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Field notes from Mars’s latest roving explorer

11 November 2021

The Perseverance rover’s early scientific results detail dust lifting and ancient flood deposits at Jezero Crater.

Kodiak Butte, within Jezero Crater on Mars.
Kodiak Butte, as captured by Perseverance’s Mastcam-Z looking west at dawn. The inclined layers clinch the feature’s identity as an ancient river delta. Credit: NASA/JPL-Caltech/ASU/MSSS

The Perseverance rover departed Earth in July 2020 to seek chemical evidence of ancient microbes on Mars and collect samples of rocks and regolith for the eventual return home by a potential mission in the 2030s. After reviewing images taken from orbit that hinted at signs of ancient water-formed features, NASA chose Jezero Crater as the landing site for the mission, known as Mars 2020. The 45-kilometer-wide crater lies on a plain called Isidis Planitia, 18° north of Mars’s equator, that is located inside a giant impact basin. In the months since landing at Jezero, the rover has been investigating rocks, measuring the composition and properties of the atmosphere, and snapping photos.

State-of-the-art instruments aboard the rover are now documenting evidence of a rich history of watery processes and an atmospheric environment that has striking similarities to Earth’s. Here are some of the findings presented at last month’s annual meetings of the Geological Society of America and the American Astronomical Society’s Division for Planetary Sciences.

A crater’s watery past

The discovery: The cliffs along the western side of Jezero Crater are ancient river deltas that fed into a lake. An era of substantial flooding followed the period of river flow.

  • How we know: The prominent Kodiak Butte is the site of sloped sedimentary strata sandwiched between horizontal ones in layers measuring 8 to 10 meters thick. The sloped beds mark the delta’s leading edge as it expanded into the lake; the horizontal layers correspond to different water levels that once filled the lake. Conglomerates of rounded boulders and cobbles as large as 1.5 meters in diameter dominate the delta’s top layers. Transporting boulders requires high-energy flows, which points to the flooding explanation. “The features are too large to be river bars, and they contain cobbles too large to be moved by wind, so they cannot be wind-formed,” says Sanjeev Gupta, a geologist and planetary scientist at Imperial College London and a coinvestigator on the mission.
  • What we’d thought: Orbital imagers had shown fan-shaped landforms at the crater’s northern and western edges. Researchers suspected that they were river delta deposits but lacked direct evidence. As for the subsequent flooding, Gupta says there were no previous hints. “It was a total surprise.”
  • Key tools: Mastcam-Z, a set of zoom cameras, acquired close-up views of cliff faces from across the basin. “The early-morning images were spectacular,” says Gupta. Those photos provided targets for the Remote Microscopic Imager (RMI), a subsystem of the SuperCam optical measurement tools, to obtain detailed views of the layers. The RMI was able to resolve boulders from 2 kilometers away.
  • What’s next: The rover will examine and sample fine-grained rocks that likely fell out of suspension at the delta’s base and settled in deep water, where organic material might have been preserved. Future missions could return the samples to Earth.
Jezero Crater from above.
This overhead view of part of Jezero Crater comes from NASA’s Mars Reconnaissance Orbiter. The Perseverance rover is located at center bottom. Kodiak Butte is to the lower left, and scarps (labeled a–d) along the delta are on the upper left. Credit: NASA/JPL-Caltech/University of Arizona/USGS

Rock–water interactions

The discovery: Along with once hosting surface water, Jezero Crater also sustained groundwater, which over time altered the composition of the rocks it seeped through.

  • How we know: Spectral analyses of rough rocks on the crater floor indicate the presence of iron-rich minerals and salts that were left behind when water evaporated. “The spectacular thing here is rock–water interactions,” says Linda Kah, a geologist at the University of Tennessee and a mission coinvestigator. Fluid alters a rock’s chemistry until the composition becomes a mixture of the original rock and the original liquid. Discrete mineral layers in a rock’s pores provide information about historical episodes of water flow through the rock.
  • What we’d thought: Orbital views had indicated that there was once a lake in Jezero Crater, as well as regional raised ridges—likely part of a large fracture system—that could have provided conduits for subsurface flow. But absent closer inspection of the minerals present, that connection was inconclusive.
  • Key tools: An abrasion tool scraped weathered materials off surfaces to reveal undisturbed rock. The Scanning Habitable Environments with Raman & Luminescence for Organics & Chemicals (SHERLOC) and Wide Angle Topographic Sensor for Operations and Engineering (WATSON) cameras then used Raman scattering to identify mineral composition and image textures with high resolution.
  • What’s next: The rover is collecting samples that researchers hope to eventually bring home for geochemical analysis, which could tease out the history of fluid interactions with the crater’s original rock.

Dust devils

Dust devils on Mars.
Dust devils appear in this image acquired by Perseverance’s Navigation Camera. Credit: NASA/JPL

The discovery: Dusty convective vortices, or dust devils, lift a lot of dust into the atmosphere over the crater during spring and early summer.

  • How we know: Rapid pressure drops and changes in wind speed and direction indicate convective vortices that can carry material aloft. Many vortices contain significant amounts of dust. “We also see dust lifting by strong wind gusts,” says Claire Newman of Aeolis Research, a research organization devoted to planetary science. She is a coinvestigator on the mission who co-leads the Atmospheres Working Group. Understanding how dust is lifted outside of dust storms is important because Mars’s atmosphere is always dusty, which affects temperatures and visibility on the planet and the functionality of rovers and landers.
  • What we’d thought: Other Mars missions have observed dust activity, but Perseverance is the first to carry a full toolkit to explain how background dust lifting occurs.
  • Key tools: Measurements of pressure, wind, and radiative flux by a sensor package called the Mars Environmental Dynamics Analyzer (MEDA) tracked the passage of vortices and dust devils, while cameras captured dozens of dust devils.
  • What’s next: Measurements as the rover moves to new locations will show how location, season, and sol-to-sol variability influence lofting of atmospheric dust.

Wind patterns

The discovery: Regional- and local-scale slope winds dominate Jezero’s atmospheric circulation.

  • How we know: Winds propagate from the east and southeast during the daytime and from the west and northwest at night. Those directions are consistent with winds controlled by daytime upslope and nighttime downslope flows on the slopes of the crater and of the basin where Jezero is located.
  • What we’d thought: Observations by the Curiosity rover in Gale Crater suggested that the crater’s huge slopes strongly controlled the wind patterns. But the effect of the slopes had never been fully measured due to problems with making observations at night. “The [Jezero] crater’s environment and Perseverance’s atmospheric sensors are a match made in atmospheric and aeolian heaven,” says Newman.
  • Key tools: MEDA’s wind sensors revealed strong regional and local slope controls. SuperCam’s microphone has provided a first “listen” of high-frequency wind variations.
  • What’s next: Piecing together how the prevailing wind directions and strengths may have driven observed erosion patterns on the crater surface will help researchers interpret Martian landscape features and evolution.

The mission continues

Perseverance is currently traversing a sand-filled region of Jezero called Séítah. The olivine-rich composition of the rocks there suggests that they have an origin different from that of the rocks studied so far. “One big effort that we’re still puzzling over is the Séítah region and its relationship with the rough crater floor,” says Vivian Sun, a NASA Jet Propulsion Laboratory planetary scientist and Mars 2020 campaign science co-lead. Next year the rover will travel around the crater to examine rocks in the river delta. “We want a solid story about the geology in Séítah before we get to the delta,” says Sun.

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