2016 GHOST Rover Tests: Day 2

The team awoke fresh faced and ready to get back into their traverses on day 2. After a chat around breakfast, coffee, and stick throwing for our resident Martian dogs, Ruby, Becca, Sarah, and John prepared themselves to head back out and do their science teams’ bidding, and the TIGER team headed out to finish their in-situ investigations of the field site.


Left: Ruby Rover with our "Martians," Quinn and Neva; Center: The Tiger team, getting ready to head out for the day (from left: Barbara Cohen, Becky Williams, Tom Chidsey)

Left: Ruby Rover with our “Martians,” Quinn and Neva; Right: The Tiger team, getting ready to head out for the day (from left: Barbara Cohen, Becky Williams, Tom Chidsey)

While the rovers and instruments were out gathering data, the science teams remained at base camp, plotting their next moves. They had all of day 2, and a brief bit of time the following day to finish their investigations, and still had many questions to be answered, and quite a bit of ground to cover.


Left: Aileen (left) and Linda (right) planning their next moves; Right: Becca Rover (right) receiving instructions from Michelle (left)

Left: Aileen (left) and Linda (right) planning their next moves; Right: Becca Rover (right) receiving instructions from Michelle (left)


Throughout the day, the rovers and instruments struggled (but succeeded) to not give away anything when receiving instructions from their science teams. Everyone was wondering what the science teams would find, and if they would find the rock that had been unanimously named the “most interesting” unit of the whole site – a cap rock containing a carbonate and silica microbial mat that the Tiger team had named “SWAMM” (Siliceous WAvy Microbial Mat). The walkabout team (Geoff and Michelle) had encountered this unit on day 1, but luck had it that the location they imaged was not as nice of a structure, and they interpreted the linear features as fractures. Towards the end of day 2, the linear team (Aileen and Linda) happened to have Ruby take a mid-drive image in just the right location, and noticed a float rock from that unit. They squeezed in a detailed investigation of the float rock and surrounding area before the end of the day, which ended up re-focusing the remainder of their investigative efforts on day 3.


"Ruby Rover" and ChemMin (John Gemperline) gathering data on the fateful SWAMM float blocks.

“Ruby Rover” and “ChemMin” (John Gemperline) gathering data on the fateful SWAMM float blocks.


It’s important to note that in this case, Aileen and Linda’s serendipitous initial image of the SWAMM unit, and Michelle and Geoff’s alternate identification had nothing to do with the merits of linear vs. walkabout methodology, nor Michelle and Geoff’s abilities as planetary scientists. It was simply a matter of sheer dumb luck – which is always a factor in remote investigations. Aileen and Linda asked Ruby Rover to take a mid-drive image at just the right location at just the right time of day (with a good lighting angle to see a particular feature).  When taking her pictures, Ruby just happened to start low enough in her field of view that Linda and Aileen saw an interesting float block down near her feet. The other fateful part of this equation was that Linda was looking at the image. With decades of experience looking at exactly these structures, and a picture of a beautiful example sitting right in front of her, she was immediately interested. While Geoff is also very familiar with microbial mat structures, the location he and Michelle happened to get a picture of did not have the same distinctive features, and was easily missed. All of these variables were discussed at length at the end of the week, but for now, neither team knew what the other had seen.


Left: The less distinct SWAMM outcrop as imaged by the walkabout team - interpreted as fractures/fracture fill; Right: The characteristic SWAMM unit in a float block, first recognized as a potential biosignature by the linear traverse team.

Left: The less distinct SWAMM outcrop as imaged by the walkabout team – interpreted as fractures/fracture fill; Right: The characteristic SWAMM unit in a float block, first recognized as a potential biosignature by the linear traverse team.


The diagnostic SWAMM unit outcrop

The diagnostic SWAMM unit outcrop


Day 2 ended with discussion over a delicious dinner, Becca’s first s’more, and light up bocce ball.


Aileen, the "field mom," showing Becca how to make her first s'more.

Aileen, the “field mom,” showing Becca how to make her first s’more.


Other 2016 GHOST rover posts:

2016 Utah “Rover” Tests: Our Mission

2016 GHOST Rover Tests: Our Tools

2016 GHOST Rover Tests: Our Team

2016 GHOST Rover Tests: Day 1

2016 GHOST Rover Tests: Day 3

2016 GHOST Rover Tests: Day 1

The GHOST team arrived onsite Monday evening, and began our rover investigations early Tuesday morning. The day began with a coordination of teams, and laying out an initial work plan, by the team’s PI, Aileen Yingst.


Morning briefing

Morning briefing


This year’s TIGER team (our team of geologists free to roam the site) consists of Becky Williams, Barbara Cohen, and Tom Chidsey. Aileen Yingst, Linda Kah, and Ruby Schaufler make up the linear traverse rover team, while Michelle Minitti, Geoff Gilleaudeau, and Becca Thomas are conducting the walkabout rover investigations. Site god, Brian Hynek, is overseeing rover operations and providing logistical support. Sarah Black is operating the rovers’ “ChemCam” (VNIR), and John Gemperline is operating the “CheMin” (XRD/APXS).


Both rovers and ChemCam (Becca Thomas, Ruby Schaufler, and Sarah Black) were deployed into the field – given specific locations to stop at, and instructions for sampling/imaging. As the day progressed, samples were taken to analyze with XRD/APXS (John Gemperline), and the rovers and ChemCam continued along their traverses – making it about 1/3 to 1/2 of the way around the loop the team roughly sketched out – using remotely sensed data – before arriving at the site.


A linear traverse team meeting, and "Ruby Rover" surveying the site

A linear traverse team meeting at base camp (from left: Linda Kah, Aileen Yingst, and Ruby Schaufler), and “Ruby Rover” surveying the site

A walkabout team meeting, and "Becca Rover" surveying the site

A walkabout team meeting at base camp (from left: Becca Thomas, Geoff Gilleaudeau, and Michelle Minitti), and “Becca Rover” surveying the site


Day 1 operations spanned several Martian sols (days), and the rover teams began to characterize the lower half of the stratigraphy. Both teams kept the rovers and “ChemCam” extremely busy running back and forth between the field site and base camp, and the linear traverse team also ran several samples on the XRD/AXPS. Science team members fluctuated between happy, frustrated, excited, and confused throughout the day as their rover teams returned more data – often contradicting their expectations. Operations wound down as dinnertime approached, and the GHOST team pondered the next day’s moves to the sound of gale force winds howling outside their tents.


Other 2016 GHOST rover posts:

2016 Utah “Rover” Tests: Our Mission

2016 GHOST Rover Tests: Our Tools

2016 GHOST Rover Tests: Our Team

2016 GHOST Rover Tests: Day 2

2016 GHOST Rover Tests: Day 3

2016 GHOST Rover Tests: Our Team

We have an excellent team working on the GHOST project this year!  Check out their bios below:


Dr. Aileen Yingst, PI


IMG_9080Dr. R. Aileen Yingst is a Senior Scientist at the Planetary Science Institute, a research institution headquartered in Tucson, AZ. She is a Participating Scientist on the Mars Exploration Rover Mission and Deputy Principal Investigator for the Mars Handlens Imager instrument on the Mars Science Laboratory rover Curiosity. She is also an associate on the Dawn at Ceres mission. Other missions that Dr. Yingst has worked on include Dawn at Vesta, Mars Pathfinder, Mars Polar Lander, and Galileo. Dr. Yingst served as Director of the Wisconsin Space Grant Consortium for 14 years.


Dr. Yingst received her AB from Dartmouth College in Physics and Astronomy, and her M.Sc. and Ph.D. in Geological Sciences from Brown University. She lives with her family in Brunswick, Maine.


Dr. Barbara A. Cohen


IMG_9084Dr. Barbara Cohen leads the planetary science group at the Marshall Space Flight Center. Originally from upstate New York, Dr. Cohen earned her BS in Geology from the State University of New York at Stony Brook and her PhD in Planetary Science from the University of Arizona. She is now a planetary scientist at NASA’s Marshall Space Flight Center interested in geochronology and geochemistry of planetary samples from the Moon, Mars and asteroids.


Dr. Cohen serves within NASA representing science interests and capabilities within human spaceflight planning. She is a Principal Investigator on multiple NASA research projects, a member of the mission teams operating the Opportunity and Curiosity rovers on Mars, and the principal investigator for Lunar Flashlight, a lunar cubesat mission that will be launched in 2018. She is the PI for the MSFC Noble Gas Research Laboratory (MNGRL) and is developing a flight version of her noble-gas geochronology technique, the Potassium-Argon Laser Experiment (KArLE), for use on future planetary landers and rovers. She has participated in the Antarctic Search for Meteorites (ANSMET) over three seasons, where she helped recovered more than a thousand pristine samples for the US collection, and asteroid 6186 Barbcohen is named for her.


Dr. Cohen has been involved in GHOST team activities since their inception in 2010. She brings her experience on Mars rover operations and human field simulations to the GHOST rover team and planning activities, while gaining further geologic field skills.


Dr. Brian Hynek


IMG_9043Brian grew up in Iowa and paid for part of college selling sweet corn on the street corner.  Ever since he was little he had a love of rocks and space, so a career in planetary geology fit the bill.  After earning his Bachelors at the University of Northern Iowa, he taught high school physics and chemistry in an inner-city school in San Antonio, TX.  Then he headed to Washington University and worked with Roger Phillips on various Mars surface process issues.  Disliking the flatlands, he headed to Colorado as a post-doc at the the University of Colorado-Boulder.  He became a permanent research scientist, and later a tenured professor.


Brian’s research focuses on: (1) planetary geologic mapping of Mars and Mercury, (2) the fluvial history of Mars, (3) Mars volcanism, (4) astrobiology, (5) fieldwork studying hydrothermal systems on modern Earth and how they relate to relic systems on Mars.  The latter provides a chance to climb into active volcanoes around the world and understand how they work and how those on early Mars operated.


Dr. Linda Kah


IMG_9077Dr. Linda C. Kah is the Kenneth Walker Professor of carbonate sedimentology and geochemistry in the Department of Earth and Planetary Sciences at the University of Tennessee.


Linda grew up in the Cuyahoga Valley region of northeastern Ohio and has been pursuing her love of science since kindergarten, when she announced her intention to become a geologist. It only seemed natural….her mom (a polymer chemist) and dad (a metallurgist) had met in a geology class in college and had gone fossil hunting as a first date!  After growing up immersed in nature, Linda received concurrent BS and MS degrees in Geology from MIT in 1990, followed by a PhD in Earth and Planetary Sciences from Harvard in 1997.  Following postdoctoral research at the University of Missouri, she joined the faculty at the University of Tennessee in 2000.


In her research, Dr. Kah combines her knowledge of sedimentary geology, isotope geochemistry, and biology to decipher how ecosystems arise on planets and how biological processes are interacting with, and are recorded in, geological systems. Dr. Kah’s research has taken her to some of the most remote places on Earth, including more than 120 weeks of field work in the Canadian Arctic, Saharan West Africa, the Ural mountains of Russia, China, and the high Andes of Argentina. In 2004, Dr. Kah set her sites on an even more remote field locality when joined Malin Space Science Systems in their proposal to supply the Mars Science Laboratory mission with the MARDI, MAHLI, and Mast Cameras. Since August 2012, she has worked as a science team member and payload uplink lead in Curiosity’s investigation of Gale Crater.


This is Dr. Kah’s first involvement with GHOST team activities.  Fundamentally, Dr. Kah brings to the table her skill as a field geologist.  The last few years of rover mission activities, however, have opened her eyes to the necessity of human field simulations as a mechanism to advance our rover planning abilities.


Dr. Michelle Minitti


IMG_9074Michelle Minitti, a Senior Scientist at the Planetary Science Institute, began her academic career at the University of Arizona where she earned a B.S. in materials science and engineering in 1995. Through a planetary science elective at the University of Arizona, she discovered she could apply her materials science training to the study of planetary materials, and thus a career in geology was born. Michelle earned her M.Sc. (1998) and Ph.D. (2001) in geological sciences from Brown University, investigating a range of topics including the effect of impact shock on water and hydrogen isotopes in amphibole and potential links between the Martian meteorites and lithologies detected by both landed and orbital Mars missions.


After a one year postdoctoral fellowship at the Carnegie Institute for Science Geophysical Laboratory in 2001, Michelle began a ten-year tenure at Arizona State University (ASU). She gained research and management experience through a variety of roles including a postdoctoral research associate position in the NASA Astrobiology Institute, the interim and assistant director of the Center for Meteorite Studies and a faculty research associate. At ASU, her research interests focused on the interpretation of spectral and chemical data from orbital and landed Mars missions, but she also started her own involvement with a Mars mission as a Co-Investigator on the Mars Hand Lens Imager (MAHLI) investigation for the Mars Science Laboratory (MSL) mission.


Since the successful landing of MSL’s Curiosity rover in Gale crater, Mars in 2012, Michelle has been involved with both MAHLI and the Mars Descent Imager (MARDI), supporting strategic planning and tactical use of both cameras through operations roles, and analyzing and interpreting their data to further our understanding of the Gale crater landing site.


Michelle joins the GHOST team for the first time, looking to apply her experience with Curiosity rover operations to the field test. In turn, she seeks to apply lessons learned in the field to maximizing the science return of Curiosity and future landed missions.


Dr. Rebecca Williams


IMG_9051“Why?” has been Becky’s favorite question since three years of age as she interrogated her geologist father conducing his dissertation research in Montana. To this day, she still enjoys teasing out answers from the rock record at field sites in Utah, California, Australia and the Atacama Desert in Chile. She received her training at Franklin & Marshall College for undergraduate and pursued a doctoral degree in planetary geology at Washington University in St. Louis. Becky is a senior scientist with the Planetary Science Institute and works from Madison, Wisconsin where she resides with her husband and two daughters. Becky is a science team member of the THEMIS and CTX instruments and a participating scientist with the Mars Science Laboratory Curiosity rover. This is Becky’s first GHOST mission as part of the Tiger Team. She is looking forward to advancing protocols that maximize the scientific return from future rover missions.


Tom Chidsey


IMG_9085Tom grew up in the Washington DC metropolitan area. As the “senior citizen” of the GHOST mission, Tom followed the early days of human space exploration throughout his childhood, from when in the third grade he watched Alan Sheppard blastoff in the Redstone rocket to the first landing on the moon to help celebrate his 17th birthday, July 20, 1969. Tom has been fascinated with planetary geology and is thrilled to help the Tiger Team of the GHOST mission. Tom graduated with Bachelor and Master of Science degrees in geology from Brigham Young University. For his thesis, Tom investigated the complex structures and mapped the surface geology of the House Range in western Utah under the direction of the late, great Lehi Hintze known as the “Father of Utah Geology.” After spending 13 years in the petroleum industry with Exxon in South Texas and Questar in the Rocky Mountain region, Tom joined the Utah Geological Survey in 1989 where he is a Senior Scientist. His research includes petroleum reservoir studies (especially carbonates including microbialites), oil and gas field summaries, carbon dioxide capture and sequestration, the geology of Utah’s parks, and outcrop reservoir and occasional Mars analog investigations. The Tiger Team is drawing on Tom’s many years of experience and extensive knowledge of Utah geology to assist with the GHOST mission.


Dr. Rebecca Thomas


IMG_9070Dr. Rebecca Thomas is a Research Associate in planetary geology at the Laboratory for Atmospheric and Space Physics at the University of Colorado, Boulder.


Rebecca grew up in Oxfordshire in the UK, and took a rather circuitous route to planetary geology. She initially gained her Masters in Archaeology from Edinburgh, Scotland, in the late 90s. She then spent 10 years as an internet entrepreneur in the Caribbean and Malta, before giving in to the urge for discovery and returning to the UK to gain a BSc in Earth Sciences from Birkbeck College, University of London. During these studies it became clear to her that she found the geology of other planets even more fascinating than that of our own, so, for her PhD, she moved to The Open University, UK, to research the planet Mercury. Using brand-new data from NASA’s MESSENGER spacecraft, then orbiting the planet, she made few discoveries about surprisingly recent explosive volcanism and active sublimation from Mercury’s surface.


On achieving her PhD, a life-long interest in Mars and a strong interest in future human presence there led her to seek a post-doctoral position where she could broaden her research to the Red Planet. Luckily, the GHOST mission’s Site God, Brian Hynek, was seeking a postdoctoral researcher to work on both Mercury’s and Mars’ geology in Boulder, CO – a perfect fit.  She has been at LASP since January 2016, getting stuck in to projects on both planets.


She will be lending her legs to the GHOST team as a rover (endeavoring to keep her geological interpretations to herself!) and looks forward to seeing how both the decision-making processes within teams and the trade-offs in time and science between teams pan out.


Dr. Geoff Gilleaudeau


IMG_9072Geoff was born in Queens, New York, and did not have natural sciences on his radar at all as a kid. He went to Binghamton University in rural upstate New York as an undecided major, and left with a newfound love for the outdoors and geology. A cross-country trip to Death Valley cemented his love for travelling and field geology. He did a PhD in sedimentology, stratigraphy, and geochemistry at the University of Tennessee, with an interest in the Precambrian Earth. Specifically, he became interested in the history of animal evolution, ocean chemistry, and the history of Earth surface oxygenation as recorded in sedimentary rocks. After his PhD, he taught Earth System History at Bucknell University in Pennsylvania, before moving on to a postdoc on metal isotope geochemistry at the University of Copenhagen in Denmark. After two years in Scandinavia, Geoff is currently a NASA astrobiology postdoctoral fellow at Arizona State University. He brings an expertise in field sedimentology and stratigraphy to the GHOST team as his first experience in planetary geoscience.


Sarah Black


IMG_9065Sarah Black received her Geology BA in 2004, and Geology MS in 2006 – both from the State University of New York at Buffalo.  For her MS, Sarah worked with Dr. Tracy Gregg (who is 100% responsible for luring Sarah away from her original undergraduate plan of biomedical science and stem cell research – thank goodness), and conducted a morphological and statistical analysis of volcanoes on Io – the innermost moon of Jupiter.


After completing her MS, Sarah worked at Malin Space Science Systems, where she targeted the Mars Orbiter Camera (MOC) on the Mars Global Surveyor (MGS) spacecraft, and the Context Camera (CTX) on the Mars Reconnaissance Orbiter (MRO) spacecraft.  She then returned to her hometown in Upstate New York, where she taught introductory geology courses at Skidmore College for several years.


Sarah is currently a third year Ph.D. student at the University of Colorado Boulder in Brian Hynek’s Surface Processes And Continuing Evolution of Contemporary Analogous TerraneS (SPACECATS) lab.  For her dissertation research, Sarah is studying hydrothermal systems in Costa Rica and Iceland, which may be useful analogs for early Mars.  Sarah’s current research focuses on instrumentation techniques (VNIR, XRD, Raman), mineralogy, geochemistry, and astrobiology.  She is also interested in physical volcanology, computer modeling, and geological mapping.  Sarah has fallen in love with fieldwork over the years, and has been fortunate enough to travel to Hawaii, Yellowstone, all over the desert southwest, New Zealand, Costa Rica, and now Iceland, and call it “work.”


Besides the trials and tribulations of grad school, Sarah enjoys time with her two crazy dogs, and exploring the beautiful trails all over Colorado.  She is currently training for her first 100 mile running race, because she does stupid things.


For this year’s GHOST project, Sarah will be operating the VNIR instrument and enjoying wandering the Utah desert.


John Gemperline


IMG_9067John Gemperline is beginning a PhD program in planetary geology at CU Boulder in the Fall of 2016 with Dr. Hynek.  He studied geology and geography as an undergraduate at both East Carolina University and the University of North Carolina at Greensboro, and has also dabbled in classics and music.


John first began studying planetary geology in middle school when his science club participated in the Mars Student Imaging Project in 2002.  He interned at NASA Goddard Spaceflight Center in 2012 where he studied craters around Martian outflow channels and visited Mars analog sites in Arizona.  For the past year John has been mapping the area around the Rembrandt impact basin and studying lobate scarps on Mercury.


While sitting in on Dr. Hynek’s class, John was able to visit a previous GHOST field site on a class field trip that involved each student drawing a nominal rover traverse.  John is excited to be the XRD instrument and not on rover ops after his own imaginary rover ended up driving off a cliff last fall.  He has been honing his XRD skills and will be providing crystallographic and mineralogical analysis for the two rover teams and Tiger team.


Ruby Schaufler 


IMG_9045Ruby is an undergraduate student at Gustavus Adolphus College in St.Peter MN.  Ruby was brought on to the GHOST team this fall and plans to do some additional research with the team for her senior thesis.  She will be working as a rover in the field this week and is looking forward to meeting everyone!







Dr. Julie Bartley


Julie Bartley grew up in Southern California and completed an AB in Chemistry at Bryn Mawr College and an MS in Chemistry at UCLA before becoming a geologist and earning a PhD in Geology at UCLA. Following postdoctoral research at NASA Ames Research Center and Harvard University, Julie joined the faculty at the University of West Georgia. She moved to Gustavus Adolphus College in 2009, where she is now an associate professor and chair of the Geology Department.


Julie’s research interests lie in the interface of biology, chemistry, and sedimentary processes on the early Earth. She studies microbial ecosystems, the fossilization of microbes, and the geologic structures left behind by microbes. This interest in ancient and microbially-dominated ecosystems has taken her to saline lakes in the Andes and to spectacular microbial reefs of West Africa and the Canadian Arctic. Recently, she’s worked on relatively young microbialites in Wyoming and relatively old ones in southern Ontario. This is her first GHOST project, and she’s sitting out this round of fieldwork because her hobby, judo, got in the way of geology in the form of a broken leg. She’ll remain firmly “planet-side” as the GHOST team explores its Mars-analog region.


Other 2016 GHOST rover posts:

2016 Utah “Rover” Tests: Our Mission

2016 GHOST Rover Tests: Our Tools

2016 GHOST Rover Tests: Day 1

2016 GHOST Rover Tests: Day 2

2016 GHOST Rover Tests: Day 3


2016 GHOST Rover Tests: Our Tools

Instruments onboard the MSL rover in Gale Crater (Image: JPL/NASA)

Instruments onboard the MSL rover in Gale Crater        (Image: JPL/NASA)

While we are out in the field pretending to be Mars rovers, we need to be able to gather the same kind of data that we acquire on Mars.  There are many impressive instruments on both Spirit and Opportunity – the Mars Exploration Rovers (MER) – as well as Curiosity – the Mars Science Laboratory (MSL).  For this week, we are limited to those instruments which we are capable of taking out into the field, and many of the MER and MSL instruments do not have field-portable analog instruments here on Earth.


Fortunately, we have two field-portable instruments that are excellent analogs for those on board the current Mars rovers:


Visible Near Infrared Spectroscopy (VNIR)


VNIR spectroscopy measures the spectrum of light that is reflected by a material between 0.35 and 2.5 um (350 – 2500 nm).  This range of wavelengths covers all of the visible light spectrum (0.38 to 0.78 um) and into the near-infrared wavelengths.

The electromagnetic spectrum. (Image source)

The electromagnetic spectrum. Note: Here, visible light wavelengths are written as nm. (Image source)

Every material on Earth (or Mars, in this case) has its own characteristic pattern in the wavelengths of light that it reflects.  A spectrometer measures the reflected light coming off a material, and displays it as a reflectance spectra:


Reflectance spectra of hematite - a common iron-oxide mineral.

Reflectance spectra of hematite – a common iron-oxide mineral.  Hematite appears red to the human eye because it reflects light around 0.7 um – the red wavelength in the visible light spectrum.  The light that it reflects at longer wavelengths is not visible to the human eye.

The dips in the spectra are called absorption bands, and are due to the material – whatever it may be – absorbing light at that particular wavelength.  The wavelengths that a material absorbs are determined primarily by its chemical composition, crystal structure, and grain size.  By comparing the reflectance spectra from a material of unknown composition – such as a rock on Mars – to reflectance spectra of known composition (called library or reference spectra), we can match each of the absorption features and determine the composition of our mystery material.


VNIR on Mars


CRISM image of Jezero crater showing variations in mineralogy represented as different colors. (image credit: NASA/JPL/JHUAPL/MSSS/Brown University)

CRISM image of Jezero crater showing variations in mineralogy represented as different colors. (image credit: NASA/JPL/JHUAPL/MSSS/Brown University)

VNIR is a commonly used tool for planetary science, and is used at a variety of scales.  VNIR instruments are on satellites, such as the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) on the Mars Reconnaissance Orbiter (MRO), and the Observatoire pour la Minéralogie, l’Eau, les Glaces et l’Activité (OMEGA) on the Mars Express (MEx) orbiter.  VNIR from orbit allows planetary scientists to gather compositional data across a wide area, up to a resolution of about 18 m/pixel (for CRISM).  The ability to measure large areas provides excellent context for in-situ (ground-based) measurements, allows us to gather compositional data where we don’t have ground-based rovers, and can show large scale variations in surface composition.  However, orbital VNIR measurements do not allow us to observe small-scale details, since all the materials in that 18 meter wide pixel add together into one spectra, and often things are lost.  Additionally, orbital measurements have to deal with the effects of looking through Mars’ atmosphere.  The gas (primarily CO2) and dust in the atmosphere also absorb light energy and need to be corrected for before any surface compositions can be identified.


In addition to orbital measurements, VNIR is also incorporated into each of the current rover cameras.  Both the MER PanCam and MSL ChemCam (via the passive LIBS function) are capable of taking images in the VNIR spectral window.  These ground-based instruments allow planetary scientists to investigate rock compositions on a much finer scale than what we can see from orbit, which allows us to delve deeper into the geologic history of Mars.  These rover-mounted spectrometers are the ones we are simulating in Utah.


Variations in mineralogy across Home Plate in Gusev Crater, measured by the Spirit rover's PanCam instrument. (Figure adapted from Schmidt et al., 2009)

Variations in mineralogy across Home Plate in Gusev Crater, measured by the Spirit rover’s PanCam instrument. A: False color image of Home Plate; B: Various mineralogies – interpreted from the measured spectra – represented by different colors (see original paper for details); C; Pie charts showing the changes in mineralogy across Home Plate, based on the sampled spectra.  (Figure adapted from Schmidt et al., 2009)


Our instrument: Field-portable VNIR


The TerraSpec Halo VNIR instrument (image source: ASD, Inc.)

The TerraSpec Halo VNIR instrument (image source: ASD, Inc.)

The VNIR spectrometer we will be using this week is the TerraSpec Halo from ASD, Inc.  This instrument also measures reflectivity – just like the MER PanCam and MSL ChemCam, and allows us to make the same types of geological interpretations as the planetary scientists who are working with the Mars rover data.


To sample a rock, the sensor of the Halo gun is placed in contact with the material.  When the trigger is pulled, the Halo shines a light onto the rock, and measures what wavelengths are reflected back.  The internal computer then cycles through all the library (known) spectra and finds those that best match the sample.  Very often, more than one spectra can be considered a match, since rocks often consist of more than one mineral.  If further analysis (or confirmation) is needed, the spectra are then exported and manually investigated in the spectral analysis software, ENVI.


MER and MSL rovers are capable of gathering VNIR spectra across a wide field of view, such as a large rock outcrop, while the Halo’s contact probe only samples a small circle (about 1 cm diameter).  To simulate PanCam and ChemCam’s ability to gather data on the outcrop scale, we will gather several spectra both horizontally and vertically across any outcrops of interest.  This will allow our science team to see any spatial variations in the mineralogy, just like we do on Mars.


X-Ray Diffraction (XRD)


X-Ray diffraction also measures the mineralogical composition of a sample, but through a different process, and on a very small scale.  To analyze a sample with XRD, it must first be ground into a powder.  On Mars, this can be done with the MSL drill.  The powdered sample is then loaded into the XRD instrument, where it is bombarded with x-rays.


When a sample is shot with x-rays, the majority of the x-rays are scattered.  But when the x-rays hit the sample at just the right angle (which is dependent on the crystal structure of the material), the diffracted x-rays result in constructive interference.  (Start here for a more detailed description, including Bragg’s Law.)  This constructive interference is recorded as peaks in the resulting diffraction pattern, such as the one seen here:


The X-Ray Diffraction pattern for quartz - a common silicate mineral. (image source: RRuff)

The X-Ray Diffraction pattern for quartz – a common silicate mineral. (image source: RRuff)


Just like with VNIR, each mineral has its own characteristic diffraction pattern.  For XRD, the diffraction pattern is dependent on the crystal structure of the mineral – specifically, the spacing of the atoms (the “d-spacing”) within the crystal.  Because XRD is so sensitive to slight variations in the atomic structure of a mineral, it is useful for identifying elemental substitution, which can subtly alter the d-spacing within a crystal.


XRD is a commonly used tool for sample identification because it provides a bulk rock analysis (the act of grinding up the rock should homogenize the sample), does not require a large amount of material for analysis, and can be used to identify complex samples that may contain several different minerals.  One place XRD tends to fall short is phyllosilicate (clay) identification.  The complex and often poorly-ordered crystal structure of phyllosilicates, combined with the abundance of elemental substitution within their structures makes identification very difficult with this analytical method.  Often, XRD is used in conjunction with VNIR (which is excellent for phyllosilicate identification)  in order to get a more complete analysis.


XRD on Mars


The MSL CheMin instrument is currently conducting XRD analysis in Gale Crater.  CheMin has the ability to do 74 XRD analyses, and possibly more, since the sample cells (where the powder is loaded to be analyzed) can potentially be re-used beyond their original design.


For analysis, powdered drill tailings are loaded into the body of the rover where CheMin is located.  A small amount of sample is loaded into a sample cell and inserted into the instrument, where it is shot with a high-powered x-ray and the diffractogram is gathered.


The Buckskin drill hole and corresponding XRD pattern. Peaks marked with a T are attributed to the mineral tridymite - a high temperature polymorph of SiO2 (image source: JPL/NASA)

The Buckskin drill hole in Gale Crater, and corresponding XRD pattern. Peaks marked with a T are attributed to the mineral tridymite – a high temperature polymorph of SiO2. (image source: JPL/NASA)


Our instrument: Field-portable XRD


The Terra Portable XRD instrument deployed in the field.

The Terra XRD deployed in the field.

The XRD instrument we will be using this week is the Terra Portable XRD from Olympus.  This instrument was designed in conjunction with CheMin, with the goal of being a functional analog instrument for planetary geologists to use here on Earth.


To analyze a sample with the Terra, it must first be ground into a powder.  Once the sample is powdered, a small amount (~ 15 mg) is loaded into one of the sample windows, and then inserted into the instrument.  While the sample is being hit with x-rays, the Terra also vibrates it to ensure that the crystals are being hit from every possible angle, which will provide the most accurate diffraction pattern.


During analysis, the diffraction pattern is displayed on the associated laptop, which connects to the Terra via its own wireless signal.  Once analysis is complete, the diffraction pattern may be saved, and further analyzed in software such as XPowder.


Other 2016 GHOST rover posts:


2016 Utah “Rover” Tests: Our Mission

2016 GHOST Rover Tests: Our Team

2016 GHOST Rover Tests: Day 1

2016 GHOST Rover Tests: Day 2

2016 GHOST Rover Tests: Day 3

2016 Utah GHOST “Rover” Tests: Our Mission

On April 18th, a group of us will descend on a mystery location in Utah where will will spend five days roaming around the desert pretending to be Mars rovers for the GeoHueristic Operational Strategies Testing (GHOST) program.  These rover tests have no actual rovers, as those are extremely expensive and logistically difficult to get out in the field.  Rather, we have people pretending to be the rovers, and others (myself included) acting as the instruments onboard those rovers.


This year’s objective is to assess the effectiveness and efficiency of utilizing a walkabout approach to investigate the field site, instead of the commonly-used linear traverse.


Walkabout approaches simulate what a human geologist would do if plunked down at a site, and tasked with interpreting the geologic history of that area.  Instead of starting to take detailed measurements, samples, etc. right off the bat, a geologist would first walk around the whole area to get a feel for what is there.  They would then go back to key points and make more detailed observations to fill out the data set.  This method was first utilized on Mars just recently, when Curiosity reached Pahrump Hills in Gale Crater.


Curiosity's walkabout at Pahrump Hills (image source: JPL/NASA)

Curiosity’s walkabout at Pahrump Hills (image source: JPL/NASA)


Linear traverses have been used by Mars rovers because they allow the science team to go to a spot, gather data, and quickly move along to a new location, never to return again.  While this may be faster, it might not be the best method, since something far more interesting/useful may go unnoticed if an initial site survey is not done.


Our 2016 field test will have three teams: one team of human geologists, and two separate “rover” teams.  One rover team will conduct a linear traverse of our field site, while the other will assess the site using a walkabout approach.  Both rover teams have “science teams” (AKA: Earth-based humans) who will be sequestered at base camp – unable to wander the site themselves.  The science teams will have to interpret the geologic history of the area based solely on the data they get from their “rover” – just like planetary geologists do for Mars.  At the end of the week, the rover teams will compare their results with each other, as well as with the team of human geologists that were allowed to wander the field site (and should therefore have the most complete picture).  The accuracy and completeness of the rover interpretations will be assessed in conjunction with how much time their analysis would have taken if this were an actual Mars rover and science team.  We may find that a walkabout approach results in a more complete geologic interpretation and is worth the extra bit of time it takes to double back to a location, which could influence how we conduct rover operations in the future.


Other 2016 GHOST rover posts:

2016 GHOST Rover Tests: Our Tools

2016 GHOST Rover Tests: Our Team

2016 GHOST Rover Tests: Day 1

2016 GHOST Rover Tests: Day 2

2016 GHOST Rover Tests: Day 3