NASA’s Curiosity rover is using a new experiment to better understand the history of the Martian atmosphere by analyzing xenon.
While NASA’s Curiosity rover concluded its detailed examination of the rock layers of the “Pahrump Hills” in Gale Crater on Mars this winter, some members of the rover team were busy analyzing the Martian atmosphere for xenon, a heavy noble gas.
Curiosity’s Sample Analysis at Mars (SAM) experiment analyzed xenon in the planet’s atmosphere. Since noble gases are chemically inert and do not react with other substances in the air or on the ground, they are excellent tracers of the history of the atmosphere. Xenon is present in the Martian atmosphere at a challengingly low quantity and can be directly measured only with on-site experiments such as SAM.
“Xenon is a fundamental measurement to make on a planet such as Mars or Venus, since it provides essential information to understand the early history of these planets and why they turned out so differently from Earth,” said Melissa Trainer, one of the scientists analyzing the SAM data.
A planetary atmosphere is made up of different gases, which are in turn made up of variants of the same chemical element called isotopes. When a planet loses its atmosphere, that process can affect the ratios of remaining isotopes.
Measuring xenon tells us more about the history of the loss of the Martian atmosphere. The special characteristics of xenon – it exists naturally in nine different isotopes, ranging in atomic mass from 124 (with 70 neutrons per atom) to 136 (with 82 neutrons per atom) – allows us to learn more about the process by which the layers of atmosphere were stripped off Mars than using measurements of other gases.
A process removing gas from the top of the atmosphere removes lighter isotopes more readily than heavier ones, leaving a ratio higher in heavier isotopes than it was originally.
The SAM measurement of the ratios of the nine xenon isotopes traces a very early period in the history of Mars when a vigorous atmospheric escape process was pulling away even the heavy xenon gas. The lighter isotopes were escaping just a bit faster than the heavy isotopes.
Those escapes affected the ratio of isotopes in the atmosphere left behind, and the ratios today are a signature retained in the atmosphere for billions of years. This signature was first inferred several decades ago from isotope measurements on small amounts of Martian atmospheric gas trapped in rocks from Mars that made their way to Earth as meteorites.
“We are seeing a remarkably close match of the in-situ data to that from bits of atmosphere captured in some of the Martian meteorites,” said SAM Deputy Principal Investigator Pan Conrad.
SAM previously measured the ratio of two isotopes of a different noble gas, argon. The results pointed to continuous loss over time of much of the original atmosphere of Mars.
The xenon experiment required months of careful testing at NASA’s Goddard Space Flight Center in Greenbelt, Maryland, using a close copy of the SAM instrument enclosed in a chamber that simulates the Mars environment. This testing was led by Goddard’s Charles Malespin, who developed and optimized the sequence of instructions for SAM to carry out on Mars.
“I’m gratified that we were able to successfully execute this run on Mars and demonstrate this new capability for Curiosity,” said Malespin.
NASA’s Mars Science Laboratory Project is using Curiosity to determine if life was possible on Mars and study major changes in Martian environmental conditions. NASA studies Mars to learn more about our own planet, and in preparation for future human missions to Mars. NASA’s Jet Propulsion Laboratory, a division of the California Institute of Technology in Pasadena, manages the project for NASA’s Science Mission Directorate in Washington.
NASA’s Low-Density Supersonic Decelerator (LDSD) project will be flying a rocket-powered, saucer-shaped test vehicle into near-space from the Navy’s Pacific Missile Range Facility on Kauai, Hawaii, in June.
The public is invited to tune in to an hour-long live, interactive video broadcast from the gallery above a clean room at NASA’s Jet Propulsion Laboratory in Pasadena, California, where this near-space experimental test vehicle is being prepared for shipment to Hawaii. During the broadcast, the 15-foot-wide, 7,000-pound vehicle is expected to be undergoing a “spin-table” test. The event will be streamed live on www.ustream.tv/NASAJPL2 on March 31, from 9 a.m. to 10 a.m. PDT. JPL’s Gay Hill will host the program while LDSD team members will answer questions submitted to the Ustream chat box or via Twitter using the #AskNASA hashtag.
The LDSD crosscutting demonstration mission will test breakthrough technologies that will enable large payloads to be safely landed on the surface of Mars, or other planetary bodies with atmospheres, including Earth. The technologies will not only enable landing of larger payloads on Mars, but also allow access to much more of the planet’s surface by enabling landings at higher-altitude sites.
More information about the LDSD space technology demonstration mission is online at:
The LDSD mission is part of NASA’s Space Technology Mission Directorate, which is innovating, developing, testing and flying hardware for use in future missions. NASA’s technology investments provide cutting-edge solutions for our nation’s future. For more information about the directorate, visit:
A team using the Sample Analysis at Mars (SAM) instrument suite aboard NASA’s Curiosity rover has made the first detection of nitrogen on the surface of Mars from release during heating of Martian sediments.
The nitrogen was detected in the form of nitric oxide, and could be released from the breakdown of nitrates during heating. Nitrates are a class of molecules that contain nitrogen in a form that can be used by living organisms. The discovery adds to the evidence that ancient Mars was habitable for life.
Nitrogen is essential for all known forms of life, since it is used in the building blocks of larger molecules like DNA and RNA, which encode the genetic instructions for life, and proteins, which are used to build structures like hair and nails, and to speed up or regulate chemical reactions.
However, on Earth and Mars, atmospheric nitrogen is locked up as nitrogen gas (N2) – two atoms of nitrogen bound together so strongly that they do not react easily with other molecules. The nitrogen atoms have to be separated or “fixed” so they can participate in the chemical reactions needed for life. On Earth, certain organisms are capable of fixing atmospheric nitrogen and this process is critical for metabolic activity. However, smaller amounts of nitrogen are also fixed by energetic events like lightning strikes.
Nitrate (NO3) – a nitrogen atom bound to three oxygen atoms – is a source of fixed nitrogen. A nitrate molecule can join with various other atoms and molecules; this class of molecules is known as nitrates.
There is no evidence to suggest that the fixed nitrogen molecules found by the team were created by life. The surface of Mars is inhospitable for known forms of life. Instead, the team thinks the nitrates are ancient, and likely came from non-biological processes like meteorite impacts and lightning in Mars’ distant past.
Features resembling dry riverbeds and the discovery of minerals that form only in the presence of liquid water suggest that Mars was more hospitable in the remote past. The Curiosity team has found evidence that other ingredients needed for life, such as liquid water and organic matter, were present on Mars at the Curiosity site in Gale Crater billions of years ago.
“Finding a biochemically accessible form of nitrogen is more support for the ancient Martian environment at Gale Crater being habitable,” said Jennifer Stern of NASA’s Goddard Space Flight Center in Greenbelt, Maryland. Stern is lead author of a paper on this research published online in the Proceedings of the National Academy of Science March 23.
The team found evidence for nitrates in scooped samples of windblown sand and dust at the “Rocknest” site, and in samples drilled from mudstone at the “John Klein” and “Cumberland” drill sites in Yellowknife Bay. Since the Rocknest sample is a combination of dust blown in from distant regions on Mars and more locally sourced materials, the nitrates are likely to be widespread across Mars, according to Stern. The results support the equivalent of up to 1,100 parts per million nitrates in the Martian soil from the drill sites. The team thinks the mudstone at Yellowknife Bay formed from sediment deposited at the bottom of a lake. Previously the rover team described the evidence for an ancient, habitable environment there: fresh water, key chemical elements required by life, such as carbon, and potential energy sources to drive metabolism in simple organisms.
The samples were first heated to release molecules bound to the Martian soil, then portions of the gases released were diverted to the SAM instruments for analysis. Various nitrogen-bearing compounds were identified with two instruments: a mass spectrometer, which uses electric fields to identify molecules by their signature masses, and a gas chromatograph, which separates molecules based on the time they take to travel through a small glass capillary tube — certain molecules interact with the sides of the tube more readily and thus travel more slowly.
Along with other nitrogen compounds, the instruments detected nitric oxide (NO — one atom of nitrogen bound to an oxygen atom) in samples from all three sites. Since nitrate is a nitrogen atom bound to three oxygen atoms, the team thinks most of the NO likely came from nitrate which decomposed as the samples were heated for analysis. Certain compounds in the SAM instrument can also release nitrogen as samples are heated; however, the amount of NO found is more than twice what could be produced by SAM in the most extreme and unrealistic scenario, according to Stern. This leads the team to think that nitrates really are present on Mars, and the abundance estimates reported have been adjusted to reflect this potential additional source.
“Scientists have long thought that nitrates would be produced on Mars from the energy released in meteorite impacts, and the amounts we found agree well with estimates from this process,” said Stern.
The SAM instrument suite was built at NASA Goddard with significant elements provided by industry, university, and national and international NASA partners. NASA’s Mars Science Laboratory Project is using Curiosity to assess ancient habitable environments and major changes in Martian environmental conditions. NASA’s Jet Propulsion Laboratory in Pasadena, California, a division of the California Institute of Technology, built the rover and manages the project for NASA’s Science Mission Directorate in Washington. The NASA Mars Exploration Program and Goddard Space Flight Center provided support for the development and operation of SAM. SAM-Gas Chromatograph was supported by funds from the French Space Agency (CNES). Data from these SAM experiments are archived in the Planetary Data System (pds.nasa.gov).
Observations by NASA’s Curiosity Rover indicate Mars’ Mount Sharp was built by sediments deposited in a large lake bed over tens of millions of years.
This interpretation of Curiosity’s finds in Gale Crater suggests ancient Mars maintained a climate that could have produced long-lasting lakes at many locations on the Red Planet.
“If our hypothesis for Mount Sharp holds up, it challenges the notion that warm and wet conditions were transient, local, or only underground on Mars,” said Ashwin Vasavada, Curiosity deputy project scientist at NASA’s Jet Propulsion Laboratory in Pasadena, California. “A more radical explanation is that Mars’ ancient, thicker atmosphere raised temperatures above freezing globally, but so far we don’t know how the atmosphere did that.”
Why this layered mountain sits in a crater has been a challenging question for researchers. Mount Sharp stands about 3 miles (5 kilometers) tall, its lower flanks exposing hundreds of rock layers. The rock layers – alternating between lake, river and wind deposits — bear witness to the repeated filling and evaporation of a Martian lake much larger and longer-lasting than any previously examined close-up.
“We are making headway in solving the mystery of Mount Sharp,” said Curiosity Project Scientist John Grotzinger of the California Institute of Technology in Pasadena. “Where there’s now a mountain, there may have once been a series of lakes.”
Curiosity currently is investigating the lowest sedimentary layers of Mount Sharp, a section of rock 500 feet (150 meters) high, dubbed the Murray formation. Rivers carried sand and silt to the lake, depositing the sediments at the mouth of the river to form deltas similar to those found at river mouths on Earth. This cycle occurred over and over again.
“The great thing about a lake that occurs repeatedly, over and over, is that each time it comes back it is another experiment to tell you how the environment works,” Grotzinger said. “As Curiosity climbs higher on Mount Sharp, we will have a series of experiments to show patterns in how the atmosphere and the water and the sediments interact. We may see how the chemistry changed in the lakes over time. This is a hypothesis supported by what we have observed so far, providing a framework for testing in the coming year.”
After the crater filled to a height of at least a few hundred yards, or meters, and the sediments hardened into rock, the accumulated layers of sediment were sculpted over time into a mountainous shape by wind erosion that carved away the material between the crater perimeter and what is now the edge of the mountain.
On the 5-mile (8-kilometer) journey from Curiosity’s 2012 landing site to its current work site at the base of Mount Sharp, the rover uncovered clues about the changing shape of the crater floor during the era of lakes.
“We found sedimentary rocks suggestive of small, ancient deltas stacked on top of one another,” said Curiosity science team member Sanjeev Gupta of Imperial College in London. “Curiosity crossed a boundary from an environment dominated by rivers to an environment dominated by lakes.”
Despite earlier evidence from several Mars missions that pointed to wet environments on ancient Mars, modeling of the ancient climate has yet to identify the conditions that could have produced long periods warm enough for stable water on the surface.
NASA’s Mars Science Laboratory Project uses Curiosity to assess ancient, potentially habitable environments and the significant changes the Martian environment has experienced over millions of years. This project is one element of NASA’s ongoing Mars research and preparation for a human mission to the planet in the 2030s.
“Knowledge we’re gaining about Mars’ environmental evolution by deciphering how Mount Sharp formed will also help guide plans for future missions to seek signs of Martian life,” said Michael Meyer, lead scientist for NASA’s Mars Exploration Program at the agency’s headquarters in Washington.
JPL, managed by Caltech, built the rover and manages the project for NASA’s Science Mission Directorate in Washington.
Reddish rock powder from the first hole drilled into a Martian mountain by NASA’s Curiosity rover has yielded the mission’s first confirmation of a mineral mapped from orbit.
“This connects us with the mineral identifications from orbit, which can now help guide our investigations as we climb the slope and test hypotheses derived from the orbital mapping,” said Curiosity Project Scientist John Grotzinger, of the California Institute of Technology in Pasadena.
Curiosity collected the powder by drilling into a rock outcrop at the base of Mount Sharp in late September. The robotic arm delivered a pinch of the sample to the Chemistry and Mineralogy (CheMin) instrument inside the rover. This sample, from a target called “Confidence Hills” within the “Pahrump Hills” outcrop, contained much more hematite than any rock or soil sample previously analyzed by CheMin during the two-year-old mission. Hematite is an iron-oxide mineral that gives clues about ancient environmental conditions from when it formed.
In observations reported in 2010, before selection of Curiosity’s landing site, a mineral-mapping instrument on NASA’s Mars Reconnaissance Orbiter provided evidence of hematite in the geological unit that includes the Pahrump Hills outcrop. The landing site is inside Gale Crater, an impact basin about 96 miles (154 kilometers) in diameter with the layered Mount Sharp rising about three miles (five kilometers) high in the center.
“We’ve reached the part of the crater where we have the mineralogical information that was important in selection of Gale Crater as the landing site,” said Ralph Milliken of Brown University, Providence, Rhode Island. He is a member of Curiosity’s science team and was lead author of that 2010 report in Geophysical Research Letters identifying minerals based on observations of lower Mount Sharp by the orbiter’s Compact Reconnaissance Imaging Spectrometer for Mars (CRISM). “We’re now on a path where the orbital data can help us predict what minerals we’ll find and make good choices about where to drill. Analyses like these will help us place rover-scale observations into the broader geologic history of Gale that we see from orbital data.”
Much of Curiosity’s first year on Mars was spent investigating outcrops in a low area of Gale Crater called “Yellowknife Bay,” near the spot where the rover landed. The rover found an ancient lakebed. Rocks there held evidence of wet environmental conditions billions of years ago that offered ingredients and an energy source favorable for microbial life, if Mars ever had microbes. Clay minerals of interest in those rocks at Yellowknife Bay had not been detected from orbit, possibly due to dust coatings that interfere with CRISM’s view of them.
The rover spent much of the mission’s second year driving from Yellowknife Bay to the base of Mount Sharp. The hematite found in the first sample from the mountain tells about environmental conditions different from the conditions recorded in the rocks of Yellowknife Bay. The rock material interacted with water and atmosphere to become more oxidized.
The rocks analyzed earlier also contain iron-oxide minerals, mostly magnetite. One way to form hematite is to put magnetite in oxidizing conditions. The latest sample has about eight percent hematite and four percent magnetite. The drilled rocks at Yellowknife Bay and on the way to Mount Sharp contain at most about one percent hematite and much higher amounts of magnetite.
“There’s more oxidation involved in the new sample,” said CheMin Deputy Principal Investigator David Vaniman of the Planetary Science Institute in Tucson, Arizona.
The sample is only partially oxidized, and preservation of magnetite and olivine indicates a gradient of oxidation levels. That gradient could have provided a chemical energy source for microbes.
The Pahrump HIlls outcrop includes multiple layers uphill from its lowest layer, where the Confidence Hills sample was drilled. The layers vary in texture and may also vary in concentrations of hematite and other minerals. The rover team is now using Curiosity to survey the outcrop and assess possible targets for close inspection and drilling.
The mission may spend weeks to months at Pahrump Hills before proceeding farther up the stack of geological layers forming Mount Sharp. Those higher layers include an erosion-resistant band of rock higher on Mount Sharp with such a strong orbital signature of hematite, it is called “Hematite Ridge.” The target drilled at Pahrump Hills is much softer and more deeply eroded than Hematite Ridge.
Another NASA Mars rover, Opportunity, made a key discovery of hematite-rich spherules on a different part of Mars in 2004. That finding was important as evidence of a water-soaked history that produced those mineral concretions. The form of hematite at Pahrump Hills is different and is most important as a clue about oxidation conditions. Plenty of other evidence in Gale Crater has testified to the ancient presence of water.
NASA’s Jet Propulsion Laboratory, a division of Caltech in Pasadena, manages the Mars Reconnaissance Orbiter and Mars Science Laboratory projects for NASA’s Science Mission Directorate in Washington, and built the Curiosity rover. NASA’s Ames Research Center, Moffett Field, California, developed CheMin and manages instrument operations. The Johns Hopkins University Applied Physics Laboratory, Laurel, Maryland, developed and operates CRISM. For more information about Curiosity, visit: