Project Manager Richard Cook said, "The final set of planned commands were sent on Jan. 6 to place the spacecraft in UHF safe mode.

"Since then, we've had a series of relay communications sessions using Mars Global Surveyor to listen for the lander around the clock. These efforts have ended today, concluding our attempts to recover the spacecraft," said Cook.

JPL's efforts are now directed toward trying to do a post-mortem -- which is rather difficult without the corpse. MGS is continuing to photograph the probable landing area in an atempt to photograph the lander or (more likely) its parachute, or the crater it may hve left if it crashed at high speed.

No evidence has been sighted so far -- and though the effort will continue through early February, the resolution even of MGS's high-powered camera may not be high enough to do so. The MGS team is also carrying out a more thorough study of possible terrain hazards in the area, which may be more useful.

In the meantime, though, there have been interesting developments on two fronts.

First, a new theory of the cause of the failure has received very widespread publicity -- namely, that MPL might have landed on the side of what is often described as a "precipitous canyon" located within its probable landing area, and tumbled down the slope to destruction.

This theory was first put forth by an unnamed source within Lockheed Martin. However, the feeling of this writer is that it is extremely doubtful.

Mars Global Surveyor, with its laser altimeter, constructed a very detailed topographic contour map of MPL's selected landing site some time before the landing attempt -- and (contrary to some published reports) this map clearly showed the "canyon" at the time.

However, the map -- publicly available at JPL's Mars Global Surveyor Website -- makes it clear that the "canyon" is actually a relatively gentle depression or hollow.

At the center of MPL's estimated landing area at the time the "canyon" theory first came out, the slope is a gentle 4 degrees, which is certainly safe. There is a region at the core of the depression where the slope rises to about 20 degrees -- which might indeed cause landing problems -- but this area is only 6 or 7 km across, and it is located about 25 km south of that estimated landing point.

Central Landing Ellipse Features: This illustration shows a summary of the landforms seen within the November 26th MOC image in different colors. It is clear that the smoothest surface (green at bottom of frame) is rare in this part of the landing ellipse. Sand dunes (black) and really rough terrain (orange) are also fairly rare. Much of the surface is ridged with gullies or pits.

Since then, a brief note in the Jan. 10 "Aviation Week" indicates that the central point in MPL's estimated landing area (which is still fairly uncertain) has been readjusted and is now a lot closer to the core of the depression -- "only about 10 km" from its bottom.

However, as Lockheed's vice president of flight systems Noel Hinners has recently pointed out, the dangerous slopes in the landing region still cover such a small part of its overall area that it is "crazy" to peg such a slope as the "probable" cause of the crash. The most we can say at this point, he says, is that this is only one possible cause among many.

And while MPL was designed to handle slopes of up to 10 degrees with complete certainty, Aviation Week points out that in reality it might very well have been capable of handling distinctly steeper slopes.

In fact, two of the Lunar Surveyors back in the '60s touched down successfully on fairly steep slopes: Surveyor 3 landed on a crater slope of 14 degrees, and Surveyor 5 actually landed on the side of a small crater a little over twice as wide as the spacecraft, ending up at a tilt of fully 20 degrees. Neither of them came anywhere near toppling or tumbling.

(Surveyor 3 did make a bouncing multiple landing that slightly damaged it, but this was due not to the slope but to the fact that bright rocks on the crater's rim confused the spacecraft's radar, so that it landed with its rockets still thrusting -- something that was immediately corrected in the radar design of all later soft-landers. Had it not been for this, Surveyor 3 would also have been undamaged.)

In short, the cause of MPL's failure (and that of the two Deep Space-2 impact probes, which may be a separate failure) still remains a puzzle -- and one which may never be solved, forcing us to redesign future landers to deal with several possible causes at once.

But that takes us to the second recent development: rumors that have begun to seep out about what may be done with the 2001 Mars Surveyor Lander, which is almost identical with MPL in its overall design and landing system.

In particular, the Dec. 17 "Science" quotes NASA's space science chief Edward J. Weiler as saying that the lander (which has already been partially built) may end up being scavenged for electronic parts that could be used in a 2003 orbiter that would be "an orbiting telecommunications satellite, with high-resolution cameras that could scout out safe landing sites for later missions and provide a stronger link between landers and Earth." A similar rumor is reported in the Dec. 20 Aviation Week.

It seems to this writer, though, that this strategy really does not make much sense. The U.S. already plans to launch one -- and perhaps two -- miniature "Mars Micromission" craft at the 2003 opportunity which would serve as data relay comsats for Mars landers -- and both the 2001 Mars Surveyor Orbiter (which still seems likely to be launched on schedule) and the 2003 European Mars Express orbiter also have a similar data relay capability.

Moreover, both the 2001 and the Mars Express orbiters also already carry cameras capable of photographing large areas of the Martian surface at high resolution.

The camera on the 2001 Orbiter can photograph several percent of the surface at 20 meters resolution, while the far more effective camera on Mars Express will photograph over 50 percent of Mars' surface at 15 meters sharpness -- and it has just been augmented with an ability to photograph smaller areas at only two meters resolution, as sharp as the high-powered telephoto camera on MGS. Thus providing still another Mars orbiter for these purposes seems redundant to me.

This writer still thinks that a more effective use for the 2001 Mars Surveyor Lander would be to modify it and launch it in 2003, in order to test two very important new innovations before they are used on the much more expensive sample-return landers to follow.

First is the test -- already planned for the 2001 lander -- of a controlled entry system which can guide landers to within a few km of their target points, thus greatly increasing their safety and scientific effectiveness.

Moreover, a very similar guidance system will also be needed to directly "aerocapture" future Mars orbiters into orbit around Mars by skimming them through the medium-altitude regions of Mars' atmosphere -- and the French orbiter planned for the first sample return mission will, in fact, use this technique, providing still another reason to test out the entry guidance system in advance.

Second would be a landing obstacle avoidance system, which could take two forms. A previous study has already shown that the descent camera carried on MPL and the 2001 lander could be modified, for only several million dollars, to identify rough-looking surface areas and steer the lander away from them.

However, Aviation Week quotes JPL's space science chief John Casani as saying that it might be better to provide a more expensive system like that planned for the cancelled Deep Space-4 comet lander, in which a scanning laser altimeter would actually build 3-D maps of the landing area, so that not only rough areas but dangerously steep slopes (such as the one near the MPL landing area) could be located and avoided.

At any rate, Casani says, "I think all future landers will have hazard avoidance" -- and, again, it would be wise to test such a system before committing sample-return landers to it.

And, of course, the 2001 lander, even if delayed, could still provide very useful scientific data in an area unexplored by the sample-return landers -- especially since the 2003 launch opportunity is the best of the decade, so that relatively few of the Lander's currently planned instruments might have to be removed even to make room for the needed new engineering systems.

In October, JPL decided that the primary landing site for the 2001 mission would be the highlands south of the Isidis plain, riddled with fairly smooth patches which are suitable for landing and which are surrounded by ancient water-flow channels and tall, scientifically useful hills.

However, the "Science" article quotes Mars Surveyor 2001 Project Scientist Steve Saunders as saying, "It could be we should put more emphasis now on the smoother [backup landing] area", which is a region where MGS has identified an huge and intriguing patch of coarse-grained hematite which seems to have been deposited during Mars' early days either by a big lake or by a region of hot springs.

This area is thought to be less scientifically interesting than Isidis because it has no hills and probably fewer rocks on the surface -- but, by the same token, it's safer.

In any case, we may get our first clues as to the form of the future Mars program very soon. NASA's main Mars Program Independent Assessment Team will not be issuing its recommendations until mid-March, which is also about the time that a JPL board will issue its conclusions on possible causes of the MPL failure.

But another JPL team, headed by Mars Surveyor Program manager Chris P. Jones, is supposed to present its own preliminary conclusions as to the best modifications for the U.S. Mars program (including the sample return missions) to Edward Weiler during the week of Jan. 17, according to "Aviation Week". With luck, those preliminary findings will be publicly released within a couple of weeks.