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NASA's Mars‐2020 Perseverance rover spent its first year in Jezero crater studying the mafic lava flows of the Máaz formation and the ultramafic cumulates of the Séítah formation, both of which have undergone minor alteration and are variably covered by coatings, dust, and/or soil deposits. Documenting the rock and soil characteristics across the crater floor is critical for establishing the geologic context of Perseverance's cached samples—which will eventually be returned to Earth—and for interpreting the deposition and modification of the Máaz and Séítah formations. Mastcam‐Z, a pair of multispectral, stereoscopic zoom‐lens cameras, provides broadband red/green/blue and narrowband visible to near‐infrared images (VNIR, 440–1,020 nm). From multispectral observations from sols 0 to 380, we compiled a database of ∼2,400 representative Mastcam‐Z spectra. We analyzed principal components, spectral parameters, and laboratory spectra of pure minerals and natural rock surfaces to interpret the spectral diversity of rocks and soils. We define eight spectral classes of rocks: Dusty, Hematite‐like, Coated, Low‐Ca Pyroxene‐like, Olivine‐like, Weathered Olivine‐like, Fe‐rich Pyroxene‐like, and Dark Oxide‐like. The variability of soil spectra in the Jezero crater floor is controlled primarily by the amount of dust and indicates a largely consistent soil mineralogy across the traverse, with the exception of the area disturbed by the landing event. In comparison to rock spectra from the Curiosity rover's Mastcam instrument in Gale crater, rocks on the Jezero crater floor are generally less spectrally diverse, but the Olivine‐like rocks within the Séítah formation represent a new spectral rock class in Mars surface exploration. Plain Language Summary: NASA's Mars‐2020 Perseverance rover spent its first year in Jezero crater studying rocks that formed in lava flows. These rocks were altered slightly by small amounts of water and are covered with dust and other coatings. Understanding these rocks, and the soils across Perseverance's traverse, is important for two reasons: Perseverance has collected rock and soil samples, which will be the first samples from Mars to be sent back to Earth, and they give insights into the history of Jezero crater. Here, we describe a database of spectra that we compiled from the Mastcam‐Z instrument, which is a pair of science cameras on Perseverance's mast. We analyzed ∼2,400 spectra representing the diversity of rocks and soils across the first 380 Martian days of the mission. We find that the amount of dust in the soils controls their spectral variability. We define eight classes of rock spectra, which are controlled by varying amounts of pyroxenes, olivines, hematite, and other oxides. Compared to spectra from the Mastcam instrument, which documented the Curiosity traverse in Gale crater, the Mastcam‐Z spectra are generally less diverse. However, the Mastcam‐Z spectra of olivine‐like rocks are new, as they have not been previously encountered on Mars. Key Points: We compiled a database of Mastcam‐Z spectra from the first 380 sols of Perseverance's mission in the floor of Jezero crater, MarsSoil spectral variability is controlled primarily by amounts of dust and indicates a largely consistent soil mineralogy across the traverseRock spectral variability is controlled by varying amounts of pyroxenes, olivines, hematite, and other oxides [ABSTRACT FROM AUTHOR]

The Mastcam-Z radiometric calibration targets mounted on the NASA's Perseverance rover proved to be effective in the calibration of Mastcam-Z images to reflectance (I/F) over the first 350 sols on Mars. Mastcam-Z imaged the calibration targets regularly to perform reflectance calibration on multispectral image sets of targets on the Martian surface. For each calibration target image, mean radiance values were extracted for 41 distinct regions of the targets, including patches of color and grayscale materials. Eight strong permanent magnets, placed under the primary target, attracted magnetic dust and repelled it from central surfaces, allowing the extraction of radiance values from eight regions relatively clean from dust. These radiances were combined with reflectances obtained from laboratory measurements, a one-term linear fit model was applied, and the slopes of the fits were retrieved as estimates of the solar irradiance and used to convert Mastcam-Z images from radiance to reflectance. Derived irradiance time series are smoothly varying in line with expectations based on the changing Mars-Sun distance, being only perturbed by a few significant dust events. The deposition of dust on the calibration targets was largely concentrated on the magnets, ensuring a minimal influence of dust on the calibration process. The fraction of sunlight directly hitting the calibration targets was negatively correlated with the atmospheric optical depth, as expected. Further investigation will aim at explaining the origin of a small offset observed in the fit model employed for calibration, and the causes of a yellowing effect affecting one of the calibration targets materials. [ABSTRACT FROM AUTHOR]