Space & Astronomy/Space and Astronomy (October 1993).iso/pc/text/jplnews1/0634.pr

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OFFICE OF PUBLIC INFORMATION
JET PROPULSION LABORATORY, CALIFORNIA INSTITUTE OF TECHNOLOGY
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
PASADENA, CALIFORNIA.  TELEPHONE [phone]

FOR RELEASE:  AM'S OF MONDAY, NOVEMBER 13, 1972

                       MARINER 9 MISSION

         The Mariner 9 spacecraft, which reached Mars one year
ago today, circled the planet 698 times in 349 days, gathering
a wealth of science data that has revised all previous concepts
of Mars.
         From Mariner's vantage point in Mars orbit for more
than one-half Martian year, the spacecraft maintained an in-
strumented surveillance of the planet as the seasons changed
below.
         Some of the major findings of the mission, which
concluded on October 27, 1972, were:
         -- A geologically active planet with volcanic
mountains and calderas larger than any on Earth.
         -- An equatorial crevass several thousand miles long
and three to four times the depth of the Grand Canyon.
         -- Indications that free-flowing water may have ex-
isted in Mars' geologic history.
         -- The evolution of a monumental dust storm that raged
to an altitude of 50 to 60 kilometers (31 to 37 miles) above
the surface.
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         -- And the realization that dust storms and cloudiness
account for much of the puzzling variability of Mars' appear-
ance over the years.
         The Mariner Project, managed for NASA's Office of Space
Science by the Jet Propulsion Laboratory in Pasadena, Calif., was
planned around a two-spacecraft mission to Mars during the 1971
launch opportunity.  Mariner 8 and Mariner 9 were designed, built
and tested at JPL and launched from Cape Kennedy in May, 1971.
         The second stage of the Atlas-Centaur launch vehicle
failed during the early minutes of Mariner 8's flight on May 8.
Plans were revised to allow the remaining spacecraft to conduct
the missions of both Mariners.
         Mariner 9 was launched successfully on May 30.  A
trajectory correction maneuver on June 5 was made so accurately
that no additional corrections were necessary during the 167-day
Earth-to-Mars flight.
         As the spacecraft approached the planet in mid-
November, its TV cameras took three series of pictures while
Mars revolved several times on its axis.  The pictures verified
the existence of a colossal dust storm that had enveloped the
entire Martian globe.
         The storm had been watched for several months by Earth-
based astronomers.  This Martian weather condition would persist
for nearly six weeks more, delaying the planned mapping sequences
but allowing scientists to study the meteorological phenomenon.

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         On November 13, 1971, Mariner 9 had completed the 248-
million interplanetary crossing and was inserted into orbit
around Mars by a 15-minute firing of its rocket engine.  It had
become the first man-made object to orbit another planet.
(Soviet spacecraft Mars 2 and Mars 3 arrived later in November.)
An orbit trim maneuver was executed during the fourth revolu-
tion, refining Mariner's average orbital period to 11.97 hours.
The post-trim periapsis (low point in the orbit) was 1387 kilo-
meters (862 miles).  An orbit inclination of 65 degrees was
selected so that Mariner could map more than 70 percent of the
planet and examine Mars' variable features.
         During the first six weeks of orbital operations, the
Mariner 9 mission was characterized thusly:
         -- Mariner's instruments were peering down through the
most extensive dust storm observed on Mars since 1924, or per-
haps longer.  Only the bright waning ice cap at the south pole
and four dark mountain peaks were visible through the planet-
wide haze.  Later photos revealed the four dark spots were
giant volcanic mountains with large caldera-type craters at
their peaks.  One, Nix Olympica, is about 500 kilometers (300
miles) across at the base and its peak stands at least 17 kilo-
meters (10 1/2 miles) above the surrounding plain.
         -- Phobos and Deimos were photographed close-up for
the first time.  The tiny Martian moons were found to be syn-
chronous with Mars (one side always facing the planet).  Both
moons are heavily cratered, apparently from meterorite impacts.
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         -- Because of a previously unknown gravity field
variation in Mars' equatorial plane, the orbital period was
found to be slightly too short, gradually changing the time
relationship of the periapsis to the Earth tracking stations.
         -- The dust storm continued beyond most predictions,
and it became apparent that the planned mapping of the planet
could not be completed during Mariner 9's basic 90-day mission.
         Between Christmas, 1971, and New Year's Day, the Mar-
iner cameras and the other instruments all detected a large-
scale clearing of the dust storm.  The entire mission was
revised to begin mapping the surface on January 2, 1972.
         A second trim maneuver was made on December 30, 1971,
correcting the orbital period for coordination with the 64-
meter antenna at the Goldstone station of the Deep Space Net-
work.  The maneuver also raised the periapsis to 1650 kilo-
meters (1025 miles), allowing broader camera coverage and
permitting the mapping objective to be achieved.
         During the first few weeks of January, the Mariner in-
struments looked at a brand new target, a clear Mars.  The
pictures revealed a shrinking south polar cap; sinuous channels
which appeared to be water-cut; so-called "chaotic" terrain
first seen in 1969 by Mariner 6 and Mariner 7; and huge impact
craters, their floors covered with wind-blown dunes.
         On January 12, a swath of mapping pictures included a
photograph of a 300-mile section of a vast chasm near the
equator with branching canyons eroding the adjacent plateau-
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lands.  Later, overlapping sequences showed that the chasm
stretches some 2500 miles, nearly one-fourth the circumference
of the Martian globe.  Mariner's ultraviolet spectrometer mea-
sured the chasm depth of nearly six kilometers (20,000 feet).
         By mid-March photo, thermal and chemical maps covered
nearly 85% of the planet and plans were made of an extended
mission through the summer and fall of 1972.
         From April 2 to June 4, Mariner's science instruments
were turned off while the spacecraft's orbit took it into Mars'
shadow during each twice-a-day revolution.  These frigid solar
occultation periods, which Mariner 9 was to survive, ranged from
a few seconds per orbit to nearly 100 minutes per orbit.
         The spacecraft cameras and other instruments were
operated again on June 11, recording the first of 10 additional
tapeloads of pictures and other data.  Extended mission targets
included the north polar region which was not visible earlier in
the year, features that vary as the Martian seasons change and
possible landing sites for the Viking 1975 Project.  Mapping
coverage was extended to 100 percent of the planet.  The final
playback of pictures was received at JPL on October 17 and
brought the total number of photos to 7329.
         Mariner 9's mission ended on October 27 when engineering
telemetry signals ceased during its 698th orbit of Mars. Distance
from Earth at that time was 383,675,000 kilometers (238,416,000
miles).  Stored in its tape recorder were another 15 pictures
and related science data which had been taken the day before.
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         The spacecraft's supply of attitude control gas was
depleted just minutes before Mariner was to play back the final
tapeload of data.  Engineers at JPL sent the final command --
the last of 45,960 commands -- to turn off Mariner's radio
transmitter.  The spacecraft is expected to remain in Mars
orbit for 50 or more years.
         A brief Mars science summary:
              Television experiment (surface) -- Mars can be
subdivided into at least four major geological provinces.
First is the Nix Olympica - Tharsis volcanic province.  Second
is the Ophir-Eos equatorial plateau region with faults and
rifts.  A third includes cratered and smooth terrains, perhaps
more ancient than the first two types, found in both northern
and southern hemispheres.  Large circular basins (Argyre I and
Hellas) resemble impact basins on the moon.  Fourth is the
south polar cratered terrain blanketed by glacial sediment
layers up to 100 meters thick.  Similar deposits appear in the
north polar region.  If large quantities of water exist on
Mars, they are undoubtedly locked in the permanent polar caps.
              Television experiment (atmosphere) -- After the
global dust storm subsided, much of Mars above 45 degrees north
was found to be covered by a north polar hood of variable
clouds.  They appeared to have a general west-to-east flow pat-
tern, with some systems resembling small cyclones.  Cloud
believed to contain water-ice were observed elsewhere,
particularly over large volcanoes.  Several localized dust
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storms were seen after the global storm cleared.  Dust clouds
appeared highly convective, probably due to vertical air motion
generated by absorption of solar radiation by the dusty
atmosphere.
              Ultraviolet Spectrometer experiment -- Ozone was
detected over both Martian polar regions and at latitudes south
of 50 degrees (s) and north of 45 degrees (n).  The amount of
ozone was less than one percent that present in Earth's
atmosphere.
              The UVS instrument, by making 30,000 individual
measurements of relative surface brightness, produced a
preliminary topographical map of Mars.  Two areas showed very
abrupt elevation changes -- one the canyon area in the Tharsis
region, the other volcanic belt.
              Infrared Interferometer Spectrometer experiment
-- Mars' north pole is much colder (about 200 degrees below
zero, Fahrenheit) and drier than the coldest spot on Earth,
Antarctica (-125 degrees, F.).  Again carbon dioxide was shown
to be principal constituent of Martian polar atmosphere.
During the dust storm, the dust-laden atmosphere lowered
maximum surface temperatures (about 40 degrees above zero near
the equator to about 125 degrees below zero in polar regions)
and appeared to stablize them.  Atmospheric winds reach speeds
up to 115 miles per hour.
              Infrared Radiometer experiment -- Surface
temperatures ranged from 81 degrees above zero Fahrenheit to
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189 degrees below zero.  The low was found at both poles; the
high in the equatorial zone.  Average temperatures remained in
the range indicated by Mariner 6 and 7 measurements, but there
are hundreds of areas on Mars significantly warmer or colder
than the averages.  The variations are attributed to
differences in reflectivity, local topography, surface thermal
properties, and possibly internal heat.  However, no clearcut
examples of internal heat -- that is, active volcanoes -- are
apparent from the Mariner 9 IRR data.
              Radio Occultation experiment -- Mars' atmospheric
pressures were measured to a low of 2.8 millibars in near-
equatorial regions, with a high of 8.9 and a mean surface
pressure of 5 millibars, in the central areas.  At 65 degrees
North Latitude, surface pressures range from 7.2 to 10.3
millibars, with the mean 8.9.  Altitudes in this low-lying
region showed a mean of -2.6 km (-1.6 miles).  Mars is more
flattened than its gravity field, with the bulgy equatorial
zone showing lowest atmospheric pressures.  Pressures near the
Martian poles range from 5 to 13 millibars.  (Earth sea-level
pressure norm:  1000 millibars.)
              Celestial Mechanics experiment -- Mars bulges at
the equator 27.2 kilometers (16.9 miles).  Variations in
Mariner 9 orbital times showed the planet to be that much out
of round.  However, 17.8 kilometers (11 miles) of this is attri-
buted to Mars' own spin around its polar axis.  Strong Martian
gravity anomalies imply large stresses at work on the planet's
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crust, suggesting current or recent geological activity.  The
celestial mechanics team conducted an experiment to test the
Einstein relativity theory in September, 1972.  Analysis of the
data is continuing.
              The Mariner 9 science results laid the groundwork
for America's next venture to Mars, the 1975 Viking lander to
search for evidence of life on the planet.


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