April 10, 1998

PLANS FOR SECOND CLUSTER OF TARGETED IMAGING

On Sunday, April 12th, at 8:22 AM PDT and at 8:01 PM PDT, MGS will again attempt to image the sites of the Viking Landers on two consecutive orbits.

On Monday, April 13th, at 7:40 AM PDT, MGS will again attempt to image the site of the Mars Pathfinder landing. The coordinates of the site have been refined since the first imaging attempt.

On Tuesday morning, April 14th, at 6:56 AM PDT, MGS will again image a portion of the Cydonia region. Because the image of the "Face" was successful in the last attempt, the target area will be shifted slightly to the southwest of the "Face" to capture an image of the features known as "The City". This area contains features identified as "mounds", "city square", "pyramid" and the "fortress". The "city square" will the target point.

The same probabilities of success of 30% to 50% will apply to these attempts based on navigation uncertainties and spacecraft performance. Experience with the first cluster of targeted images has shown that winter weather in the northern hemisphere of Mars at this time causes hazy, surface frost and heavy cloud cover to be significant factors in the success of seeing the targets clearly. The weather effects are not included in the probability of success estimates.

Results of the Cydonia imaging will be posted on the Internet, in the same manner as in the first observation attempt, at approximately mid-evening Pacific Time on Tuesday, April 14th. If the landers are within the resulting images and can be identified, the image(s) containing it (them) will be released

.

FIRST MGS IMAGE OF CYDONIA REGION

Here's are the processed Mars Global Surveyor images of the Cydonia region:

http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA01236

This shows two strips of data, the raw image is on the left, and the processed image is on the right. The "Face" is well lit and shows no deep shadows that was exhibited in the Viking images. In the higher-resolution MGS image, the "Face" is just an ordinary looking hill, and with no shadows there are no facial features present at all.

In this image:

http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA01237

The "Face" has been rotated to appear in the same orientation as the Viking image. Again, nothing out of the ordinary.

The original Viking image is here:

http://photojournal.jpl.nasa.gov/cgi-bin/PIAGenCatalogPage.pl?PIA01141

You can compare the Viking image with the Mars Global Surveyor image. MGS took the image of the "Face" from a different viewing angle than Viking, but you can line up the nearby craters to see how they compare.

Ron Baalke

April 6, 1998

The first Mars Global Surveyor image of the Cydonia region including the "Face on Mars" is now available. The raw image is available at these locations:

http://mars.jpl.nasa.goc/mgs/target/CYD1/index.html

* http://www.jpl.nasa.gov/marsnews/mgs/cydonia/

A processed version of the raw image will be released later today. If you have difficulty reaching any of these sites due to the high demand, try one of the mirror sites listed below.

Ron Baalke

CYDONIA PHOTO CAPTION

Orbit:  220
Range:  444.21 km
Resolution:  4.32 m/pixel
Image dimensions:  1024 X 19200 pixels, 4.42 km  X 82.94 km
Line time:  0.69 msecEmission angle:  44.66 degrees
Incidence angle:  64.96 degrees
Phase angle:  61.97 degrees
Scan rate:  ~0.1 degree/sec
Start time:  periapsis + 375 sec
Sequence submitted to JPL:  Sat 04/04/98 15:15 PST
Image acquired by MOC:  Sun 04/05/98 00:39:37 PST
Data retrieved from JPL:  Mon 04/06/98 09:05 PDT

JET PROPULSION LABORATORY

March 31, 1998

GLOBAL SURVEYOR SCHEDULES IMAGING OPPORTUNITIES FOR VIKING, PATHFINDER, CYDONIA REGIONS OF MARS

Three opportunities to image each of the four sites using the spacecraft's high-resolution camera will take place over the next month, beginning on April 3 at 1:58 a.m. Pacific time, when Global Surveyor passes over the Viking 1 landing site. The spacecraft will next pass over the Viking 2 landing site at 1:37 p.m. Pacific time on April 3. On April 4, Global Surveyor will try to image the now-silent Mars Pathfinder spacecraft at 1:16 a.m. Pacific time. It will then capture a portion of the Cydonia region of Mars, location of the so-called "Face on Mars," on April 5 at 12:33 a.m. Pacific time.

Attempts to rephotograph the sites will occur during two additional opportunities falling about nine days apart. A detailed schedule of the imaging attempts is listed below. Uncertainties in both the spacecraft's pointing and the knowledge of the spacecraft's ground track from its navigation data will provide only a 30- to- 50-percent chance of capturing the images of each site.

All of the selected targets are located south of Global Surveyor's periapsis, or point of closest approach to the Martian surface. Shortly before the spacecraft reaches this point, the Global Surveyor spacecraft will rotate slightly so that when it nears the selected target, the camera's field-of-view will sweep across the target as the spacecraft flies south and rises away.

The spacecraft will begin transmitting to Earth data stored on its onboard solid-state recorders about seven hours after the images are acquired, concluding about three hours later. Currently it takes radio signals from Mars Global Surveyor about 20 minutes to travel from the spacecraft to Earth.

Data will be received at one of NASA's Deep Space Network tracking stations at Goldstone, CA, near Madrid, Spain or near Canberra, Australia, and then sent by satellite to NASA's Jet Propulsion Laboratory, Pasadena, CA. There the images, along with all of the rest of Global Surveyor's science and engineering data, are placed in the project database for access by flight controllers. This process takes only seconds for each bit of data. Consequently, the image data will not be available be on the ground until about 10.5 hours after they are acquired. Data received overnight will not be retrieved until 9 a.m. Pacific time on the following workday.

When image data are retrieved by camera operators, the information is assembled into "raw" images. Raw images may contain data errors or drop-outs introduced by noise in the telecommunications channel between the spacecraft and the ground, as well as very slight picture element variations inherent in the camera. This data processing takes about 30 minutes.

Raw images will posted on three web sites: JPL's Mars news site, the Mars Global Surveyor project home page, and NASA's Planetary Photojournal site. Information identifying the acquisition time, predicted center latitude and longitude of the target location, and the local solar time will accompany these images. Contrast enhancement will be performed by JPL's Multimission Image Processing Laboratory and posted on World Wide Web a few hours later. The Global Surveyor project home page also contains spacecraft orbital velocity and distance to the planet in real time.

Images of the Viking and Mars Pathfinder landing sites will not be posted until image enhancement and identification of the vehicles have been completed, because the small spacecraft will be at the limits of the camera's resolution. This process will take about 24 hours.

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.

               Mars Global Surveyor Imaging Schedule


First opportunity
                                                    Approximate
                             Orbit                  Internet
Date    Time (UTC/Pacific)   Number  Target         Posting

4-3-98  09:58/1:58 a.m.      216  Viking Lander 1   April 6
4-3-98  21:37/1:37 p.m.      217  Viking Lander 2   April 7
4-4-98  09:16/1:16 a.m.      218  Mars Pathfinder   April 7
4-5-98  08:33/12:33 a.m.     220  Cydonia           April 6 (mid-a.m.)

Second opportunity
                                                    Approximate
                             Orbit                  Internet
Date    Time (UTC/Pacific)   Number  Target         Posting

4-12-98 15:23/ 8:23 a.m.     235  Viking Lander 1   April 14
4-13-98 03:01/ 8:01 p.m.     236  Viking Lander 2   April 15
4-13-98 14:40/ 7:40 a.m.     237  Mars Pathfinder   April 15
4-14-98 13:57/ 6:57 a.m.     239  Cydonia           April 14 (mid-p.m.)

Third opportunity
                                                    Approximate
                             Orbit                  Internet
Date    Time (UTC/Pacific)   Number  Target         Posting

4-21-98 20:45/1:45 p.m.      254  Viking Lander 1   April 23
4-22-98 08:23/1:23 a.m.      255  Viking Lander 2   April 24
4-22-98 20:02/1:02 p.m.      256  Mars Pathfinder   April 24
4-23-98 19:18/12:18 p.m.     258  Cydonia           April 24 (mid-a.m.)

NASA Headquarters, Washington, DC
Jet Propulsion Laboratory, Pasadena, CA

March 26, 1998

MARS GLOBAL SURVEYOR TO ATTEMPT IMAGING OF FEATURES OF PUBLIC INTEREST

The spacecraft will turn on its payload of science instruments on March 27, about 12 hours after it suspends "aerobraking," a technique that lowers the spacecraft's orbit by using atmospheric drag each time it passes close to the planet on each looping orbit. Aerobraking will resume in September and continue until March 1999, when the spacecraft will be in a final, circular orbit for its prime mapping mission.

It will not be possible to predict on which orbit the spacecraft will pass closest to specific features on Mars until Global Surveyor has established a stable orbit and flight controllers are able to project its ground track. This process should be completed in the next few days. The exact time of observations and the schedule for the subsequent availability of photographs on the World Wide Web are expected to be announced early next week.

"Global Surveyor will have three opportunities in the next month to see each of the sites, including the Cydonia region, location of the so-called 'Face on Mars,' " said Glenn E. Cunningham, Mars Global Surveyor project manager at NASA's Jet Propulsion Laboratory, Pasadena, CA. "The sites will be visible about once every eight days, and we'll have a 30- to- 50-percent chance of capturing images of the sites each time."

Several factors limit the chances of obtaining images of specific features with the high-resolution mode of the camera on any one pass. These factors are related primarily to uncertainties both in the spacecraft's pointing and the knowledge of the spacecraft's ground track from its navigation data. In addition, current maps of Mars are derived from Viking data taken more than 20 years ago. Data obtained by Global Surveyor's laser altimeter and camera during the last few months have indicated that our knowledge of specific locations on the surface is uncertain by 0.6 to 1.2 miles (1 to 2 kilometers). As a result, the locations of the landing sites and specific features in the Cydonia region are not precisely known.

In addition, the Mars Pathfinder and Viking landers are very small targets to image, even at the closest distance possible, because they are the smallest objects that the camera can see. The Cydonia features, on the other hand, are hundreds to thousands of times larger and the camera should be able to capture some of the features in that area.

Global Surveyor's observations of the Viking and Pathfinder landing sites will provide scientists with important information from which to tie together surface observations and orbital measurements of the planet. Data from landing sites provide "ground truth" for observations of the planet made from space.

As for the "Face on Mars" feature, "most scientists believe that everything we've seen on Mars is of natural origin," said Dr. Carl Pilcher, acting science director for Solar System Exploration in NASA's Office of Space Science, Washington, DC. "However, we also believe it is appropriate to seek to resolve speculation about features in the Cydonia region by obtaining images when it is possible to do so."

Information about Viking observations of the Cydonia region and a listing of those images are available on the World Wide Web.

New images of the landing sites and Cydonia region taken by Mars Global Surveyor will be available on JPL's Mars news site and on the Global Surveyor home page.
These sites will also carry detailed schedules of the imaging attempts once they have been determined. Images will also be available on NASA's Planetary Photojournal web site.

So far in the aerobraking process, Global Surveyor's orbit has been reduced from an initial 45-hour duration to less than 12 hours. During the aerobraking hiatus, the spacecraft will be orbiting Mars about once every 11.6 hours, passing about 106 miles (170 kilometers) above the surface at closest approach and about 11,100 miles (17,864 kilometers) at its farthest distance from the planet. The pause in aerobraking allows the spacecraft to achieve a final orbit with lighting conditions that are optimal for science observations.

Mars Global Surveyor is part of a sustained program of Mars exploration, managed by JPL for NASA's Office of Space Science, Washington, DC. Lockheed Martin Astronautics, Denver, CO, which built and operates the spacecraft, is JPL's industrial partner in the mission. Malin Space Science Systems, Inc., San Diego, CA, built and operates the spacecraft camera. JPL is a division of the California Institute of Technology, Pasadena, CA.

MARS GLOBAL SURVEYOR COMPLETES FIRST AEROBRAKING PERIOD AND PREPARES TO PHOTOGRAPH THE MARS PATHFINDER LANDING SITE AND FEATURES IN THE CYDONIA PLAIN

The opportunities to see these targets from the Surveyor spacecraft will occur in three clusters of two and a half days each during the next month. Each target will be visible once in each cluster and the clusters will be separated by eight days. It will not be possible to predict on which orbits, and thus, on which days, the spacecraft will come closest to the targets until after aerobraking has been terminated on Friday, March 27th. Then several orbits of navigation tracking data have been obtained in order to pin point Surveyor's new orbital characteristics.

The exact time of the observation opportunities and the schedule and process for the release of the resulting photographs will be announced in a few days. Within a few days before the actual observations, a detailed sequence of the spacecraft's activities will be posted on this webpage, and the project staff will provide a near real time commentary on the events as they occur.

Surveyor's science instruments will be turned on again on Friday, March 27th, after having been off since February 20th when the orbital period became too short for both science and aerobraking operations to be conducted simultaneously. Now that aerobraking will be on hold for five months, Surveyor can return to acquiring science data.

PHOTOGRAPHING THE FEATURES IN THE CYDONIA PLAIN

TARGETS FOR OBSERVATIONS

Latitude and Longitude of four targets located in East longitude

  Target             Latitude         Longitude
  Cydonia Region     41.0 North       350.5 East
  Pathfinder         19.01 North      33.52 East
  Viking 1 Lander    22.27 North      312.03 East
  Viking 2 Lander    47.67 North      134.48 East

HOW THESE OBSERVATIONS WILL BE MADE

The orbital conditions chosen for the next five month period when Surveyor will not be aerobraking offer a particularly advantageous pattern of near overflights of these targets. Because of the position of the targets in longitude around the planet (Viking 2 is 182 degrees to the east of Viking 1, Mars Pathfinder is 14 degrees to the east of Viking 1, and Cydonia is 24 degrees east of Viking 1) the near overflights will occur in clusters of five orbits every 17 orbits. Surveyor's orbital period of 11.6 hours, which is slightly less half a Martian day, causes the spacecraft's ground track to alternate sides of the planet on consecutive revolutions. At every closest approach to the planet or periapsis, the spacecraft is about 190 degrees to the east of where is was one orbit ago and about 20 degrees to the east of where it was two orbits ago.

These observations are termed "targeted" because mission controllers will take extraordinary steps to try to assure that the selected targets are within the high resolution camera's field of view. This is a difference process than has been used in the past or will be used in the future to collect images of Mars from Global Surveyor. The normal manner of acquiring images and other science data is to point the instruments straight down at the surface or to take science data as the instrument fields of view sweep across the planet as the spacecraft performs maneuvers to accomplish aerobraking. During the aerobraking hiatus last Fall, the instruments were pointed straight down at the surface during the few minutes that the spacecraft was closest to the planet.

During the two years of mapping that will start in March 1999, the instruments will always point straight down at the planet's surface.

The photographs that have been acquired during the just concluding aerobraking phase were acquired on each orbit, a few minutes after the closet approach to the planet's surface and after aerobraking had completed, as the spacecraft was being rotated from the aerobraking attitude to the array normal spin attitude used during the rest of each orbit.

WHY ARE THESE OBSERVATIONS BEING MADE NOW?

The upcoming opportunities appear to be the best of the period because the periapsis location will be migrating to higher latitudes and going over the north pole later in the period, and thus, the distance to the targets will be increasing. In the next few weeks the elevation of the sun will be between 15 and 20 degrees at the high latitude targets (Cydonia and Viking 2) which will make for good imaging. The sun elevation will be between 40 and 45 degrees for the low latitude sites (Viking 1 and Mars Pathfinder) which will make for acceptable imaging.

HOW WELL WILL WE BE ABLE TO SEE THE TARGET IN THE IMAGES?

The Mars Pathfinder and Viking landers are very small targets, at the limit of resolution of the camera, even at the closest distance. It will be an extraordinary event if they are recognized in the images. Features in the Cydonia region, however, being hundreds to thousands of times larger, will be very easily seen, even at the more distant ranges, and while all features in this area may not be within the field of view due the expected targeting errors, there is a high probability that many will be seen with good resolution. The best known location of the "Face" will be the target point in Cydonia.

WHAT IS THE PROBABILITY THAT THIS IMAGING WILL BE SUCCESSFUL? OR ARE WE SURE WE'LL GET THE PICTURES?

One such error source relates to how good the current maps of Mars are. As all early explorers on Earth found, early maps contain many inaccuracies. The data obtained by Surveyor's laser altimeter and cameras in the last few months have indicated that locations of observed objects on the surface are displaced 1 to 2 km (0.6 to 1.2 miles) from where the Viking era maps locate them.

Another source of error is the accuracy with which the spacecraft's trajectory is predictable. This involves where the ground track of the flight path lies or will lie on the surface, and the time the spacecraft will fly over or near the desired targets. The accurate prediction of the ground track allows the mission controllers to decide how much to rotate the spacecraft to point the camera, and the timing prediction will be used by the camera operators to control when to record the image. In preparing the Surveyor's sequences for these observations, mission controllers will use the results of orbit computations made as near to the planned observation time as possible in order to minimize this uncertainty.

In addition, some error is introduced by the planet's rotation translating downtrack error into crosstrack error.

The last source of error is how accurately the spacecraft can be rotated and pointed. The design specifications for Global Surveyor call for it to be pointable with an accuracy of 10 milliradians ( 0.057 degrees), that is, mission controllers should be able to point the instruments to within 10 milliradians (0.057 degrees) of a target. Experience with the spacecraft indicates that it actually performs much better, and that a pointing accuracy of 3 milliradians (0.017 degrees) is possible.

Combining these error sources together in the proper statistical manner with the distance from the spacecraft to the targets tells us the probability that the targets will be within the camera's field of view. This probability varies from about 70% when the targets are 1000 km (621 miles) from the spacecraft, to about 25% when the targets are 400 km (249 miles) from the spacecraft.

WHY ARE THESE IMAGES IMPORTANT?

In addition, the observations of the previous landing sites provide scientists with important knowledge to tie together the observations made on the surface from the landers with those made from orbit above the planet.

The Viking 1 Lander site is the first location on Mars where humans were able to see and touch the Martian surface at a familiar scale. This site, the following higher latitude Viking 2 Lander site and the Pathfinder site play a large role in understanding the processes which have operated on the Martian surface over time and the state of the surface and atmosphere at present. These sites serve as "ground truth" locations where ideas developed from orbital observations can be tested, verified and then extended to other regions of Mars such as those we may wish to visit in the future.

Several examples of this use of the sites for ground truth illustrates their significance. One of the results of the Viking Orbiter Infrared Thermal Mapper experiment was a rock abundance map based on the observed change in surface temperature over time (large rocks cool more slowly than sand or dust). The only way to verify the results of this rock abundance map was with the two Viking landing sites where, fortunately, numerous rocks were present. Rock abundance knowledge helps in understanding the depositional history of the surface and large rocks represent a landing hazard. Mars Global Surveyor carries an advanced version of the Viking instrument called the Thermal Emission Spectrometer (TES) which will be able to map rock abundance at more than one hundred times higher spatial resolution than Viking and the TES experimenters will have another site (Pathfinder) to use to verify their deductions.

The high resolution mode of the Mars Orbiter Camera (MOC) carried by the Mars Global Surveyor spacecraft is capable of returning images of objects as small as 1.4 meters across. Some of the largest rocks in the area of the landing sites may be visible and such rock or boulder fields have been seen in MOC images at other locations on Mars. The careful surveys which have been done of the distribution of rocks as a functions of rock size can now be used with MOC images to estimate rock populations at other locations on Mars.

THE CURRENT STATUS OF MARS GLOBAL SURVEYOR

WHAT'S NEXT AFTER THESE SPECIAL OBSERVATONS?

The "Face On Mars"

Background: The Viking Images

The results of these tests indicated that Mars contained no life, at least at these landing sites. However, Viking gathered volumes of data on the weather, soil chemistry and other surface properties and mapped the surface using low-to-moderate resolution cameras on the two orbiters.

Shortly after mapping began in 1976 an interesting image taken by the Viking 1 Orbiter was received at the Jet Propulsion Laboratory, Pasadena, Calif., which contained a surface feature resembling a human or ape-like face. The photo was immediately released to the public as an interesting geological feature and dubbed the "Face on Mars." Shortly afterwards other photos of the same area were taken, and some scientists believed that the formation appeared to be a face due to the lighting angles as seen from the Orbiter.

Origin Of Features Examined

Most planetary geologists familiar with the set of photos, however, concluded that the natural processes known to occur on Mars -- such as wind erosion, Mars quakes, and erosion from running water in the distant past -- could account for the formation of the complicated fretted terrain of the Cydonia region, including the face.

Because the entire data set includes only nine low-to-moderate resolution photos, scientists say that there just is not enough data available to justify what would be an extraordinary conclusion that the features are not natural in origin (many scientists question whether images alone would be enough to settle the matter). Such a proven discovery of extraterrestrial life or artifacts would be one of the greatest discoveries in human history, and, as such, demand the most rigorous scientific investigation.

However, despite the phenomenal nature of such a potential discovery, no one in the scientific community -- either in the U.S. or worldwide -- has ever proposed an investigation for a mission to study these features. Until more data is gathered, many scientists consider the probability that the features are anything other than natural in origin are just too low to justify the major expenditure of public funds which such an investigation would entail (more on this below).

What is agreed on is that a greater number of high resolution images of this area should be gathered. Following the failure of the Mars Observer mission in August, 1993, NASA proposed a decade-long program of Mars exploration, including orbiters and landers. The program, called Mars Surveyor, would take advantage of launch opportunities about every 2 years to launch an orbiter and a lander to the Red Planet. The first mission, consisting of an orbiter to be launched in 1996, will map the surface and take high- and medium-resolution images of particular features on the Martian surface that are of high interest. NASA intends to make observations of the Cydonia region making the best effort feasible, either with the first orbiter or on follow-on missions, to obtain images of the "face" and nearby landforms.

Quite aside from the interest generated by these curious features, Cydonia has long been regarded as an area of high scientific importance, ever since the first detailed images were returned by NASA's Viking spacecraft in the late 1970s. The Cydonia region of Mars is part of the so-called fretted terrain, a belt of landforms that circles Mars at about 30-40 degrees North Latitude. In this region, the ancient crust of Mars has been intensely eroded by weathering processes, leaving high remnants of older crust surrounded by lower plains of eroded debris.

The landforms of Cydonia resemble in some respects those of terrestrial deserts, but they probably have been shaped by a unique range of peculiarly martian agencies: wind, frost and possibly running water in ancient times. Deciphering the geological age and origin of this terrain will yield important insights into the evolution of the martian surface, into the role of ice and water in its development and into the nature of the martian climate in times past.

Proposing Investigations

When NASA receives permission to proceed with a science mission, the Agency publishes an Announcement of Opportunity (AO). The AO solicits interest in providing high priority scientific investigations and instruments that will be part of the new mission. The AO receives the widest possible circulation throughout the university and research communities and industry.

Proposals are submitted and reviewed through a competitive peer review process. In this process, scientists from various institutions and organizations evaluate each proposal's scientific and technical merit, and then rank the relative merit of each. NASA receives the reports of the review panels and makes a final selection as to which instruments will be built and actually flown. This rational selection process ensures that only the most useful research, with a high probability of returning good science, is done at taxpayer expense.

After selection, each Mars Surveyor Principle Investigator (PI) team will develop its instrument, build it, test it and prepare it for launch and the 10-month journey to Mars. They are also charged with developing, testing, and using the software required to properly calibrate their instrument's data. Most of the scientists working on the various Mars Surveyor missions will have several years invested in their instrument before the spacecraft arrives at Mars and they can actually receive the bulk of the data they have been waiting for.

Obtaining Images of the "Face" and Other Planetary Data

The most noteworthy image of the 'face' feature is available to the public, for a nominal fee, through Headquarters and JPL. A photo catalogue can be provided to select images.

The phone numbers for ordering photos are:

HQ: 202/358-1900
JPL: 818/354-5011

All imaging data obtained by the Mars Surveyor program, as well as other types of data, will be deposited in open data archives. Two such archives widely used are the Planetary Data System (PDS), an open archive accessible to thousands of scientists and other individuals, and the National Space Science Data Center (NSSDC) where images and other data will be readily available to the general public (generally on CD-ROMs or as hard copy, as appropriate), for a nominal charge that covers the materials and time needed to produce the copies. For information about ordering copies of NASA science mission images, including on CD-ROM format, contact the NSSDC at:

National Space Science Data Center
Request Coordination Center
Goddard Space Flight Center
Greenbelt, MD 20771
Telephone: 301/286-6695

Listed below are the photo numbers of every image taken by Viking of the 'face' feature and the surrounding Cydonia terrain. When ordering from the data archive centers, refer to the Viking picno (photo number).

                                                        Sun
 Picno     Scale     Emission   Incidence   Phase    Elevation   Period of
         (m/pixel)     (deg)      (deg)     (deg)                   Day
                                                       (deg)
 035A7247.13        10.53      79.89       86.26   10.11        morning
 070A1343.42        12.36      62.61       71.77   27.39        morning
 561A25162.7        32.83      76.59       45.63   13.41        morning
 753A33232.82       10.25      35.3        25.12   54.7         afternoon
 753A34232.51       10.13      35.15       25.14   54.85        afternoon
 814A07848.86       38.15      65.93       103.25  24.07        too low
 257S69821.24       42.06      43.83       8.66    46.17        cloudy
 673B54226.02       23.22      64.94       77.76   25.06        morning
 673B56225.7        21.33      67.77       76.7    22.23        morning

NASA Headquarters
Public Affairs Office
Washington DC 20546-001

Document: FS-1995-08-016-HQ
Modified: August 1995

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