For the most part, this phase of the mission was uneventful. The data was decoded by computer and displayed on teletype machines, computer printers, monitor screens, and a 30" X 30" plotter, which had a nasty habit of spitting red ink on our white shirts.
Two levels of expertise existed for each scientific instrument - scientists who proposed experiments, and the parameters to be measured, and engineers, who actually designed them to their specifications. Since Mariner IV was the first spacecraft to leave Earth for the outer reaches of the Solar System, conditions in inter-planetary space were of interest, only secondary to Mars exploration, the primary mission. The Sun ejects vast quantities of particles and radiation which travel outward. Of great interest was to correlate Earth-based observations with conditions in inter-planetary space. Mariner was equipped with instruments to measure the "solar wind", streams of particles radiating from the Sun. AGIWARN, a service which reported solar activity observed from Earth, was correlated with observations obtained from Mariner. In addition to measuring the energy and magnetic fields generated by particles from the Sun, a micrometeorite detector measured speeding inter-planetary grains of matter impacting the spacecraft. Also included was a cosmic ray detector, to measure highly energetic radiation from distant galaxies. (For a list of MIV instruments, see Appendix B). In addition to the scientific measurements, engineering parameters such as temperatures, pressures, voltages, currents, etc., were measured to ensure that everything on board was performing properly.
Engineering data was multiplexed into a "line", as were science data. These lines were transmitted alternately to Earth and decoded by computers. To indicate the start of each frame, each one was preceded by an identifier, binary 1111111 for engineering, 000011101100101 for science. The computer, seeing either of these sequences, would decode the data accordingly. Occasionally there would be a gap in the received data - the S/C signal might be temporarily lost or a glitch occurred at the tracking station or in the connection between there and JPL. The computer would search for the next occurrence of either of the synchronization signals. It was quite possible that 1111111 could occur anywhere in the data. If the computer locked on this, its output would be gibberish until it picked up sync once again. In this event, it was necessary to visually inspect the raw data for the true occurrence of a line start. We were required to continuously monitor the data. Who knew if there had been a micrometeorite hit during the loss of synchronization? In another case, the receiving station might lock onto a sideband instead of the carrier, and the data became inverted, 1s turning into 0s and 0s into 1s. We had developed methods for coping with this condition as well. These were welcome diversions from monitoring the usually boring data.
December, 1964, the Plasma Probe measurements were degraded by a component failure, and unfortunately, we lost the Ion Chamber in February, 1965.
To refine our trajectory, a "mid-course correction" (although it was actually performed 8 days into the mission) was required. Calculations were made to determine in which direction the thrust would be directed, and the length of burn time. The gyros were turned on, and after stabilization, attitude control was transferred from the optical sensors to gyros. Once these parameters were established, a series of commands were sent to the S/C.
Although the commands were set up at JPL, sending them was the responsibility of the tracking station. The commands were entered, and the console operator pushed the "send" button. In the midst of the command sequence, an engineer entered the control room, noting that one of the switches on the console was not in its usual position, reached over and - flipped it off. Only the first part of the command had been sent. The vital second part, telling the S/C to re-orient itself so the solar panels were again facing the Sun was never sent. Could such a simple error ruin the mission? Everyone held their breath until, finally, a message was received from the S/C that the onboard computer was ignoring this "defective command". After a collective sigh of relief, the correct command was sent, and all was well.
Well, not exactly. That pesky Canopus sensor acquired various dust motes and after it falsely locked on half a dozen different stars finally found its proper goal again. This happened several more times before Mariner reached Mars.
A Change of Plans
Some time before the planet was expected to be in view, power was applied to the scan subsystem and TV camera. When Pyro fired their squib, the protective TV and scan lens covers were blown off. Due to the importance of planetary images, it was decided not to take a chance on the scan subsystem centering the TV on the planet and keeping it there, but to send a ground command to freeze its motion manually. I'm not sure what I did to deserve it, but I was elected to come up with the correct procedure. This was a truly awesome responsibility - one tiny slip, and no Mars pictures. I checked and rechecked my calculations and presented my method to as many fellow engineers I could think of, and a few I couldn't.
At encounter, Mariner was approximately 220 million kilometers (136 million miles) from Earth, and radio signals, traveling at the speed of light, took 12 minutes to travel one-way. The scan platform was put into motion several hours before the expected encounter. Included in the data from the S/C was the platform's relative position as it swung up and down. These data were not continuous, but discrete points which we plotted on a long sheet of graph paper. By connecting the dots we could tell where the platform had been pointing 12 minutes previously and where it would be at any time in the future.
Also in the data was an output signal from the scan sensor, which had a field of view of 40 degrees. Prior to acquiring the planet, its output was zero (pointing at black space). The moment it reported a signal, we knew when the planet had been centered in the sensor 12 minutes before and, therefore, when it should be stopped 12 minutes later.
Now came the tricky part - when to send the stop command. It had to arrive at the S/C exactly when the planet was centered in the sensor, therefore it had to leave the Earth 12 minutes earlier. There were some other inherent delays to be factored in.
The calculations were completed and DC-24, the stop platform command was sent. Actually, it was sent twice, to make sure. The time came, the button was pushed, and then the eternity of the wait. If it didn't work, there wouldn't have been time to restart the platform and try again. Finally - a great sigh of relief when the platform stopped with the scan image centered smack on the planet. All that remained was to wait until the TV camera (with its narrow field of view, one degree) showed that it was looking at the planet and not empty space, 39 minutes. We held our collective breaths.
No one had been to Mars before, so we really had no idea what to expect, but made some educated guesses. One was that Mars had a magnetic field, but the magnetometer output showed no such thing. Oh, well - scratch one more instrument (as it turned out, Mars really doesn't have a significant field). The scan platform sensor was supposed to output a smooth transition as it passed across the planetary limb, but shortly after the planet came in view it immediately shot up offscale. Oops - another failure! Actually, either the planet was brighter than we thought, or too many safety factors had been built in.
In any event, there was nothing we could do except hope and pray that the TV system was clicking off pictures as Mariner zoomed by 6188 miles high above the surface July 15, 1965. Due to the vast distance to Earth, TV data could not be sent back as the pictures were taken; they were stored on tape for later playback.
Another daring experiment involved having the S/C pass behind the planet after encounter (occultation). The density of the atmosphere could be inferred from changes in the radio signal during these occurrences. As it passed behind the planet, it would be in Mars' shadow, and have to rely on battery power alone. Also, there would be no radio contact during that time. Suppose something went wrong, and contact couldn't be re-established? That would mean that the precious images, stored in the tape recorder, would be lost.
As planned, the spacecraft passed behind the planet and we lost contact for an hour. A high level of anxiety lasted until we once again picked up the signal. Fortunately, all went well, and results showed that the atmosphere was far thinner than had been anticipated, of vital importance to planning future landers, as air resistance would play a great part in their descent phase. As usual with such things, some sleazy tabloid newspaper picked up this loss of signal and attributed it to interference by an alien UFO! As time went on and later missions took clearer pictures, the wackos started seeing "faces" and "pyramids" on Mars ....
Left: Our first picture of Mars. Note the cloud at top right. Right: Image showing the heavily cratered region.
Now came the moment of truth - had we really obtained pictures? After the six hour delay for the 40,000 pixels (picture elements) to be transmitted the first picture was displayed. But what was that just above the limb? A cloud? Impossible. Everyone knew there weren't clouds on Mars - it must be a crack in the camera lens. Oh, no, another instrument failure. Of course, as it later turned out there really are clouds on Mars. And then the real wonder came - picture after picture showing that the surface was dotted with craters! It appeared uncannily like that of our own Moon, deeply cratered, and unchanged over time. No water, no canals, no life. Right at the limit of vision, apparently those early observers had barely seen little dots, and arranged them into straight lines. Although at first great elation gripped the crew at realizing we had really done it, that was tempered by what had been revealed.
So there we were - a barren, cratered moon-like world devoid of life. Of course, as we know now, that wasn't the end of the story. The 1% of the planetary surface which we had mapped just happened to be heavily cratered.
After passing Mars, the S/C continued out into space. Radio contact was lost Oct. 1, 1965, but re-established in late 1967. By Dec. 8 the attitude control gas was depleted, so Mariner could not be attitude stabilized, but during Dec.10 -11, it was hit by 83 micrometeorites. Dec. 21, 1967 contact was finally lost, and Mariner IV continued into space, eventually settling into orbit around the Sun. In spite of some minor problems, the spacecraft did everything and more than it was designed for, not the least of which was allowing us to get our first glimpse of the red planet.
The Moons of Mars
In 1726 Jonathan Swift published Gulliver's Travels, in which he made a startling statement - that Mars has two moons, long before they could have been seen in the telescopes of that day. When they were discovered by Asaph Hall in 1877 the "lunatic fringe" claimed that Swift had psychic powers, or perhaps knowledge from the denizens of Atlantis, who had developed powerful telescopes. His source may have been more mundane, for in 1610 Johannes Kepler "knew" that Mercury was the Sun's moon, Venus had none, Earth had one and Jupiter four (more were not discovered until later). To make the solar system more mathematically perfect he postulated that Mars would have had to have two.
Hall named the planet's two companions after the attendants of Mars (the war god) named in Homer's Iliad Phobos (fear) and Deimos (terror). They are both quite small and potato-shaped. The outer moon, Deimos, orbits in 30 hours, Phobos in 7 1/2. The inner moon is slowly spiraling down towards the planet. Some external force must be responsible for this behavior. Even though thin, Mars does have an atmosphere which becomes thinner the farther away from the planet. Outside of the atmosphere proper is the "exosphere", an extremely thin region of atmospheric components. Calculations showed this would be insufficient to act on Phobos in this manner. Russian astrophysicist Iosif Shlovsky theorized that to fit the facts, the "moon" would have to be extremely light and therefore must be hollow - an artificial satellite! Currently, the mechanism is not fully understood, but it has been postulated that Phobos may be slowing down from collisions with dust that it shed itself.
Many missions followed the Mariner Program; flybys, orbiters, and landers by other countries as well as the United States. The two flybys after Mariner IV saw much the same heavily cratered surface. Next came Mariner 9, which arrived just as the greatest dust storm ever recorded completely blotted out the planet for three months. As the dust started clearing, the only features seen were three puzzling circular features, which turned out to be the tops of gigantic volcanoes. When it cleared a whole different marscape showed volcanoes, lava flows, great canyons, what appeared to be dry riverbeds, and a number of other enigmatic features. A large area of the planet, the "Tharsis Bulge" rises 4 miles above the surface. The area around it is cracked, with "Valles Marinaris" (named in honor of Mariner spacecraft) a gigantic canyon 3,000 miles long, 150 miles wide and 4 miles deep.
In 1976 Vikings I and II dropped landers onto the surface of Mars. Part of the payloads consisted of three life-detection experiments: PR (Pyrolytic Release), GSX (Gas Exchange) and LR (Labeled Release). Great excitement gripped the World when it was announced that LR had detected life! Or had it? The other two experiments were negative on the subject. In the LR experiment, two Martian soil samples were scooped up. The control sample was sterilized to kill any life forms present. Radioactive nutrients were added to both samples, and they were then checked for the evolution of radioactive carbon gas. The gas was detected only from the unsterilized sample. Presumably this indicated a byproduct of metabolism. On the other hand, perhaps some strange Martian chemistry involving superoxides was at work (See Links, Appendix D 1, 6). The question remains moot. Viking, with a design life of 90 days, operated for seven years!
Later, Pathfinder landed its Sojourner Robot which wandered about on the surface, sending back closeup pictures but saw only rocks and sand. However, if an alien probe happened to land in the middle of the Gobi desert, it would no doubt indicate a planet devoid of life.
In 1996 a startling announcement was made - analysis of meteorite ALH84001, recovered in 1984 from Antarctica, showed evidence of what appeared to be extremely small fossils. This rock, 4.5 billion years old, had traveled from Mars to Earth after being ejected by a meteorite impact. Was this evidence that life had evolved on Mars when it was warmer, with liquid water on its surface?
The atmosphere is very thin, only 0.6% of Earth's, and consists of mostly carbon dioxide, subjecting the surface to killing solar radiation, with just a trace of oxygen. The pressure is so low that liquid water cannot exist on the planet, except as vapor or ice. Current thinking assumes that liquid water is required for life to exist. Diurnal temperature variations are extreme, ranging from a high of 68 degrees F. to -100 in the most favorable location. Humans could not live on the surface without protection and breathable air supplies.
A giant volcano, Olympus Mons, rises 15.6 miles above the surface, whereas its largest Earth counterpart is Mauna Kea "merely" 6.6 miles high as measured from the ocean floor. The chain of Hawaiian islands were formed as a crustal plate moved across a magma vent from Earth's interior. In other words, the vent remained fixed while the sea floor slid by it. Mars, however, does not have a moving crust, so a volcano remains located over the vent and builds to enormous size. Other volcanoes formed comparatively recently as evident from minimal weathering.
Convective currents in Earth's liquid core, combined with its rotation, are believed to produce our magnetic field. Internal heat, either residual from the planet's formation or decay of radioactive substances, heat the interior to temperatures high enough to liquefy rock which then makes its way to the surface as volcanic lava. A similar mechanism seems to have been at work on Mars many years ago, but has since ceased. Possibly due to its smaller size, this heat may have been lost many years ago. The core then solidified, which manifests itself in a lack of a magnetic field.
Images from orbiters indicated that at some time in the past catastrophic floods reshaped the surface. Whether this was water flowing on the surface, from rain or due to volcanism heating frozen underground deposits is unknown. Care must be taken in ascribing surface features to the same forces that shaped similar ones on Earth. No direct evidence of water was seen until 2002, when Odyssey detected what appears to be a substantial quantity, frozen in the form of ice (permafrost). Liquid water may also exist in underground caverns. This would be good news for future explorers, who would be able to convert it to fuel and drinking supplies, thus obviating the need to drag them all the way from Earth.
Although current thinking suggests that volcanism and epic floods were early shapers of the planet, most surface changes now occur due to wind-borne dust. Mars' predominant red color is believed to be due to iron oxides. Light and dark areas are formed by wind patterns removing dust from some areas and depositing it on others. One of the yet unexplained features is why the southern hemisphere is more heavily cratered than the northern. Many mysteries remain to be explored and explained.
Life on Mars
To consider the question of life on Mars, past or present, it is instructive to consider how it may have arisen on Earth. Conventional thinking follows Charles Darwin proposal that life came to be by inorganic molecules clumping together spontaneously in shallow pools by the seashore. At first there was abundant water and an atmosphere consisting mostly of carbon dioxide, but little oxygen, which would have been fatal to proto-life due to its oxidizing properties. As algae flourished in the seas it used solar energy to convert carbon dioxide into organic molecules and excreted oxygen as a waste product. Over millions of years the carbon was "fixed" by dead algae and sank to the sea floor where pressure and heat turned it into peat and coal. Atmospheric oxygen, in turn, became a larger and larger part of the atmosphere, which made it possible for the rise of organisms which consumed oxygen and excreted carbon dioxide. Over the years a perfect balance was struck between plants and animals, the former using carbon dioxide and excreting oxygen, and the latter using oxygen with carbon dioxide as a waste product, the "carbon cycle".
(That is, until humans came along and started burning the fossil fuels which plants had been storing in "carbon sinks" for millenia and using oxygen in the process. Thus, carbon stored in the Earth was now being combined with atmospheric oxygen to produce carbon dioxide faster than plants could fix it. The net result is "the greenhouse effect", global warming from the increase in carbon dioxide, not to mention the decrease in atmospheric oxygen for breathing purposes plus an increase in other contaminants.)
For many years it was believed that all life depended on the carbon-oxygen cycle, requiring adequate water, sunlight and moderate temperatures. Recently "extremophiles" have been discovered, organisms that thrive on essentially waterless, below freezing antarctic plains. Others have been found in steaming hot geyser pools. Still stranger are "tube worms", creatures that live in the ocean deeps near "white smokers" (volcanic vents), which, in the absence of sunlight, obtain their energy from sulfur. The range of environments under which life can live and thrive are being widened continuously. There is some evidence that life on Earth evolved from thermophiles in hot vents, rather than tidal pools.
Could life have evolved long ago in a wetter, warmer Mars? If so, could some hardy organisms yet survive hidden away in crevices, or in pools of liquid water beneath the surface, heated perhaps by volcanism? There is evidence of what appear to be extensive martian flooding. Might this be evidence of copious water on the planet in previous times, or was it due to sudden release of melted ice by volcanism? If there is no life on Mars now, could there have been in the past, perhaps leaving a fossil record? At one time in its history the planet may have had lakes and even oceans which could have trapped lifeforms in sediments. These questions can only be examined by future missions.
There is evidence that life may have traveled from Mars to Earth by meteorite. Is it possible that Earth was thus seeded and we are actually Martians? Can life really arise from inorganic compounds spontaneously? In future missions we will better understand whether life arose there, still exists, or ever did.
Our perception of Mars has changed drastically over the years - from a place of vast oceans, to a dry, lifeless cratered landscape, then evidence that water had once flowed there, possible discovery of evidence of fossils, to the latest startling discovery that vast quantities of water may lie beneath the surface. A mysterious planet indeed - who knows what we will find on future missions?
Our Perceptions of Mars - A Timeline
Naked eye observations: A mysterious red dot which not only moved among the "fixed" stars, but at times appeared to go backwards. We now know that this "retrograde" motion occurs when the Earth, moving faster, catches up to and passes Mars, which makes it appear to reverse its course.
Telescopic observations (~1610): Appeared to be similar to the Earth, with polar caps and rotation of about one Earth day, with markings (vegetation?) that changed with the seasons.
Percival Lowell: (1895 ): Obviously a water-starved, dying planet, whose surviving inhabitants have constructed a giant system of canals to carry water from the poles to their farmlands.
Mariner IV (1965 ): A dead, waterless, airless planet peppered by meteor craters.
Mariner 9 (1971): Detected volcanoes, canyons and what appeared to be ancient river beds. Had there once been life on Mars, but no more?
Viking (1976): Analysis of soil samples showed signs of life. Or was it due to chemical reactions? The question is still moot.
ALH8400 (1996): " Fossils" found in a 4 billion year old meteorite which had traveled from Mars to Earth. A definite sign of previous life on Mars, or the result of chemical reactions? Question not yet resolved.
Pathfinder (1997): Landed "Sojourner" robot, explored composition of rocks. No sign of life found.
Odyssey (2002): Significant amounts of water still exist frozen below the surface.
A: Summary of the Mariner Program Missions
B: Mariner IV Science Instruments
C: DSIF Stations
E: Further Reading
F: Activist Mars Societies
Proceed to Page 3, Appendices
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