Small-scale maps cover relatively large areas and to date, are the most common scale of geologic map in planetary science. These are often completed at scales of between 1:500,000 to 1:5,000,000. For reference, a 1:500,000 scale map means that 1 mm on the map equates to 500,000 mm (or 500 km) on a planet’s surface. Though maps have historically covered large areas, with crewed lunar missions on the horizon and other missions across the solar system in the planning stages, large-scale, small-area maps are starting to steal the limelight. These large-scale, small-area maps provide highly detailed views of the surface and allow scientists to investigate complex geologic relationships both on and beneath the surface. These types of maps are useful for both planning for and then conducting landed missions.

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Olympus Mons is the tallest volcano in the solar system, but a new map of the caldera by Dr. Peter Mouginis-Mark (University of Hawai’i Manoa) revealed a surprise - the highest point isn’t where you would expect. This new detailed map highlights the complex volcanologic history of the caldera and builds on Dr. Mouginis-Mark’s past work which found multiple caldera collapses had occurred in Olympus Mons’ past. Dr. Mouginis-Mark thinks this could explain the curiosity of Olympus Mons’ highest point.

“Probably the most interesting thing about the map is the addition of the contours (Mars maps almost never have this) and these contours have allowed the identification of the late-stage inflation of the summit (in other words, the contours show that some young lava flows appear to flow uphill),” remarks Dr. Mouginis-Mark.

Map readers can visualize the caldera complex more easily due to the detail that is available at the 1:200,000 scale and the addition of contour lines to the map. The map covers a region that is roughly the size of the Dallas-Ft. Worth metropolitan area and is a detailed look at the volcano’s summit that we have not seen before. This new view of the Olympus Mons caldera complex allows scientists to more easily compare it to  similar features on Earth (known as terrestrial analogs) such as Hawaii’s Mauna Loa.

Dr. Mouginis-Mark mentions his inspiration behind such a large-scale map, saying, “I wanted to be able to fit the entire caldera onto a sheet of paper that could easily be hung on a wall.  A scale of 1:100,000 or even 1:150,000 would not allow this.  Conversely, a scale of 1:500,000 would prevent the reader from seeing the details, particularly of the contours (shown on the map at 100 m intervals). So, 1:200,000 works quite well... I decided to try something that is rarely done, and I think it turned out quite well!”

View the interactive map of the Olympus Mons Caldera (USGS SIM 3470)

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Approximately 5,000 kilometers to the west of Olympus Mons is the Aeolis Dorsa (Greek and Latin, respectively, for “Wind Ridge”) region of Mars. This geologically diverse area is around the size of the state of Arizona and has a complex depositional history. Much like on Earth, sediments on Mars were primarily deposited by wind, flowing water, or ice. One particularly interesting feature that hints at Mars’ watery past is the sinuous ridge, which is a winding, narrow ridge that looks like an inverted river channel. These ridges are interpreted to be aqueous (formed by water), making them possible clues about the history of water on Mars. Aeolis Dorsa is not lacking in sinuous ridges - in fact, it has hundreds of them to study. Dr. Devon Burr (Northern Arizona University) and colleagues recently completed a new map of the Aeolis Dorsa region with these fluvial (river) features in mind. “The original motivation for this map was to try to understand the history of these numerous inverted fluvial features.,” says Dr. Burr.

Dr. Burr and colleagues used the various shapes and textures of the sinuous ridges to separate the  Aeolis Dorsa ridge into six distinct geologic units. Because the map was completed at a large scale (small area), map authors could identify regional environmental changes that occurred over billions of years. The new map of Aeolis Dorsa adds to the hypothesis that Mars was once wet and had abundant active river systems in the past before aqueous activity decreased over time. This change caused the primary depositional methods in the region to shift from rivers (fluvial) to sediment fans with intermittent deposition (alluvial) and eventually to a dry and wind-driven (aeolian) system. This local pattern mimics our current understanding of the global environmental history of Mars. When asked if educating the public about Mars’ paleoclimate could help us to better understand our own climate change on Earth, Dr. Burr said “Understanding the fascinating story of Mars’ evolution would help people recognize the magnitude of possible change in planetary climates.”

View the interactive map of Aeolis Dorsa (USGS SIM 3480)

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Although Aeolis Dorsa has spectacular fluvial features, it is not the only location on Mars with possible fluvial systems. Fluvial systems and floods go hand in hand, and there are many areas on Mars that may have experienced flooding in the past. The Athabasca Valles region of Mars was long thought to be the result of a large flood. However, there was much debate about whether the features in this area were from a flood of water or a large eruption of blisteringly hot, runny lava. Today, many scientists interpret the terrains in the Athabasca Valles as young flood basalts, with the geologically recent Athabasca Valles “flooding” event flowing across the landscape, leaving a series of detailed, pristinely preserved geologic interactions visible in the region.

Dr. Lazlo Kestay and colleagues worked on their map of Athabasca Valles for many years. The scientifically curious nature of the area and the addition of high-resolution data from instruments like the Thermal Emission Imaging System (THEMIS), the High Resolution Imaging Science Experiment (HiRISE), and the Context Camera (CTX) since 2005 paved the path for Dr. Kestay and colleagues to create one of the most detailed geologic maps of a large, pristinely preserved region of Mars. “We originally planned to make four maps to allow mapping at a higher resolution but as we progressed, we decided this would be more confusing than helpful, (…) The interpretation of the small features were discussed in separate publication so we don’t feel anything is really missing.” says Dr. Kestay.

The geologic relationships in the Athabasca Valles region are not only in mint condition, but they are also quite complex and puzzling. This leaves more room for future planetary scientists to explore the volcanic systems present in the region. “The fact that the InSight lander identified earthquakes in this area suggests that geologic activity here is not done. (…) . There will continue to be a great need for looking at the big picture and mapping at the more traditional regional and global scales. But more and more of the new discoveries will be from detailed mapping – especially at the rover scale. Mapping at that scale will be more familiar to terrestrial geologists!”

View the interactive map of Athabasca Valles (USGS SIM 3477)

The mission of the USGS Astrogeology Science Center is to serve the Nation, the international planetary science community, and the general public’s pursuit of new knowledge of our Solar System. The Team’s vision is to be a national resource for the integration of planetary geosciences, cartography, and remote sensing. As explorers and surveyors, with a unique heritage of proven expertise and international leadership, USGS astrogeologists enable the ongoing successful investigation of the Solar System for humankind. For more information, visit http://astrogeology.usgs.gov