Mars Exploration: AAAS Ponders: “Where do we go from here?”

After the session was over, reporters descended upon JPL Center Director Ed Stone. The questions had to do with recent reports that the Mars Polar Lander may have had a software and sensor design flaw that caused the lander to shut its descent engines off after misinterpreting the jolt of heat shield being jettisoned. Stone would not comment other than to say that there will be a report delivered to NASA Administrator Dan Goldin on 16 March 2000.

More detailed discussions of Mars were held that afternoon in a session chaired by Planetary Society Executive Director Lou Friedman. Some of the highlights follow.

Ken Edgett from Malin Space Science Systems (MSSS) spoke about the imagery received from the Mars Orbiter Camera (MOC) aboard the Mars Global Surveyor (MGS) and what scientists think it means – so far. MGS began its mapping phase in March of 1999 after a year or so aerobraking into its circular mapping orbit of 380 km. The camera is capable of taking photos at various resolutions, the highest being 1.5 meters per pixel. This is sufficient to observe objects the size of small automobiles on the surface of Mars. As Edgett was soon to demonstrate, this resolution can provide breathtaking insight into the surface of Mars.

Edgett focused first on observations of the Martian polar caps. He showed a series of pictures that portrayed the progression of surface features on a specific portion of the southern polar cap as it retreated (which are due to be posted on the MSSS website on 22 February 2000). An image from 9 August 1999 showed a surface completely covered with frost. By 30 September 1999, spots of dark material and similarly dark streaks were visible as the frost had begun to disappear. By 6 February 2000, the frost was completely gone – as are the dark spots and the dark streaks. According to Edgett, the wind has been “mobilizing” some sort of material as the frost disappeared. Other slides showed larger areas on which clear patterns of dark streaks could be seen – apparently indicative of prevailing winds. Update These images were posted on the MSSS website on 22 February 2000: “A High-Resolution Look at the Spring Thaw of the Martian South Polar Cap“

Edgett then showed slides from different regions of Mars. These photos were of large flat plains criss crossed with roughly straight lines. Edgett noted that he and his colleagues had taken to calling them “Europa Streaks” since they did not know their origin – yet. The streaks were similar in general appearance to surface features on Europa. As Edgett and his team examined these streaks they came to believe that there actually tracks left by dust devils” small swirling columns of dust which had been sighted previously on Mars. Indeed, one striking (yet to be released) image taken of Prometheus Terra showed a meandering, track with loops leading up to active dust devil which had quite obviously been caught in the act of leaving its mark.

Next, Edgett showed some slides comparing a crater as viewed in February 1998 and as it appeared in November 1999 – a space of 0.92 Martian year. Specifically, Edgett drew the audience’s attention to dark streaks extending downward into the crater from its rim. High resolution photos have lead geologists to conclude that the material is not fluid, but rather dry material mobilized by wind or landslides. Comparing the two photos showed features that had appeared in the interval between the time when each photo was taken, showing that these features can form over a very short period of time.

At this point, Edgett stopped to note that the Mars Global Surveyor had astonished the scientists whose job it is to analyze the data. He said that the Mars that he and his colleagues had expect to find for 30 years was not there at all. The most notable feature being the incredibly detailed layering that had been seen in a number of locations. Specifically, he pointed to one photo in particular that appeared on the cover of Science magazine in 1998 of Vallis Marineris.

Edgett then showed some images (also not yet released) of dramatic stratified cliffs that have been formed within the crater Terby [Viking Atlas: (1) (2) ] and equally dramatic images of the stratified layers in the walls of the crater Trouvelot [Viking Atlas: (1) (2) ]. These images will not be posted on the MSSS website until papers are presented at the upcoming Lunar and Planetary Science Conference in mid-March 2000.

David Smith from NASA GSFC’s Mars Orbiter Laser Altimeter (MOLA) Science Investigation team spoke about the Mars Global Surveyor’s Mars Orbiter Laser Altimeter (MOLA) and the effect its measurements have had upon our view of Mars. MOLA transmits infrared laser pulses towards Mars at a rate of 10 Hz. The instrument measures the time it takes for a pulse to be sent and return to determine the distance between MGS and the Martian surface. These measurements are then used to construct a precise topographic map of Mars.

Analysis of MOLA data has shown conclusively that Mars’ northern hemisphere is extremely smooth, one of the smoothest regions seen on any planet. The southern hemisphere, on the other hand, is very rough- indeed; Mars is shaped with a gentle slope such that north is “downhill” from south on Mars. The north pole of Mars is 6 km lower than the south pole. This is of extreme importance when consideration is give to the behavior of liquid water on the surface of Mars.

The global maps made of Martian topography show what would seem to be a large ocean basin in Mars northern hemisphere compete with drainage system running from South to North which could have fed it with water. The images his team generated have different colors assigned to different elevations. Blue is lowest (5 km below the average planetary mean) white is highest (23 km above). While Smith was leery of suggesting that there was indeed an ocean, he did point out that it would have had to have existed long ago. Some channels which seem to have been caused by flowing water lead from the highlands all the way up to the present ice cap and have left channels in the flat northern plains. This could only have happened after the area was free of water.

Just as Martian oceans were described as being quite ancient, the age of the current polar caps was described as being quite the opposite. While the southern ice cap is at a higher elevation than the northern cap, they both show a similar profile and are thought to be composed of water ice covered and/or mixed wit with carbon dioxide ice. When one looks at the way in which Mars poles wander over time and the effect this has on lighting conditions at the poles, it becomes clear that there were periods where the poles would receive sufficient sunlight so as to cause the caps to melt and not reform.

Indeed, the caps are rather dynamic constructs whose shape and size vary not just seasonally, but on a daily basis. MOLA sounding of the atmosphere over the poles has shown that clouds form overnight and are dispersed as soon as sun hits at dawn each day. Smith said that he and his team believe that what they are seeing are clouds forming from materials at the poles and that carbon dioxide falls out of these clouds onto the poles as ‘snow’ at a temperature of 158°K.

Steven Squyres from Cornell University spoke next on the status of Mars exploration programs. In light of the back to back failures of Mars Climate Orbiter and Mars Polar Lander (which also carried the twin DS-2 probes), NASA is currently reevaluating its entire program. Two investigative teams, one run by JPL, the other a “blue ribbon” or external review panel, are due to report back to NASA on 16 March 2000 on the causes of these failures and the direction(s) they think the Mars program needs to follow. Indeed two of the subgroups involved in this process, the Mars Architecture Peer Review Team and the Mars Exploration Program Analysis Group, will be meeting at NASA JPL during the week of 21 February.

Squyres noted that a number of options are currently on the table for consideration. Previously, NASA had a rather strict time table that called for samples to be returned from Mars by 2008 and that this would be accomplished via a series of dual launches (an orbiter and a lander) at every 26 month launch opportunity. According to Squyres, the ground rules set by NASA’s Associate Administrator for Space Science Ed Weiler allow options to be considered that do not adhere to this previous game plan.

As far as what will be recommended, Squyres gave an overview of what has been considered. He expects the 2001 Orbiter to be launched. Although the orbiter has much in common with the ill-fated Mars Climate Orbiter, the cause of the crash, i.e. bad math, had nothing to do with the inherent design of the spacecraft.

As far as the 2001 lander goes, this is still up for consideration. Speculation has arisen in other meetings that some of the science equipment might be removed so as to add more communications capability. Other stories have emerged that there won’t be a lander at all. Some study groups have discussed elimination altogether of the Marie Currie rover (an identical twin of Sojourner) which is scheduled to ride to Mars on the 2001 lander.

As for what the two review groups are likely to report, Squyres offered a broad overview. Orbiters would continue to be sent to Mars to do planetary science and sample return. They may now also be sent for the main purpose of determining landing site hazards and doing reconnaissance. There may also be a series of synchronous satellites placed in Mars orbit for the sole purpose of communications on and around Mars (part of the Interplanetary Internet?). One of the main dilemmas faced by the Mars Polar Lander team was a lack of a robust communications infrastructure at Mars with which to locate and communicate with MPL when its planned capabilities were no longer functioning.

Landers would be sent to perform sample return missions and in-situ experiments. They may also be sent to do additional landing technology demonstrations (ala Pathfinder) and serve to scouts to evaluate different types of landing sites for future missions. Rovers would still be considered for in situ scientific measurements and sample collection.

The theme weaving throughout these investigations is that spacecraft such as Mars Pathfinder and Mars Global Surveyor, once they manage to make it to Mars, have the capability of dramatically adding to our knowledge of Mars. When a spacecraft instrument makes a major discovery, the whole community of scientists who study Mars rejoice in the accomplishment. When one of these missions fails, the whole community feels the loss – yet they regroup, reorganize, and press on.

The theme of NASA’s Mars exploration program is to gain a thorough understanding of Mars as a planet with a special emphasis upon understanding whether it ever harbored life. According to Ken Edgett, these spacecraft can make a substantial contribution to achieving that goal, “but robots and orbiters alone won’t answer that question.”

Related Links

° A High-Resolution Look at the Spring Thaw of the Martian South Polar Cap, 22 February 2000, MSSS

° SUV Tracks On Mars? The `Devil’ Is In The Details 30 July 1998, NASA JPL

° Wind Action–The Dust Devils of Amazonis Planitia 10 August 1999, NASA JPL

° Large Martian Dust Devils Caught in the Act 1 July 1999, NASA JPL

° First Global 3-D View of Mars Reveals Deep Basin and Pathays for Water Flow, NASA GSFC press release

° Possible Ancient Oceans on Mars: Evidence from Mars Orbiter Laser Altimeter Data, NASA GSFC

° MOC Image Tests of the Mars Ocean Hypothesis, 1 October 1999, MSSS

° MGS MOC Images Listed By Release Date, MSSS

° Mars Program Independent Assessment Team Returns to JPL, 4 February 2000, NASA HQ press release

° Second Status Report: Mars Team Continues Review With Visit to Lockheed Martin
Astronautics, 21 January 2000, NASA HQ press release

° Mars Program Independent Assessment Team Begins Work, 7 January 2000, NASA HQ press release

° Mars Polar Lander Search Goes Global, 29 January 2000, SpaceRef

° Mars Global Surveyor Provides Evidence of Ancient Martian Oceans, 9 December 1999, SpaceRef

° Brown geologist finds evidence supporting ancient ocean on Mars 9 December 1999, press reelase