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On Mars: Exploration of the Red Planet. 1958-1978



OTHER RESULTS



[414] Viking's explorations and discoveries did not stop with the search for life. The great disappointment felt by the biologists was tempered to a degree by the wealth of other findings.

Radio Science

One group of Viking investigators who did not have any scientific instruments of their own ^* on the four spacecraft but whose work assisted many scientists was the radio science team led by William H. Michael of the Langley Research Center. By analyzing the radio beams sent from Viking to Earth, specialists could determine precisely where the landers touched down and certain atmospheric and ionospheric properties of Mars, as well as gather data about the surface and internal properties of the planet and [415] about the solar system. The team's work can be divided into three general areas, as shown in table 55.



Table 55: Viking Radio Science Investigations.

Viking Radio Science Investigations


1. Dynamical, surface. and internal properties of Mars: Spin-axis orientation and motion; Spin rate; Gravity field; Figure; Surface dielectric constant

2. Atmospheric and ionospheric properties of Mars: Pressure, temperature, and density-altitude profiles; Electron-number density-altitude profiles

3. Solar system properties: Ephemerides ^a of Mars and Earth; Masses of Martian satellites; Interplanetary medium; Solar corona; Tests of general relativity


^aEphemerides are tabular statements of the predicted positions of celestial bodies at regular intervals.



Investigations of the locations of the Viking landers and the dynamical properties of Mars use primarily radio tracking of the landers, with some reliance on radio tracking of the orbiters for calibration. Determination of the gravity field and atmospheric and ionospheric properties use radio tracking of the orbiters, while the solar system and surface properties investigations rely on combinations of orbiter and lander radio tracking data. On Earth, the scientists use the transmitting, receiving, and data collection facilities of NASA's Deep Space Network at the 64-and 26-meter stations in California, Australia, and Spain. ⁸⁰
Although radio science operations began during Viking's cruise to Mars when the orbiter high-gain antenna was activated and tracking data were received, this activity was mostly related to checkout procedures, with some effort devoted to data and systems calibration. More immediately useful work began after the first landing, as doppler and range data became available for the first time between Earth and a spacecraft on another planet. From the first few days of tracking, the radio science specialists were able to ascertain "the location of the lander, the radius of Mars at the landing site, and the orientation of the spin axis of Mars." Additional data from both landers led to an initial determination from Viking findings of the spin rate of the Red Planet. After analyzing signal amplitude data from the lander-orbiter relay link, Michael and his colleagues were even able to suggest that the surface material around the first lander had electrical properties similar to that for pumice or tuff, a volcanic rock.
[416] The precision of future Mars maps will be improved considerably, especially in the 30° south to 60° north latitudes, as a result of the radio science team's work during the extended mission's low-altitude gravity survey. As the second orbiter assumed a lower orbit (about 300 kilometers), the scientists measured the effect Martian gravity had on orbiter accelerations. They noted that Olympus Mons produced a very large gravitational acceleration, while prominent, though smaller, perturbations were observed over Tharsis Montes and Elysium Planitia. Results from a bistatic radar experiment will also help specialists identify Martian features more accurately by shedding light on surface reflectivity, surface roughness, slopes at various scales, and electrical properties of the surface in regions not accessible to Earth-based radar. These surface parameters are derived "from spectral analyses of signals transmitted toward specific locations on Mars from the orbiter antennas, reflected from the surface of Mars, and received at the Earth tracking stations." Besides being useful for mapping and geological interpretations, these findings will simplify the identification of future landing sites on Mars. ⁸¹
Other questions include confirming the Einstein theory of relativity by a time-delay test-measuring how much the spacecraft signals are slowed as they pass near the sun and how the precession rate of Mar's orbital perihelion varies. During conjunction, data were gathered for studies of the solar corona. The team was also interested in more accurately measuring the distance between Earth and Mars and in determining the masses of Martian moons Phobos and Deimos. Viking's extended mission promised to be a busy time for the radio science experimenters, as did the period immediately following actual data acquisition. It would take many years to analyze all the results.

Physical Properties

The physical properties team was to draw conclusions from a composite of data from other experiments, to define the physical properties of the Martian soil. Richard W. Shorthill, team leader, stated that the team had been successful in describing the characteristics of the soil. But what it encountered was unlike any soils on Earth.
At the Viking 1 site were two kinds of surfaces to investigate, the so-called rocky flats and the sandy flats. The bulk density (the number of grams per cubic centimeter) in the rocky flats area was slightly higher than in the sandy flats. At the second landing site, the bulk density was higher than the sandy area. The team determined the properties of the Martian soil by examining photographs of the trenches dug by the surface sampler. Cohesion (how the particles stick to each other) was ascertained by taking the dimensions of the trenches and the heights of the side walls and noting the collapsed state of the walls. The cohesion exhibited in the Martian trenches was similar to that found on Earth in a trench dug in wet sand. However, since the Martian soil is so very dry, the cohesion must have been [417] caused by the electrical properties of the soil. Adhesion (tendency of the particles to stick to other objects) was determined by observing the soil that stuck to the sides of the surface sampler head before and after it vibrated. "We actually did some laboratory accelerometer tests on the vibrator at Martin Marietta while we were still on the surface of Mars to get a calibration of the adhesive forces," remarked Shorthill. By pushing the surface sampler into the surface until the force of the action turned on a micro- switch, the soil's penetration resistance could also be measured. ⁸²

Magnetic Properties

The magnetic properties experiment produced some interesting data, too. This investigation revealed an abundance of magnetic particles on the Martian surface, in both the soil and the very fine dust. On Earth, the most common magnetic particles are either iron metal or iron oxides, indicating that the red coloration of Martian soil may be caused by a highly oxidized iron, which is normally nonmagnetic on Earth. Robert B. Hargraves, leader of this experiment team, noted that two kinds of iron oxide exist on Earth-magnetite and hematite. Since hematite is nonmagnetic, perhaps the red mineral on Mars is magnetite with a coating of red hematite. But Mars is not Earth. "From what we've seen from the Martian imagery, these magnetic particles themselves appear red and they appear virtually indistinguishable from the average surface material on Mars." Hargraves admits that they have no direct information with which to resolve the mystery of the magnetic red soil, but the specialists planned to continue studying supporting data from other experiments in the hope of determining its properties more accurately. ⁸³

Inorganic Chemistry

In the inorganic chemistry investigation, scientists analyzed the chemical elements in the Martian soil with an x-ray fluorescence spectrometer. Lander 1 acquired five soil samples successfully, three collected during the primary mission and two during the extended mission; the second lander acquired four samples for a combined total of 620 cubic centimeters of Martian soil. Each sample was sifted through a funnel to measure the precise size of the sample and then charged with high-velocity particles from an x-ray source.
When the spectrometer was supplied with a sample, the data were sufficient to detect the presence of iron (12-16%, maximum limits), calcium (2-6%), silicon (15-30%), titanium (0.1-1%), aluminum (1.5-7%), magnesium (0-8%), sulfur (2-7%), cesium (0-2%), and potassium (0-2.5%) Lander 2 attempted to retrieve rock samples three times and failed, because what appeared to be rocks in lander images were actually small crustal particles that crumbled when disturbed. The scientists believe there are pebbles but were unable to analyze one. ⁸⁴
[418] Benton C. Clark, deputy team leader of the inorganic analysis team. commented that the "most striking factor between the two Viking landing sites is that the soil composition [chemical] is extremely similar in both cases. This is true for all elements we can detect in the soil including the very high" sulfur content, almost 100 times greater than the amount of sulfur found in Earth or lunar soil. One specialist remarked that they would be hard pressed to find such a closely matched pair of samples at such widely divergent sites on Earth, or even on the moon. The chemists think the giant dust storms that occur approximately every two years probably have mixed up the soil very efficiently and distributed it all over the planet as a fairly uniform mixture.
Despite the similarity of the soil from the two sites, different samples from the same location did indicate some differences in soil chemistry. ÒIn one case, we get a higher sulphur content when we pick up a little dirt clod. In other cases, when we push a rock aside and sample the surface directly beneath it, we in general get a lower iron content and a somewhat higher sulphur content." Perhaps the soil under the rock was an older soil, whereas material out in a free area may have been the result of more recent dust storms-"recent in this case meaning the last thousands to millions of years." The chemists' findings have led them to believe that the Martian soil may have been derived from rocks with a very high magnesium and iron content. ⁸⁵


: X-ray fluorescence spectrometer




[419] The Media

Public interest may have been diminished by the failure to detect life, but many science writers continued to pursue the Viking science results. Almost weekly until the end of the prime mission in November when Mars disappeared behind the sun during conjunction, the press carried reports of scientific news from Mars. As Jerry Soffen told reporters at the second Viking science forum in August 1976, he and his colleagues were gratified by "the splendid coverage" they were getting, and he did not mean just the volume, which was considerable. The scientists had been impressed by the quality, as well:
: All of us really want to thank you and tell you how grateful we are for the remarkable clarity that has emerged as a result of this very open style that we are developing right now... We have tried to each time answer your questions as clearly as we could and I know how difficult it is, as a reporter, to try to cover and clarify issues that seem to emerge one day and sometimes....appear to be contradictory on the next day. ⁸⁶

One example of the coverage given Viking is a series of articles in Science News by Jonathan Eberhart, the journal's correspondent in residence at the Jet Propulsion Laboratory during the primary mission. Respected by all his colleagues, Eberhart had a way of making understandable the complexities of science on Mars. Eberhart reported, among other accounts, efforts to move one of the rocks with the second lander's sampler arm, to find soil that had not been exposed in recent time to harsh ultraviolet radiation. As with all other maneuvers of the arm, the preparations took more than three weeks of consultations with more than a dozen specialists. The first attempt was a failure. The rock, blocking the first sample-acquisition site, refused to budge. Some persons thought that the rock might be frozen in place, but Priestley Toulmin of the inorganic analysis team argued that it was probably just the "tip-of-the-iceberg"; more of the rock was likely hidden below the surface. "Mr. Badger," ^** the second candidate for displacement, was successfully moved. As the Viking lander team continued its investigations of the immediate region around the landers-pushing rocks, digging trenches, taking pictures, and measuring their findings-the science writers continued to report on the events. ⁸⁷
All the Viking mission activities prompted Gerald Soffen to comment in his Dryden lecture at the American Institute of Aeronautics and Astronautics' 16th Aerospace Science Meeting in Huntsville, Alabama, in January 1978, "How remarkable! We are performing chemical and biological experiments as though in our own laboratories. Taking pictures at will, listening for seismic shocks and making measurements of the atmosphere [420] and surface. All of this from the first spacecraft ever to be landed successfully on Mars." ⁸⁸

Management

At the end of the primary mission in November 1976, some major changes took place within the management structure of the Viking Project Office. Several persons who had led Viking since its inception moved onto new positions. Jim Martin left NASA to become vice president of advanced programs and planning at Martin Marietta Aerospace in Bethesda, Maryland. ⁸⁹ Tom Young, who had been serving both as Viking mission director and as Martin's deputy for JPL operations, took the post of director of lunar and planetary programs at NASA Headquarters. ⁹⁰ For a time, Soffen maintained his position as Viking project scientist, but he was often called on to be a roving ambassador for the Mars project, traveling around the world telling scientific and lay audiences about the "real Mars" they had discovered. When Viking entered the extended mission phase in mid-December 1976, following the end of solar conjunction, however, many familiar faces still remained to complete the project. G. Calvin Broome had become project manager and mission director, and Conway Snyder, formerly orbiter scientist, first acted and then assumed full authority as project scientist. ⁹¹
With the start of the extended mission, one phase of Mars exploration had come to an end. The goal of landing and successfully operating an unmanned scientific laboratory on the surface had been achieved, and vast archives of new and exciting information about the Red Planet had been amassed. The extended mission properly belongs to the post-Viking era, a period of evaluation and appraisal, With this initial scientific reconnaissance over, the issue facing the National Aeronautics and Space Administration was, What next? Viking, scientists hoped, was only a first step. The debate over subsequent steps would require decisions about not just exploring Mars but also how exploring Mars fitted into the overall scheme of NASA's planetary programs. One chapter closed, it was time to begin a new one.
^* An X-band downlink on the orbiters was added specifically to enhance radio science capabilities and to conduct communications experiments.
^** Henry J. Moore II named four large Martian rocks after characters - Mr. Badger, Mr. Mole, Mr. Rat, and Mr. Toad - from Wind in the Willows by Kenneth Grahame.