Missions to Mars during the Third Millenium Part-1 - Remote Sensing Application - Completely Remote Sensing, GPS, and GPS Tutorial
Missions to Mars during the Third Millenium Part-1

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. 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 President's speech given on January 14, 2004 at NASA Headquarters which can be read at this NASA history site; this talk strives 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 Odyssey 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.

Here is an artist's rendition of the Odyssey spacecraft:

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. A gamma ray spectrometer (GRS) obtains 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 next 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.

Color composites made by combining THEMIS Day and Night images have revealed additional information. In the color assignment used, reds generally mark exposed bedrock, blues denote loose, often sandy debris, and yellows may indicate coarser particulates derived from bedrock. Here are two image examples:

Day/Night THEMIS IR image of the terrain in Meridiani Planum about 400 km northeast of the Opportunity Rover site.
Day/Night THEMIS IR image of the interior of the large Gale Crater.

THEMIS is adept at picking out surfaces containing a variety of clay minerals (blue), as shown in this image:

The dark blue indicates a surface containing considerable clay minerals.

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.

How are gamma rays and neutrons produced by cosmic rays? Incoming cosmic rays--some of the highest-energy particles--collide with atoms in the soil. When atoms are hit with such energy, neutrons are released, which scatter and collide with other atoms. The atoms get " excited" in the process, and emit gamma rays to release the extra energy so they can return to their normal rest state. Some elements like potassium, uranium, and thorium are naturally radioactive and give off gamma rays as they decay, but all elements can be excited by collisions with cosmic rays to produce gamma rays. The HEND and Neutron Spectrometers on GRS directly detect scattered neutrons, and the Gamma Sensor detects the gamma rays.

A preliminary map (below, 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.

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.

Russian co-investigators 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).

Calculations indicate there is enough water present in rocks and soil near the surface so, if released, water could cover the entire planet by up to 10 cm (4 inches) in thickness.

Although up to 20 elements can be detected by GRS, efforts were concentrated on these six: H, Fe, Si, K, Cl, and Th. Here are the results for Iron, Silicon, and Thorium:

Another 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 GRS map of potassium distribution on Mars.

But water continues to be the focus of intense investigations. Improved water maps (based on hydrogen absorption of neutrons) continue to be released to the scientific community. 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 only in water; hydrous minerals may contain both water and OH). Intermingled water increases to around 50% (yellows and oranges) to 70% (dark red to black) at the surface 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 shadowed portions of martian craters:

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°. 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 significant amounts of water ice, when/if confirmed by future landings (preferably, polar latitudes), 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 of which started for Mars in 2003 when the planet was 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 was radioed to Earth that would validate a successful landing. Meagre evidence indicates that either the probe was destroyed enroute or did not deploy 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 has sent abundant data back, thus rescuing the effort from total disaster.

So, 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 became operational in 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:

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.

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 with crater data on martian plains, rough actual ages can be estimated).

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 by the MARSIS radar.

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, on the right:

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 Express's HRSC imagery):

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 segment 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 areas 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 top 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.

The most significant finding by Mars Express was released in March of 2007. The MARSIS has completed enough of its scheduled survey of the southern polar ice cap to produce this map of the thickness of the frozen water below a surface of mixed water ice and frozen carbon dioxide:

Radar-determined thickness of martian ice at the South Polar Cap.

The maximum thickness is 3.7 km (about two and a half miles). The ice seems to have a purity of > 90% H20. If all of this ice were melted, there is enough to cover the entire martian surface with an "ocean" 11 meters (about 35 feet) deep.

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 emerging from its now opened inflated airbags.

This schematic diagram shows the main instruments on a MER.

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.

The manner of its landing (much like the earlier Pathfinder) is spectacular: consider that the vehicle needed instructions (some were preprogrammed) sent over a distance of more than 100 million miles) and each step had to be perfect in execution. Using both parachutes and complex airbags, the landing sequence is depicted here:

Schematic sequence of the landing modes for the MERs.
True size photo of the inflated airbags.

Source: http://rst.gsfc.nasa.gov