Where do you think you’d be more likely to survive if stranded – the moon or Mars?
Before you recall the violent dust storm on Mars that nearly killed Mark Watney in the film The Martian and say “the moon,” let us tell you a story about new research produced by the Planetary Science Lab (PSL) at LSU revealing complex geology on the red planet. Why? Because the moon’s simple geology also means fewer opportunities for the development of life-sustaining minerals such as clays and limestone that typically occur in the presence of water bodies.
“It’s much easier to survive on a complex planetary body bearing the mineral products of complex geology than on a simpler body like the moon or asteroids,” David Susko said. David is a graduate student in the LSU Department of Geology and Geophysics and author of a new study revealing that Mars’ mantle, or the layer between the planet’s crust and its warmer core, may be more complex or complicated than we previously thought. Then again, complex geological processes such as potentially active volcanoes could bring on a whole new set of hazards for martian explorers.
In a paper published today in Nature-affiliated journal Scientific Reports, researchers at LSU document geochemical changes over time in the lava flows of Elysium, a major martian volcanic province. LSU Geology and Geophysics graduate researcher David Susko led the study with colleagues at LSU and beyond, including his advisor Dr. Suniti Karunatillake. They found that the unusual chemistry of lava flows around Elysium is consistent with primary magmatic processes, or processes involving magma under Mars’ crust. These processes could be related to a laterally heterogeneous mantle beneath Mars’ surface or the weight of the overlying volcanic mountain causing different layers of the mantle to melt at different temperatures as they rise to the surface over time.
Elysium is a giant volcanic complex on Mars, the second largest behind Olympus Mons. For scale, it rises to twice the height of Earth’s Mount Everest, or approximately 16 kilometers. Geologically, Elysium is more like Earth’s Tibesti Mountains in Chad, the Emi Koussi in particular, than Everest. This comparison is based on images we have of the region from the Mars Orbiter Camera (MOC) aboard the Mars Global Surveyor (MGS) Mission.
Elysium is unique among martian volcanoes. It’s isolated in the northern lowlands of the planet, whereas most other volcanic complexes on Mars cluster in the ancient southern highlands. Elysium also has patches of lava flows that are remarkably young for a planet often considered geologically silent.
“Most of the volcanic features we look at on Mars are in the range of 3-4 billion years old,” David said. “There are some patches of lava flows on Elysium that we estimate to be 3-4 million years old, so three orders of magnitude younger. In geologic timescales, 3 million years ago is like yesterday.”
In fact, Elysium’s volcanoes hypothetically could still erupt, David said, although further research is needed to confirm this. “At least, we can’t yet rule out active volcanoes on Mars,” David said. “Which is very exciting.” David's work in particular reveals that the composition of volcanoes on Mars may evolve over their eruptive history.
In earlier research led by Suniti Karunatillake, assistant professor in LSU's Department of Geology and Geophysics, researchers in LSU's PSL found that particular regions of Elysium and the surrounding shallow subsurface of Mars are geochemically anomalous, strange even relative to other volcanic regions on Mars. They are depleted in the radioactive elements thorium and potassium. Elysium is one of possibly only two igneous provinces on Mars where researchers have found such low levels of these elements.
“Because thorium and potassium are radioactive, they are some of the most reliable geochemical signatures that we have on Mars,” David said. “They act like beacons emitting their own gamma photons, radiation we can detect, which other elements emit only indirectly. Potassium and thorium also often couple in volcanic settings on Earth.”
In their new paper, David Susko and colleagues started to piece together the geologic history of Elysium, an expansive volcanic region on Mars characterized by strange chemistry. They sought to uncover why some of Elysium’s lava flows are so geochemically unusual, or what makes thorium and potassium levels so low here. Is it because, as other researchers have suspected, glaciers located in this region long ago altered the surface chemistry through aqueous processes? Or is it because these lava flows arose from different parts of Mars’ mantle than other volcanic eruptions on Mars?
Perhaps Mars' mantle has changed over time, meaning that more recent volcanic eruptions differ chemically from older ones. If so, David could use Elysium’s geochemical properties to study how Mars’ bulk mantle has evolved over geologic time, with important insights for future missions to Mars. Understanding the evolutionary history of Mars’ mantle could help us gain a better understanding of what kinds of valuable ores and other materials we could find in the crust, as well as whether volcanic hazards could unexpectedly threaten human missions to Mars in the near future. Mars’ mantle likely has a very different history than Earth’s mantle, because the plate tectonics on Earth are absent on Mars as far as researchers know. The history of the bulk interior of the red planet also remains a mystery.
David and colleagues at LSU analyzed geochemical and surface morphology data from Elysium using instruments on board NASA’s Mars Odyssey Orbiter (2001) and Mars Reconnaissance Orbiter (2006). They had to account for the dust that blankets Mars’ surface in the aftermath of strong dust storms, to make sure that the shallow subsurface chemistry actually reflected Elysium’s igneous material and not the overlying dust.
“The most challenging parts of this research were collecting and analyzing over 400 images of the Elysium Volcanic province,” David said. “Also, the crater counting was painstakingly slow as we logged over 1,300 craters in the region.”
Through crater counting, the researchers found differences in age between the northwest and the southeast regions of Elysium – about 850 million years of difference.
“We were surprised to realize just how young the Southeastern flows are. Some of them are essentially brand new by martian standards,” David said. The researchers also found that the younger southeast regions are geochemically different from the older regions, and that these differences in fact relate to igneous processes, not other processes like the interaction of water or ice with the surface of Elysium in the past.
“We determined that while there might have been water in this area in the past, the geochemical properties in the top meter throughout this volcanic province are indicative of igneous processes,” David said. “We think levels of thorium and potassium here were depleted over time because of volcanic eruptions over billions of years. The radioactive elements were the first to go in the early eruptions. We are seeing changes in the mantle chemistry over time.”
“Long-lived volcanic systems with changing magma compositions are common on Earth, but an emerging story on Mars,” said James Wray, study co-author and associate professor in the School of Earth and Atmospheric Sciences at Georgia Tech. “At Elysium we are truly seeing the bulk chemistry change over time, using a technique that could potentially unlock the magmatic history of many more regions across Mars.”
David speculates that the very weight of Elysium’s lava flows, which make up a volcanic province six times higher and almost four times wider than its morphological sister on Earth, Emi Koussi in northern Chad, has caused different depths of Mars’ mantle to melt at different temperatures. In different regions of Elysium, lava flows may have come from different parts of the mantle. Seeing chemical differences in different regions of Elysium, Susko and colleagues concluded that Mars’ mantle might be heterogeneous, with different compositions in different areas, or that it may be stratified beneath Elysium.
Overall, David's findings indicate that Mars is a much more geologically complex body than originally thought, perhaps due to various loading effects on the mantle caused by the weight of giant volcanoes.
“It’s more Earth-like than moon-like,” David said. “The moon is cut and dry – it lacks the abundance of different mineral types on Earth’s surface. It often lacks the secondary minerals that occur on Earth due to weathering and igneous-water interactions. For decades, that’s also how we envisioned Mars, as a lifeless rock, full of craters with a number of long inactive volcanoes. We had a very simple view of the red planet. But the more we look at Mars, the less moon-like it becomes. We’re discovering more variety in rock types and geochemical compositions, as seen across the Curiosity Rover’s traverse in Gale Crater, and more potential for viable resource utilization and capacity to sustain a human population on Mars. It’s much easier to survive on a complex planetary body bearing the mineral products of complex geology than on a simpler body like the moon or asteroids.”
Susko plans to continue clarifying the geologic processes that cause the strange chemistry found around Elysium. In the future, he will study these chemical anomalies through computational simulations, to determine if recreating the pressures in Mars’ mantle caused by the weight of giant volcanoes could affect mantle melting to yield the type of chemistry observed within Elysium.
“The most rewarding part of this research for me was being able to work to piece together a geologic history for a specific region on a planet that is over 100 million miles away from us,” David said. “It makes looking at Mars through telescopes here on Earth much more personal.”
Study: Susko et al. (2017) A record of igneous evolution in Elysium, a major martian volcanic province. Scientific Reports 7.
David Susko led this study with LSU undergraduate student Taylor Judice, mentored by their advisor Suniti Karunatillake. This multi-institutional and international investigation was co-authored by Gayantha Kodikara at the University of Ruhuna in Sri Lanka; John Roma Skok, SETI Institute; James Wray at Georgia Institute of Technology; Jennifer Heldmann at NASA Ames; and Agnes Cousin at the Institut de Recherche en Astrophysique et Planétologie in France. NASA’s Mars Data Analysis Program (MDAP) funded the project at LSU, which used data from several missions, including the 2001 Mars Odyssey Gamma Ray Spectrometer (GRS) and the High Resolution Imaging Science Experiment (HiRISE) aboard the Mars Reconnaissance Orbiter (MRO).