Space Spin - Opportunity finds mineral vein deposited by water

Opportunity has found bright veins of a mineral, apparently gypsum, deposited by water.

Analysis of the vein will help improve understanding of the history of wet environments on Mars.

"This tells a slam-dunk story that water flowed through underground fractures in the rock," said Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for Opportunity. "This stuff is a fairly pure chemical deposit that formed in place right where we see it. That can't be said for other gypsum seen on Mars or for other water-related minerals Opportunity has found. It's not uncommon on Earth, but on Mars, it's the kind of thing that makes geologists jump out of their chairs."

The latest findings by Opportunity were presented Wednesday at the American Geophysical Union's conference in San Francisco.

The vein examined most closely by Opportunity is about the width of a human thumb (0.4 to 0.8 inch, or 1 to 2 centimeters), 16 to 20 inches (40 to 50 centimeters) long, and protrudes slightly higher than the bedrock on either side of it. Observations by the durable rover reveal this vein and others like it within an apron surrounding a segment of the rim of Endeavour Crater. None like it were seen in the 20 miles (33 kilometers) of crater-pocked plains that Opportunity explored for 90 months before it reached Endeavour, nor in the higher ground of the rim.

Last month, researchers used the Microscopic Imager and Alpha Particle X-ray Spectrometer on the rover's arm and multiple filters of the Panoramic Camera on the rover's mast to examine the vein, which is informally named "Homestake." The spectrometer identified plentiful calcium and sulfur, in a ratio pointing to relatively pure calcium sulfate.

Calcium sulfate can exist in many forms, varying by how much water is bound into the minerals' crystalline structure. The multi-filter data from the camera suggest gypsum, a hydrated calcium sulfate. On Earth, gypsum is used for making drywall and plaster of Paris. Observations from orbit had detected gypsum on Mars previously. A dune field of windblown gypsum on far northern Mars resembles the glistening gypsum dunes in White Sands National Monument in New Mexico.

"It is a mystery where the gypsum sand on northern Mars comes from," said Opportunity science-team member Benton Clark of the Space Science Institute in Boulder, Colo. "At Homestake, we see the mineral right where it formed. It will be important to see if there are deposits like this in other areas of Mars."

Credit: NASA/JPL-Caltech/Cornell/ASU
High resolution image

This color view of a mineral vein called "Homestake" comes from the panoramic camera (Pancam) on Opportunity. The vein is about the width of a thumb and about 18 inches (45 centimeters) long. Opportunity examined it in November 2011 and found it to be rich in calcium and sulfur, possibly the calcium-sulfate mineral gypsum. "Homestake" is near the edge of the "Cape York" segment of the western rim of Endeavour Crater. Exposures combined into this view were taken through Pancam filters admitting light with wavelengths centered at 601 nanometers (red), 535 nanometers (green) and 482 nanometers (blue). The view is presented in approximate true color. This "natural color" is the rover team's best estimate of what the scene would look like if humans were there and able to see it with their own eyes. The exposures were taken during sol 2,769 (Nov. 7, 2011).

Credit: NASA/JPL-Caltech/Cornell/ASU
High resolution image

Exposures combined into this view were taken through Pancam filters admitting light with wavelengths centered at 753 nanometers (near infrared), 535 nanometers (green) and 432 nanometers (violet). The view is presented in false color to make some differences between materials easier to see.

Credit: NASA/JPL-Caltech
High resolution image

This view blends three exposures taken by the microscopic imager during sols 2,765 and 2,766.

Credit: NASA/JPL-Caltech
High resolution image

The navigation camera on Opportunity recorded this view of the western edge of "Cape York" during sol 2,761 (Oct. 30, 2011). Cape York is a segment of the rim of Endeavour Crater. A bright vein, informally named "Homestake," is visible on the right side of the image. The vein is about as wide as a thumb and about 18 inches (45 centimeters) long. Opportunity examined it in November 2011 and found it to be rich in calcium and sulfur, possibly the calcium-sulfate mineral gypsum.

Credit: NASA/JPL-Caltech/UA/OSU
High resolution image (3 MB)

This view shows portions of the western rim of Endeavour Crater on Mars from a perspective looking toward the northwest. The image exaggerates the landscape's vertical dimension five-fold compared with horizontal dimensions. The scene covers about 4 miles (6 kilometers) in length. Major portions of the rim are labeled. The view was generated by producing an elevation map from a stereo pair of images from the HiRISE camera on Mars Reconnaissance Orbiter, then draping one of the HiRISE images over the elevation model. Elevation data were calculated by researchers at Ohio State University, Columbus.

Credit: NASA/JPL-Caltech/UA/JHUAPL
High resolution image

This graphic combines a perspective view of the "Botany Bay" and "Cape York" areas of the rim of Endeavour Crater, and an inset with mapping-spectrometer data. Major features are labeled. In the perspective view, the landscape's vertical dimension is exaggerated five-fold compared with horizontal dimensions. Opportunity examined targets in the Cape York area during the second half of 2011. The inset presents data from the Compact Reconnaissance Imaging Spectrometer for Mars (CRISM) instrument on the Mars Reconnaissance Orbiter. In this CRISM observation, taken on March 29, 2011, data were acquired using an oversampled gimbal motion in the spacecraft's along-track direction, producing an enhanced-resolution view in that direction. Data have been processed to 13 feet (4 meters) per pixel, compared with the instrument's usual 59 feet (18 meters) per pixel. Three different infrared wavelengths -- 2.52, 1.51 and 1.08 micrometers -- are presented as red, green and blue in the image. Thermal inertia estimates from observations by the Thermal Emission Imaging System on Mars Odyssey orbiter indicate that Botany Bay is a region with extensive outcrop exposures. The feature "Shoemaker Ridge" was given its informal name after one of the founding fathers of planetary geology, Eugene Shoemaker.

Credit: NASA/JPL-Caltech/Cornell/ASU
High resolution image

The feature informally named "Shoemaker Ridge" in the "Cape York" segment of the western rim of Endeavour Crater includes outcrops that are likely impact breccias. Impact breccias are a type of jumbled rock previously examined by Opportunity at the "Chester Lake" target on Cape York. The view looks northward toward the southern edge of Shoemaker Ridge. This image combines exposures taken by Opportunity's Panoramic Camera (Pancam) through three different color filters during sol 2,715 (Sept. 13, 2011). It is presented in false color to emphasize differences among materials in the rock and soil. The filters used are centered on wavelengths of 753 nanometers (near infrared), 535 nanometers (green) and 412 nanometers (violet). Most of Cape York is covered in densely packed basaltic sands with small embedded rock clasts. Outcrops are exposed particularly on the inboard, or southeast, side of the cape.

The Homestake deposit, whether gypsum or another form of calcium sulfate, likely formed from water dissolving calcium out of volcanic rocks. The calcium combined with sulfur that was either leached from the rocks or introduced as volcanic gas, and it was deposited as calcium sulfate into an underground fracture that later became exposed at the surface.

Throughout Opportunity's long traverse across Mars' Meridiani plain, the rover has driven over bedrock composed of magnesium, iron and calcium sulfate minerals that also indicate a wet environment billions of years ago. The highly concentrated calcium sulfate at Homestake could have been produced in conditions more neutral than the harshly acidic conditions indicated by the other sulfate deposits observed by Opportunity.

"It could have formed in a different type of water environment, one more hospitable for a larger variety of living organisms," Clark said.

Homestake and similar-looking veins appear in a zone where the sulfate-rich sedimentary bedrock of the plains meets older, volcanic bedrock exposed at the rim of Endeavour. That location may offer a clue about their origin.

Opportunity and its rover twin, Spirit, completed their three-month prime missions on Mars in April 2004. Both rovers continued for years of extended missions and made important discoveries about wet environments on ancient Mars that may have been favorable for supporting microbial life. Spirit stopped communicating in 2010. Opportunity continues exploring, currently heading to a sun-facing slope on the northern end of the Endeavour rim fragment called "Cape York" to keep its solar panels at a favorable angle during the mission's fifth Martian winter.

"We want to understand why these veins are in the apron but not out on the plains," said the mission's deputy principal investigator, Ray Arvidson, of Washington University in St. Louis. "The answer may be that rising groundwater coming from the ancient crust moved through material adjacent to Cape York and deposited gypsum, because this material would be relatively insoluble compared with either magnesium or iron sulfates."

Source: Jet Propulsion Laboratory
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Opportunity finds mineral vein deposited by water

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