History of Martian exploration
Since 1962, interplanetary spacecraft have been launched to Mars for exploration of the most earth-like planet in our solar system. The first two spacecraft to successfully land and operate on Mars were the Viking spacecraft launched to Mars in 1975. These craft returned high-resolution images of the Martian surface and were used to characterize the structure and composition of the atmosphere and surface, and of course, search for evidence of life on Mars. The first Mars mission to use spectrometers and imagers to hunt for evidence of past or present water and volcanic activity on the planet was the 2001 Mars Odyssey orbiter.
Mars Rover
What is the structure of Mars?
Both Earth and Mars are terrestrial planets (also called telluric planets) composed primarily of silicate rocks or metals. Over time different constituents of a planetary body, because of their physical or chemical behavior, develop into compositionally distinct layers; the denser materials of a planet such as iron sink to the center, while less dense materials rise to the surface, generally in a magma ocean. Such a process tends to create a core and mantle. Sometimes a chemically distinct crust forms on top of the mantle, and volcanic activity brings magma materials to the surface of the planet and lava.
Basalt is the most common volcanic (igneous) rock type on Earth, being a key component of oceanic crust as well as the principal volcanic rock in many mid-oceanic islands. The dark areas visible on Earth’s moon, the lunar maria, are plains of basaltic lava flows. The surface of Mars is primarily composed of tholeiitic basalt, (one of two main magma series in igneous rocks), although parts are more silica-rich than typical basalt and may be similar to andesitic rocks on Earth.
On October 17, 2012, the NASA Curiosity rover on the planet Mars at “Rocknest” performed the first X-ray diffraction analysis of Martian soil. The results from the rover’s CheMin analyzer revealed the presence of several minerals, including feldspar, pyroxenes and olivine, and suggested that the Martian soil in the sample was similar to the “weathered basaltic soils” of Hawaiian volcanoes.
Martian rocks
Rocks on the Martian surface and in the crust consist predominantly of minerals that crystallize from magma. Most of our current knowledge about the mineral composition comes from spectroscopic data from orbiting spacecraft, in situ analyses of rocks and soils from six landing sites, and study of the Martian meteorites. Volcanic structures and landforms cover large portions of the Martian surface. The most conspicuous volcanoes on Mars are located in Tharsis and Elysium. Geologists think one of the reasons volcanoes on Mars were able to grow so large is that Mars has fewer tectonic boundaries in comparison to Earth. Lava from a stationary hot spot was able to accumulate at one location on the surface for hundreds of millions of years.
Studying Mars with analogous samples
The availability of Earth-bound terrestrial sites that are analogous to Martian geologies allow researchers to investigate Mars using knowledge gained on Earth. Among the terrestrial analog sites for Mars is Craters of the Moon National Monument in Idaho, U.S.A. Craters of the Moon National Monument is home to over 60 basalt lava flows. This area contains the largest basaltic lava field in the contiguous United States composed mostly of lava from current geological time period, the Holocene epoch. The area contains the best examples of open rift cracks in the world, including the deepest known on Earth at 800 feet (240 m). There are excellent examples of almost every variety of basaltic lava.
Many of the basaltic rocks measured by rovers on Mars are thought to have experienced chemical weathering during aqueous interactions; however, few basalt weathering rates exist for earth environments to help interpret these processes. Craters of the Moon represents a basalt flow chronosequence, and therefore allows for the investigation of basalt weathering as a function of time.
Sources of analogous Martian rock samples
Analogous to the relatively cold and dry modern Mars, the Craters of the Moon National Monument is located on the Snake River Plain, a volcanic province that was created by a series of cataclysmic caldera-forming eruptions that started about 15 million years ago. The region implicates a migrating hotspot thought to now exist under Yellowstone Caldera in Yellowstone National Park. This hot spot was under the Craters of the Moon area some 10 to 11 million years ago but ‘moved’ as the North American Plate migrated southwestward. Pressure from the hot spot heaves the land surface up, creating fault-block mountains. After the hot spot passes the pressure is released and the land subsides.
Leftover heat from this hot spot was later liberated by Basin and Range-associated rifting and created the many overlapping lava flows that make up the Lava Beds of Idaho. The largest rift zone is the Great Rift; it is from this ‘Great Rift fissure system’ that Craters of the Moon, Kings Bowl, and Wapi lava fields were created. The Great Rift is a National Natural Landmark.
Several Crater of the Moon flow basalts, including rocks of the over 18,000-year-old Kimama flow, have high iron oxide, titanium oxide and phosphorus pentoxide contents similar to the rocks analyzed by the Mars Exploration Rover Spirit.
The youngest basalts of Crater of the Moon flows have similarities in silicon dioxide, alkali contents, and mineralogical norms with select clasts in the Martian meteorite Northwest Africa (NWA) 7034. These similarities over a range of flow ages therefore suggest that Crater of the Moon basalts have the potential to shed important light on specific igneous processes occurring on Mars.
X-ray diffraction and X-ray fluorescence
Studies have analyzed Craters of the Moon National Monument basalts as unshocked compositional and weathering analogs for Martian rocks and meteorites. Scientists at Thermo Fisher Scientific recently acquired basalt samples from Craters of the Moon National Monument. Using X-ray diffraction (XRD) and X-ray fluorescence (XRF), they demonstrate a fast and efficient solution to syngestically analyze Martian analog samples.
An X-ray diffractometer enabled a full analysis of geologic materials from qualitative phase assemblages to full quantitative phase analysis. A 30-minute measurement time was chosen to maximize intensities of minor phases. Paired with an Energy-Dispersive XRF spectrometer for elemental information, a complete analysis of the alkaline basalt sample has been obtained. The study shows that benchtop XRD and EDXRF instrumentation is an ideal combination for geologic research and process applications.
For details, download “XRD and XRF investigation of Martian analog basalt from terrestrial craters”.
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