MARSBUGS: The Electronic Astrobiology Newsletter Volume 6, Number 26, 27 August 1999. Editors: Dr. David J. Thomas, Biology and Chemistry Division, Lyon College, Batesville, AR 72503-2317, USA. Marsbugs@aol.com or dthomas@lyon.edu Dr. Julian A. Hiscox, School of Animal and Microbial Sciences, University of Reading, Reading, RG6 6AJ, United Kingdom. J.A.Hiscox@reading.ac.uk Marsbugs is published on a weekly to quarterly basis as warranted by the number of articles and announcements. Copyright of this compilation exists with the editors, except for specific articles, in which instance copyright exists with the author/authors. While we cannot copyright our mailing list, our readers would appreciate it if others would not send unsolicited e-mail using the Marsbugs mailing list. The editors do not condone "spamming" of our subscribers. Persons who have information that may be of interest to subscribers of Marsbugs should send that information to the editors. E-mail subscriptions are free, and may be obtained by contacting either of the editors. Article contributions are welcome, and should be submitted to either of the two editors. Contributions should include a short biographical statement about the author(s) along with the author(s)' correspondence address. Subscribers are advised to make appropriate inquiries before joining societies, ordering goods etc. Back issues and Adobe Acrobat PDF files suitable for printing may be obtained from the official Marsbugs web page at http://www.lyon.edu/webdata/users/dthomas/marsbugs/marsbugs.html . The purpose of this newsletter is to provide a channel of information for scientists, educators and other persons interested in exobiology and related fields. This newsletter is not intended to replace peer-reviewed journals, but to supplement them. We, the editors, envision Marsbugs as a medium in which people can informally present ideas for investigation, questions about exobiology, and announcements of upcoming events. Astrobiology is still a relatively young field, and new ideas may come out of the most unexpected places. Subjects may include, but are not limited to: exobiology and astrobiology (life on other planets), the search for extraterrestrial intelligence (SETI), ecopoeisis and terraformation, Earth from space, planetary biology, primordial evolution, space physiology, biological life support systems, and human habitation of space and other planets. ---------------------------------------------------------------- CONTENTS 1) EARTH BATTERED THROUGH HISTORY BY COMETS--RESEARCHERS SAY IMPACTS CAUSED GLOBAL CRISES, MASS EXTINCTIONS By Robert S. Boyd 2) MARS POLAR LANDER TO ARRIVE ON SMOOTH, LAYERED TERRAIN JPL release 3) WATER OF THE STARS By Greg Clark 4) GALILEO'S CLOSE-LOOK IMAGES OF JUPITER'S MOON IO AVAILABLE ON WEB JPL internet advisory 5) DEEP SPACE SYSTEMS PROGRAM INCLUDING EUROPA ORBITER, PLUTO- KUIPER EXPRESS, AND SOLAR PROBE Announcement of opportunity (AO 99-OSS-04) 6) MARS GLOBAL SURVEYOR STATUS REPORT JPL release 7) MARS SURVEYOR 98 MISSION STATUS JPL releases 8) THIS WEEK ON GALILEO JPL release 9) STARDUST STATUS REPORT JPL release 10) NEW MARS GLOBAL SURVEYOR IMAGES By Ron Baalke ---------------------------------------------------------------- EARTH BATTERED THROUGH HISTORY BY COMETS--RESEARCHERS SAY IMPACTS CAUSED GLOBAL CRISES, MASS EXTINCTIONS By Robert S. Boyd San Jose Mercury News 17 August 1999 Recent scientific discoveries are shedding new light on why great empires such as Egypt, Babylon and Rome fell apart, giving way to the periodic "dark ages" that punctuate human history. At least five times during the last 6,000 years, major environmental calamities undermined civilizations around the world. Some researchers say these disasters appear to be linked to collisions with comets or fragments of comets like the one that broke apart and smashed spectacularly into Jupiter five years ago this summer. The impacts, yielding many megatons of explosive energy, produced vast clouds of smoke and dust that circled the globe for years, dimming the sun, driving down temperatures and sowing hunger, disease and death. Get the full story at http://www7.mercurycenter.com:80/premium/nation/docs/disaster17. htm ---------------------------------------------------------------- MARS POLAR LANDER TO ARRIVE ON SMOOTH, LAYERED TERRAIN JPL release 25 August 1999 A strip of gentle, rolling plains near the Martian south pole will serve as a welcome mat when NASA's Mars Polar Lander touches down on the red planet on December 3. NASA unveiled the landing site, a swath of terrain measuring about 4,000 square kilometers (1,500 square miles), at a briefing today at NASA Headquarters, Washington, DC. "We looked for a site with slopes no steeper than 10 degrees," said Project Scientist Dr. Richard Zurek of NASA's Jet Propulsion Laboratory, Pasadena, CA. "We chose a location with some surface features but no cliffs or jagged peaks, because the spacecraft will be able to land safely, yet we'll still accomplish our science goals." The landing site is located at 76 degrees south latitude and 195 degrees west longitude, near the northern edge of the layered terrain in the vicinity of the martian south pole. "We believe this layered terrain is a record of climate changes on Mars and, in a sense, digging into its surface will be like reading tree rings or layers in an ice core," Zurek said. "The presence of fine layers of dust and ice with varying thickness will indicate changes in weather patterns and layer formation that have been repeated in recent history. In addition, we may find evidence of soil particles that formed in ancient seas on Mars and were later blown into the polar regions." The landing will be targeted to the center of the site, a rectangular area 200 kilometers (125 miles) long and 20 kilometers (12.5 miles) wide. The site was selected after the project team studied pictures and altimeter information gathered by NASA's Mars Global Surveyor, which is currently orbiting the planet. The search was narrowed to four sites before the final location was chosen. A backup landing site is located nearby, at 75 degrees south latitude and 180 degrees west longitude. "For the next several weeks, we'll study newly transmitted Mars Global Surveyor images," said Flight Team Manager Dr. Sam Thurman at JPL. "If necessary, we can retarget for the backup landing site as late as early October, when the flight team begins preparations for landing." The December 3 landing occurs toward the end of spring in the martian southern hemisphere. The sun will shine all day, moving higher and lower in the sky but never dipping below the horizon. This nonstop sunshine will power the lander's solar panels for 90 days, until the martian seasons change and the lander's mission ends. Launched on January 3, 1999, Mars Polar Lander will study the soil and look for ice beneath the surface of the martian south pole. The lander also carries two Deep Space 2 microprobes that will be deployed about five minutes before the spacecraft enters the Martian atmosphere. The microprobes will smash into the planet's surface and penetrate the soil to look for water ice. The microprobes were developed under NASA's New Millennium Program. Images of the landing site and additional information about Mars Polar Lander are available at http://mars.jpl.nasa.gov/msp98/lander/ Additional information about Deep Space 2 is available on the web at http://nmp.jpl.nasa.gov/ds2/ JPL manages Mars Polar Lander and the New Millennium Program for NASA's Office of Space Science, Washington, DC. JPL is a division of the California Institute of Technology, Pasadena, CA. ---------------------------------------------------------------- WATER OF THE STARS By Greg Clark Space.com staff writer 26 August 1999 A pair of scorched rocks that fell from space onto a west Texas town last year may have delivered a bonanza to planetary scientists that could turn out to be the most significant discovery in years: purple extraterrestrial salt and miniature bottles of primordial water. A team of scientists led by Michael Zolensky, a mineralogist at NASA's Johnson Space Center, thinks it has found several minute samples of water sealed inside the salt crystals in the Monahans meteorite. The minute droplets of salty brine, which would have traveled through the solar system for millions of years as tiny ice crystals, could reveal the details of early solar-system chemistry. They may also tell scientists how and where water formed, whether it was in the early days of the solar system, or farther away and back in time somewhere in interstellar space. Get the full story at http://www.space.com/science/astronomy/meteorite_water.html ---------------------------------------------------------------- GALILEO'S CLOSE-LOOK IMAGES OF JUPITER'S MOON IO AVAILABLE ON WEB JPL internet advisory 26 August 1999 The closest pictures ever taken by NASA's Galileo spacecraft of Jupiter's volcanic moon Io will be unveiled Friday, August 27, at 8 a.m. Pacific Daylight Time, at the following Internet addresses: http://photojournal.jpl.nasa.gov http://www.jpl.nasa.gov/galileo/sepo http://www.jpl.nasa.gov/galileo http://www.jpl.nasa.gov The images are in true color (as they would appear to the naked eye) and in enhanced false color. They reveal a patchwork of pastels, punctuated by areas of black, brown, green, orange and red, near Io's active volcanic centers. The pictures were taken on July 3, 1999, as Galileo passed closer to Io than it has since it entered orbit around Jupiter in December 1995. The spacecraft is continuing to lower its orbit toward Io, the most volcanic body in our solar system, in preparation for two closer flybys of Io in October and November. The upcoming flybys are expected to yield images of unprecedented clarity and detail. The radiation belts of Jupiter are very intense at Io's distance from the huge planet, and this can disrupt spacecraft functioning. To insure that Galileo will be able to perform science observations from this unique vantage point, the Galileo flight team is preparing contingency plans to protect against radiation-related problems. Galileo has been orbiting Jupiter and its moons since December 1995. Its primary mission ended in December 1997, but the spacecraft is currently in the midst of a two-year extended mission. More information about the Galileo mission is available at http://www.jpl.nasa.gov/galileo/. JPL manages Galileo for NASA' s Office of Space Science, Washington, D.C. JPL is a division of the California Institute of Technology, Pasadena, CA. ---------------------------------------------------------------- DEEP SPACE SYSTEMS PROGRAM INCLUDING EUROPA ORBITER, PLUTO- KUIPER EXPRESS, AND SOLAR PROBE Announcement of opportunity (AO 99-OSS-04) 27 August 1999 Release Date: September 10, 1999 Proposals Due: December 10, 1999 through June 6, 2000 The National Aeronautics and Space Administration (NASA) is releasing a NASA Announcement of Opportunity (AO 99-OSS-04) entitled Deep Space Systems Program Including Europa Orbiter, Pluto-Kuiper Express, and Solar Probe. This AO will solicit proposals for investigations that require the development of space flight instruments on the three different missions. In addition, the AO will solicit scientific participation as a member of facility science teams for the Europa Orbiter mission. Proposal due dates for the three missions will be staggered at approximately 90 day intervals: December 10, 1999 (Europa Orbiter), March 9, 2000 (Pluto-Kuiper Express), and June 6, 2000 (Solar Probe). Participation is open to all categories of organizations, foreign and domestic, including educational institutions, industry, nonprofit organizations, NASA centers, and other Government agencies. Upon the release date, specific guidance for proposal preparation will be available via the World Wide Web site: http://spacescience.nasa.gov/research.htm Further information about Europa Orbiter and Pluto-Kuiper Express can be obtained from Dr. Jay Bergstralh, Research Program Management Division, Code SR, Office of Space Science, NASA Headquarters, Washington, DC 20546-0001; E-mail: (jay.bergstralh@hq.nasa.gov); TEL: (202) 358-0313. Further information about Solar Probe can be obtained from Dr. W. Vernon Jones, Research Program Management Division, Code SR, Office of Space Science, NASA Headquarters, Washington, DC 20546-0001; E- mail: (Vernon.Jones@hq.nasa.gov); TEL: (202) 358-0885. ---------------------------------------------------------------- MARS GLOBAL SURVEYOR STATUS REPORT JPL release 19 August 1999 Launch / Days since Launch = Nov 7, 1996 / 1016 days Start of Mapping / Days since Start of Mapping = April 1, 1999 / 140 days Last Orbit Covered by this Report = 2003 Total Orbits = 3685 Total Mapping Orbits = 2003 Recent Events The mm006 sequence is currently executing the daily science data collection and return and will continue execution through August 25. The mm007 sequence has been completed and will be uplinked Monday August 23. The mm007 sequence will initiate stoppage of the HGA auto-tracking during non-Earth communications periods as an additional change in nominal mapping operations to reduce microphonics noise in the Thermal Emission Spectrometer (TES) instrument. Work continues on the development of a Magnetometer (MAG) calibration sequence to be executed on the spacecraft August 31. This test is comprised of a series of solar array motions on the night side of the orbit that will be used to more fully characterize the magnetic signature of the spacecraft. HGA Anomaly The HGA gimbal is currently operational with full redundancy on side-A. The fault protection threshold for HGA stuck gimbal is at 25 seconds (50 counts). Spacecraft Health All subsystems continue to report nominal status. Uplinks There have been 13 uplinks to the spacecraft during the last week, including new star catalog and ephemeris files, and instrument command loads. Total command files radiated to the spacecraft since launch is 3858. Upcoming Events 1) MM007 sequence to be uplinked Monday Aug 23. 2) MAG calibration on Aug 31. ---------------------------------------------------------------- MARS SURVEYOR 98 MISSION STATUS JPL releases 18 August 1999 Mars Climate Orbiter (MCO) The MCO spacecraft continues operating nominally in late cruise. Today the flight team conducted its second Operational Readiness Test (ORT) in preparation for Mars arrival next month, the first of two exercises simulating the aerobraking phase of the mission. Following Mars Orbit Insertion, the orbiter will be maneuvered so that its flight path passes through the upper reaches of the Martian atmosphere. Over the course of about 45 days (September 25 through November 9), repeated passes through the atmosphere will cause MCO's orbit to get shorter and lower in altitude, becoming nearing circular. This process, pioneered by the Magellan mission to Venus in 1993 and used successfully by Mars Global Surveyor during 1997-1999, has been dubbed aerobraking. The Mars '98 flight team will conduct its second aerobraking ORT next week, then prepare for a final ORT rehearsing Mars Orbit Insertion itself. Mars Climate Orbiter is 36 days from MOI. Mars Polar Lander (MPL) Mars Polar Lander continues to perform well, now in late cruise. Entry/Descent/Landing and surface mission stress testing continues in the MPL simulator facility, while the rest of the flight team maintains its present focus on test and training for the orbiter's arrival at Mars. August 25, 1999 Mars Climate Orbiter (MCO) Two separate in-flight checkout activities were conducted on Friday and Saturday (August 20 & 21), exercising both the primary encoder (encoder "A") on the solar array inner gimbal drive and the inner gimbal assembly itself. These tests indicated no anomalous behavior and confirmed that the inner gimbal and the "A" encoder are fully functional. Special high- rate telemetry data did indicate larger than expected structural oscillations of the solar panel-the attitude and articulation control group at Lockheed Martin Astronautics (LMA) in Denver is investigating via comparison of ground-based simulations of the test with flight data. Subsequently, evaluation of the temporary stoppage of the inner gimbal drive after Trajectory Correction Maneuver #3 (TCM-3) on July 25 is now focusing on the gimbal movements performed to move the solar array out of its passive restraint, shortly after the TCM-3 burn was completed. On Monday (August 23) the Deep Space Network (DSN) initiated the demonstration phase of its Near-Simultaneous Tracking (NST) program, using the Mars Global Surveyor (MGS) spacecraft already orbiting Mars as a form of calibration target for navigation of the MCO spacecraft during its approach to Mars. In NST tracking passes a single ground station will first track one spacecraft for 2-4 hours, then switch over in 20 minutes to track a second spacecraft for a similar (2-4 hours) time period. Two-way Doppler and range data are recorded from the two spacecraft sequentially, then processed within the navigation software system to obtain estimates of the approaching spacecraft's flight path relative to the other spacecraft (and hence Mars itself) that are substantially more accurate than would otherwise be possible. Following a 30 day demonstration phase, the DSN will begin NST tracking of Mars Polar Lander and MGS, in preparation for the critical 45 day period leading to landing, in which the NST technique will be used operationally for precision guidance of the lander toward its target entry conditions. Yesterday (Tuesday, August 24), the flight team conducted its second test and training exercise for MCO aerobraking, simulating the development and execution of sequences for three successive drag passes during the final "end-game" phase of aerobraking, including a simulated "jack" procedure to perform a maneuver rapidly following a yellow alarm limit violation on drag pass constraints. Several minor problems were identified for correction in the operation of the uplink system for flight. Otherwise, the team successfully met all key objectives for aerobraking test and training, and is now beginning preparations for the final Mars Orbit Insetion (MOI) operational readiness test, which will take place on September 2. Mars Climate Orbiter is 29 days from MOI. The approach campaign has begun. Mars Polar Lander (MPL) In addition to the MCO training activites yesterday, NASA formally approved a target landing site for Mars Polar Lander, following a briefing given to senior management from the Office of Space Science (OSS). OSS accepted the recommendation made by the flight team of a primary target area centered at 76 deg S Latitude, 195 deg W Longitude, which is believed to lie well onto the layered terrain in the south polar region of Mars. This site was chosen after a detailed evaluation of images and laser altimetry obtained from the mission target sector by the Mars Global Surveyor (MGS) spacecraft. The Mars Orbiter Camera (MOC) onboard MGS will continue to image the target area at high resolution through August and September, given the opportunities provided by MGS orbit geometry. Following NASA's approval of the target site, the flight team proceeded with final targeting computations for the upcoming site adjustment maneuver. Development of the command products for this maneuver has begun, in preparation for transmission to the spacecraft early next week. The site adjustment maneuver is scheduled to begin at 10:00 PDT on Wednesday, September 1; the maneuver will be 2.3 meters/second in magnitude. For more information on the Mars Surveyor 98 mission, please visit our web site at http://mars.jpl.nasa.gov/msp98. ---------------------------------------------------------------- THIS WEEK ON GALILEO JPL release 23-29 August 1999 The time between encounters has been getting shorter over the past few flybys for Galileo, as the mission approaches its encounters with Jupiter's fiery moon Io later this year. Evidence of this is that the spacecraft passes though apojove on Saturday of this week, only 16 days since it passed perijove. Apojove occurs when the spacecraft is furthest from Jupiter; perijove occurs when the spacecraft is at its closest approach to Jupiter. During the Europa Campaign there were typically at least 30 days between perijove and the following apojove. This week's data return is dedicated exclusively to the return of a recording of the Io torus and Jupiter's magnetosphere. The data were collected by the Fields and Particles instruments and are stored on the spacecraft's onboard tape recorder. Data playback is interrupted twice this week. On Thursday, the spacecraft will execute a small flight path correction. Late Sunday night, the spacecraft performs a standard gyroscope performance test. The Fields and Particles Instrument suite is comprised of the Dust Detector, Energetic Particle Detector, Heavy Ion Counter, Magnetometor, Plasma Detector, and Plasma Wave Instrument. Their recording is one in a series planned for each of the four encounters of the Perijove Reduction Campaign (Galileo's previous three encounters, and Galileo's next encounter). During these encounters, the spacecraft's perijove distance is being reduced from orbit to orbit to allow a future flyby of Io. These recordings provide valuable high-resolution data describing Jupiter's inner magnetosphere and Io torus environment at varying distances from Jupiter. The Io torus is particularly interesting, as it is a region of intense plasma and radiation activity, in which there are strong magnetic and electric fields. Constantly replenished by the volcanic activity on Io, it is a vital part of the Jovian magnetosphere. The Fields and Particles instruments make measurements of the magnetic fields and particle interactions within these regions, including measurements of radio signals and electromagnetic waves. These measurements will contribute to the study of the dynamic processes within the torus in particular and the Jovian magnetosphere in general. For more information on the Galileo spacecraft and its mission to Jupiter, please visit the Galileo home page at http://www.jpl.nasa.gov/galileo. ---------------------------------------------------------------- STARDUST STATUS REPORT JPL release 20 August 1999 What was planned as a busy week for Stardust turned out to be a quiet week instead. A decision was made last Friday, August 13, to delay the All-Stellar demonstration and transition until the Payload and Attitude Control Interface (PACI) board reset problem is better understood. The Anomaly Investigation Team is still working on the problem. The interrupt of the Star Camera PACI transfer sequence has been reproduced in the Spacecraft Test Laboratory. If the root cause is not readily found, consideration is being given to a flight software patch that would re-enable operation if an interrupt occurred again. More than normal tracking coverage was available this period, planned for the All-Stellar transition with tracks on August 14, 17, and 18. Background flight sequence SC008, which will run for four weeks, started on August 16. The spacecraft remains in a nominal mode, the Cometary Interstellar Dust Analyzer (CIDA) and Dust Flux Monitor (DFM) instruments are powered off. A very successful, and well-received, Stardust Teachers Workshop was held on August 16 through 19 at JPL. There were seminars and hands-on activities, and tours of the JPL Oak Grove facility and the Goldstone Tracking Complex (while the 34-meter antenna (DSS-25) was tracking the Stardust spacecraft). For more information on the Stardust mission--the first ever comet sample return mission--please visit the Stardust home page at http://stardust.jpl.nasa.gov. ---------------------------------------------------------------- NEW MARS GLOBAL SURVEYOR IMAGES By Ron Baalke 25 August 1999 The following new images taken by the Mars Global Surveyor spacecraft are now available: *Mars Global Surveyor Views of the Mars Polar Landing Site The images reside on the Mars Global Surveyor web site at http://mars.jpl.nasa.gov/mgs/msss/camera/images/index.html The image captions are appended below. Mars Global Surveyor was launched in November 1996 and has been in Mars orbit since September 1997. It began its primary mapping mission on March 8, 1999. Mars Global Surveyor is the first mission in a long-term program of Mars exploration known as the Mars Surveyor Program that is managed by JPL for NASA's Office of Space Science, Washington, DC. Malin Space Science Systems (MSSS) 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. Mars Global Surveyor Mars Orbiter Camera Mars Global Surveyor Views of the Mars Polar Landing Site MGS MOC Release #MOC2-174, 25 August 1999 High-resolution views of the Mars Polar Lander landing zone were essential to the selection of a safe place for the December 3, 1999, landing to occur. The Mars Global Surveyor (MGS) Mars Orbiter Camera (MOC) took its first pictures of the landing zone in December 1997 and January 1998. After that time, the south polar region was not accessible to the camera until June 1999, when the south polar winter was ending and the sun began to dawn on this region once again. Since the beginning of June 1999, an intense period of imaging has been conducted over the landing zone so that a safe site could be found. The final site has now been identified, and the pictures shown here give some idea of what the Mars Polar Lander will encounter a little more than three months from now. MOC2-174a: MGS MOC Coverage of Mars Polar Lander Region This figure shows the zone originally proposed by the Mars Volatiles and Climate Surveyor (MVACS) science team for the Mars Polar Lander mission, which spanned the region from 72° to 78°S latitude and 170° to 230°W longitude. The thin white boxes and lines crossing the proposed zone outline MOC images taken between the first week in June 1999 and the first week in August 1999. The longest images were taken at 12 by 18 meters (39 by 59 feet) per pixel; there are three sets of long images, each taken during a given week in June as the terminator (the line separating "night" from "day") moved south across the landing zone. Smaller swaths represent images at higher resolution. The best resolution so far achieved is about 4 meters (13 ft) per pixel; better images will be taken in September and October as the sun rises farther and the surface becomes better illuminated. This figure shows the location of the primary (blue) and secondary (white) landing ellipses, which were selected on the basis of interpretation of the MGS data, in particular data from the Mars Orbiter Laser Altimeter and the Mars Orbiter Camera. The selection criteria were to find a place that was relatively flat and relatively smooth, but which displayed characteristics of the south polar layered materials. The inset (upper left) shows the location of the landing zone with respect to the south polar residual (year-round) ice cap. The base map used here is a mosaic of Viking Orbiter images from the U.S. Geological Survey. MOC2-174b: Mars Polar Lander and Mars Pathfinder Sites Compared This figure shows a comparison at the same scale (about 5 meters--16 feet--per pixel) of the 1997 Mars Pathfinder landing site (left) and a representative portion within the primary landing ellipse designated for the Mars Polar Lander (right). Familiar landmarks at the Mars Pathfinder site include the "Twin Peaks" (center left), "North Peak" (top), and "Big Crater" (lower right). The south polar layered deposits are generally devoid of the large craters and hills seen at the Pathfinder site. The "wavey" texture at the Pathfinder site (the result of the movement of sediment by the large flood that swept through that location billions of years ago) is replaced at the proposed Mars Polar Lander site by a random arrangement of very low ridges and grooves that suggest the surface has been exposed to erosion by ablation of ices. When the picture on the right was taken, the surface was still mostly covered by winter-time carbon dioxide frost. However, as the sun rises higher, the carbon dioxide frost sublimes (goes directly from solid to vapor), creating the dark spots that are just barely visible in this image. Illumination is from the lower right in both pictures. MOC2-174c: Mars Polar Lander Site Surface Details This picture is an enlargement of a portion of a MOC image taken in late July 1999, showing the onset of defrosting of the seasonal carbon dioxide frost cap (small, occasionally fan- shaped dark spots seen throughout this image). Two craters are seen in this image, a very rare occurrence on the south polar layered deposits. Shown for comparison at the same scale is a picture of Jack Murphy (now Qualcomm) Stadium in San Diego, California. Clearly visible in the inset is the baseball diamond and pitcher's mound; less clear but certainly visible are a number of automobiles (small light dots) in the parking lot west (to the left) of the stadium. The elevation of the sun in the Mars image is about 10°; the sunlight is coming from the bottom (north) in this image. The shadow of the rims of the craters can be used to determine their depths. The smaller crater in the bottom right corner is about 60 m (197 feet) across and 7 m (23 feet) deep; the large crater just below the inset is 175 m (574 feet) across and 17 m (56 feet) deep. Similar calculations for other features in the images indicate that much of the surface is smooth and flat. Relief is typically much less than 1-2 meters (3-7 feet) in height over areas of 10-15 meters across (33-49 feet). MOC2-174d: Mars Polar Lander Site Compared With Washington, D.C. This figure compares five representative views of the Mars Polar Lander primary ellipse near 76°S, 195°W, with a similar-sized view of the U.S. capital for scale. Each box is approximately 1.2 km (0.75 mi) on a side. The brightness variations from one box to another among the Mars images reflects different amounts of frost cover, and possibly the differing compositions of frost (i.e., carbon dioxide vs. water ice). The brightness also depends upon surface texture both above and below the scale of these images (about 5.5 meters--18 feet--per pixel). These pictures show the range of surface texture and morphology that is found within the landing ellipse. Mounds and valleys that range from a few meters to as much as one hundred meters (328 ft) across--with relief of a few meters--dominate the landing site. All of the frost seen here is expected to be gone by the time the Mars Polar Lander arrives in December 1999. The Mars images are illuminated from the lower right. The view of Washington D.C. shows the Capitol Building at the center right and the National Air and Space Museum at center left (immediately below the grassy rectangles of the Mall). Additional MOC Pictures of the Mars Polar Lander and Mars Pathfinder landing regions: * "South Polar Layered Deposits near Proposed Mars Surveyor '98 Landing Site," MOC2-25, March 9, 1998 * "Additional Images of South Polar Layered Deposits near Proposed Mars Surveyor '98 Landing Site," MOC2-26, March 9, 1998 * "Pathfinder Landing Site Observed by Mars Orbiter Camera," MOC2-46, April 25, 1998 * "Mars Pathfinder First Anniversary Special--Refined Landing Site Location in MOC Image 25603," MOC2-56, July 3, 1998 ---------------------------------------------------------------- End Marsbugs Vol. 6, No. 26