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Goals: Mission Results

Goal 1: Determine Whether Life Ever Arose on Mars

From the tiniest bacterium to the largest tree, all life as we know it requires water. Though we don't yet know if life ever existed on Mars, within weeks of arriving, NASA's Mars Exploration Rover Opportunity discovered that the plains of Meridiani were once a water-soaked place.

This horizontal mosaic of false-color images shows a laterally exposed, pinkish-gray expanse of finely layered rock interspersed with cracks filled with grayish-blue sand. On the upper right is a patch of blue-grey, bead-shaped concretions of rock. Upon magnification, tiny, tabular niches are visible all over the rock surface. Also visible are the same bead-like concretions embedded within the rock layers.
Opportunity Gets Lucky

Rover scientists found signs of water in the first rocks they encountered on Mars. This outcrop, nicknamed "El Capitan," exhibited physical features and minerals pointing to a watery past.

Credit: NASA/JPL-Caltech/Cornell
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While analyzing rocks and soils on Mars, the robotic geologist, equipped with a toolbox of scientific instruments, found hard spheres the size of peppercorns. Sometimes the spheres, nicknamed "blueberries," were loosely scattered across the surface; other times, they were anchored within individual rock layers. After weeks of meticulous measurements, Opportunity demonstrated that the spheres consisted primarily of the mineral hematite. On Earth, hematite generally -- though not always -- forms in the presence of water. Water provides the oxygen atoms that bind with iron atoms in the mineral. On Mars, it appeared possible that groundwater carrying dissolved iron had percolated through the sandstone to form the tiny spheres.

Water-Soaked Past

Rocks near the Opportunity rover's landing site, such as those in this false-color image, contained pearl-shaped rocks that formed in pre-existing wet sediments, as well as finely layered ripples, crossbeds, and niches where crystals once grew and were later redissolved.

Credit: NASA/JPL-Caltech/Cornell
Full Image (NASA's Planetary Photojournal)
This striking, false-color image shows relatively flat, upward-facing, pinkish-white rocks with terraced surfaces insterspersed with cracks filled with turquoise-gray sand and pearl-shaped concretions.

When Opportunity later discovered the mineral jarosite, scientists were ecstatic. Jarosite only forms in the presence of acidic water, so this mineral provides clues to what the environment was like when water was around. Acidic water is harsh, but we know that microbes on Earth can thrive in it.

In this color photo taken in southwestern Spain, the calm, red-infused waters of the Rio Tinto lap gently against the edges of a horizontal, bulbous exposure of yellowish rock coated in places with a whitish, blotchy crust. In the foreground, at the bottom of the frame, the pool of circulating river water becomes shallower and reveals a riverbed of yellow-colored sediment.
Mars on Earth
On Earth, microbial communities thrive in highly acidic waters rich in iron and sulfur, such as the blood-red waters of the Rio Tinto in southwestern Spain. Among the minerals dissolved in the Rio Tinto is jarosite, an iron- and sulfur-bearing mineral also found on Mars. Whether life ever existed on Mars has yet to be deteremined.
Credit: NASA/JPL-Caltech
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Perhaps most stunning of all was Opportunity's discovery of centimeter-scale rock layers overlapping and cutting into each other. Known as crossbeds, these layers had shapes and sizes that indicated that water once flowed on the surface of Mars. In nearby "Endurance Crater," a thick stack of exposed rock layers, some deposited by wind, suggested that water was intermittently present. Rich in the elements sulfur, chlorine, and bromine, many of the minerals studied by Opportunity had settled to the bottom of a salty body of water, known as a brine, to form deposits similar to those seen in salt flats in desert regions on Earth.

Signs of Flowing Water

One characteristic of rocks formed by flowing water are fine, undulating layers of sediment, like those at the bottom of a stream, that flow over and cut into one another, known as crossbeds.

Credit: NASA/JPL-Caltech/Cornell/USGS
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This black-and-white mosaic of microscopic images shows fine, undulating, horizontal layers of rock-hard sediment stacked atop each other and interspersed with bead-shaped concretions of rock. Some of the layers curve upward in the shape of a smile. Here and there, an overlying layer cuts into previously deposited layers, creating a truncation in the underlying layers that curves upward at its lateral edges. These undulating, down-cutting layers are known as crossbeds.

On Mars, wind and water eroded the rocks containing these minerals and carried pieces of them to their current location. These grains piled up with bits of volcanic rock and solidified to form sandstone. Many such layers, stacked atop one another and containing minerals that had initially settled as water evaporated, indicated that water was present for a long, long time. Opportunity discovered tiny cavities in the rock that were similar in shape and size to rock cavities on Earth that are left behind when certain minerals are dissolved and dispersed by groundwater.

This horizontal color panorama of images shows an imposing stack of layers of rock topped by a cap of boulders. The entire outcrop is reddish-brown and is interspersed with cracks filled with grayish-brown sand. The leading edge of the rover's gray solar panels is visible at the bottom right in the foreground. In the left foreground, at the lower edge, are waves of sand lapping at the foot of the outcrop.
Story in the Rocks

A rock wall 10 meters (33 feet) high, known to rover science team members as "Burns Cliff," in honor of a geologist who predicted that jarosite would be discovered on Mars, contained many layers of rock, some deposited by water and some by wind.

Credit: NASA/JPL-Caltech/Cornell/USGS
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Understanding how water contributed to the environment on Mars is the first step in determining whether the red planet could ever have supported life. Evidence of water also points the way to promising sites for investigation by future missions.

This photo, taken on the floodplain of the Rio Tinto in southwestern Spain, shows the head and shoulders of a man with a reddened, sun-weathered face wearing a white hat with a floppy brim hunched over a patch of yellow soil on the ground. In his right hand, he is using a pair of tweezeres to pick up soil sample and place them in a small, white, plastic vial that he is holding in his left hand. He is wearing a plaid shirt with the sleeves rolled up to his elbows and a black and yellow lanyard around his neck bearing the words, 'Mauna Kea Observatory.' A pair of black, wire-rimmed glasses protrudes slightly from beneah the brim of his hat. He is smiling. To his left is a black pack lying on the ground. Beyond him, in the distance, is a hill covered with shrubby green trees.
Looking for Mars on Earth

Planetary scientist and chemist Richard Morris, of NASA's Johnson Space Center, collects a soil sample in the Rio Tinto area of Spain. The soil contains jarosite, a water-bearing mineral rich in iron and sulfur that was found on Mars by NASA's Opportunity rover.
Credit: NASA/JPL-Caltech
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