December 4, 1997
The Viking soil analyses and the information from the 12 meteorites assumed to be of Martian origin pointed to a rather primitive surface composition of Mars. The first in-situ analyses of rocks during the Pathfinder mission showed that the Martian crust is probably as highly differentiated as the Earth's crust.
To obtain rock samples for chemical analyses from the surface of a remote planet requires tools, which are very difficult to accommodate on and to operate from light-weight landers. For this reason, the cosmochemistry group at the Max-Planck-Institut fur Chemie in Mainz has concentrated its efforts from the very beginning on the design of a sensor with the capability to analyse almost all major and minor elements in any sample with which it is brought into contact. An instrument employing such a sensor -- the Alpha Proton X-ray Spectrometer (APXS) -- was originally designed and built by the MPI Mainz in cooperation with an international group of researchers (including colleagues from the USA and Russia) for a Russian mission to Mars (Mars-92). This mission was postponed twice (Mars-94, Mars-96) and then unfortunately lost soon after launch. Evidently, the group at the MPI Mainz was very pleased when asked by the Pathfinder project to also provide such an APX-Spectrometer for the NASA Mars Pathfinder mission to be mounted on the Sojourner microrover.
APXS results will for the first time be published in an article in SCIENCE, entitled "The Chemical Composition of Martian Soil and Rocks Returned by the Mobile Alpha Proton X-ray Spectrometer: Preliminary Results from the X-ray Mode" by R. Rieder, T. Economou, H. Wanke, A. Turkevich, J. Crisp, J. Bruckner, G. Dreibus and H.Y. McSween, Jr.
Soil analyses at the Pathfinder landing site gave almost identical values for each of the five spots visited. These compositions are also very similar to the ones measured at the two Viking landing sites. The soil is obviously -- at least up to mean latitudes -- thoroughly homogenized by dust storms on a planet-wide scale. It is rich in Mg and Fe, indicating mafic rocks as the dominant surface component, diminuated by impacts and weathering, and by reactions of the diminuated rock material with volcanic gases like SO2 and HCl, respectively.
On top of this, Pathfinder yielded the first chemical analyses of Martian rocks: The first rock analysed was called "Barnacle Bill". Its composition was a big surprise to all Mars scientists, as it turned out not to be mafic at all. The concentration of Mg was in fact quite low, but Si and Al were high, indicating a felsic composition as opposed to the general believe of a rather primitive mafic composition of Mars' surface material. Much to the contrary, this rock appears to be highly fractionated, similar to typical highly evolved terrestrial crustal rocks, and this also with respect to its high abundance of K, hinting at high abundances of all incompatible elements.
Comparing the composition of the rocks at the Pathfinder landing site -- which again appear quite similar to one another -- with the composition of the soil into which they are embedded and which is distinctly different from that of the rocks, it is obvious that this soil cannot be made from rocks typical for this site: Material from mafic geological provinces, compositionally similar to rocks that we can hold in our hands (the Martian meteorites, alias SNC meteorites), needs to be added after diminuation.
The researchers conclude that Mars must possess a variety of geological provinces with very different compositions, and that Mars is a planet, much more evolved than previously assumed. Thus, mobility is a must for all future landing missions to Mars, if Science wish to unravel the geological and chemical evolution of our neighbour planet, which appears to be almost as complex as that of our home planet -- the Earth.
December 5, 1997
ITHACA, N.Y. -- After studying more than 9,500 images taken during the acclaimed Mars Pathfinder mission, scientists report in today's journal Science (Dec. 5) that surface photographs provide strong geological and geochemical evidence that fluid water was once present on the red planet.
"We now have geological evidence from the Martian surface supporting theories based on previous pictures of Mars from orbit that water played an important part in Martian geological history," said James F. Bell, Cornell senior research associate in astronomy and a member of the Mars Pathfinder imaging team.
Bell, along with lead author P. H. Smith of the University of Arizona; Robert J. Sullivan Jr., Cornell research associate in planetary science; and 23 other scientists authored the paper, "Results from the Mars Pathfinder Camera." The report is part of a complete Mars Pathfinder mission report published in Science.
During the first 30 days of the Mars Pathfinder mission, the Imager for Mars Pathfinder (IMP) returned 9,669 pictures of the surface. These pictures appear to confirm that a giant flood left stones, cobbles and rocks throughout Ares Vallis, the Pathfinder landing site. In addition to finding evidence of water, the scientists confirmed that the soils are rich in iron, and that suspended iron-rich dust particles permeate the Martian atmosphere.
Bolstering their evidence for once-present water, the imaging team found evidence for a mineral known as maghemite -- a very magnetic iron oxide. Bell explained that maghemite forms in water-rich environments on Earth and could likely be formed the same way on Mars. Bell explained that reddish rocks like Barnacle Bill, Yogi and Whale rock show evidence of extensive oxidation on their surfaces. He said the oxidation -- or the rusting of the iron -- is possible only if water existed on the surface at some time and played an important role in the geology and geochemistry of the planet.
Mars Pathfinder's camera also revealed that Mars' atmosphere is more dusty and dynamic than expected, Bell explained. Surprisingly, the scientists found wispy, blue clouds, possibly composed of carbon dioxide (dry ice), traveling through Mars' salmon-colored sky. White cirrus-like clouds, made of icy water vapor, also circulate throughout the thin Martian atmosphere.
"We were surprised to see such variations in the clouds, particularly since Mars has such a thin atmosphere," Bell said. "We figured the atmosphere would be the same everyday, but there is a lot of real weather occurring there. It's a small atmosphere, but a vigorous one."
Looking at Martian rocks like Yogi, Barnacle Bill and Scooby Doo reveals that the rocks have been sitting on the planet's surface for billions of years, enduring a slow-motion sandblasting from a usually weak, dusty Martian wind. To carve rock with such a weak wind force requires a vast amount of time, Bell explained. "The slow, persistent weathering and erosion of the rocks is like water torture to the max," he said. "Mars really is an ancient world. We're still trying to sort it all out."
University of Chicago News Office
November 13, 1997
The answer, says a University of Chicago climatologist and his French colleague, is reflective carbon-dioxide ice clouds that retain thermal radiation near the planet's surface. The scientists' theory is published in the Friday, Nov. 14, issue of the journal Science.
"This is a problem that has perplexed scientists ever since the '70s, when Viking provided the first detailed images of Mars," said Raymond Pierrehumbert, University of Chicago Professor of Geophysical Sciences. "How can you account for Mars being warm enough to have flowing water, especially when the sun was actually fainter early in Mars' evolution?"
Pierrehumbert collaborated with French climatologist Francois Forget, from the Laboratoire de Meteorologie Dynamique du CNRS in Paris.
Previous models of the atmosphere of ancient Mars have incorporated carbon dioxide in the atmosphere to use effects similar to global warming to heat the planet. "The problem was," said Pierrehumbert, "when you try to put enough CO2 in the atmosphere to warm it sufficiently, the carbon dioxide condenses out. It was thought that the thick clouds that form as a result would reflect sunlight back to space and actually cool the planet.
"When we re-examined this, we found that this dry-ice 'blanket' actually warms the planet because it reflects infrared light back to the surface more than it reflects solar radiation outward."
The curious property of carbon dioxide ice clouds, as opposed to the water ice clouds found on Earth, is that the particles are large enough to scatter infrared light more effectively than visible light coming from the sun. Ordinary, Earth-type clouds absorb heat from the planet's surface and re-emit it both back to the surface and to outer space, losing half of the heat in the process.
"But the carbon dioxide clouds act like a one-way mirror, and, although not a lot of sunlight gets through to the planet's surface, what does reach the planet is converted to heat, which the clouds then reflect back to the surface," said Pierrehumbert. "This mechanism produces a large enough effect that it can, in fact, warm the planet to the point where it is possible to have liquid water."
Pierrehumbert said this climate model provides some clues as to the types of life forms that might have evolved on Mars. "If we're going to be looking for analogues of terrestrial life forms on Mars," he said, "then we should be looking for the kinds of organisms that might evolve in extreme environments, like the bottoms of oceans or in caves.
"The conditions on early Mars -- some four billion years ago -- were a little more like the conditions at the bottom of the ocean than like a rainforest. It would have been dark, warm enough for liquid water, but without a large energy source for photosynthesis," he said.
Pierrehumbert and Forget's model also extends the habitable zone on extrasolar planets and increases the likelihood that life exists outside our solar system. Previously, scientists thought that only planets orbiting within 1.37 astronomical units (one AU is the distance between Earth and the Sun) of a star could have water above the freezing point. But if the planets have carbon-dioxide ice clouds, they could have liquid water as far away as 2.4 AU. Mars is 1.52 AU from the Sun.
Similarly, carbon-dioxide ice clouds could have played a role in warming Earth when the Sun was fainter than it is today, preventing a global freeze that could have kept Earth locked forever in ice. If the Earth had ever cooled to the point where its oceans had all frozen, it would never have warmed up again because too much solar radiation would have been reflected back to space by all of the surface ice.
Pierrehumbert and Forget say their model fits well with a theory proposed by Carl Sagan and Christopher Chyba, and published in Science earlier this year, that a methane and ammonia atmosphere warmed early Mars. "The problem with methane," said Pierrehumbert, "is that it breaks down very quickly when exposed to sunlight, so you need a biological engine -- life on Mars -- to feed the atmosphere as the methane is depleted. Our model provides the starting conditions under which life could have evolved and started the production of methane gas. And once the gas forms, the carbon dioxide ice clouds actually shield the methane from sunlight and keep it from breaking down as quickly."
Pierrehumbert and Forget next plan to tackle the problem of what weather might have been like on early Mars, including the possibility of carbon dioxide blizzards and carbon dioxide-ice glaciers.
JET PROPULSION LABORATORY
October 9, 1997
Those observations, along with new images taken by the Mars Pathfinder rover and lander, and an update on the condition of the spacecraft, were presented at an Oct. 8 press briefing originating from NASA's Jet Propulsion Laboratory.
"What the data are telling us is that the planet appears to have water-worn rock conglomerates, sand and surface features that were created by liquid water," said Dr. Matthew Golombek, Mars Pathfinder project scientist at JPL. "If, with more study, these rocks turn out to be made of composite materials, that would have required liquid water flowing on the surface to round the edges in pebbles we see on the surface or explain how they were embedded in larger rocks. That would be a very important finding."
Golombek also stressed the amount of differentiation -- or heating, cooling and recycling of crustal materials -- that appears to have taken place on Mars. "We're seeing a much greater degree of differentiation -- the process by which heavier elements sink to the center of the planet while lighter elements rise to the surface -- than we previously thought, and very clear evidence that liquid water was stable at one time in Mars' past.
"Water, of course, is the very ingredient that is necessary to support life," he added, "and that leads to the $64,000 question: Are we alone in the universe? Did life ever develop on Mars? If so, what happened to it and, if not, why not?"
Despite recent communications problems with Earth, the Mars Pathfinder lander and rover are continuing to operate during the Martian days, when they can receive enough energy to power up spacecraft systems via their solar panels. The mission is now into Sol 94, or the 94th Martian day of operations, since landing on July 4.
"Everything that we have seen over the last 10 days (with respect to communications) is like a twisty little maze with passages all alike," said Jennifer Harris, acting mission manager. "I am happy to report that we have made contact with the spacecraft using its main transmitter. We were able to confirm that we could send a command to the spacecraft to turn its transmitter on and then turn it off.
"We don't know yet whether we are receiving that signal over the low-gain or high-gain antenna," she added, "but we should be able to determine this over the next few days."
The Mars Pathfinder team began having communications problems with the spacecraft on Saturday, Sept. 27. After three days of attempting to reestablish contact, they were able to lock on to a beacon signal from the spacecraft's auxiliary transmitter on Oct. 1, which meant that the spacecraft was still operational.
At that time they surmised that the communications problems were most likely related to depletion of the spacecraft's battery and uncertainties in the onboard clock. The last successful data transmission cycle from Pathfinder was completed at 3:23 a.m. Pacific Daylight Time on Sept. 27, which was Sol 83 of the mission.
Since then, efforts have been made during each Martian day to reestablish contact with both the primary and auxiliary transmitter and obtain engineering telemetry that would tell the team more about the health of the lander and rover. On Oct. 7, the team was able to lock on to Pathfinder's signal, via NASA's Deep Space Network 34-meter-diameter (112-foot) dish antenna in Madrid, Spain, for about 15 minutes, using the main transmitter. However, in repeating the process on Oct. 8, they did not receive a signal.
The rover, which receives its instructions from Earth via the lander, is currently running a contingency software program that was preprogrammed to start up if the vehicle did not hear from the lander after five Martian days. That program was powered on Oct. 6, on Sol 92 of the mission. In this contingency mode, the rover is instructed to return to the lander and begin circling it. This precaution is designed to keep Sojourner close to the lander in the event that the spacecraft was able to begin communicating with it again.
If normal communications are reestablished, the rover team will send new commands to Sojourner to halt the contingency circling and begin a traverse to a specific location.
Dr. William Folkner, an interdisciplinary scientist at JPL, presented data on the rotation and orbital dynamics of Mars, which are being obtained from two-way ranging and Doppler tracking of the lander as Mars rotates. Measurements of the rate of change in Mars' spin axis have important implications for learning more about the density and mass of the planet's interior. Eventually, scientists may be able to determine whether Mars' core is presently molten or fluid. The size of the core also can be used to characterize the thickness, or radius, of Mars' mantle.
"By measuring the spin axis of Mars, we can learn something about the interior of the planet, because the speed of the change in its orientation is related to how the mass is distributed inside," Folkner said. "If the core is fluid, its spin and the way in which the planet wobbles slightly will be different from the spin and wobble of a planet with a solid core.
"If Mars' core is solid, then it can't be less than about 1,300 kilometers (807 miles) in radius, out of the planet's total radius of 3,400 kilometers (2,112 miles)," Folkner added. "If the core is made up of something less dense than iron, if it's a mixture of, say, iron and sulfur, then the core would be bigger, but it couldn't be bigger than about 2,000 kilometers (1,242 miles) in radius."
New close-up images of dunes around the landing site are showing some scientists clear evidence that there is sand on the surface of Mars. Identification of sand, as opposed to dust or pebbles, is a significant factor in establishing that weathering processes such as erosion, winds and flowing water all contributed to Mars' present landscape.
"We've made significant progress in establishing that water was a dominant agent in forming the surface, and now we can say that there is another agent at work, and that is the wind, that has created and modified some of the landforms on a smaller and medium scale," said Dr. Wes Ward of the U.S. Geological Survey, Flagstaff, AZ, a member of the Imager for Mars Pathfinder team. "And because the water is no longer there, wind probably is the dominant agent shaping the Martian surface at this moment."
Ward showed images of Ares Vallis, taken by the rover and Viking 1 orbiter images to point out the structural difference in these surface features. While Viking 1 surface features around a rock nicknamed "Big Joe" showed drifts, the dune-like surfaces in the Ares Vallis flood basin resemble sand that has been blown southwest over the landing site. The presence of sand also points to the likely presence of liquid water, needed to create these small, 1-millimeter-diameter granules, and weathering agents such as wind to blow them into small ridges and moats present around the Ares Vallis rocks.
"The wind is quite an active agent," Ward said. "Sand is the smoking gun, and as far as I'm concerned, the gun is smoking and has Colonel Mustard's prints all over it. We are seeing sand at the landing site."
Dr. Greg Wilson, of Arizona State University, who is on the Pathfinder atmospheric experiment team, reported increases in the pressure of the Martian atmosphere and a drop in surface temperatures.
"We expect to see a continued increase in pressure and decrease in temperatures as the dust season approaches and winds begin to lift more dust into the Martian atmosphere," he said. "The dust season on Mars usually begins in the next few weeks."
Additional information, images and rover movies from the Mars Pathfinder mission are available on JPL'S Mars news media web site or on the Mars Pathfinder project's home page. Images from Mars Pathfinder and other planetary missions are available at NASA's Planetary Photojournal.
The Mars Pathfinder mission is managed by the Jet Propulsion Laboratory for NASA's Office of Space Science, Washington, DC. The mission is the second in the Discovery Program of fast-track, low-cost spacecraft with highly focused science goals. JPL is a division of the California Institute of Technology, Pasadena, CA.