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In early 2002, another spacecraft, Mars Odyssey, began taking data that provides maps showing thermal state and composition of selected elements, including hydrogen, on the martian surface. These recent satellites and landers have also greatly improved surface geological and topographic mapping and crustal thickness estimates. The European Space Agency got "into the Mars game" with a strong success achieved by its Mars Express. The latest achievement has been the successful landing and deployment of a pair of Mars Explorer Rovers, a surface-traversing vehicle, Spirit on January 3, 2004 and Opportunity on January 24, 2004. Also on this page is a look at future plans for visiting Mars. The page also briefly treats the two tiny martian moons, both of which were imaged by Mariner 9.

Missions to Mars during the Third Millenium

A series of spacecraft have been or will be sent to Mars in the first decade of the 21st Century. The first, the Mars Climate Orbiter, was launched on December 11, 1998. but failed to reach its planned orbit. This was followed on January 3, 1999 by the Mars Polar Lander which apparently did not achieve a proper setdown, as no signal was ever received. Orbiters and landers that have reached Mars and are returning data are described in this page (and its continuation reached by clicking on NEXT at the bottom). There will be a series of Mars probes launched in the next 10 years culminating in a mission which will gather samples for a return to Earth, perhaps by 2014. All of this is connected with the (considered, but not yet approved) U.S. decision to eventually send astronauts to Mars (the year 2030 has been mentioned but is so far just speculative), after the planet has been thoroughly explored with these probes. This decision is embodied in the speech given on January 14, 2004 at NASA Headquarters which can be read at this White House site; this talk tries to restructure NASA's goals for the next decade, but it has engendered both praise and much opposition (both in its emphasis and its cost).

The Mars Ocyssey Mission

One successful probe already is Mars Odyssey, launched on April 7, 2001. Access its Home Page at JPL's site. JPL's Webcast series has three broadcasts that cover the Odyssey mission. Access these through the JPL Video Site, then the pathway Subject--> Solar System --> Format -->Webcast --> Search to bring up the list the following: "Mars Odyssey: The Mapping Mission begins", Mar 1, 2002, then for more results "2001 Mars Odyssey Webcast", November 14, 2002, and finally "Live from Mars", March 13, 2002 (this last is oriented towards students and comes from the THEMIS project people at Arizona State University). To start any of these, once found, click on the blue RealVideo link.

Because of the important discoveries Odyssey has been making, here is an artist's rendition of the spacecraft in orbit around the Red Planet.

Artist's conception of Mars Odyssey above the martian surface, with its GRS water-seeking boom extended.

Odyssey was inserted into orbit on October 20, 2001 and has now aerobraked to descend to about 300 km from the planet. One of its sensors, THEMIS, a thermal infrared emission spectrometer, is surveying the gross mineralogy of MARS. GRS, includes a gamma ray spectrometer that will obtain compositional data covering 20 elements, in particular evidence of hydrogen that is tied with oxygen as water. There are actually three instruments in the GRS: the Gamma Ray subsystem, the Neutron Spectrometer, and the High Energy Neutron Detector (built by the Russians). In its fully operational mode, the GRS is located at the end of the boom (see spacecraft picture above) which was deployed in June, 2002, Here is one of the first results: a visible image and an associated thermal map, made from THEMIS data:

Part of the martian surface as imaged by Mars Odyssey; and an associated temperature distribution determined by its THEMIS sensor.

Bands 5, 7, and 8 on THEMIS were used to produce this color composite of Ganges Chasma in Valles Marineris. The scene is about 150 km (100 miles) on a side. Blues are correlated with basalts; the purples indicate a high olivine content, which is typical of basalts with lower SiO2 contents.

Thermal band color composite of Ganges Chasma in which blues and purples denote basalts with varying olivine content.

Similar variability in olivine content (magentas and purples) is evident in this THEMIS image covering part of Syrtis Major.

Olivine variation in Syrtis Major.

This next image from THEMIS shows a nighttime view of chaotic terrain on Mars. Note its similarity to nighttime thermal images shown in Section 9.

Nighttime thermal image made by THEMIS, showing part of the Hydapsus Chaos terrain.

Referring to the GRS instruments, the principle behind production of neutrons from cosmic rays is illustrated here:

Chart explaining production of neutrons from extraterrestrial cosmic rays.

Incoming high energy cosmic radiation interacts with atoms in surface materials, generating fast neutrons which either directly escape beyond the surface to a detector or interact while leaving to be slowed to epithermal and thermal neutrons having lesser energies. The energy spectral distribution is a function of the elements involved. Note that gamma rays are also produced.

One of the elements detected by analyzing the produced neutron flux is potassium. This global map of potassium distribution on Mars shows higher concentrations than initially predicted:

Neutron flux determined map of potassium distribution on Mars.

A preliminary map (top) of the global distribution of epithermal neutrons and a closer look at the South Polar region (bottom) appear below. Blue indicates conditions explainable by high hydrogen content; hydrogen moderates (absorbs) neutrons better than the heavier elements. While several explanations could account for this, the most probable is hydrogen bound with oxygen as water. More observations will be needed to confirm this, but most Mars scientists favor the model described in the next paragraph.

Map of the distribution of epithermal neutrons emanating from the martian surface.

Epithermal neutron map of the South Polar region; blue indicates higher hydrogen content in surface materials.

Maps made by the Neutron Spectrometer, released in December 2002, indicate even more potential water (higher hydrogen content in purple) than earlier announced. This pair of global martian maps shows the hydrogen distribution first when the south polar cap was largely free of CO2 and later when the CO2 had sublimated of the north polar cap and to some extent resolidified at the south cap.

Global Maps made from Mars Odyssey data showing hydrogen distribution (highest in purple, then blue); note concentrations around the North and South Polar Caps.

A 2003 map based on neutron data from Mars Odyssey emphasizes the wide variation in water ice at the northern pole beteen martian summer and winter. This is displayed best when first the CO2 has sublimed off the cap leaving a dominance of the hydrogen-rich (low neutron count) substance whose identity is almost certainly water:

Water variation (in terms of low hydrogen content [blue] at the northern martial polar region; as determined by Mars Odyssey.

The Russians have produced a map of high energy fast neutron results which also show similar distributions of water:

HEND map of fast neutrons.

For close comparison, this diagram shows the general distribution of all three types of neutrons:

Thermal, Epithermal, and Fast neutron global distribution maps from the Odyssey GRS; all provide evidence of the localization of water (based on its hydrogen response to cosmic rays).

A recent map of regions with variable water content has now been published (below). Calculations indicate there is enough water present in rocks and soil near the surface so, if melted, the entire planet would be covered by water up to 10 cm (4 inches) in thickness.

Distribution of water on Mars based on MGS and Odyssey data.

As of June 20, 2003 no maps or data of the multi-element survey beyond hydrogen by the GRS have been released.

But improved water maps (based on hydrogen absorption of neutrons) continue to be released to the scientific community. The two maps below were displayed at an International Mars Conference at JPL in early August of 2003:

Hydrogen distribution in non-polar regions of Mars

Using same data, hydrogen in the polar regions.

Both MOLA and MGS data are used in making these maps. Hydrogen data come from the neutron spectrometer on Odyssey. In the blue areas, the amount of water ice is between 2 and 10% (assuming that all hydrogen is present in water; hydrous minerals may contain both water and OH). Water increases to around 50% (yellows and oranges) to 70% (dark red to black) mainly around the poles; estimates approach 90% near the North Pole). But water highs are found in Arabia Terra and other areas at lower latitudes.

Compare the next two global maps, both made by Mars Odyssey. The top one, dating from 2001, shows a qualitative distribution determined without actual percentages of water. A global map released in August 2004 casts the immediate subsurface water content (dominantly as ice) in the fractional percentage (lower limits) of water present in the top meter:

Water content on Mars, in a 2001 version made from Odyssey data.

Calculated water content in the top 1 meter of the martian surface cover.

Thus, the current conclusion from these neutron data sets is that there is much more water at and just under the martian surface than had been anticipated from all previous hints from earlier missions. In the polar and high latitude parts of Mars, it appears that water ice is quite abundant in the top meter or so of the debris that seems to cover most of the planet. The layer may be similar to permafrost in terrestrial rock and soil materials in Alaska, Siberia, and other high latitude land cover. Some of this martian layer can be considered as an ice bed, with subordinate amounts of rock fragments. This may grade into a predominance of fragments cemented by subordinate water.

As indicated above, some ice seems to extend into the low latitudes of Mars. There may be both a permanent subsurface layer and transient coatings. This perspective view of the Charitum Montes area (near Argyre Planitium), made by combining red and blue band MOC images with MOLA altimeter elevation data, shows a coating of (water?) frost on the hilly surface.

Frost-covered hills on Mars in the Charitum Montes region at about 57 degrees north latitude; MSSS image.

Frost had actually been seen closeup from the Viking 2 lander, as shown here:

Frost (white) coating some of the martian surface adjacent to the Viking 2 lander.

Frozen water has also been observed in shadlowed portions of martian craters:

A MOC image of a martian crater in which the lightest tone outside the rim may be snow or frost.

During each martian year a fraction of the water ice evaporates and is transported in the thin atmosphere to other locations. The transportation mechanism may be condensation of sublimed water and CO2 as coatings on dust stirred up by the strong martian winds. Estimates of the amount of water thus bound to the surface environment have ranged from the total present in Lake Superior to much higher.

Such observations have led Philip Christensen and associates, planetary geologists at Arizona State University, to postulate that for periods of thousands of years conditions on Mars have permitted snow, frost, and ice to accumulate over wide expanses between the polar ice caps. This happens during certains phases of the change in Mars' rotation axis from 15° to 35° from the vertical relative to the orbital ecliptic plane. (They postulate from their model that early in martian history the shift ranged from 0 to 60 degrees.) The change proceeds at a rate of approximately 1 degree per 100000 years. This shift is oscillatory, currently going from 15 to 35 and back to 15 degrees. During the process the climate changes owing to the different angles at which solar radiation hits the martian atmosphere and surface. At the higher angles, the poles receive more radiation, thus causing more water and carbon dioxide to evaporate and redeposit as snow and frost in lower latitudes. As the pole returns to lower angles (presently, now at 23°), this frost and snow resublimes and returns to the polar regions.

Besides the frost observations, another line of evidence they cite is the presence of the local gullies, such as those in the crater above. They believe that the water may be covered during low latitude accumulation and perhaps converted to ice. But climatic conditions at some stage bring about melting that carries the water just below the surface to crater walls and cliffs where the outflow of this groundwater gives rise to the numerous small gully channels.

MOC images may be monitoring transient "fogs" in the circulating atmosphere that are made up of water vapor and perhaps ice crystals. Look at this image:

MOC image of martian fog, which develops ripples as it enters a crater; MSSS image.

The uniform gray is thought to be the "fog". As it passes across a crater (66°S), the topography causes a disturbance that produces ripples in the water-bearing thin atmosphere.

In a widely held model, many martian specialists believe the planet began with an active magnetic core, had a much thicker atmosphere than present, was warmer, probably had water, and may have had primitive life. Mars probably changed dramatically in its early years to become more passive ("dead") but the possibility of water ice, when/if confirmed by landings in 2004 and later, indicates that somehow life of some kind may have survived since its glory days in the first billion years.

This seemingly valid discovery of surface and atmospheric water needs verification and more specific new data. Needless to say, the likelihood of abundant water has galvanized that segment of the scientific community that promotes an ultimate manned mission to Mars. Presence of extractable water not only supplies drinking needs but processes exist to break down the water into hydrogen and oxygen gases which can be made part of a fuel system to power vehicles returning to Earth. Oxygen thus released could be used for breathing in any base established on Mars for continuing manned exploration. A number of missions to continue exploration have either been approved or are being carefully planned and considered. Among these that already have happened are ESA's Mars Express and two NASA Mars Explorer Rovers (MER) both targeted to start for Mars in 2003 when Mars will be in an orbital position that brings it as close as 35 million miles from Earth.

(The Japanese Space Agency sent a Mars probe, called Nozoma, in July, 1998. Because it failed to get enough "kick" to its thrust towards Mars it had to receive the needed boost by repeated orbits past the Sun. This meant that the total trip was 4 1/2 years long. As it approached Mars, onboard systems failed and the spacecraft was lost without achieving any of its goals).

The Mars Express Mission

The European Space Agency's Mars Express was successfully sent towards Mars on June 2, 2003, and arrived in December of that year. It is pictured in a sketch below.

Artist's sketch of the Mars Express.

Its instruments are described at this Mars Express site. Among its 9 instruments is MARSIS, a radar capable of penetrating many meters into the Mars surficial deposits. It also carried a lander, named "Beagle 2. This view is an "exploded" diagram of the prime instrument on this spacecraft:

Principal instruments on ESA's Mars Express.

Mars Express orbited Mars successfully and on December 23, 2003 released and propelled the Beagle 2 towards its landing site. After initiation, nothing has been radioed to Earth indicating a successful landing. Meagre evidence indicates that either the probe was destroyed enroute or has not deployed correctly (even if intact, its radio antennae may be pointed such that no signal is leaving the surface). Thus, this part of the mission failed but the Express will send data back, thus rescuing the effort from total disaster.

But the Express orbiter is working well, as indicated by the next two images covering parts of Valles Marineris. Its imaging device produces stereo, so that the resulting views have a more 3-dimensional character than normal (but, of course, previous orbiters have yielded 3-D imagery after processing). The ground-penetrating radar deployed its three booms (holding antennae) and will become operational by May, 2005. Examples of a vertical and a perspective image of a region are given by these views of part of Valles Marineris.

Another Mars Express near vertical view of V. Marineris.

A perspective view of the terrain near Valles Marineris, imaged by the Mars Express orbiter.

Another pair of examples are the chaotic terrain in Aureum Chaos near Valles Marineris. The nature of that terrain is evident in the diversity of forms in the vertical view. When part of the image is converted to a perspective view, the nature of the hills displayed leads to questions about their origin. One view considers them to be the result of differential settling as underlying ice was melted.

Chaotic terrain in the Aureum Chaos region.

Perspective view of part of Aureum Chaos, highlighting the 'bumpy' hills.

Another image shows curved grabens (uplifted) and horsts (downdropped) blocks caused by faulting in the Tharsis region, in which the martian crust has been generally raised and stretched causing tensional stresses that result in this faulting.

Curvilinear faulting in the Acheron Fossae section of the Tharsis region.

This Mars Express image shows the Reull Vallis, interpreted by ESA scientists as a valley that almost certainly was formed by low viscosity fluid erosion, namely water.

Mars Express orbiter camera view of Reull Vallis, believed to have been formed by running water.

One surprise Express find: a standing body of frozen water in a large "pond" within a crater some 35 km (21 miles) diameter in the Vastitas Borealis region at a high latitude south of the Northern Ice Cap:

Frozen water ice at the bottom of a crater; this 'pond' is about 10 km (6 miles) wide.

Mars Express has also confirmed the presence of water in the South Polar Cap ice. It has an instrument, Omega, that has a Visible-IR spectrometer. Below, the right image is a visible color view of part of that Cap; in the center, the blue pattern demarcates the frozen carbon dioxide; in the left image, the blue indicates a frozen water response:

Mars Express Omega images for water (left), carbon dioxide (center), and a visible color rendition.

Among significant findings by Mars Express so far are the detection, using the Planetary Fourier Spectrometer [PFS]) of trace amounts (10 parts per billion[ppb]) of methane (CH4) and water vapor in the martian atmosphere. These seem to be more concentrated in certain regions. Consider the next two diagrams and an MGS MOC image of an area in Arabia Terra:

PFS spectral curve, showing CH4 and water vapor W absorption blips.

Map of water vapor in the lower atmosphere over much of Mars, from PFS data.

Terrain in Arabia Terra, with small volcanic vents mainly on the left half of the image.

The methane may be residual from early days in the evolution of the atmosphere but its presence may indicate some youthful source(s). One could be from vaporized comet(s) that impacted the surface, but no large young craters have been found. A second possibility is from volcanic release, but again no visual evidence of recent volcanism has been detected. The third option is both provocative and conjectural: release from the decay of organic matter in surficial deposits. The co-association of methane and water vapor could point to either of the second and third options. But the presence of small volcanoes over the "highs" in Arabia Terra place this last option as presently the most favored Further observations are needed to determine if the CH4 is uniformly distributed or is concentrated geographically. Ultimately, to prove an organic nature for the methane, a future probe or lander hosting a mass spectrometer will be needed, since the isotopic proportions of C12 to C14 can clearly distinguish between an inorganic and an organic (biologic - bacterial decay) origin of the methane.

A recent idea from martian scientists based on Mars Express imagery claims to see evidence that water has been expelled from larger volcanoes over hundreds of millions of years. This conclusion is based on two arguments: 1) there are numerous small channels on the gentle slopes of these volcanoes that are possibly from water (but some could be lava channels); and 2) using crater counts and other age dating methods, the various overlapping flows on the volcanoes can be relatively dated (and from comparison wi6h crater data on martian plains, rough actual ages can be estimated). Here are the images released in support of these claims:

On February 23, 2005, at a European conference on Mars Express results, researchers presented information that interpretation of topography in Elysium Planitia can be evidence for a vast field (800 by 900 km [450 x 560 miles]) of what could be frozen water ice covered by a protective layer of volcanic ash. The flat plates, the fracture patterns, and the curved rims of inpact craters (typical of craters that form in ice) are the basis for their claim. They believe the ice to be a once liquid "lake" that quickly froze, perhaps as recently as 2 to 5 million years ago. This observation is a high priority for confirmation when the MARSIS radar on Mars Express is activated in May of 2005.

Mars Express image covering part of the so-called buried ice field in Elysium Planitia.

In one locality, the Mars Express image seems to indicate the ice is at or very near the surface, over a wide area, such that one interpretation holds it to be pack ice. In the image below, pack ice from the Arctic is shown next to the martian ice for comparison.

Martian and Arctic pack ice side by side for comparison.

In another region, the Mars Express may have detected a flowing glacier presumably of ice. It is shown here compared with a typical small terrestrial glacier:

A presumptive martian glacier compared with a terrestrial glacier.

In December 2005 various groups involved in Mars Express data analysis revealed important new information at a press conference. First, was confirmation that parts of Mars have phyllosilicates (flaky clay minerals) that resulted from weathering of ancient volcanic rocks. These clays contain water introduced when it was plentiful enough to produce these minerals during a hydrous phase of surface activity, probably early in martian history. Here is one map showing the clay mineral distriution, as mapped by OMEGA, shown in brown (the perspective view was created using the HRSC imagery acquired by Express):

Distribution of clay minerals (brown) associated with outcrops on the Valles Marineris section of Mars.

OMEGA also can detect certain sulfate minerals that, as will be discussed in the Mars Exploration Rover on the next page, have been found elsewhere besides the MER sites. This illustration portrays detectable Bieberite (a magnesium sulfate mineral) depicted in blue that forms almost exclusively through the action of water. The area shown is the Marwth Valley; other area where this mineral has been found include Arabia Terra, Terra Meridiani (within which the two MER spacecraft landed), and Syria Major.

Bieberite distribution in Marwth Valles.

That press briefing also included several of the first images created by MARSIS (described at this ESA website. The first image shows surface radar reflections from an area that includes part of the South Polar ice cap.

Strong surface reflections, probably from near surface ice; the lower image shows the ice cap (right) off the South Pole - the red line is the trace of the radar signal traverse.

Note that the radargram (an echo signal) splits under the ice cap. The top bright echo is a surface reflection from the ice; the bottom echo marks the base of the ice. The thickness is up to 1.1 km (0.65 miles).

In this region, deep radar penetration has detected reflections from a large (250 km; 156 mile diameter) bowl-shaped feature which is being interpreted as a buried impact basin.

Radar images suggesting a buried impact structure.

The outline of this buried basin is plotted on this map of Chrysae Planitia.

Outline of the buried basin.

A large number of images are being made by the M.E. spacecraft and some are released periodically. Seek these on the Mars Express home page site.

The Mars Exploration Rover (MER) Missions

The American Rovers are another story with happy results. The place to start is the JPL Rover Home Page; after looking at its options choose Overview. Also, visit the JPL movies that set the stage for the Rover program. Access through the JPL Video Site, then the pathway Format-->Video -->Search to bring up the list that includes "Rough Guide to Mars", February 4, 2003 and "Rover Mission to Mars", June 6, 2003. To start either one, once found, click on the blue RealVideo link. A third webcast in the series also concentrates on the Rovers but is brought online through a different pathway, Access it through the JPL Video Site, then the pathway Subject-->Von Karman Series 2003 --> Format -->Webcast --> Search to bring up the list that includes "The Mars Exploration Rovers", August 21, 2003. To start it, once found, click on the blue RealVideo link.

The two MERs are both designed to search for water using a variety of instruments, including a mini-Thermal Emission Spectrometer, a Mossbauer Spectrometer, and Alpha Particle X-ray Spectrometer. Each MER looks like this:

Artist's painting of a MER with principal instruments labeled.

The labeled components show up better in this schematic diagram:

Schematic of the MER.

The Mars people at the Jet Propulsion Lab have produced a video of both landing and then deployment that can be accessed at this website. I have downloaded Microsoft MediaPlayer (MPEG links) to monitor the animation (QuickView also works). This overview is highly recommended, especially since it highlights the technical achievements involved (shown on a PBS NOVA program prior to the landing).

The four major components of the MER spacecraft are sketched and labeled in this schematic (see caption for more information):

The four major components of the MER: top = the stage with the main propulsion rockets; second = the back shell that separates with the Rover, includes the parachute; third = the Rover itself and its landing support (cushions); bottom = the heat shield that separates from the Rover before final descent.

General communications with, and data from, the two rovers are transmitted either directly back to Earth (about 20% of the total) or are related to Odyssey, MGS, or Mars Express, according to this scheme:

Signal communication scheme for the Mars Rovers.

MER-1, nicknamed "Spirit" was launched towards Mars on June 10, 2003. MER-2, called "Opportunity", was launched on July 7, 2003. Here is a plot of the landing sites for Express's Beagle 2 (failed) and the two MER set on a backdrop of the Nars surface in a global projection:

Landing sites on Mars for the three recent probes now enroute to the planet; ignore the click statement (doesn't work in this download).

Spirit arrived at the Red Planet on time and sent its Rover to the surface with a successful landing at 8:35 PM (PST) on January 3, 2004. The manner of its landing is spectacular (consider the vehicle needed instructions [some were preprogrammed] sent over a distance of more than 100 million miles) and perfect in execution.

Spirit is settled in the expansive Guzev Crater, which may contain frozen water inside. Opportunity will go to Meridiani Planum and land among rocks rich in hematite (iron oxide) which can be associated with water-rich conditions. Here are the landing sites as mapped using Mars Orbiter data:

Map showing the two rover sites

This map places Gusev Crater in context with its regional surroundings:

Map showing the region that includes Gusev Crater.

The crater, which is about 200 km wide (125 miles) appears as follows in a Mars Orbiter image and below it a Mars Global Surveyor image:

Gusev Crater.

MGS image of Gusev crater; note the dark patch (basaltic flow?) and the lighter (gray) tone around some of the features inside the crater.

A map of elevations in and around the crater appears here:

Map of Gusev crater, the MER-1 landing site; note the ellipse that defines the targeted landing site.

The rationale behind choice of Gusev as one of the MER sites was based on several criteria: 1) the apparently smooth, flat surface is typical of lake beds (Gusev was postulated to have been filled with water at some time); 2) a long 800 km [500 mile], sinuous channel, Na'adim Vallis, seems to have breached the crater walls; 3) faint layering is visible in high resolution images of the crater walls. In addition, another constraint on site selection was to have it about 180° from the second rover site, so that one site faced Earth during an approximately 12 hour period (allowing signal transmission) and the second site could broadcast during the other 12 hour time frame (Mars' day is a little longer than 24 hours).

Soon after touchdown, Spirit was located by the Mars Global Surveyor, in this MOC image, which also shows what is interpreted to be surface disturbances caused by the bouncing (an estimated 28 times) of the airbag-cushioned rover as it moved up and down after first impact:

MOC image of the Spirit rover touchdown site; the large dark circular feature appears to be an impact crater, named Bonneville, showing dark material underneath..

The Spirit Rover took a picture of itself using the Navigation camera mounted on a pole at the top. Here it is sitting on the surface:

Looking down on Spirit as it rests on the surface inside Gusev crater.

Pre-landing interpretation of the Gusev floor's geology led to the assumption that this crater;s floor was once covered with water, i.e., it was an ancient lake. Thus rocks within, and perhaps the soil, might show some signs of life, since water normally is a prerequisite. The first color image produced by Spirit does not show any direct evidence of lake deposits; in fact, it closely resembles surfaces imaged by the Vikings and Pathfinder:

First color image of the immediate surface around Spirit in Gusev Crater.

None of the rocks looked at during the early traverses (examples just below) seem to show lacustrine layering (lake bed deposits on Earth often show narrow bands of alternating composition - light/dark/light/dark - indicating seasonal changes). First impressions are that these rocks are similar to basalts, which may be the dominant rock type on Mars. Even if Gusev does contain lake deposits, many (most?) of the surface rocks at the site could be ejecta from impacts beyond the crater that penetrated into basaltic bedrock. The hope for confirming lake beds rests mainly with the presence of their characteristic rocks as ejecta from local smaller craters within Gusev Crater. These rocks may be lighter in color/tone; several lighter rocks have been spotted so far

Rocks close to the MER Spirit landing area.

While waiting to deploy the Rover on its first excursion, sensors on Spirit acquired various imagery and data. Look first at a 360° panorama around the touchdown site, made using more than 200 images (scroll horizontally to see the full extent):

Panorama of the landscape around the Spirit landing site.

The surface within the crater is not all flat. Low hills are seen in the background. These initially were called the East Hills. Chances are the hills themselves are upthrown floor or interior peak rocks made during Gusev's impact formation and would likely be older martian crust (basaltic) rather than lake bed deposits.

Closer view of the East Hills.

Later seven crests along the hills were remaned after the 7 astronauts who died in the Columbia Shuttle disaster. Here they are, seen first in a map and then in a panoramic view from Spirit:

MGS view of the Gusev crater interior showing the low topographic features now named Columbia Hills.

The names of the 7 Columbia astronauts tied to their respective hills.

The onboard MTES (Mini Thermal Emission Spectrometer) has produced spectra for the area close to the instrument. Both silicates and CO2 were detected; the latter is not in the rock/soil but in the martian atmosphere. Here are the plots.

Bound water signature in martian rocks/soil

Spectral signature for the presence of magnesium carbonate.

Spirit took off on its first excursion on January 14, 2004. The planned traverse is shown below. The first major objective was the impact crater named Bonneville which has excavated the possible lake beds to a depth of 30 m. Rocks enroute and there will be examined to see if they are compatible with the types formed in lakes. Then Spirit will head eastward towards the East Hills (probably too far away [more than 3 km] to actually reach).

The pathways from the Spirit touchdown location (green dot) to Bonnevile Crater, thence across the plains towards East Hills.

Using a special technique, the Mars Global Surveyor was able to image the Bonneville scene at 0.5 m resolution, sufficient to pick out the landing site platform, the travel track to Bonneville, and the rover itself on the edge of the crater ejecta slope (note that the surrounding blanket is lighter in tone than the general martian surface traversed).

Very high resolution MGS image of the Spirit site, revealing the rover and the track it produced as it reached Bonneville crater.

The trip to this crater (whose dark surface suggests basaltic rock) took time, as experience was gained in navigating the Rover from a million miles away. The first stop was an analysis of a football-sized rock nicknamed "Adirondack" (an American Indian name for "They of the Great Rocks". It is believed to be volcanic (likely, basalt) in nature. Here are two views of this rock, one in the normal natural color and a second in which the blue band contribution has been raised to give a sense of the rock material below its thin dust cover.

The Adirondack rock at the Spirit touchdown site.

Another view of Adirondack, with blue band emphasized.

Enroute to Adirondack, Spirit's analysis of nearby soil showed the presence of olivine, a greenish magnesium-iron silicate that is a constituent of basalt. The mineral probably is present as loose grains blown to the site by winds.

This view shows the extended robotic arm (Instrument Deployment Device: IDD) containing several of the analytic instruments up against the Adirondack rock:

Spirit's robotic arm emplaced against the Adirondack rock.

On January 21, 2004 Spirit went temporarily into a "repair mode", as it ceased to send back data although ground controllers at JPL could still communicate with it. Thereafter, several small streams of data were received but were largely unusable. The problem has been diagnosed as a software misfunction in which the storage device simply ran out of memory when commands were misinterpreted, and caused file corruption. The "flash memory" has since been purged and debugged, and functions reset. Mission Control is cautiously optimistic that the Spirit Rover can continue its excursions and collection of scientific data indefinitely and that the same problem in Opportunity can be avoided by modifying its software.

On January 30, Spirit returned a spectral analysis of the Adirondack rock, confirming it to be basaltic in composition, as seen in this spectral curve:

Spectral analysis of Adirondack; the minerals identified are consistent with a basaltic (Fe/Mg-rich; Si-poor) composition.

Then, on February 4th Spirit began a visual inspection of the Adirondack surface. On a "hunch" the operational team suspected there might be a thin coating of dust on that surface. Attached to the RAT (Rock Abrasion Tool) is a wire brush. The rover was instructed to brush off a small patch on the surface, with this result:

 Video view of part of the Adirondack surface, showing dark rock beneath light dust removed by brushing.

The dust coating (almost certainly hematite) was less than a millimeter thick; it may be adhering by electrostatic forces. This dust appears to be widespread across Mars' surfaces and may be compromising some of the compositional data obtained from the Viking sites and from orbit (e.g., Odyssey and MGS). When the dark patch was examined by the Microscope Imager (MI), this image was obtained - it appears consistent with a rock having a texture typical of basalt.

MI image of the dust-free patch of Adirondack's surface.

Adirondack is the first rock to be drilled into, using RAT (Rock Abrasion Tool). Here is the rock showing the circular cutting outline:

The RAT circular indentation made on the Adirondack rock; size of cut area about 3 cm in diameter.

As Spirit moved on, it spied one unusual rock lying as float on the surface. This rock (below) is splitting into thin flaky layers or chips. It resembles a fissile shale on Earth but is richer in iron than most shales (but there are red shales). Such layering is usually a consequence of continuing deposition in a fluid medium, usually water.

A rock block that seems to have shale-like parting.

Spirit's Microscope Imager has looked at tiny dunes (sand ripples) as it traversed towards Bonneville crater. The resulting grains on a ripple crest range from angular to round (and may relate to the spherules found at the Opportunity site?):

Grains on the crest of a wind-generated mini-dune (ripple).

On March 10th, Spirit reached the rim of Bonneville crater (about 200 meters in diameter) and looked in to see the interior:

Colorized viewfrom Spirit into Bonneville crater.

View into Bonneville taken as Spirit moved up to the rim; the rover shown has been dubbed in as a 'cartoon' by JPL artists.

At this resolution, no obvious layers of rock appear within the crater (some blocks in the far slope may be loose or may be outcrop in otherwise loose fill).

While in the rim, Spirit took a pan camera image of a scuffed (scraped) surface. It shows that darker material lies just underneath, which may be basaltic sand covered by hematitic dust:

Pan camera view of the darker surface after the topmost layer was scuffed away.

Spirit's Microscope Imager has also examined a sand deposit on the Bonneville Crater rim. After it was scraped, this image shows a crust of lighter-tone granular material overlying a darker substrate:

Crust on the 'Serpent' sand dune.

The lower zone contains particles up to about 0.5 cm in diameters mixed with much smaller grains (~50µm).

Granular materials within the dune deposit.

As it moved from Bonneville, Spirit spied a large rock which was named Mazatzal. It was partially covered by windblown sandy soil

The Mazatzal rock beyond Bonneville crater.

Several RAT grinds penetrated this rock. It revealed at least two very thin layers which have different reflectivities, as indicated in this diagram

Reflectivity curves for the surface ground by the RAT; pre- and post-grind surfaces are shown.

The pre-grind surface is darker in the visible; after grinding the rock underneath is brighter. Thus, this basalt block has experienced some process that darkens its outermost layer (or deposits it). An analogy found in Earth rocks is the formation of "desert varnish" which is blacker because of MnO2; but this composition has not been confirmed for Mazatzal. Part of that dark surface remains in the RAT hole seen in the next image:

Microscope Imager view of a RAT penetration of Mazatzal; note the conspicuous light-toned vein.

The presence of a cross-cutting vein filled with light material has caused excitement among the Spirit scientists. Although its composition is as yet unknown, the filling is postulated to be the result of deposition of mineral(s) of secondary origin that precipitated out of a hydrous solution that came from beneath the basalt before it was released (probably by impact) from its bedrock. This is believed to be an indicator of hydrothermal activity after lava emplacement and cooling. (Groundwater circulation is another suggestion.) This veining in this and another Gusev crater rock is the best evidence so far for some water having affected the bedrock present in the crater.

However, APXS data have confounded interpretations of whether a water body at least briefly covered the Gusev surface after the basalt blocks were brought to the surface. Examine this plot of Magnesium oxide (MgO) content versus SO3 content of the very thin veneer covering several Spirit rocks including Mazatzal:

APXS plot of Mg versus sulphur trioxide in the surface covering of several Spirit rocks and Gusev soil.

The three large symbols on the ordinate are from the rock materials beneath the veneer. No sulphur is present, indicating its absence in the basalt. However, fresh, brushed, and slightly RATed surface all have evidence of sulphur, shown as a trioxide but without any specific mineral type being identified (still unknown). Speculation has it that this is some type of coating that may have been associated with precipitation of sulphur-bearing minerals on the surface and in the soil. A similar pattern is found for the data that indicate Chlorine (Cl) to be present in the veneer and to increase in proportion to the rise in SO3.

APXS plot of Chlorine versus Sulphur trioxide in Spirit rocks and soils.

Both Chlorine and Bromine are found in coatings on rock from both the Spirit and Opportunity sites. On Earth Chlorine and Bromine tend to increase linearly in evaporites. The situation is somewhat different in rock coatings from both MER sites, as shown in this general plot of the concentrations of these two co-varying elements.

Concordant variation in Cl and Br content in rocks on Earth, in Mars meteorites, and in rocks from the two MER sites.

As of mid-2005, the story at the Gusev Spirit site is this: The only rock type firmly identified is basalt; hematite is of the red variety; although several rocks may contain hydrous mineral(s), no other signs of lake water or water-related sediments, including strata of any kind, have as yet been detected; however, hydrothermal or groundwater activity from subsurface sources has been verified. Coatings containing Cl, Br, and SO3 remain enigmatic. One hypothesis is now more favored: the coating(s) may be dust that has been cemented as a crust onto the surface with water from an atmospheric source. In retrospect, the Gusev site does not now seem to have had a lake or extensive sediments, still, water activity is probable but not to the extent favoring life, and the sinuous channel may not be fluvial in nature. The possibility that Gusev contains sediments below a basalt layer as established from the composition of the rocks scattered about the surface, the latter thus being a later emplacement of covering lava, cannot yet be discounted but later cratering into the basalt has not penetrated to the depths of these possible deposits.

Spirit has in early 2005 reached the Columbia Hills, where hints of layering can be seen through its pan camera. Enroute, Spirit has examined other surface rocks, especially those lighter in tone, as seen in these views, to test the surface coating hypothesis or find alternate explanations:

View towards the Columbia Hills, showing both lighter and darker toned rocks (probably basalts) on the surface.

Spirit has spent considerable time on the Columbia Hills, visiting a number of outcrops. These two maps show the traverses to and then on the Columbia Hills.

Traverse to the Columbia (East) Hills; Bonneville crater is in the upper left.

More detailed look at the traverse pattern.

As the Columbia Hills were approached, possible outcrops were detected:

Possible outcrops at Columbia Hills, seen by the Pan camera on Spirit.

As seen in this MOC image from MGS, the Columbia Hills appear as below.

MGS MOC image of the Columbia Hills.

As Spirit closed in, the rounded nature of these hills becomes more apparent, as shown in the above images. From these images, one might get the impression that they are rather high. In actuality, the highest point is just 90 meters above the edge of the float block apron. This MOC image shows that these Hills are just a "blip" on the surface inside Gusev Crater. Nevertheless, they may reveal the nature of materials in the pre-impact surface.

MOC image of the Columbia Hills and two large craters (one largely buried) within the Gusev Crater basin.

This next image is a perspective of the Columbia Hills made from the same MOC data. It shows the path being followed at West Spur by Spirit during its explorations.

Computer-generated perspective view of the Columbia Hills; black line traces the exploration pathway for Spirit on West Spur.

West Spur was examined in early June, then moved to Lookout Point, and finally has run over a low pass into the Columbia Hills Inner Basin,

As these hills were neared, Spirit stopped to trench the outer slope sediments and found suggestive proof of water action. The trench showed varying amounts of Mg and SO4 (expressed as sulphur), with signatures suggesting possible Kieserite, a magnesium sulphate mineral present in abundance at the Opportunity site. Note this plot:

Plot of Mg vs Sulphate content of soil entrenched near the Columbia Hills.

An outlier (West Spur) of the Columbia Hills was reached in mid-June. This view shows inconspicuous, non-definitive evidence of layers.

Spirit at the base of the Columbia Hills

However, the loose float around this spot was indeed bedrock of a blocky nature. Some rocks were more slablike, possibly of a sedimentaary nature. Instrumental measurements will zero in on the question of their origin. Here are two scenes containing rocks.

Rock float at the base of the Columbia Hills; possible nodules occur on theee rocks; note wind-formed ripples">

Close-up of rocks, including one nicknamed 'Pot-of-Gold', at the approach to the main group of Columbia Hills.

Pot-of-Gold, the flat rock in the image above, may also be layered. Inspection with the Microscope Imager has revealed rather peculiar nodules, some at the end of tiny columns.

Closeup of the surface of Pot=of-Gold, revealing irregular shaped nodules, about 2 mm in long dimension, sitting atop material acting as a pedestal.

Mossbauer (spelled in label as Moessbauer to obviate use of 'o umlaut' in German) spectra for Pot-of-Gold shows the presence of Fe+2 peaks attributable to olivine and pyroxene, and four extra peaks representing Fe+3 which is best explained as hematite. The rock seems to be a basalt that has been altered to some extent to hematitic iron oxide.

Mossbauer spectra for Pot-of-Gold.

While on West Spur, Spirit got its first good look at thin dark layers outcropping midst the regolith, rock fragments and small boulders. This is likely to be older basalt flow rock than seen elsewhere that was brought up from the crater floor during the Gusev cratering event.

Side of West Spur, with thin outcrop of dark rock near the left edge and isolated slabs in the lower right.

A lighter-toned outcrop, dubbed "Clovis" rock, was found on West Spur. It is currently being analyzed.

Clovis rock on West Spur; note wheel tracks of Rover in softer, darker material; hill in background is 15 km away.

APXS plots for a basaltic rock (Humphrey) and the Clovis rock show one major difference: At least some of the Clovis rock contains Magnesium, Sulpher, and Bromine - indicators of either a sedimentary unit or alteration that includes Magnesium Sulphate (Epsom salts).

Spectra for the Humphrey and Clovis Rocks.

In December, 2004 results in a delayed processing of Mossbauer data from Clovis has brought to light the most rewarding discovery yet at the Meridiani site. The mineral Goethite, hydrogen iron oxide, HFeO2, containing 10% water by weight has been identified, as shown here:

Mossbauer spectra from the Clovis rock, which shows the presence of Goethite.

On Earth, Goethite - a very common mineral associate with Limonite - is found as an alteration product or as a direct precipitate in the so-called "bog iron" deposits, which are the result of a reducing, water-rich swampy environment. That form of Goethite is usually produced with the aid of bacteria but can also form inorganically. The mode of origin of the Clovis Goethite is still "up for grabs" but the very presence of this mineral indicates a significant role for water in Mars' past.

Looking at other nearby parts of the Columbia Hills, blocks of rock appear to be basalt covered with iron coating

Blocks that look like basalt covered by iron mineral(s).

But of renewed interest in the possibilities of significant layered rock units are these two views looking further from the West Spur position. The lower image is a closer view (less sharp) of the inclined layers seen in the upper image. As of August 18, these rocks are slated for a visit by the Spirit rover soon in the future.

Layered rocks and lighter rocks in the Columbia Hills.

Closer view of the inclined light-dark rock units.

The first close-up view of layered rocks is the detached block named Tetl, shown here:

The Tetl rock, a float block with layering, on the Columbia Hills.

Tetl comes from an outcrop area that consists of distinct layered units, seen in this composite image.

The Tetl outcrop in the Columbia Hills.

As Spirit drove off the Columbia Hills it encountered in the soil and rock fragments a pronounced white encrustation that looked much like a crystalline coating. Chemical analysis show this to be mostly magnesium sulphate. Whether formed by surface water evaporation or by groundwater seepage containing dissolved salts, the discovery is the best evidence yet for the onetime activity of water at the Gusev crater site.

Encrusted magnesium sulphate on a Columbia Hills outcrop.

Despite "limping" along with two of its six wheels having problems, Spirit has visited more individual layering features - outcrops and loose rock. Uchben is an example where there is some evidence that the layering is caused by volcanic ash deposition. Microscope Imager views of surfaces close-up show angular flaky particles similar to those occurring in terrestrial ash deposits. Water has been found in its composition: the water may have been in the volcanic material derived from the interior, or may have been present in later altering hydrothermal solutions, or could have been incorporated from a standing body of water once at the site of the Columbia Hills (probably before their present uplift). So far, deposition by direct ashfall, by wind action, or in water all remain possibilities:

Layers in the Uchben rock and its surroundings.

Because of wheel problems the Spirit rover is now being more cautiously guided. By disabling its front right wheel, and proceeding slowly, Spirit has covered much of the first ridge in the Columbia Hills, has moved over West Spur, and is now in the flats:

As Spirit traversed the West Spur, it encountered a rock nicknamed "Wishstone" whose appearance enticed the JPL team to decide to investigate it in some detail. The RAT was used to cut into its surface. The next two images show Wishstone (near center) after the abrasion hole was produced and a close-up of what was exposed:

The Wishstone rock.

Exposed subsurface in Wishstone after the RAT had cored into it; scene is about 5 cm across.

The exposed interior shows that Wishstone has a granular texture. A few dark fragments are noted. The texture is consistent with either a volcanic tephra deposit or water-deposited fine particles; the interpretation remains ambiguous. The APXS instrument produced this plot of elements detected. The most significant feature is a higher than average (using West Spur results as reference) amount of phosphorus. This points to some mode of aqueous activity affecting the rock before it left its initial location (by impact ejection or by rolling over the West Spur slope).

As Spirit then moved over the flatter terrain, its camera sent back an image in which the soil had a noticeable amount of very light tones. The APXS examined this soil and found it to consist of at least 50% of salts, including iron sulphate, and a higher phosphorus content (whose host mineral[s] have not been identified).

False color image of the disturbed soil described above; the light tones are richest in sulphur and phosphorus.

Spirit continues to move beyond the Columbia Hills visiting Rover team-named landmarks as seen in this perspective from orbit:

The Columbia Hills being traversed by Spirit.

These hills seem to be underlain by layered rocks. Most evidence so far points to volcanic deposits, perhaps of several types such as flows and ash falls. At an outcrop named Methuselah, a rock called Keystone shows thin layers:

Closeup of the surface of Keystone rock, showing strong hints of layering.

With one exception (shown on next page), trenches in and beyond the Columbia Hills did not disclose a light-colored bedrock unit comparable to that we shall see at the Opporutnity site. The layers seen in the Columbia Hills appear to be made up of grains of basalt loosened and transported into thin units as local deposits. The interpretation now favored has subsurface water leaching out chemicals from bedrock and soil, rising towards the surface, and depositing the sulphate salt near the surface as a cement for the granular units. This is the best evidence to date for the action of water at the Gusev Crater site; this water probably came from beneath the surface rather than from any standing surface water.

From time to time, both Spirit and Opportunity's cameras have captured the quick passage of atmospheric micro-cyclones or "dust devils". One was shown on page 19-11; here is another example:

A 'dust devil' passing near the Spirit rover.

In a remarkably serendipitous event, Spirit has been given a new rebirth that makes its already exceeded design lifetime even longer. Over the year plus of operation both Spirit and Opportunity have been gradually coated with martian dust. Their solar panels were becoming sufficiently plastered by dust to cut the efficiency that the panels should have for generating electricity from solar photon input. This cuts down operational time and threatens to fall to minima in which instruments cannot work. Then, sometime between March 5 and 15, 2005, the power output of Spirit dramatically spiked upwards. By looking at its surroundings, the JPL team concluded that a dust devel, the atmospheric whirlwind that occurs in large numbers of mini-tornados, must have swept over Spirit, sucking up (vacuuming) the dust coating, and exposing the solar plates to near optimum efficiency. TV images of a part of the spacecraft taken before and after this lucky encounter show conclusively that Spirit has been cleaned:

A small area on the Spirit rover seen dust-covered (left) and nearly dust free after March 15, 2005, presumably swept clean by a passing dust devil.

(The Opportunity team is hoping intensely for a similar quirk of fate to rejuvenate its power supply.)

As of late August, 2005 Spirit has climbed Husband Hill, a peak in the Columbia Hills (see map above), and spent several months gathering data. Here is a panoramic view made as Spirit (put in the scene by trick photography) in November started its descent from the top; in the scene are some layered rocks which will likely be visited in the future:

Spirit looks at the surrounding plains from the side of Husband Hill.

Thus, the history of exploring the Gusev crater site was at first suggestive of the absence of any strong evidence for water activity but once the Columbia Hills were reached, that evidence was acquired in several settings. The results from the MER Opportunity rover, which discovered minerals almost certainly of hydrous origin, are covered on the next page (19-13b).

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Primary Author: Nicholas M. Short, Sr. email: [email protected]