There is a parable about a group of blind men encountering an elephant for the first time and coming to different conclusions about it depending upon which small piece of it they are touching. Exploring other planets faces a similar challenge: landed missions provide detailed information about a small area. To make sense of the results, these observations need to be placed into a broader context.
USGS and JPL Release New Geologic Map of Mars 2020 Perseverance Rover Landing Site
To avoid this pitfall with the upcoming Perseverance Mars 2020 rover mission, the U.S. Geological Survey has worked with authors from NASA’s Jet Propulsion Laboratory to publish a new geologic map of Jezero crater—the landing site of the Mars 2020 Perseverance rover—and the surrounding Nili Planum region. Geologic maps are tools that describe the distribution of rocks and sediment in both space and time. By understanding the kinds of rocks and sediments that occur on a planet’s surface and how they relate to each other, geologists can better understand the processes that created them. These tools help scientists synthesize observations and then make interpretations about the geologic history of an area.
This new map represents a snapshot of the Mars science community’s knowledge and hypotheses about the Jezero crater and Nili Planum region and will help to provide context for the rover’s discoveries once it arrives at Mars on February 18, 2021. “Since the beginning of the Mars 2020 landing site selection process, the science community has largely considered the geology of Jezero crater and Nili Planum to be separate and distinct,” said map co-author and Mars 2020 deputy project scientist Dr. Kathryn Stack. “Our map shows, in detail, the relationship between the intriguing lake, delta, and basin deposits inside Jezero and the ancient crust exposed outside of Jezero, in Nili Planum. This map will be invaluable as the Perseverance rover begins its exploration in Jezero crater, and as the Mars 2020 Science Team begins to plan a strategy for exploration beyond the crater as the mission unfolds.” Though the map is not detailed enough to guide daily operations of the rover – 1 mm on the printed map represents about 75 meters on the surface of Mars, or roughly the wingspan of a 747 jet – it will help the science team link global and regional geologic units to those observed at the rover scale, allowing them to interpret the geology beyond the reach of the rover.
Unlike geologic maps of the Earth, which are based on direct exploration of a region by geologists, planetary geologic maps are based on the best available data from orbit, with no first-hand knowledge of what the rocks look like on the ground. Instead, planetary geologic mappers document the distribution of characteristics like the shape and texture of rock surfaces and whether one unit sits above or below another. The challenge of creating a geologic map of another planetary body requires scientists to synthesize many different types of information collected from orbit and forces them to clearly identify their hypotheses about the mapped area. This process helps highlight areas of uncertainty and identify where more detailed, surface-based rover observations are needed to answer questions.
The new USGS map of Jezero crater puts forward several new hypotheses to be tested by the Perseverance rover. “This map builds on previous research in the Jezero crater and Nili Planum area to advance our understanding of how the rocks inside Jezero crater are related to the rocks in Nili Planum,” said map lead author and JPL scientist Dr. Vivian Sun. “This correlative work can lead to new hypotheses, for example, that the Jezero crater floor may be an airfall deposit rather than a volcanic unit, which can be tested by the Mars 2020 Perseverance rover and carries implications for what samples might be obtained from each unit.” The map also proposes an important new timeline for the existence and activity of liquid water in the region, and identifies a new, relatively young geologic unit, suggesting that the rocks in the region (estimated to be 3.5 to 4 billion years old) span a longer period of time than previously thought. Finally, it links the minerals present in the area with specific geologic units, so that the presence of those minerals can be extrapolated beyond the limited number of locations where they have been identified from orbit.
The USGS Astrogeology Science Center has a long history of working with NASA to ensure that maps made of other planets are held to the same high standards as maps of the Earth. “Spacecraft exploration of Mars provides a dramatic context that improves our understanding of what geologic units, events, and processes sculpted its surface. This map is a great example of how orbital and landed spacecraft observations work together to expand our knowledge of worlds beyond our own,” said USGS geologic map coordinator Jim Skinner.
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