The color coding on this composite image of an area about 3 kilometers (2 miles) across on Mars is based on infrared spectral information interpreted as evidence of various minerals present. Carbonate (green) and olivine-bearing rocks (yellow) occupy the same level in the stratigraphy, and it is thought that the carbonate formed by involvement of water in altering olivine-bearing rocks.

The scene is eroded terrain in the Nili Fossae region of northern Mars. Beneath a rough-textured capping rock unit (purple) lie banded olivine-bearing layers (yellow), which in some places have been partially or wholly altered to carbonate (green). Beneath the olivine-and-carbonate unit are rocks with iron-magnesium smectite clays (light blue). Olivine is also found in sand dunes (near bottom right corner, for example), and it probably eroded from the nearby rocks.

The image overlays the color-coded spectral information from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) onto a grayscale image from the High Resolution Imaging Science Experiment (HiRISE) camera. CRISM and HiRISE are two of the six science instruments on NASA's Mars Reconnaissance Orbiter.

The infrared spectral information comes from a CRISM image catalogued as FRT00003E12. The composite view here was made using 2.38-micrometer-wavelenghth data as red, 1.80 micrometer as green and 1.15 micrometer as blue.

The base black-and-white image is catalogued as PSP_002888_2025_RED by the HiRISE team.

Image credit: NASA/JPL/JHUAPL/University of Arizona/Brown University

Four Types of Deposits From Wet Conditions on Early Mars

Each of these four panels shows a close-up view of a different type of geological deposit formed with the involvement of water, based on observations by NASA's Mars Reconnaissance Orbiter. All four date from the earliest period of Martian history, called the Noachian Period.

The upper-left panel shows carbonates overlying clays in the Nili Fossae region of Mars. The view combines color-coded information from infrared spectral observations by the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) with an underlying black-and-white image from the High Resolution Imaging Science Experiment (HiRISE) camera. Beneath a rough-textured capping rock unit (purple) lie banded olivine-bearing layers (yellow), which in some places have been partially or wholly altered to carbonate (green).

The upper-right panel shows phyllosilicates and chlorides in the Terra Sirenum region, observed by CRISM and HiRISE. Medium-toned, finely fractured rocks containing chloride salts either underlie higher-standing, light-toned phyllosilicates or fill in low spots between them. Both sit on dark, eroded volcanic material.

The lower-left panel shows the upper portion of canyon wall in Coprates Chasma, observed by HiRISE and CRISM. The chasm rim cuts across the middle of the image. The wall slopes down to the top of the image and continues outside the region shown, exposing multiple phyllosilicate-bearing layers in a section of rock 7 kilometers (4 miles) thick. Two of the layers shown here are finely fractured aluminum clays that dominate the lower half of the image, underlain by thin beds of iron-magnesium clays at the top of the image. The dark material is a remnant of an overlying layer of basaltic sand that has been partly eroded away by the wind.

The lower-right panel shows phyllosilicates with vertically layered compositions in Mawrth Vallis, observed by HiRISE (presented in enhanced color) and CRISM. The brown-colored knob in the middle of the scene is a remnant of cap rock that overlies aluminum clays (blue-gray), which in turn overlie iron-magnesium clays (buff).

Image credit: NASA/JPL/JHUAPL/University of Arizona/Brown University