a fluvial conglomerate is the range of grain sizes in the rock.
“If you see a bunch of different grain sizes all jumbled together, it means that there was a very high-energy process taking place,” Squyres said. “Only strong flowing water will produce a rock made of rounded pebbles.”
Significance of the Streams
Although Curiosity has found evidence of water on Mars, it is not the first evidence scientists have discovered on the Red Planet. Direct evidence of water on the surface of Mars was first found in 1972 by the Mariner 9 space orbiter, which took pictures of riverbeds and canyons. More recently, the Spirit and Opportunity rovers found evidence of water in Martian stones in 2004. Squyres explained that the discovery of the fluvial conglomerate by Curiosity was a new form of evidence for a process scientists already know occurred on Mars.
“It’s not a surprise, but it’s cool to see,” Squyres said. “This is a cool thing and we happened to come across it in the first month of the mission.” Squyres is the Chairman of the NASA advisory Council and Principal Investigator for the Mars Exploration Rovers.
The primary focus of the Curiosity rover mission is to assess whether Mars has ever offered conditions favorable for microbial life. To accomplish this goal, Curiosity has an arsenal of advanced tools at its disposal.
Many instruments on the Curiosity rover set it apart from its predecessors. The new sampling system on Curiosity allows it to drill into rock and extract powdered samples. This system allows the rover to then place the extracted rock into the rover for chemical analysis. Two important instruments are used to conduct the analysis.
The first is SAM, or Sample Analysis at Mars. SAM is a system of instruments that can detect organic molecules at extremely low concentrations. This aids scientists in determining whether or not the environment on Mars is, or was, suitable for microbial life. The second instrument is CheMin, short for Chemistry and Mineralogy. This instrument uses X-ray powder diffraction to determine, with high precision, the minerals present in rock samples. Data from CheMin is useful in the search for biosignatures — indicators that the environment was habitable in the past.
ChemCam, or the Chemical Camera instrument, is a tool that allows scientists to fire a laser at a rock from a few meters away. The energy from the laser turns atoms from the rock into plasma, which scientists can analyze and use to determine the rock’s constituent elements.
“This instrument is used as a survey. You can shoot a series of rocks with the laser to get a rough idea of the elements present,” Squyres said.
A complementary tool to ChemCam is APXS, or the Alpha Particle X-Ray Spectrometer. APXS is an instrument located at the end of Curiosity’s robotic arm. This tool will be used to interpret the minerals that compose Martian rocks and help select materials for other instruments to sample.
“If you see something that stands out [from ChemCam], you can use [APXS] to get more specific information,” Squyres said.
The advanced technology aboard the Curiosity rover is currently in the checkout phase.
“It takes a long time to get good at this. Curiosity is a very complicated rover,” Squyres said.
Ground Zero: The Gale Crater
Gale, a crater on the surface of Mars, is the primary location of interest for the Curiosity mission. The crater contains a thick sequence of layered sedimentary rocks, which preserve detailed information about what conditions were like when they were laid down. According to Squyres, the sedimentary rock layers are particularly important to scientists.
“A geologist can look down into the Ithaca gorges and see the layered rocks,” he said. “From these rocks, we know that millions of years ago Ithaca was under a shallow sea. We can find fossils in Ithaca to prove this. We don’t expect to find fossils on Mars, but with basic training and tools we can read the rocks and the story they tell.”
Gale appeared to have a large amount of valuable information for scientists involved in the mission. Using spectrometers, scientists determined that the rocks in Gale contained clay minerals, which form in the presence of water. Because water is an essential component of life, Gale became the target location for the Curiosity expedition.
Although Curiosity has already landed within Gale, it is not yet at the stack of sedimentary rocks that scientists want to study.
“We need to drive kilometers before we get to the interesting stuff,” Squyres said. Because scientists are still in the engineering checkout phase of the mission, it may be some time before new discoveries are made.
“You don’t know when the discoveries will come. It will take years, maybe.” Squyres said. “Geology is like a forensic science and a geologist is like a detective looking for clues among the rocks.” he said.