2007 will feature Phoenix - the first of the relatively low-cost "Mars Scouts" selected by NASA from competitive proposals by different scientific teams - which is actually the cancelled stationary Mars Surveyor lander originally planned for 2001, re-instrumented to land on the near-surface layer of ice-saturated ground discoverd by the Mars Odyssey orbiter in Mars' north polar regions to study the ice itself and its potential for preserving biochemicals. 2009 will see the launch of two spacecraft.

The Mars Telecommunications Orbiter is the first Mars comsat, which will orbit the planet at high altitude to tremendously increase the rate at which landed vehicles can return science data to Earth.

And the Mars Science Laboratory (MSL) - a rover weighing 600 kg, which is likely to be powered by plutonium-fueled RTG generators rather than less reliable solar arrays - will drive as much as 50 kilometers across the Martian surface over 22 months, after making a precision landing within less than 10 km of a scientifically interesting target point selected by the earlier orbiters.

While the current MERs each carry only 5 kg of instruments to carry out fairly simple geological and chemical studies and look for signs that early Mars sometimes had significant amounts of liquid water on its surface, MSL will use ten just-selected experiments weighing 65 kg to actually grind up Mars rocks and carry out an extremely detailed analysis of them, looking for traces of actual organic chemicals that might perhaps be the fossil remains of ancient Martian life, as well as determining the detailed mineralogy of the local rocks and thus gauging the geological and climate history of early Mars with far more clarity and precision than any mission before it.

Beyond 2009, however, our plans for Mars exploration are still extremely vague and flexible.

This is partly due to the simple fact that we don't yet know what discoveries this decade's complex remaining missions will reveal - Mars, over the last decade, has thrown one unexpected scientific curveball after another at us.

It's also due to the great difficulty of the search for evidence of fossilized ancient microscopic life, which is very difficult to identify with any confidence even in Earth rocks.

We have some reason to think that Mars may actually have a much greater potential to preserve the fossilized remains of microbes from its first billion years than Earth does, because such fossil-destroying phenomena as crustal-rock recycling and large-scale water erosion haven't existed there - but, given the tiny quantities of Mars material that will be examined over the coming decades either by in-situ robotic landers or by actually flying a few kilograms of selected samples back to Earth, the search for evidence of Martian life will require a huge amount of luck even if we strainingly make every possible effort to pick out the very best sites for landers to look for it.

And that careful advance search for optimal landing sites will probably also require recognizing and understanding some more geological and chemical phenomena on Mars whose existence we do not yet even know about.

The possibility also can't quite be ruled out that, if life did evolve on Mars during its earliest "Noachian" era - its first billion years, when it definitely had a dense carbon dioxide atmosphere, and may or may not have been warm enough for genuinely large amounts of unfrozen water to exist on its surface - some tough germs may have evolved to survive the planet's loss of almost all its atmosphere and the greenhouse effect from that atmosphere, and may still be huddled in a few protected places on the planet.

Any such surviving germs, however, are likely to exist only hundreds or even thousands of meters below the surface, in deeply buried aquifers of water that are warmed above the freezing point by the planet's remaining internal warmth, or perhaps in pockets of liquid water at the very base of its polar caps.

So searching for them will also be very difficult.

So trying to pre-plan the Mars exploration program in any precise detail beyond this decade is asking for trouble.

However - given the huge expense of Mars probes, and the need to design them and to develop well in advance the new technologies they'll need - we do still have to do a great deal of advance planning.

In 2003, the Office of Management and Budget decided that NASA was in fact going dangerously overboard in trying to plan the advance details of America's Mars program for the years 2010-2020, and enforced its skepticism by cutting off all funds that NASA had requested for planning the details of the first unmanned mission to return Mars samples to Earth - a centerpiece of any possible Mars exploration program.

The OMB agreed to release those funds again only if NASA instead followed a strategy of developing several alternative "Pathway" sequences of Mars missions, one of which could be chosen depending on the results from this decade's missions.

NASA responded by developing four alternative Pathway mission sequences for the next decade, any one of which could be chosen depending on this decade's discoveries.

One of those four - which would have been based on the discovery that Mars never had significant amounts of liquid water on its surface even during its earliest days - has now been pretty much derailed by the discoveries of the Mars Exploration Rovers at both the Meridiani and Gusev sites (although huge questions still remain about the actual amount and duration of episodes of liquid water at those two sites).

The other three, however, still remain valid possibilities.

All three Pathways would fill three of the five Mars mission launch opportunities - including the one in 2011 - with more Mars Scouts, both to keep down the Mars program's overall cost and to allow it to be more flexible in following up new discoveries or carrying out purely geological or atmospheric science that has nothing to do with the search for evidence of Martian life.

The Pathway most likely to be followed judging from what we now know - a "Search for Evidence of Past Life" preserved in Mars' sedimentary rocks - would launch the first Mars sample return mission in 2013 to return about half a kilogram of Mars rocks and soil in 2016, enabling the extremely detailed, super-sensitive and flexible analyses that only the huge and highly changeable instruments in Earth labs can possibly do.

(This first sample return would be a simplified "Groundbreaker"-type mission, in which a stationary lander would simply use a mechanical arm and cameras to scoop up all its sample from the surface right next to the lander, rather than dispatching a rover to select and collect samples from several hundred meters around the lander as had been previously planned.

This stripped-down first sample return would be limited to giving us a better general understanding of the geological and climate history of Mars, rather than having any real chance at all of finding actual fossil evidence - but it would still provide a major science return for half a billion dollars less cost.)

The 2018 mission would be an ambitious lander to search specifically for biological evidence and identify it with confidence using sophisticated in-situ robotic instruments, whose design would be largely determined by our earlier discoveries on the planet.

This would most likely take the form of the "Astrobiological Field Lab" - a rover similar in general design to the 2009 Mars Science Lab, but carrying those more sophisticated instruments and a more complex system to deliver precisely selected samples to them, with the rover also being much more carefully cleaned than MSL was of any possible germs or organic contaminants from Earth that could interfere with its measurements.

Depending on the earlier results, however, those more sophisticated and super-clean instruments might be put not on a rover, but on a "Deep Drill" lander which would sit in one place and drill up its samples from 30 to 60 feet below the surface, where trace biochemicals are much more likely to be protected from the destructive radiation and chemicals found near Mars' surface, and where even living or frozen and hibernating microbes might possibly be found.

Then in the 2020s, those more sophisticated sample-return missions utilizing sample-collecting rovers would finally start to fly.

Two alternative Pathways were worked out in the event that this decade's missions turn up two possible discoveries which are less likely than the sedimentary rocks which we already know exist, but which would be sensationally important if we do find them.

One Pathway - "Explore Hydrothermal Habitats" - would be sent to any possible small geothermally heated spring of liquid water which this decade's orbital probes locate somewhere on Mars' surface, even if that spring died out billions of years ago and can be identified only by the mineral deposits it left behind.

Such springs would be one of the most promising places for microbial life to evolve and survive on Mars, leaving clear and concentrated fossil evidence behind.

(NASA had also demanded that one of the four Pathways should be designed without any Mars sample return mission at all in the 2010s, to cover the possibility that budgetary or technical problems delayed such a mission, and this was the Pathway chosen for that exercise.

Its 2013 mission would be the Astrobiology Field Lab rover to study such a spring site, and its 2018 mission would be the Deep Drill to probe much more deeply into the stacked layers of mineral deposits left behind by an ancient spring or into the warmer and more hospitable underground liquid water in a still-active one.

Of course, in reality, any of the three next-decade Pathways might end up including a sample-return mission or not, depending on both the funds available and the scientific discoveries that have been made by then.)

The third Pathway, "Search for Present Life", would be based on the sensational discovery during this decade of reason to believe that there really is a good chance that some Martian microbes are still alive today in a few last redoubts fairly near the planet's surface - whether in still-active hydrothermal vents, or in the near-surface ice layers in Mars' polar regions which may conceivably contain frozen and hibernating germs that come back to life only on those rare occasions when the ice thaws briefly during Mars' hundred-thousand-year cycles of variable climate as its polar tilt keeps changing.

In this case, the third Mars Scout mission would be flown in 2013, right after the second one, while the next big Mars mission after MSL would be a full-scale 2016 Mars sample return with a sample-collecting rover - which is by far the best type of mission to carry out this sort of study, since samples must be carefuly selected from the small crannies where germs may still be living near the surface, and those samples must then be subjected to extremely complex and careful analyses by sophisticated Earth labs to make sure that we are not instead observing Earth germs carried on the lander as contaminants.

After a 2018 Scout mission, the next big mission would be a 2020 Deep Drill to do in-situ analyses of more deeply buried material from the area, followed later by missions to return such deeply buried samples to Earth.

So far, so good.

But during the year since the Pathways scheme was developed, some more important developments have occurred.

First, the MERs have landed and made their discoveries.

Second, President Bush in 2004 announced his radically revised "Exploration Initiative" to steer NASA's future over the coming decades - which places a greater emphasis on manned deep-space exploration of the Moon and later Mars, and also involves a radically revised and more rational procedure to carry out its planning and budgeting.

Previously, eight general "Enterprises" dealing with different aspects of space exploration delivered their proposed activity "strategies" directly and separately to the NASA Administrator's office, where the allocations made to each of them in the proposed NASA budget were decided in an informal and poorly organized in-office slugfest once a year.

NASA's planning instead now involves the design of 13 "Strategic Roadmaps" covering its major long-term goals, plus 15 more "Capability Roadmaps" involving programs to develop the technologies it will need to achieve these goals.

Each Roadmap is to be developed by a committee made of members from NASA itself, industry, and the academic science community. Their output will be sent to a new "Advanced Planning and Integration Office" at NASA to be carefully coordinated and blended into an "Integrated Space Architecture", which will in turn serve as a stable plan which the NASA Administrator's office can use as a guide for the next three years in making its choices among the annual money requests from the four "Mission Directorate" sub-branches of NASA (which have replaced those former eight "Enterprise" branches).

The NASA Administrator, in turn, constantly feeds back a list of "agency objectives" both to the Integrated Architecture Office and to the lower-level Mission Directorates, to help guide their choices.

Each Strategic Roadmap is to set broad scientific and exploration objectives and priorities for its particular subject, decide the sets of missions to satisfy these, identify important decision points at which alternative choices must be made, estimate timelines and risk, and identify the needs for various capabilities and infrastructure and how to satisfy them.

These Roadmap Committees are to hold two meetings each by mid-April to develop their initial Roadmaps, send those to the National Research Council of the National Academy of Sciences for an independent review, take the NRC's advice into account in revising their Roadmaps during two final meetings by the end of July, and then send them to the Integration Office, which will weave them into its proposed Integrated Space Architecture by mid-October.

That Architecture will in turn be reviewed by the NRC and by the NASA Advisory Council before it is used to guide NASA's next budget request in February 2006.

In 2008, the Roadmap Committees will be formed again and start the process of designing NASA's next three-year Architecture plan.

And on January 4 through 6, the Committee to develop a strategic roadmap for the future "Robotic and Human Exploration of Mars" held its first meeting at Caltech - the very first meeting by any of the Roadmap Committees - to decide the general course of the next 30 years of Mars exploration.

It was headed by Alphonso Diaz (the new co-chair of NASA's "Space Science" mission directorate), Charles Elachi (head of the Jet Propulsion Laboratory), and Tom Young, the former Lochheed Martin official who headed the team that investigated the failures of America's 1998 Mars probes.

The eleven other members present at this meeting included planetary scientists Steve Squyres of Cornell and Ray Arvidson of Washington University (both closely involved with the Mars Exploration Rovers), Laurie Leshin of Arizona State University, and Paul Mahaffy of the Goddard Space Flight Center (who has the biggest experiment to be chosen for the Mars Science Lab rover); former Shuttle astronauts Sally Ride, Shannon Lucid and Linda Godwin; and movie director James Cameron (who has been on the NASA Advisory Council for two years, and who revealed during the conference that he's turned himself into a skilled expert on the U.S. space program).

This first conference was necessarily introductory in nature.

It consisted largely of listening to a parade of detailed descriptions from various speakers - NASA officials, scientists, and engineers - of the overall format and science goals of NASA's Mars Exploration Program (which will cost $1 to $1.25 billion per year), and of the design of the important Mars missions planned for the future.

This included a few interesting new revelations.

For instance, the 2009 Mars Telecommunications Orbiter (MTO) - which will relay back data from future Mars landers anywhere on the planet at a rate of ten to 100 times the daily rate at which our current Mars orbiters are relaying back data from the two MER rovers, and which will also run a separate experiment to test the feasibility of relaying data from Mars to Earth via laser beam at up to 30 million bits per second - has also been planned from the start to test the feasibility of a plan to have a Mars orbiter automatically rendezvous with an orbiting spherical container of Mars samples launched into orbit around the planet by a Mars Sample Return lander and scoop it up in a basket to fly back to Earth with it.

This is the procedure favored for the Mars sample-return mission, but MTO was originally supposed to limit itself to ejecting a dummy sample canister and then precisely tracking it at distances of thousands of kilometers as it gradually drifted away.

However, MTO project manager Roger Gibbs revealed that the test has now been souped up.

MTO will actually repeatedly rendezvous with the canister in its high Mars orbit six to twelve times - approaching from halfway around the planet to within only 10 meters of the canister each time.

Steve Squyres, the principal scientific investigator for the spectacularly successful Mars Exploration Rovers, summarized their most recent science findings - which seem to center around the fact that, while they have indeed discovered proof that some places on Noachian-era Mars were exposed to enough episodes of liquid water for long enough to modify them chemically, it still has not been established that any place on Mars ever featured a really long-lasting body of standing surface water, which would be hugely important for the evolution of native life.

The now-famous light-colored layered sedimentary rocks of the Meridiani plain where the Opportunity rover landed were certainly exposed at some point in the Noachian era to liquid water laced with sulfuric acid, which converted layers of basalt sand into sulfate-rich soft rock riddled with billions of little embedded round "blueberries" of gray hematite that were first sensed from orbit.

Some of these fine rock layers are arranged in fine "cross-bedded" ripples, establishing pretty firmly that streams of liquid water must actually have run across the tops of the original sediment layers.

But other, similar layers laid down at other times, and studied by the rover during its six months poking around in the depths of the 160-meter-wide Endurance Crater, have far bigger cross-bedding ripples meters long, showing that those layers must have been physically arranged by Martian winds instead, after which they were covered over by other sediment layers and later soaked by acidic liquid water while they were underground.

In short, the impression of the Meridiani plains that we now have indicates that the region - rather than being the site of a long-lasting lake or sea - was repeatedly but temporarily soaked by shallow flows of liquid water interrupted by long periods in which the surface dried out completely again.

This is a less promising environment for the possible evolution of Martian life out of nonliving organic chemicals.

And the 100-meter-high "Columbia Hills" on the floor of Gusev crater, which the Spirit rover drove 2.6 km to reach, have also turned out to consist of layers of basalt grit which were clearly exposed to liquid water.

However, these rocks are less dramatically chemically altered - suggesting either less acidic water or a shorter exposure time.

The Hills are definitely one of the remaining uneroded "islands" of Gusev's oldest surviving crater floor - most of the crater's original floor was completely stripped away by wind erosion, and later partially refilled with flows of completely water-free basalt lava such as covers most of Mars - but they don't seem to have been exposed to enough liquid water to be sediments from the bottom of an ancient Noachian lake filling the crater, such as many scientists had hoped.

Instead, they seem to consist of layers of either volcanic ash or fine debris from a giant meteor impact in or near Gusev, which were laid down from the air and later exposed to limited amounts of water from cool sources, hydrothermal springs, or maybe even just prolonged acidic fog from volcanic vents.

Moreover, the density of impact craters on them suggests that they are only a little older than the later totally dry lava flows laid down across most of Gusev's floor, suggesting that the period in which Gusev had even such moderate amounts of groundwater may have been rather short.

In short, the 2003 rovers have indeed made a spectacular scientific find, but not the most spectacular one that some optimistic scientists hoped they might possibly find on Mars.

Squyres also noted that the "OMEGA" near-infrared mapping spectrometer on Europe's Mars Express orbiter - which can identify different minerals from the longer-wavelength infrared instruments on America's two Mars orbiters - has definitely found some patches of sulfates of magnesium and calcium in other places on Mars, both near Meridiani and at various places in the gigantic Valles Marineris gash and its side canyons.

They are always found where orbital photos show layered sedimentary rocks.

This suggests strongly that the same kind of water exposure that Opportunity found at Meridiani has taken place in a fair number of other places on Mars, and at different times in the planet's early history - although so far Meridiani is the only place on Mars where both sulfates and gray hematite have been identified together from orbit.

JPL's Pete Theisinger and Mike Meyer (chief engineer qnd scientist of the 2009 Mars Surface Lab) confirmed that the current plan is to have MSL land using a strange, Rube Goldbergian system known as "Skycrane".

The airbag-cocoon landing system of Mars Pathfinder and the MER rovers - in which the craft drops to within a few hundred feet of the surface at high speed on a parachute and then suddenly fires a powerful solid rocket to slam itself to a stop at the last second - has gotten a tremendous amount of favorable publicity, having succeded three times.

But it's not really all that good; it's very heavy, dangerously vulnerable to crosswinds, and leaves the airbag-wrapped lander bouncing and rolling for hundreds of meters after touchdown, preventing any really precise landing.

A lander that steers itself to a gentle landing using throttleable rocket engines controlled by a radar system avoids these problems.

But one with legs is also big and heavy, while a "pallet" lander that simply crunches down directly onto a broad base to which its landing engines are fastened may be tipsy and likely to leak left-over fuel onto the surface - and both of these also require a big ramp for the MSL rover to drive down after landing.

The tentative plan is instead to use "Skycrane" - a strange system in which the lander will hover five meters above the surface, using engines fastened along its outer edges, while the rover is quickly reeled down on a bundle of three cables and unfolds to touch down directly on its wheels.

Then the rover cuts itself loose from the cables, and the released lander lifts back up and arcs to a crash landing a fair distance away.

This system is lightweight and wind-resistant, but it has one big problem - the rover can swing back and forth like a pendulum during the landing unless the lander hovers very precisely, and spreading the three cables further apart to prevent this could lead to the lander itself rocking back and forth even more seriously during the lowering.

Tests will be run this year on a big simulation rig to see if a lander can be designed which can control itself precisely enough to prevent this - if not, the pallet-lander design may have to be chosen instead.

Laurie Leshin and JPL's Mark Adler described the currrent status of the Mars Sample Return mission design.

This is an extremely important mission scientifically, given the tremendously greater sensitivity of huge ground-based analytical instruments as compared to the tiny instruments carried on Mars landers themselves - as well as the fact that the samples can be repeatedly inspected for decades after their return with as many new instruments and techniques as the combined ingenuity of all Earth's scientists can devise.

Any remaining evidence of past - or even present - life on Mars may be so rarified and subtle that ultimately the only way of proving its nature with any confidence at all may be through returned samples.

(As an example of this problem, Steve Squyres stated that the best chance for finding any evidence of microbes in the sedimentary rock layers we've now found at Meridiani - since the ferric iron they contained while still wet may have quickly reacted with and destroyed any organic chemicals in the remains of such microbes after they died - may be to cut open some of the tiny hematite "Blueberries" and inspect cross-sections of them with a high-powered microscope for signs of visible microbe fossils.

But the "Blueberrries" are in reality closer to the size of birdseed, and it's probably impossible to devise a lightweight instrument that could do such delicate work on Mars itself.

Instead, we would have to bring some Blueberries back to Earth.)

But MSR is also a very difficult, complex and expensive mission to fly.

Moreover, its cost has recently lofted even higher.

This is partly because France has withdrawn from its plans to serve as an equal partner with the US on the mission (forcing the US to now provide not only the lander but also the sample-return orbiter).

But it's also because the tentative plan to make the first sample-return mission a cheaper "Groundbreaker"-type mission, in which the stationary lander would simply use an arm to grab a sample from the surface immediately nearby, has now been dropped.

Thanks to the spectacular discoveries of the Mars rovers - especially Opportunity, which would have been unable to reach the scientifically spectacular sedimentary rock layers only 10 meters from its landing spot had it been a stationary lander - the original, more expensive plan to have a rover collect samples from several hundred meters around the sample-return lander, and then return them to the lander and its "Mars Ascent Vehicle" which will launch them back into Mars orbit, is now planned again even for the very first sample-return lander.

The result is that this mission will cost an absolute minimum of 2.5 to 3 billion dollars.

Mars Exploration Program manager Firouz Naderi expressed his belief that its real cost will certainly end up above $4 billion, largely because of the need to go to great lengths to keep from contaminating the returned samples with Earth germs or organic contaminants - as well as the need to rule out even the extremely long-shot possibility that it might contain live Mars germs capable of leaking out and harming some part of Earth's ecosystem (or, less plausibly, harming human beings directly).

NASA will have to build a ground "Sample Receiving Facility" to initially examine the samples for any evidence of either living or recently-dead germs.

If none is found, the samples will be sterilized and then released to outside labs; but if any possible evidence of present-day life is found, the SRF will have to be augmented so that the samples can undergo detailed scientific study inside it.

This facility must have both the capabilities of a biohazard lab used to store possibly very dangerous disease organisms, and those of a cleaner improvement on the Lunar Receiving Lab to keep the samples themselves from being contaminated by even the tiniest trace of Earth germs or substances - which means that it will be very expensive by itself, costing about $300 million.

And, to meet all the necessary government regulations, its overall design must be completed xxxxxxx just in order to get it finished by mid-2016, the date at which the first Mars samples would be returned after the first MSR mission is launched (as is currently planned) in 2013.

And the SRF must be built even if - as an added precaution - the container of Mars samples is also sterilized by exposure to the gamma rays from a piece of radioactive cobalt on the spacecraft itself during its long return flight to Earth.

(Such sterilization would probably kill any living Mars germs en route without actually doing scientifically disastrous damage to their corpses, but it's not absolutely certain that it would get the killing job done.)

While the Committee wasn't surprised to get the latest confirmation of the high complexity, cost and risk of the Mars Sample Return mission, it wasn't happy.

First, further delays of two years or more could easily occur before the mission is even ready to launch.

(It may be another year before we even know this one way or another.) Second, there's the major dilemma of how carefully to appraise different possible landing sites for the mission in advance, given its great cost and the extreme difficulty in trying to find provable biological fossil evidence on Mars from such a tiny and localized sample.

The super-detailed photographic and infrared mineral maps which this year's Mars Reconnaissance Orbiter will make of the entire planet will help greatly in such a selection.

But all witnesses before the Committee agreed that the advance evidence from the 2009 Mars Surface Lab rover will also be a crucial addition in the MSR site selection process - because only that rover can (1) carry out very detailed studies of the mineralogical nature of Mars rocks to allow us to clearly understand their geological and climate history, and (2) look for tiny traces of complex organic molecules which might perhaps be actual biological compounds, and thus find out what kind of places and rocks on Mars are most likely to contain such possible evidence of life.

Indeed, if the MSL does find such traces of complex organics at its landing site, then the first MSR is likely to be sent to the same site as the MSL.

(The same thing will be true - if it flies before the actual Sample Return mission - for the more sophisticated Astrobiology Field Lab rover that would make a really detailed on-site chemical and microscopic examination of such possible evidence of Martian life, to try to firmly settle whether it really is biological material rather than just complex organic compounds from nonliving sources.)

And so, for this reason and others, the Committee leaned unanimously toward its first important new recommendation: one MSL mission is definitely not enough in the Mars Exploration Program.

First, if the 2009 MSL doesn't turn up evidence of such organic compounds at its landing site, we will be rather in the dark as to what alternative place we should send the first sample return mission or the first Astrobiology Field Lab, despite the good mapping data of the whole planet we've gotten from the Mars Reconnaissance Orbiter.

Second, even if the first MSL picks out a promising-looking landing site for a more ambitious follow-up biology mission (MSR or AFL), there's an alarmingly high chance that the organic compounds that the MSL found at that site will ultimately turn out not to be biological in origin - just as the traces of fairly complex organic compounds found in the Mars meteorites that have landed on Earth have turned out not to be provably biological, and indeed very likely not to be biological in origin at all.

In that case, we'll still have to look elsewhere to find a good place to resume the search with more sample returns or complex in-situ biological field labs - and we'll likely need more of the somewhat simpler MSLs to serve as advance scouts to help us decide promising landing sites for those next big missions, especially in the case of the alarmingly expensive sample-return landers.

Third, while the Mars Surface Lab rover is an expensive mission - about a billion dollars - most of that expense, as with most spacecraft, is in the initial design work.

Firouz Naderi estimated the cost of a duplicate MSL mission at only about $400 million - barely more than the cost of a new Mars Scout mission.

And, indeed, there was considerable apprehension on the committee that a single Mars Surface Lab, by itself, might not even be scientifically cost-effective enough to be worth that billion-dollar initial cost.

Turning two or more of them out on a production line to investigate other places on Mars in great detail, both biologically and geologically, might make for a far more scientifically effective Mars program overall.

In fact, the committee - concerned over the very serious chance that the overall cost of the Mars Exploration program will grow to unacceptable levels - also favors trying to re-use the electronic core package of the MSL rover design (its "avionics"), for all other big Mars landers in the near-future program - even for stationary landers like the MSR, which was already scheduled to use a close copy of MSL's descent stage and Skycrane.

Mass production lines where possible are a promising cost-cutter for the Mars program.

There's also another possible idea, which was rejected last year but is now making a comeback.

While NASA now wants very much to include a sample-collection rover on even the first sample return mission, this adds a lot of complexity and expense itself.

If that rover does even simple in-situ chemical analyses to pick the best possible samples for the very small sample set that the mission can fly back to Earth - instead of just deciding these on the basis of their visual appearance - it will be heavy enough that it may have to be landed on a separate vehicle that would touch down within only one kilometer of the Ascent-Vehicle lander.

However, if the Ascent Vehicle lander touches down near the current location of one of the MSLs, that MSL could itself drive to the lander and hand over a bunch of samples collected not just from a range of a few hundred meters, but from its entire previous 50-kilometer drive.

The 2009 MSL will probably not be working by the time the first sample-return vehicle lands on Mars - but later MSLs, sent to Mars at a launch window only two years before a sample-return lander, could do this.

Indeed, dividing up a sample-return mission among more launches this way may be necessary in any case, both to stretch out its cost and to minimize risk.

Two sample-collection rovers could be launched during one Mars launch window; two ascent-vehicle landers could be landed during the next window to land near those rovers (and if one rover had failed, both the landers could be landed near the remaining one); and then one orbiter to retrieve the sample containers launched into Mars orbit by those landers and return them to Earth could be launched at a third launch window two years later. (If the orbiter itself failed, the sample containers could stay safely in Mars orbit until a backup retrieval orbiter could be launched during still a fourth launch window.)

If we're going to use the MSL as the centerpiece of our Mars Exploration Program during the 2010s, however, we must make sure that the design actually works.

Some apprehension was expressed at the meeting that there may be difficulty cramming all ten of the planned experiments for the 2009 MSL onboard the rover - or maybe even all of the six top-priority ones - although Pete Theisinger, as chief engineer, declared his confidence that it can be done.

Finally, there's the other very new problem which the Committee had to deal with - picking out the completely new line of "Mars Testbed" missions that President Bush has added to the program as part of his new plan to start working seriously toward a manned presence in deep space, including at Mars.

While he hasn't specified an actual date for the first manned Mars landing in his space exploration "vision" (unlike his official goal of carrying out the next manned lunar landing by 2020), he has stated that this is a definite longer-term goal in the Initiative, and indeed that the new series of manned lunar landings will be flown very largely as test flights for the technology and procedures that will be needed for a Mars expedition.

And so the Mars Roadmap committee is tasked with deciding what first steps should be taken toward the design of a manned Mars mission, and what Mars-directed unmanned advance test missions are needed for such a mission.

The Committee was distinctly frustrated by the fact that manned Mars flights are still such a relatively vague part of Bush's Space Exploration Initiative.

They spent some time reviewing some of the alternative designs for such a mission, which involves a huge number of possible options.

The propulsion system may be simple chemical rockets, "nuclear thermal" engines in which an onboard reactor heats the propellant into high-temperature exhaust, a "nuclear electric" system in which a similar onboard reactor powers ion engines that turn out a trickle of thrust continuously for months on end to finally accelerate the craft to very high speeds using only a small amount of propellant expelled at very high speed, or a "solar electric" system in which such ion engines are powered instead by huge solar arrays.

(In either case, the ion engines will need several megawatts of power.) The ship may rotate end over end en route to provide the crew with "artificial gravity" so that they can avoid the known harmful health effects of prolonged weightlessness, as well as requiring less time to re-accustom themselves to Mars' gravity after landing so that they can start exploring faster - but it's uncertain yet whether artificial gravity is really necessary.

The crew's habitat on the surface of Mars, and the ascent vehicle on which they will blast back into Mars orbit to re-rendezvous with the mother ship, may be carried on the main ship's Mars landing vehicle, or they may be sent to the surface years in advance to save weight - in which case the manned lander must touch down very close to them.

The revolutionary new technique known as ISRU ("In-Situ Resource Utilization") may be used to vastly cut the weight of supplies that must be landed on Mars, by running a small chemical plant to mix Mars' carbon dioxide atmosphere with an onboard supply of liquid hydrogen and turn it into liquid methane and liquid oxygen to provide all of the ascent vehicle's heavy load of takeoff propellant (as well as the oxygen and water that the crew itself will need during its stay).

The recent confirmation that large areas of Mars have lots of ground ice near the surface raises the possibility that this too might be mined for ISRU purposes, broken down electrically so that the crew need not even take their hydrogen with them at the start.

It also seems likely that exploration of Mars' surface after such an expedition lands will be radically different from what we're used to with Apollo.

Stumping around in a spacesuit with a heavy life-support backpack attached was hard work even on the Moon, whose gravity is less than half that of Mars - and there is a very strong desire to minimize the extent to which the cabin atmosphere and the outside Mars air are blended, to avoid seriously scientifically contaminating the landing site with Earth germs and substances.

Whenever it's possible, the crew will explore Mars not by walking around on its surface in spacesuits, but by running robots by remote control from inside the cabins of pressurized Mars rovers, or from the ship cabin itself.

And a decision must be reached as to whether the crew, having landed on Mars, will simply stay on the surface for about 17 months and wait for an appropriate launch window to fly directly back to Earth, or whether there will be an "opposition-type" mission in which the crew stays on Mars for only one to three months before leaving Mars and then doubling back directly through the inner Solar System to reach Earth.

The latter design would allow the crew to carry far fewer supplies to the surface than the longer "conjunction-type" mission would - especially if ISRU turns out to be impractical.

But in every other respect, opposition-type missions are greatly inferior.

Their total mission time is actually little less than that for conjunction-type missions; they provide far less opportunity to explore Mars properly after landing; they require vastly higher propulsion requirements than conjunction-type missions (and these requirements also change wildly if the mission's initial launch must be delayed to another window of opportunity); they expose the crew to total weightlessness and to continuous cosmic and solar radiation for a much bigger chunk of the total mission time (whereas Mars' 37% of Earth gravity and the fact that the planet shields them from half the radiation that would otherwise hit them provides a healthier environment when they're on the surface); and they usually require going very far indeed into the inner Solar System during the return trip - often as close to the Sun as the orbit of Mercury, with all the resulting problems from both heat and intense solar radiation.

Finally, the Mars Roadmap Committee must firmly recommend the new sequence of "Mars Testbed" missions - added to the Mars program by the Bush Initiative - that will fly to Mars every two to four years separately from the purely scientific missions, in order to carry out the studies and technical tests that are specifically needed for humans to explore Mars.

The Jet Propulsion Laboratory's Jennifer Trosper and Frank Jordan told the Committee that one likely candidate for the first Testbed mission in 2011 is a stationary lander which would test new guidance techniques worked out to assure a "pinpoint landing" within only 100 meters of a target point on Mars' surface (as opposed to several dozen kilometers now, and 10 km for the improved self-steering landers Phoenix and MSL).

Since a lander can be blown several kilometers off course by winds just during the period in which it's hanging from a parachute, this could involve either a steerable chute, or a lander that can steer itself sideways by an angle of as much as 45 degrees during its final brief rocket-propelled descent in order to get back to its originally planned landing point.

The craft would then, after landing, study environmental hazards on Mars (such as the static electrical discharges that may be generated in Mars' atmosphere by dust storms and dust devils, and the power of Mars dust to gum up machinery), inspect the surface for signs of useful local groundwater, and run tests to determine whether Mars' air can indeed be turned into methane and oxygen by an ISRU system.

The second Testbed mission in 2016 may be a craft to test "aerocapture" - in which an arriving spacecraft, instead of using its rocket engine to slow itself by several thousand mph into orbit around Mars, uses air friction instead to brake itself by deliberately plowing through the upper atmosphere at less than 50 km altitude while huddled behind a heat shield.

This technique, once its safety is tested, could save a huge amount of fuel and mass on future orbiters - including manned ones - at other planets as well as Mars.

And the first Testbed craft thus put into Mars orbit could also carry out a very detailed radar search for underground ice.

But these Testbed missions do add further expense - for instance, that 2011 lander is likely to cost about $600 million.

And so another advantage of flying more MSL rovers to Mars is that some of the surface Testbed experiments could be carried on them instead.

In fact, they could run a better regional search for ground ice than a stationary lander.

The Committee is mulling over this possibility.

Precursor unmanned missions for manned Mars expeditions will, however, get bigger and more expensive as the series goes on - indeed, the program is likely to start merging into full-scale unmanned test flights of various components of the manned ships, as with the Apollo Program.

One Testbed mission in particular may make trouble. It turns out that the Mars landing vehicle for a 6-man expedition may, by itself, weigh as much as 80 tons - and we cannot simply scale up the landing systems for even the heaviest unmanned Mars landers currently planned and be confident that their design will work for such a big vehicle; the aerodynamic factors are too unpredictable.

We must fly a test of a much bigger unmanned lander - weighing about 4 tons - in order to be confident that we've worked out a landing system design that can be simply scaled up in size to work for a manned Mars lander, without any other major design changes.

And Frank Jordan stated, to the dismay of the Committee, that such a test flight would by itself cost about as much as a sample-return mission - $3 or $4 billion.

Any such mission must be delayed until at least the early 2020s.

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During its final day, the Committtee, having listened to all this testimony, began the work of actually deciding what to recommend.

This was very preliminary - most of the decision work will be done during its remaining meetings - but it did mull over problems and reach some tentative decisions. As Steve Squyres said, it has the task of coming up with recommendations that are not fuzzy and general but specific - including advice on how best to start scaling down the Mars Exploration Program if it develops funding problems.

Perhaps the biggest single problem is simply trying to come up with a good definition for the Program's central goal, since the search for actual Martian life is extremely difficult.

Even on Earth, the search for evidence of fossil microbial life in rocks billions of years old requires examining hundreds of kilograms of rocks; and the evidence that has been found is still frustratingly ambiguous in its chemical and visual nature, and still subject to furious scientific dispute.

It's considered likely that even the first few Mars sample returns will be unable to do more than allow us to identify more complex organic compounds (from living or nonliving sources) on Mars' surface, and to determine that its soil contains no living germs that might be dangerous to a human crew - indeed, that last goal is starting to become a more important part of the official rationale for the first sample return.

And, as Carnegie Institute microbiologist Andrew Steele forcefully emphasized during his description of the Astrobiology Field Lab rover mission, any evidence that is found is likely to be very ambiguous and capable of leading us to a false positive conclusion.

To be confident that we have really found past or present Mars life, we will have to find "multiple forms of chemical or visual evidence for it at multiple places using multiple missions", and those missions and the samples they collect must be utterly devoid of possible contamination by Earth germs or organic substances.

We're also faced with the problem that, even if ancient life did exist on Mars in some places, the conditions there may not have been right to preserve fossilized chemical or microscopic evidence of its existence - "biosignatures".

For instance, as mentioned above, Squyres believes that even in the fascinating layered water-deposited sedimentary rocks at Meridiani, the highly oxidized ferric iron dissolved in the groundwater may have efficiently broken down the organic chemical remains of any microbes as soon as they died.

And while the search for visual microscopic evidence of tiny microbe fossils there might be more promising, even the iron minerals that crystallized out of solution to make the "Blueberries" may have become gradually coarser-grained as the goethite that originally made them up slowly dried out and changed into gray hematite, and this may have broken up the recognizable microscopic outlines of any fossil microbes embedded within them.

Moreover, the search for life will be not only difficult but alarmingly open-ended.

No matter how many expensive landers are sent to look and come up empty-handed, after all, there will always still be the chance that life - or, more likely, fossil evidence of past life - exists in some tucked-away corner of the planet, or buried deep under its surface.

And the general public is likely to be distinctly unamused if, after a decades-long effort costing tens of billions of dollars, NASA is forced to say that either no life existed on Mars or that it is still unable to give the question anything like a good answer. As the Committee's co-chair Charles Elachi said, it's crucial to define a program which will not be regarded as a "failure" in that case.

The Committee has decided that a more realistic general goal for the program is to determine Mars' "habitability": that is, has it ever had, during its earliest days, physical and chemical conditions under which life could none have evolved out of nonliving organic compounds? The odds of getting a firm answer to this question are much better.

And if the answer is "yes", but the continuing search for Martian life continues to come up empty-handed anyway, that will in itself provide better and better evidence for an extremely important scientific conclusion: that the appearance of life on Earth was not none (as it has become popular to believe) virtually inevitable once the conditions were right, but that it was instead an unlikely freak event due to the fact that at some point a few organic compounds just happened to come together somewhere on the planet by pure chance in the right combination to begin the process of the evolution of life - in which case life must be much rarer in the Universe as a whole than optimists have assumed.

This is a very real possibility.

But while answering the "habitability" question may well be a scientifically worthwhile goal for the Mars program, the general public is still likely to take a dimmer view of it.

There may well be a strong backlash even after the first Mars sample return mission if it turns up no biological evidence, given its expense.

University of Colorado researcher Bruce Jakosky pointed out that NASA will be faced with the problem of trying to provide PR capable of maintaining an adequate level of public support for the Program, without none actually exaggerating its likely degree of success - a difficult balancing act, and maybe an impossible one in the long run.

In any case, Washington University's Ray Arvidson was assigned to head a subgroup to more clearly define the official goals of the Mars Exploration Program.

Two intriguing aspects of this problem, however, were little discussed at this first meeting - one an additional problem, the other an additional opportunity.

The problem - mentioned at the meeting only by Andrew Steele, although he stated it forcefully - is a fact which Mars scientists have become increasingly aware of, but which has gotten little public coverage: even if we find clear proof of past or present life on Mars, there's a good chance that we will never be able to prove that it originally evolved on Mars itself rather than just being transplanted Earth microbes.

We now know that chunks of Mars - blasted off the surface into solar orbit by any meteor impact that produces a crater more than about 15 km across - have been sprinkling down on Earth for as long as the two planets have existed.

It's estimated that at least half a ton of Mars rocks currently hit Earth each year, of which only a tiny fraction have been found yet.

And while transfer from Earth to Mars is much rarer, perhaps 10 kilograms of Earth rocks - launched into solar orbit by giant asteroid impacts on Earth tens or hundreds of millions of years ago and orbiting the Sun ever since - probably crash onto Mars yearly.

During the Solar System's chaotic and violent early days, when life was first appearing on Earth, the exchange rate was hundreds of times higher.

And studies suggest that a small but not insignificant set of those rocks may carry bacteria preserved as living spores, which can survive for tens of thousands - or even millions - of years in space if they're shielded from radiation within the rock's pores, and colonize any habitable world they land on.

This would be much harder for microbes on Earth rocks launched to Mars than on Mars rocks flying to Earth, given Earth rocks' great frictional heating when they were first blasted upwards through this planet's dense atmosphere to escape velocity (as well as the fact that meteorites currently hit Mars' surface at much higher speeds than they hit Earth's surface, due to the lack of dense Martian air to brake them during their final fall).

But there is still a very real chance that Earth germs have been ocasionally colonizing Mars, riding on meteorites hurled from Earth - especially during the Solar System's earliest days, when the two planets' artillery exchange was vastly greater and Noachian Mars still had a dense atmosphere to help brake arriving Earth meteorites.

In short, as Steele says, the two planets have been "swapping spit" since their creation, which means there is an excellent chance that a sprinkling of microbes from Earth colonized Mars during its earlier, more habitable Noachian days.

And so, even if we find Martian life, there is an excellent chance that we'll never be able to prove that it actually evolved there, rather than being just the evolutionary descendants of carpetbagging Earth microbes - unless the biochemistry of any living microbes or microbial remains found on Mars is so utterly alien that we can conclude firmly that its ancestors could not possibly have existed on Earth even during the earliest fuzzily known periods of life's existence on this planet, which may be very hard to prove.

The public's reaction if NASA is finally forced to admit this can be imagined - and, as Steele indicated, there may be absolutely nothing Mars investigators can do about this problem but cross their fingers and hope that any Martian life that turns up is none biochemically alien enough that we can prove it's a real native.

(As an alternative possibility, if we find Martian life but can't prove it's not evolutionarily separate from Earth life, we might conclude that life actually evolved from nonliving compounds only on Mars - which may in fact perhaps have had a somewhat friendlier environment than Earth during the Solar System's earliest days - and was then shipped via meteorite to Earth, so that we are all the evolutionary descendants of Mars microbes rather than Earth microbes.

But in either case, if we can't prove firmly that life originated entirely separately on two none worlds within this Solar System, there will still be a very real possibility that it appears only very rarely in the Universe as a whole rather than being common, and that this Solar System is one of the very few in which it actually did manage to evolve someplace, after which it was simply transplanted via meteorite to a second planet in the system.)

The other point that was little discussed at this meeting, however (although it was briefly mentioned a few times, by Steele and others), is not a problem but an additional opportunity.

This is the fact that a search for evidence of life on Mars may end up leading instead to the discovery of something else equally scientifically important: biochemical remnants of some of the intermediate stages by which relatively simple organic compounds gradually did evolve into more and more complex chemical forms, until they finally took on the forms of self-reproducing cells.

The chemical-physical process by which life first appeared on Earth remains one of the greatest current scientific mysteries.

While some general possible ideas have been developed, the details of virtually every theory include some serious difficulties; it's still quite possible that life appeared here only because of some staggeringly unlikely chance combination of chemicals in a single microscopic place somewhere on the planet during a period of hundreds of millions of years - a combination of chemical events so fantastically unlikely that human beings may never even be able to stumble across the way to duplicate it in our labs.

In any case, on this planet every speck of the evidence has been irrecoverably destroyed - all traces of "prebiotic" organic chemicals of intermediate complexity have been eaten by living things themselves, and even if they weren't they would have been destroyed by the processes of crustal recycling and by exposure to huge amounts of liquid water.

But if the process of prebiotic evolution began on Mars - and was then stopped partway through, as the planet lost its early dense atmosphere and its surface chilled down below the freezing point - there's a very real chance that some of those intermediate-stage organic chemicals have been preserved there, since Mars does not have crustal recycling and its surface water has been frozen over almost all the planet's near-surface for billions of years.

Discovering such preserved prebiotic evidence on another world - maybe Mars; maybe Europa or even Titan - is very likely to be the only hope we have that we may ever be able to develop a reasonably confident idea as to how life originated on Earth.

But NASA, while trumpeting to the public the possibility of finding Martian life, has been remarkably silent about advertising this other very exciting possibility.

It may be that the Mars Roadmap Committee will finally decide that NASA should be doing so, loudly.

The other major question to bedevil the Committee during these earliest deliberations was just what recommendations it should make in regard to a manned Mars program.

Indeed, it wasn't entirely sure even of the allowed range of the recommendations it's supposed to make, which were a bit fuzzily defined in the instructions it had received from the White House.

It was finally decided that it definitely does not have the responsibility of trying to develop the overall design of a manned Mars mission, but that it does have the responsibility of laying down some of the groundwork necessary to enable later NASA groups to carry out such definition work.

This certainly includes deciding the best sequence of Mars Testbed missions, and it was decided that the way to do this is to identify the Testbed flights that can be made within the Mars program's current billion-dollar-plus yearly budget, and to sequence them so that those possible technologies are tested first which would have the most radical effect in making a manned mission easier and cheaper if they work.

This includes aerocapture into Mars orbit - and it also includes ISRU: the carrying out of unmanned tests on the Martian surface to see if the planet's carbon dioxide atmosphere can indeed be successfully turned into ascent-vehicle fuel and breathable oxygen by a small manufacturing plant, and also the search to determine whether or not it's practical to mine the planet's near-surface ground ice, all of which could tremendously reduce the amount of supplies that must be lugged from Earth to the Martian surface.

It was decided, though, that the Committee's responsibilities in setting up the preliminary groundwork to enable a manned Mars mission to be designed go farther than this.

JPL's Gentry Lee and Texas A&M University's Aaron Cohen were assigned to head the Committee subgroup which will carry out this additional work, which may involve trying to identify promising personnel to carry out work on manned Mars mission design, and to set up a new program office at the Johnson Space Center for this purpose.

Mars Program manager Firouz Naderi also thinks that the Roadmap Committee should at least try to identify one to three most plausible "strawman" overall concepts for a manned Mars mission, so that it can better identify the near-term work that will be necessary to develop them.

The Committee also decided that - while President Bush's Initiative does not set any date by which a manned Mars mission should be carried out - it should recommend that by 2020 (the date at which the Initiative does none say that men should return to the Moon), enough preparatory and design work must have been done that the President at that time will be able to set such a date for Mars (perhaps 2030-35) and be confident that the nation can meet it.

This also involves the Committee trying to coordinate its activities in a major way with at least two other Strategic Roadmap Committees - the one concerned with the form of the manned lunar exploration program, and the "Exploration Transportation System" committee which will make recommendations about the future development of new launch vehicles.

The former is necessary because the stated purpose of the manned lunar program, as stated in the Bush Initiative, is very largely to "develop and test new approaches, technologies and systems to sustain" Mars exploration - including "use of lunar resources".

The Committee, however, seemed very uneasy about how much manned lunar exploration really will do to enable Mars exploration.

It seems likely that, contrary to the expressed hopes of Bush and Administrator O'Keefe, there is no advantage in launching manned Mars ships from the Moon's surface or lunar orbit - even if there is a fair amount of ground ice at the lunar poles, it's too dilute to be useful in fueling a Mars ship unless one sets up a large-scale industrial town on the Moon.

And the other new systems necessary for manned Mars trips - such as radiation protection, artificial gravity, and closed-cycle life-support systems that can keep a crew healthy for years on end without being resupplied - can all be tested just as well (or even better) and more cheaply in Earth orbit than on the Moon.

Indeed, the Committee at times seemed fairly close to a flat-out rebellion against the orders it had received from Sean O'Keefe on this point at the start of the meeting.

Firouz Naderi and James Cameron expressed concern that the manned lunar program may bleed off funds and personnel necessary to develop a manned Mars program.

Tom Young and Sally Ride went so far as to suggest that the Committee should override O'Keefe's orders by - if it finds this appropriate - officially questioning President Bush's entire emphasis on sending men back to the Moon before starting the manned Mars program. (The Committee also expressed great interest in hearing at its next meeting a description of the recent alternative overall "roadmap" for manned deep-space exploration developed last year by the International Academy of Astronautics, which regards lunar landings as an optional detour in a program that centers around the development of manned craft capable of making longer and longer trips into deep space - first to the L2 Sun-Earth libration point a million miles away from Earth's nightside, then to near-Earth asteroids with total mission times of about a year, and then finally to Mars orbit and back, with the latter missions capable of carrying separately developed manned Mars landing vehicles.)

Communication with the Transportation Roadmap Committee is also needed because the total weight of a manned Mars ship is huge - about 500 tons for a 6-man crew even if high-efficiency nuclear or SEP propulsion, ISRU, and a separate earlier launch of the Mars surface habitat and ascent vehicle are all used.

(This is the same weight as the International Space Station after it's finally finished - three times more than it now weighs.) A Mars ship that uses none of those possible weight-saving technologies would weigh an incredible 1500 tons - and the US, right now, has no plans for any booster that can launch more than 20 tons into low Earth orbit.

There has been considerable talk about the possibility of NASA funding the expensive development of a "Heavy Lift Booster" that could loft as much as 80 tons into orbit - but this may not be necessary for the manned lunar program alone, since the total weight of even the most ambitious manned lunar ship is likely to be only around 160 tons.

The Committee therefore feels it necessary to make it clear now to the Transportation Committee that a Heavy Lift Booster almost certainly is none needed if and when the US decides to get serious about sending men to Mars, since without it any such mission would require an absurdly huge series of separate smaller launches to loft the ship's components into orbit and assemble them, and since the Heavy Lift Booster's expensive development must be initiated well in advance.

(This will be true even though the first manned Mars ship will probably be capable of re-use for three or four trips to Mars - for its propellant alone for each trip will make up two-thirds of its mass.)

Finally, there is one other important point which Committee members mentioned only a few times in passing at this meeting, but which seems certain to be the subject of serious debate before it is through.

This is the problem of whether any manned landings on Mars will very seriously contaminate their landing sites with Earth germs and organic compounds, and so ruin the very studies of past or present Martian life which would be by far the most important justification for a manned trip.

Unmanned landers can be sterilized before their landings with strong heat, radiation or toxic chemicals - but human beings can't be.

Every time the airlock opens on a manned ship, microbes and compounds from Earth will be spewed out into the soil and Martian air outside.

Others will inevitably leak from even the best spacesuits, or escape from wastes and garbage dumped from the lander.

It's even possible that the first manned landings might end up seriously biocontaminating the entire planet, and so ruin the study of past or present Martian life in any way, permanently.

Mars' savage surface environment will certainly kill most - and maybe all - terrestrial germs expelled onto the surface within a few minutes.

But there's always a chance that a few will survive (maybe frozen for long periods) and find an environment under the soil where they can breed and slowly spread through any underground Martian liquid water table that may exist.

And the more promising an environment that human on-site explorers discover for the possible existence of native Martian life, the more likely it will be that the Earth germs which they themselves carry can also prosper and spread in it.

For this reason, the suggestion has been made - and was mentioned a few times at this meeting - that the best way for on-site humans to explore Mars is to limit themselves to orbiting the planet, operating sterilized robots and sample-return vehicles by remote control from their ship, without the maddening time gap of up to 20 minutes that's necessary for radio signals to pass between Mars probes and control centers on Earth and which makes the remote-control robotic exploration of any world farther away than the Moon so extremely difficult.

Steve Squyres expressed his belief that this is scientifically acceptable only for the first one or two manned expeditions to Mars, and that manned landings should follow up - but other committee members, such as Paul Mahaffy, seemed more sympathetic to the idea.

It's true, after all, that the Bush Initiative only calls for "manned expeditions to Mars" - not for actually landing humans on the planet.

But if the White House decides that manned Mars landings are mandatory despite the fact that it's been concluded that they may contaminate the planet, it could be setting the stage for a very serious showdown with the American - and world - science community.

Other questions were also briefly discussed.

The Committee is enthusiastically in favor of the 2009 Mars Telecommunications Orbiter ("MTO"), given the enormous increase it will make possible in the amount of data returned by later landers, as compared to the amount they could send back directly to Earth or relay back through the much lower-altitude scientific orbiters which fly within view of any landing site for only a few minutes twice a day.

For the same reason, it strongly supports NASA's tentative plan to launch a second MTO in 2018.

But - given MTO's importance in hugely increasing the amount of data that the 2009 MSL will send back, plus the fact that it is scheduled to be launched and arrive at Mars only a month or two before the MSL does - the Committee was apprehensive about the possibility that the first MTO might fail without allowing time for the launch of a replacement.

There was some talk about the possibility of recommending that the first MTO's launch should be sped up to 2007, but this would require a major shift in the Mars program's near-term funding.

And there's also a problem in defining the nature of the Mars Scouts two of which are scheduled to be launched in 2011, along with the first Testbed mission.

The Scouts were originally conceived of as a line of low-cost Mars probes entirely separate from the main program, selected from competitive proposals to carry out scientific investigations of Mars in areas (such as the planet's geochemistry or internal structure) which the main program, with its biological thrust, is unlikely to properly cover.

But the first Mars Scout mission, the 2007 Phoenix lander, ended up having its selection pretty much commanded by NASA Headquarters because it did none mesh well with the main program - it could carry out a detailed study of the near-surface ground ice layer covering Mars' near-polar region, and determine whether the ice might contain the frozen remains of ancient Martian germs (or perhaps even serve as an environment in which living germs could hibernate for tens of thousands of years in frozen form and then come back to life during those brief periods in which the periodic changes in Mars' axial tilt warm up its polar regions enough for the ice to partially thaw).

The question, therefore, is whether later Mars Scouts should be genuinely independent from the main Mars exploration program, or whether some of them should also have their prespecified areas of possible study at least partially limited by the needs of the main program.

(For instance, there was much talk about the recent remarkable discovery by the Mars Express orbiter and ground-based telescopes that Mars' atmosphere apparently does have tiny traces of methane in it , which is likely to be manufactured either by living subsurface Martian germs, or at least by volcanic vents which could themselves serve as a stronghold for such germs.

One of the other three finalists for the 2007 Mars Scout mission, MARVEL, was an orbiter which could have mapped concentrations of methane and any other biologically interesting trace gases all over the planet.

So: should MARVEL, or a similar mission, be mandated as one of the two 2011 Scouts?)

Arizona State University's Laurie Leshin was assigned to head a subgroup to decide this question and others relating to the Scouts - such as whether their current $400 million maximum acceptable cost limit should be raised somewhat.

(Firouz Naderi expressed his belief that unless this is done, no more Mars lander missions can be picked for the Scout program.

Even Phoenix, which had the remarkable good luck to be able to use the cancelled 2001 Lander as an already-built spacecraft, came fairly close to breaking the current cost limit.)

At any rate, the process of decision on NASA's overall plan for space exploration - developed more thoroughly in advance than it has ever been before - is now underway.

The second meeting of this Roadmap Committee occurred February 8 in Washington, although this reporter was unable to attend it.

The final reports from it and the other committees - as reappraised by the National Research Council - will be ready by August, and the new NASA Strategic Architecture itself will be ready by October to begin guiding the agency's spending plans in the coming years.

So, stay tuned.

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