PASADENA, Calif.--Some aeons-old secrets of Mars could be unveiled by spectrometers, television cameras and radiometers aboard Mariner VI and VII in the next week or so when the space- craft fly by the red planet at a distance of only 2,000 miles. Scientists will use the cameras and other experiments to seek hopeful signs of nonlunar developmental processes, including a Martian atmosphere conducive to some form of life.
With twin camera systems capable of taking close-ups 100 times more detailed than Mariner IV pictures yielded in 1965, Caltech and Jet Propulsion Laboratory scientists say this year's television experiment should provide a tentative answer to the riddle: Is Mars geologically alive, sleeping, or dead?
The 1965 Mariner's 21 history-making photographs seemed to put Mars in a class with the Moon--crater-pocked, bleak, barren, and blighting the hopes of biologists. The 1969 Mariners will be able to photograph craters 900 feet in diameter, perhaps canals, if there are any, and any features that might be Earth- like. But Dr. Robert B. Leighton, Caltech physicist-astronomer who is chief investigator for the television experiment, is not optimistic about the latter possibility.
"From the 1965 photographs, Mars appears fairly dead," says Leighton, who also headed the Mariner IV photo team. "However, we have a minimum of preconceived notions and I'm sure our preconceived notions could be wrong. We are confident that the broader sweep of Mars that will be covered by the Mariner 6 and 7 pictures, and their better definition will reveal many new features and give us new insight as to the nature of that planet."
Another member of the photo study team, Dr. Norman H. Horowitz, thinks the possibility of finding life on Mars is important enough to make the search worthwhile, although the probability may be low. "It is not optimism about the outcome, but the tremendous importance that a positive result would have, that sustains the search," he adds.
Horowitz, chief of the bioscience section at Caltech's Jet Propulsion Laboratory, says this summer's Mariners should provide valuable data for the continuing Mars exploration series. Mariner VI is scheduled to sweep by Mars July 30, Mariner VII on August 4. The flybys are conducted by JPL for the National Aeronautics and Space Administration. Caltech operates JPL for NASA.
In 1971, two Mariner-like craft are to orbit Mars and survey it for periods up to three months. Two Project Viking landing capsules are to sample the planet's air and surface in 1974. The Viking orbiter spacecraft will be built by JPL, the landers by NASA's Langley, Va., Research Center.
If all goes well, the '69 Mariners would take up to 191 pictures, ranging from full-disc portraits to overlapping close- ups. Under maximum conditions, Mariner VI will be asked to take 50 long shots, starting 48 hours before close encounter, and Mariner VII will be set for 93 long shots, beginning 72 hours out. If conditions appear less favorable, each spacecraft will take only eight long shots. These will be taken with a telescopic lens capable of reading an auto license plate three miles away.
Each spacecraft is scheduled to take 24 closeup shots, alternating its pair of cameras--a wide-angle lens with a resolu- tion of two miles, and the telescopic lens which will record features 900 feet across from the fly-by distance of 2,000 miles.
Mariner VI is concentrating on an equatorial belt roughly 90 degrees east of the 1965 photo path. Mariner VII will concentrate on a South polar fly-by, although overlapping the Mariner VI path over the Meridiani Sinus, a permanent dark area near the Equator.
What are the cameras and spectrometers shooting for? All types of classical Martian features about which conjecture has swirled. Polar caps, "blue" maria, white and blue clouds, dark and light changeable areas, "canals," and the specific size, structure and distribution of craters and other surface relief.
Sharper photos, combined with readings by infrared and ultraviolet spectrometer instruments and an infrared radiometer, could narrow the question of what kind of life, if any, could exist, on the planet. In addition, the '69 Mariners should provide the basis for the most thorough mapping of Mars yet accomplished.
Mariner IV photos covered 600,000 square miles, or one per cent of the surface. This time, far encounter photos should cover all of the planet as it rotates at least twice for each set of cameras. (Mars rotates every 24 hours, 37 minutes--an Earth day with a little solar overtime.) Closeups will be made of about 20 percent of the surface.
The 1965 photos showed some 300 craters extending in a swath from about 50 degrees north latitude to 50 degrees south latitude. They ranged in diameter from 1 3/4 miles to 110 miles. If the rest of Mars is like that, scientists estimate the planet may have as many as 30,000 craters, compared to Earth's handful.
Mariner IV also detected some linear markings tenata- tively called "crust fractures," perhaps 100 to 200 miles long and several miles wide. But Dr. Leighton does not believe these are the so-called "canals" of popular fame. An Italian astronomer, G. V. Schiaparelli, first labeled certain long, fine markings "canali" in 1877. "I am open minded concerning the existence of these canals on Mars," says Leighton.
Nor did Mariner IV find any mountain chains, great valleys, ocean basins or continental masses, or similar Earth- like features. Leighton is hopeful that Mariners VI and VII will disclose significant differences in erosion over Mars' surface. It would be most fascinating to find evidences of water erosion from ancient oceans, but he rates the chance of finding any large bodies of water today at "absolutely zero." However, he foresees "a good possibility that there are sizeable bodies of permafrost" --somewhat on the order of Antarctica or Greenland--in the polar regions.
Following the 1965 photos, Leighton and co-investigators estimated the Marian surface could be 300 million to perhaps 5 billion years old. The prevalence of craters signifies an extremely slow rate of surface erosion as compared to Earth. In fact, the door is not shut on the possibility that the Mars sur- face could be in a primitive form which might yet yield clues to orgac development that have long since disappeared from Earth.
Most people regard Mars' white polar caps as proof of the existence of large amounts of water on the planet. However, Leighton and another co-investigator, Dr. Bruce Murray of Caltech, believe the polar caps are dry ice, frozen carbon dioxide, 260 degrees below zero, F., rather than water ice, -170 degrees or warmer. Carbon dioxide is believed to be the main constituent, with little oxygen or hydrogen present, in the Martian atmosphere. Maximum temperatures at Mars' equator may be as high as 68 degrees above zero, F.
While encounter time is midsummer on Earth, it will be fall in Mars' northern hemisphere, spring in the southern half, roughly corresponding to October 15 here.
The photo experiment shares several scientific tasks with other Mariner instruments. These include determining origin and extent of hazes and dust clouds and, more importantly, locating vaporous clouds or frost patches which could indicate moisture-bearing soil. Such places are likely landing sites in 1973.
The presence of water now, or in the past, is a key factor in the search for Martian life, Horowitz says. Meanwhile, analysis of the Martian atmosphere may provide hints of life- related chemicals.
"If there is life on Mars, it will almost certainly be carbon-based, just as it is on Earth," Horowitz explains. "Carbon is the one element able to build the large, complex yet stable, molecules fundamental to organic life. If life is based on carbon and Mars' atmosphere is mostly carbon dioxide, it would be impossible for life ___ to interact with that atmosphere."
Until instruments and diggers land on the planet itself, Horowitz and his colleagues cling to that slight hope that life, however submicrobial, may exist on Mars. It could be no more than tiny algae, such as JPL scientists have found in Antarctica's permafrost. Some antarctic soil samples, on the other hand, appear to be completely sterile.
The Mariner '69 camera system is the most sophisticated yet devised for a planetary spacecraft. The two cameras, called A and B, will alternate to take pictures every 42 1/2 seconds during the flyby at a range from 6,000 to 2,000 miles. They will be set so their fields will overlap. This will enable both panoramic shots and closeups of interesting details within panoramas.
Camera A is essentially the same as the Mariner IV camera, except a wide-angle lens has replaced a small telescope. Its resolution will still be about two miles (as in 1965), but, given an approach three times closer and the wider lens, each exposure frame will be about 15 times larger.
Camera B, using a Schmidt cassegrain telescope, is expected to produce pictures ten times sharper than Camera A, and at nearest approach, narrow down to areas comparable to a large city block. Camera A employs red, green and blue filters, Camera B yellow. All pictures transmitted will be black and white.
An improved vidicon tube will store and transmit images. Its photosensitive surface receives 704 lines, with 945 dots (called pixels) per line--665,280 dots for each exposure. An electronic beam scans these for a tape recording system that will relay them to Earth receiving stations in the NASA-JPL tracking network. The quality of the pictures should be upgraded by the 30-fold increase in pixel-pickup since 1965.
The cameras are mounted on a scan platform that can be moved by Earth command 215 degrees in clockwise rotation and 64 degrees in an up and down (conic) fashion. As each Mariner approaches Mars, several days before encounter, the spacecraft's planet sensor will track the center of brightness and aim Camera B for its series of full-disc pictures of the planet. About 14 hours out, Mars will fill the entire frame. Final far-encounter pictures will zoom in on selected portions of the planet.
The scan platform then willsle3 on both azes to ready the various instruments for closeup measurements. They can be set according to pre-launch pattern, or by an updated plan decided upon during the 4-month-plus flight. It is possible to change plans up to the last day before encounter. The near encounter picture taking sequences will last about 17 minutes, and the other instruments will continue to make measurements on the shadowed, night-time side of the planet.
An added fillup may be provided by closeups of one or both of Mars' tiny moons. It is possible that the inner moon, Phobos, 12 miles in diameter, could be picked up by the cameras as it swings close to a limb (outer edge) of Mars. Phobos' orbit is about 4,000 miles from the planet. The outer moon, Deimos, only six miles in diameter, presents a less favorable target, 12,000 miles out.
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