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UPDATE #68 - March 15, 1998

PART 1: March 27 Web Chat With Jim Bell, Astronomer
PART 2: MGS Field Journal by Bill Sjogren, Gravity Experiment, PI
PART 3: Moving On: Check out Ken Edgett's Newly Revised Bio
PART 4: Mars Global Surveyor Press Release
PART 5: NASA Says Goodbye to Mars Pathfinder
PART 6: Subscribing & Unsubscribing: How to do it


Now would be a good time to sign up for MTO's upcoming Web chat with
astronomer Jim Bell. The date is Friday, March 27; the time is 11 a.m.,
PST. Jim's specialty is Mars. He studies pictures of and data about Mars
from telescopes and NASA spacecraft missions. Be sure to read Jim's bio
at: http://quest.arc.nasa.gov/mars/team/bell.html

To register for the chat go to:

[Editor's note: The following field journal was written by Bill Sjogren, the principal investigator of the gravity experiment onboard Mars Global Surveyor. To find out more about Bill and his job go to: http://quest.arc.nasa.gov/mars/team/sjogren.html]


by Bill Sjogren, Jet Propulsion Laboratory

March 6, 1998
The first thing this morning I checked on the quality of the radio
tracking data from the Mars Global Surveyor spacecraft to make sure all
transmitters and receivers onboard and at the Earth-based stations were
performing properly and there were no problems. Everything was functioning
correctly and I had no calls to make. There have been several times when
new operators at the Deep Space Network stations had negelected something
and big biases were present in the ranging data. This required calls to
the over-seas station to correct this problem for the next day's data

Next, I sent an e-mail to the Mars project radio science coordinator
listing the justification for a gravity campaign during the month of June
1998 when the low point of the Mars Global Surveyor spacecraft's orbit 
will be right over the Martian north pole and the very best gravity data
can be acquired. It is the time when the polar cap is at its maximum
extent (mid-winter) and complete coverage can be obtained without any
occultations breaking the data arc. It is the most optimal time and this
opportunity will never present itself again at this low an altitude of 170
kilometers during the entire MGS mission.

Several proposals are being generated for future missions right now
and I'm involved with two of them (an orbiter of Europa and a Mercury
orbiter) in which I must simulate the orbital gemetry and estimate how 
well we can extract the gravity field. Today the mission designer changed
the geometry and asked for a new evaluation of the Mercury gravity field
solution. So it was back to the computer and a change to the starting
conditions of my earlier work. The computer will run for eight hours
straight, computing Doppler tracking data for 60 days and produce the
statistics on how well the gravity field is recovered. I'll check the
results on Monday being this is Friday and it will not finish before I

While the computer is cranking out the above results, I will put together
a few statements about what kind of products the gravity experiment will
produce. Such things as gravity maps that can be correlated with imaging,
magnetics and altimetry, profiles over specifically interesting
topographic features like the large Caloris basin, and the numerical
coefficients which were estimated for the gravity field model.

I just returned from our Planetary Imaging Lab here at JPL,  with some
maps of Mercury (only half of Mercury has been imaged with the Mariner
10 spacecraft in 1975) and I'm looking for those large topographic
features. There are at least 20 that we should be able to detect as
gravity anonalies, plus whatever is in that other half yet to be imaged.
All in all, I'd say this has been a good day!


As the Mars missions evolve, many of the team members move on to new jobs
in new locations. Such is the case with Ken Edgett. Many of you will
remember his association with Arizona State University and the K-12
Outreach Program that he began there. Ken has just recently accepted a
new challenge
at Malin Space Science Systems in San Diego, California. To continue to
follow the adventures of Ken (who is really "Joe the Martian" in disguise)
read his updated bio at: http://quest.arc.nasa.gov/mars/team/edgett.html


[Editor's note: This MGS Press Release was written by Diane Ainsworth in
the Media Relations Office of NASA'S Jet Propulsion Laboratory in 
Pasadena, CA on Friday, March, 13, 1998. For additional information go to:

New Global Surveyor Data Reveal Deeply Layered Terrain, Magnetic 
Features and Genesis of a Martian Dust Storm

For the first time in Mars exploration, a spacecraft has
captured the full evolution of a Martian dust storm.  NASA's Mars
Global Surveyor mission also has returned new insights into the
deeply layered terrain and mineral composition of the Martian
surface, and to highly magnetized crustal features that provide
important clues about thimportant clues about the planet's interior.

These findings are among the early results from the Mars-
orbiting mission being reported in today's issue of Science

This first set of formal results comes from data obtained in
October and November 1997, while the spacecraft was just
beginning to use the drag of Mars' upper atmosphere to lower and
circularize its orbit in a process called aerobraking. At the time, 
a dust storm was brewing on Mars and had grown to about the
size of the South Atlantic Ocean.

The Global Surveyor data suggest that it began as a set of 
small dust storms along the edge of the planet's southern polar
cap, according to Dr. Arden Albee of the California Institute of
Technology, Pasadena, CA, the Mars Global Surveyor mission
scientist. By Thanksgiving, it had expanded into a large regional
dust storm in Noachis Terra that covered almost 180 degrees
longitude, while spanning 20 degrees south latitude to nearly the
tip of the Martian equator.

"As this storm obscured the Martian landscape, we followed it in detail
using several instruments onboard Mars Global Surveyor," Albee said.  "The
thermal emission spectrometer mapped the temperature and opacity of the
atmosphere while the camera followed the visual effects.  The effects of
the storm extended to great heights of about 130 kilometers (80 miles) and
resulted in great increases in both atmospheric density and variability
from orbit to orbit. These atmospheric measurements have great
significance for future Mars missions that will be using aerobraking
techniques too."

Before the storm, atmospheric dust was generally distributed
very uniformly, Albee said.  Observations of the limb of the
planet in the northern hemisphere revealed both low-lying dust
hazes and detached water-ice clouds at altitudes of up to 55
kilometers (34 miles).  Movement of these clouds was tracked by
the spectrometer as the planet rotated. Atmospheric turbulence
disrupted these cloud patterns as the small storms began to rise
and kick more dust into the air. As the storm began to abate,
small local storms began to crop up again along the edges of the
south polar cap, and ice clouds formed in depressions as the
carbon dioxide cap continued to retreat.

In addition to these unprecedented observations of a full-
blown Martian dust storm, measurements from the spacecraft's
magnetometer and electron reflectometer have yielded new findings 
about Mars' strong, localized magnetic fields. These patches of
the crust, which register high levels of magnetism, are beginning
to unlock some of the mysteries surrounding Mars' internal dynamo
and when it died, said Dr. Mario Acuna of NASA's Goddard Space
Flight Center, Greenbelt, MD.

"These locally magnetized areas on Mars could not form without the
presence of an overall global magnetic field that was perhaps as strong as
Earth's is today," says Acuna. "Since the internal dynamo that powered the
global field is extinct, these local magnetic fields act as fossils,
preserving a record of the geologic history and thermal evolution of

Magnetic fields are created by the movement of electrically
conducting fluids, and a planet can generate a global magnetic
field if its interior consists of molten metal hot enough to
undergo convective motion, similar to the churning motion seen in 
boiling water.

"The small size and highly magnetic nature of these crustal
features, which measure on the order of 50 kilometers (30 miles),
are found within the ancient cratered terrain rather than within
the younger volcanic terrain," Acuna said.  "By correlating
crustal age with magnetization, we have a perfect window on Mars'
past, which will help us to determine when Mars' internal dynamo
ceased operating."

High-resolution images of dunes, sandsheets and drifts also
are helping reveal earlier chapters of Martian history. Landforms
shaped by erosion are almost everywhere, according to Albee, and
many bear a striking resemblance to Colorado's Rocky Mountains.
Rocky ridges poke through the Martian dust just as the jagged
edges of cliffs pierce through a blanket of snow in the Rockies.
Martian dust appears to have spilled down the sides of ridges 
just as fresh snow slides down a ski slope.

"One almost expects to see ski tracks crisscrossing the
area," Albee added. "These images present a sharp contrast to the
images of boulder-strewn deserts found at the Viking and Pathfinder
landing sites."

Newly released images from the Mars Global Surveyor camera,
developed by principal investigator Dr. Michael Malin of Malin
Space Science Systems, Inc., San Diego, can be viewed on the
Internet at:

or http://www.msss.com/

The Martian crust also exhibits much more layering at great
depth than was expected. The steep walls of canyons, valleys and
craters show the Martian crust to be stratified at scales of a 
few tens of yards, which is an exciting discovery, Albee noted.
"At this point we simply do not know whether these layers
represent piles of volcanic flows or sedimentary rocks that might
have formed in a standing body of water," he said.

The thermal emission spectrometer, led by principal investigator Dr.
Philip Christensen of Arizona State University, is beginning to obtain a
few infrared emission spectra of the surface, although it is still too
cold on the surface for the best results.  The best spectra clearly
indicate the presence of pyroxene and plagioclase, minerals which are
common in volcanic rocks, with a variable amount of dust component. No
evidence was found for carbonate minerals, clay minerals or quartz.  If
present in these rocks, their abundance must be less than about 10

Their absence indicates that carbonates are not ubiquitous 
over the surface of the planet, but they may still be found in
specific locations that either favored their initial deposition
or their subsequent preservation.  This finding could have
important implications for identifying areas that may preserve
signs of ancient life on Mars, since carbonate minerals are
commonly formed in biological processes, Albee said.

Striking results also have been obtained from Global
Surveyor's laser altimeter over Mars' northern hemisphere, which
is exceptionally flat with slopes and surface roughness
increasing toward the equator, according to principal
investigator Dr. David Smith of NASA Goddard Space Flight Center,
Greenbelt, MD. The initial data for this region helps scientists
interpret a variety of landforms, including the northern polar
cap, gigantic canyons, ridges, craters of all sizes and shield
volcanoes.  Most surprising are views of extraordinarily mundane
regions -- as flat as the Bonneville Salt Flats in Utah - that 
extend over vast northern regions of the planet.

Mars Global Surveyor will complete the first phase of its
two-part aerobraking strategy at the end of March, at which time
the science instruments will be turned on again for most of the
next six months. Over this period, the spacecraft will stay in an
11 1/2-hour orbit and collect an additional bounty of data at a
closest approach of about 170 kilometers (106 miles) above the
surface, much closer than the spacecraft will pass over the
planet once it has reached its formal mapping orbit in March
1999. This closer orbit will allow the science teams to take more
detailed measurements of the Martian atmosphere and surface
without magnetic interference from the solar wind.

"When we decided to slow the pace of aerobraking to reduce
the force on the solar panel that was damaged after launch, we
knew we would get a bonus - the ability to collect much more 
science data closer to the planet than will be possible during
the prime mapping mission," said Glenn E. Cunningham, Mars Global
Surveyor project manager at NASA's Jet Propulsion Laboratory,
Pasadena, CA.  "Additionally, the six-month period between the
end of March and early September will yield an extraordinary
opportunity as the lowest point of the orbit migrates over the
northern polar cap. All of this information that is coming back
now is really icing on the cake, a spectacular precursor to the
global mapping data expected to start flowing next year."

Mars Global Surveyor is part of a sustained program of Mars
exploration known as the Mars Surveyor Program. The mission is
managed by the Jet Propulsion Laboratory for NASA's Office of
Space Science, Washington, DC.  JPL's industrial partner is
Lockheed Martin Astronautics, Denver, CO, which developed and
operates the spacecraft. JPL is a division of the California
Institute of Technology, Pasadena, CA.


All past articles about the Mars Global Surveyor mission that were
published in "Science" magazine, are now online at:


[Editor's note: This press release was written by the JPL Media Relations
Office at NASA's Jet Propulsion Laboratory in Pasadena, California on
Tuesday, March 10, 1998.]

Mars Pathfinder Mission Status

The long goodbye to NASA's Mars Pathfinder lander and the
Sojourner rover ended today when the lander failed to respond to
the final command to communicate with controllers at NASA's Jet
Propulsion Laboratory.  The Pathfinder mission, which operated
three times longer than its original 30-day planned lifetime on
the Martian surface, is acknowledged as one of NASA's most
successful endeavors as a dramatic example of the space agency's
new style of "faster, better, cheaper" planetary exploration.

Today's last-ditch effort to listen for a signal from
Pathfinder effectively ends the mission, said Project Manager
Brian Muirhead.  No further attempts will be made to communicate
with Pathfinder, he added.

Pathfinder flight controllers Ben Toyoshima and Rob Smith at
JPL spent nearly four hours today alternately commanding the
lander to turn on its transmitter, then listening for a response
via NASA's Deep Space Network's 34-meter antenna at Goldstone,
California, in the Mojave Desert.  One-way radio communications to Mars
from Earth take nearly 20 minutes.

The final Pathfinder telecommunications session ended at 1:21 p.m. PST
when no transmissions had been detected from Pathfinder.

A description of today's efforts to reestablish contact with Pathfinder
can be found at: http://mars.jpl.nasa.gov/readme.html


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