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New Mars Global Surveyor Images

NEW MARS GLOBAL SURVEYOR IMAGES

The following images taken by the Mars Global Surveyor spacecraft
are now available on the web:

http://mars.jpl.nasa.gov/mgs/msss/camera/images/6_26_98_herschel_release/index.h
tml
http://mars.jpl.nasa.gov/mgs/msss/camera/images/6_19_98_na_release/index.html
        
Image captions are appended below.

Ron Baalke
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                            Mars Global Surveyor
                             Mars Orbiter Camera

              Mars Orbiter Camera (MOC) High Resolution Images
                             SPO-2 Observations:
            Windblown Dunes on the Floor of Herschel Impact Basin



Mars Global Surveyor Mars Orbiter Camera Release:          MOC2-55a, -55b
Mars Global Surveyor Mars Orbiter Camera Image ID:         582313884.36507
                                                           P365-07

                                (A) [Image]

                             88 KByte GIF image

(A) Herschel Impact Basin. White box shows the approximate location of the
MOC image 36507 subframe shown in (B). Herschel is about 300 kilometers (186
miles) across, and its center is located around 14°S, 230.#176;W. North is
up. Picture is part of U.S. Geological Survey Viking orbiter photomosaic
1:64-scale map.

                                (B) [Image]

                            117 KByte GIF image

(B) MOC image 36507 subframe. Resolution is about 10.7 meters (35 feet) per
pixel. Illumination is from the right.

  You may need to adjust the images for the gamma of your monitor to insure
                               proper viewing.

  Note: This MOC image is made available in order to share with the public
  the excitement of new discoveries being made via the Mars Global Surveyor
  spacecraft. The image may be reproduced only if the image is credited to
     "Malin Space Science Systems/NASA". Release of this image does not
  constitute a release of scientific data. The image and its caption should
  not be referenced in the scientific literature. Full data releases to the
   scientific community are scheduled by the Mars Global Surveyor Project
  and NASA Planetary Data System. Typically, data will be released after a
                 6 month calibration and validation period.

  Click Here for more information on MGS data release and archiving plans.

                                   CAPTION

Herschel Basin, one of many meteor impact craters on Mars, has some dark
material on its floor that appeared from earlier spacecraft missions to have
been blown and/or deposited by wind. Herschel Basin was imaged at low
resolution by the Mariner 9 and Viking orbiters ((A) above) in the 1970s,
and again by the Phobos 2 orbiter in 1989.

On June 14, 1998, Mars Global Surveyor's Mars Orbiter Camera revealed that
part of the dark surface on the floor of Herschel Basin consists of a field
of sand dunes ((B) above). These dunes have a distinct crescent-like shape
characteristic of dunes on Earth called barchan dunes. They result from
winds that blow from a single dominant direction.

In the case of Herschel Basin, the dunes indicate that the strongest winds
blow approximately north-to-south. The crescent horns on the ends of some of
the dunes in this image are elongated. This condition indicates that the
dominant winds do not always blow in exactly the same direction--sometimes
the winds blow from the northeast, sometimes from the northwest, and
sometimes from the north. The local topography probably influences the wind
direction--and hence dune shape--because this dune field is located on a
narrow, low plain between a high crater rim to the east, and a narrow
mountain range-- the inner ring of the Herschel impact basin--to the west
(see image (A)).

MOC image 36507 was obtained on Mars Global Surveyor's 365th orbit around
10:51 a.m. PDT on June 14, 1998. The subframe (B) is centered around
14.27°S, 231.68°W.

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                            Mars Global Surveyor
                             Mars Orbiter Camera

              Mars Orbiter Camera (MOC) High Resolution Images
     Early SPO-2 High Resolution Imaging: The Challenge of Cloudy Skies



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                            June 19, 1998, Update:
          First Two Weeks of Science Phasing Orbit II Observations

The first two weeks of June 1998 saw cloudy mornings on Mars. This is normal
for this time of the Martian year, and the cloudiness is expected to
continue for the next several months, especially in the northern hemisphere
and especially at low elevations.

Mars Global Surveyor resumed photographing the Red Planet on June 1, 1998,
after being off for a month while Mars moved behind the sun as seen from the
Earth. At the beginning of June, the orbit of MGS was crossing the equator
at approximately 9:30 a.m. -- this means that the local time on the ground
underneath the spacecraft was about 9:30 in the morning.

As the closest point to the planet slowly moves north under the influence of
subtle variations of the gravity field of Mars, the latitude range over
which the camera can photograph also migrates. During the early part of the
mission, the camera could observe mostly in the southern hemisphere; now,
the camera mostly views the northern hemisphere. The southernmost latitude
also varies now from orbit to orbit as the pointing of the spacecraft and
the time when pictures can be taken are changed to accommodate the observing
requests of other experiments aboard the spacecraft. Unfortunately, most of
the remaining areas accessible for imaging by the Mars Orbiter Camera (MOC)
have been found to be socked-in by morning clouds, fog, and haze.

Taking pictures during the second Science Phasing Orbit period (SPO-2) has
become a considerable challenge for the MOC science team. Not only must each
picture be carefully planned and targeted by one or more Mars scientists,
but commanding and retrieving the observations from the spacecraft now takes
several days because MGS is being tracked from Earth only 8-10 hours per day
(between September and May, the spacecraft was tracked 24 hr/day). Targeting
takes place a few days before the data are acquired, often using position
predictions several days old, and the results of the targeting aren't known
until several days after the images are taken. Thus, variations on Mars that
occur on timescales of less than a few days, such as changes in weather,
cannot be anticipated in planning.

For example, between May 30 and June 9, a total of 22 orbits were targeted--
Orbits 336 through 357. The first images from these orbits were received on
June 2 (from Orbit 338, as the data planned for orbits 336 and 337 were
never received). The last of these images--Orbit 357--were received on June
13th. The time elapsed between targeting an orbit until the images are
received on Earth varied from 3 to 5 days (6 to 10 orbits). During these 3
to 5 day intervals, additional orbits are targeted with no knowledge of the
success or failure of recently-targeted pictures.

The first two weeks of SPO-2 had a spotty record for MOC high resolution
images. On any given orbit, the MOC team might select as many as 5 or as few
as 2 places to take a high resolution picture. Under SPO-2 orbital
conditions, these images vary from about 3 meters (10 feet) to 12 meters (39
feet) per pixel. For Orbits 336 to 357, about 30% of the high resolution
images were never received back from Mars owing to factors beyond the
control of the camera team and 20% were completely cloudy. This means that
about 50% of the targeted high resolution pictures for Orbits 336-357 were
essentially "lost" to science. Another 25% of the images were hazy--owing to
the clouds--and thus were of reduced resolution and contrast.

The good news is that about 25% of the images received from Orbits 336 to
357 were not hazy. A fair number of these good images were acquired during
the last three orbits of this period--Orbits 355, 356, and 357--the first
orbits targeted after the team had received sufficient images to tell just
how cloudy Mars had become. By changing the targeting strategy to observe
higher elevations (such as the Tharsis volcanoes and the heavily-cratered
Arabia Terra) rather than lower elevations (such as the canyons of the
Valles Marineris), and favoring southernly areas over those farther to the
north, it is possible to target images that avoid the clouds.

The MOC team now has a complete set of wide angle (low resolution) images
that cover the northern hemisphere as it appeared during the first two weeks
of June. The team uses these images to find cloud-free areas to target new
high resolution images for the orbits occurring since Orbit 357. (Examples
of these wide angle images were released June 12, 1998: (A) Northern Tharsis
and (B) Tempe Terra/Kasei Vallis).

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                        June 19, 1998, Image Releases

Every MOC image is targeted by one or more Mars scientists. Each orbit that
is targeted takes 2 to 5 hours to plan. Mars Global Surveyor conducts two
orbits per day. This means approximately 28 to 70 hours per week are spent
planning these observations. This week's MOC image release shows two
pictures--one that is cloudy (to show how much of the data presently
appears), and one that is not cloudy.

[Image]  Release #MOC2-53: Cloudy Image of Cerberus Rupes Dark Lineation

The first, "Cloudy Image of Cerberus Rupes Dark Lineation," shows the
difficulty that clouds have posed for the MOC team. The image was targeted
on June 5, 1998. The image was obtained by MOC during orbit 350 on June 7,
1998, and it was received and processed at Malin Space Science Systems on
June 9, 1998.

[Image]  Release #MOC2-54: Eroded Crater Adjacent to Huygens Impact Basin

The second, "Eroded Crater Adjacent to Huygens Impact Basin," shows a
successful image acquisition. This picture was targeted on June 9, 1998,
hours after the images from orbit 350 were received. The image was obtained
by MOC during orbit 357 on June 10, 1998, and it was received and processed
at Malin Space Science Systems on June 13, 1998.

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Malin Space Science Systems and the California Institute of Technology built
the MOC using spare hardware from the Mars Observer mission. MSSS operates
the camera from its facilities in San Diego, CA. The Jet Propulsion
Laboratory's Mars Surveyor Operations Project operates the Mars Global
Surveyor spacecraft with its industrial partner, Lockheed Martin
Astronautics, from facilities in Pasadena, CA and Denver, CO.
Follow-Ups: