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CRISM True Color Image Mosaic of Nili Fossae
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CRISM True Color Image Mosaic of Nili Fossae

Acquired Date: January 12, 2007
Release Date: June 20, 2017
Latitude: 22.25 N
Longitude: 77.25 E
Keywords: Fracture/Faults, Carbonate Mineral, Hydrated Mineral, Mafic minerals, Phyllosilicate minerals, Southern Highlands
Parameters: N/A

The Nili Fossae are a series of kilometer-wide fractures concentric to Isidis Planitia, an ancient impact basin. This mosaic of CRISM images enables us to look at the mineralogy associated with the fossae; we show the mosaic in red-green-blue (RGB) composites using both true-color (left) and false-color (right) wavelengths. Our eyes can detect light at wavelengths between 400-700 nanometers, but CRISM can observe reflected light over a much broader wavelength range, between 362-3920 nanometers, and as 544 separate “colors”. For interpreting mineralogy and geology, it’s often useful to display some of CRISM’s “invisible” wavelengths as colors that our eyes can see. For instance, the false-color CRISM mosaic depicts the 2529 nm wavelength as red, 1329 nm as green, and 768 nm as blue as an RGB composite; it is so brightly colored because the region is enriched in a wide diversity of rocks that include olivine, ultramafic minerals, phyllosilicate, and carbonate minerals that all exhibit distinct spectral characteristics over CRISM’s wavelength range (see related Featured Image “Carbonate Minerals in Nili Fossae” from 04-04-2014). However, this is not what the surface of Mars really looks like! The true-color mosaic represents what you would see with your own eyes from the viewpoint of CRISM in orbit around Mars. Creating a true-color image requires a series of corrections to the visible data collected by CRISM, including a filter boundary correction, a color matching function spline, creation of tri-stimulus values, calibration of the monitor you are looking at, and transformation into the RGB color space. The contrast between what you can see in the true-color image as compared to the false-color image gives you just a hint of CRISM’s power for discovering the geologic history of the planet.



The Nili Fossae are a series of kilometer-wide fractures concentric to Isidis Planitia, an ancient impact basin. This mosaic of CRISM images enables us to look at the mineralogy associated with the fossae; we show the mosaic in red-green-blue (RGB) composites using both true-color (left) and false-color (right) wavelengths. Our eyes can detect light at wavelengths between 400-700 nanometers, but CRISM can observe reflected light over a much broader wavelength range, between 362-3920 nanometers, and as 544 separate “colors”. For interpreting mineralogy and geology, it’s often useful to display some of CRISM’s “invisible” wavelengths as colors that our eyes can see. For instance, the false-color CRISM mosaic depicts the 2529 nm wavelength as red, 1329 nm as green, and 768 nm as blue as an RGB composite; it is so brightly colored because the region is enriched in a wide diversity of rocks that include olivine, ultramafic minerals, phyllosilicate, and carbonate minerals that all exhibit distinct spectral characteristics over CRISM’s wavelength range (see related Featured Image “Carbonate Minerals in Nili Fossae” from 04-04-2014). However, this is not what the surface of Mars really looks like! The true-color mosaic represents what you would see with your own eyes from the viewpoint of CRISM in orbit around Mars. Creating a true-color image requires a series of corrections to the visible data collected by CRISM, including a filter boundary correction, a color matching function spline, creation of tri-stimulus values, calibration of the monitor you are looking at, and transformation into the RGB color space. The contrast between what you can see in the true-color image as compared to the false-color image gives you just a hint of CRISM’s power for discovering the geologic history of the planet.

The CRISM mosaic shown is made up of (from north to south): FRT00003E12 (acquired January 12 2007), FRT0000B438 (June 28, 2008), FRT0000A4FC (March 8, 2008) and FRT0000871C (October 26, 2007).

The Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) is one of six science instruments on NASA's Mars Reconnaissance Orbiter. Led by The Johns Hopkins University Applied Physics Laboratory, the CRISM team includes expertise from universities, government agencies and small businesses in the United States and abroad.

CRISM's mission: Find the spectral fingerprints of aqueous and hydrothermal deposits and map the geology, composition and stratigraphy of surface features. The instrument also tracks seasonal variations in dust and ice aerosols in the Martian atmosphere, and water content in surface materials — leading to new understanding of the climate.

Credit: NASA/JPL/JHUAPL

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