Of these, "astrobiology", received much attention as the main motivator for funding Solar System exploration -- a situation that can provoke sharp feelings among scientists daling with non-astrobiologically focused research.

As a way of attracting support from the general public -- and thus funding -- the search for life on other worlds has undeniable power. After all, most people find the idea of alien life forms (even primitive ones) far more interesting as a subject than rocks or gases or magnetic phenomena.

But the very large number of planetary scientists who deal with worlds and phenomena that are virtually certain to be lifeless -- or have only a weak connection (or none) to the question of alien life forms -- naturally feel that their areas of interest will be slighted in a space exploration scheme centered around alien life, and take a bitter attitude toward the idea of making planetary exploration revolve primarily around it.

However, one point that was brought up by Bruce Jakosky and Mitchell Sogin in their presentations to the Steering Committee of the Solar System Decadal Survey was the fact that "astrobiology", when properly defined, is a very sweeping term indeed.

It includes not only the search for actual alien life forms elsewhere in the Solar System, but the issue of "prebiotic chemistry"-- which (although this has not been widely publicized) is regarded by both scientists and NASA itself as equally scientifically important.

The reason is that the question of how life first evolved out of nonliving (and initially very simple) organic chemicals on Earth is still one of the most important unsolved mysteries of science -- it must have been a tremendously complex process, and no really convincing model of it has yet been constructed.

And, unfortunately, on this planet all the evidence has been destroyed -- almost all of the more and more complex organic molecules that represented the intermediate stages were simply eaten by life forms once they did evolve, and any tiny remaining traces have been destroyed either by Earth's plate tectonics (which repeatedly drag its rocks down into its hot interior and melt them), or by ordinary chemical reactions involving Earth's supply of liquid water.

But the other worlds in the Solar System are likely to contain far better evidence. Mars and Europa are very cold worlds, without plate tectonics, and with all or a great deal of their environments lifeless and continuously below freezing for eons since their balmier early days -- so if, during those early days, they moved toward the evolution of life without ever actually reaching the point of making self-reproducing organisms, the very complex intermediate-state organic chemicals involved have a very good chance of still being preserved in large traces.

The same thing goes for those super-cold worlds in the outer Solar System -- such as Titan, Triton, Pluto and the comets -- where it's a near-certainty that life itself never appeared because of the lack of liquid water, but where many of the preliminary steps in the organic chemical reactions necessary to create it did occur in great amounts and over long time periods that no Earth lab can simulate.

In short, it now seems very likely that we will have to examine other worlds to have any real hope of finding out how life originated on our own world.

Beyond that, there is a still more sweeping astrobiological issue -- the question of just what factors make a world potentially habitable or uninhabitable for life throughout its lifetime in the Solar System, or in another star's planetary system.

This can involve an enormous range of physical and chemical factors:

• the nature of the chemicals present on such a world,
• its temperature range throughout its long and varied physical evolution from the earliest days after the Sun switched on,
• the way in which its atmosphere developed,
• the extent to which it was furiously bombarded by the giant chunks of debris that still filled the Solar System for hundreds of millions of years after the planets had initially formed,
• the extent to which it developed a magnetic field;

-- In short, practically every physical fact you can discover about the Solar System has some relevance to astrobiology in this sense.

And if everything we discover about a world, such as Mars or Europa in their early days, suggests that life could have evolved there, but we find no fossil evidence that it ever did, this in itself is vastly important -- for there is still a furious debate about whether the appearance of life on Earth was "inevitable" or a long-shot (and maybe extremely long-shot) chance accident stemming from the fact that just the right combination of organic molecules happened to come together in one or a few places on the planet.

The one real piece of evidence we have suggesting that the appearance of microbial life on Earth was inevitable -- and, therefore, that it has also appeared on most habitable worlds in the Universe -- is that fossils show clearly that bacteria did appear on Earth within, at absolute most, a billion years after the planet's surface had cooled down enough to allow them to exist at all, and maybe much more quickly than that.

If life appeared on Earth as the result of an unlikely chance accident, the odds are that it would have first appeared much later after Earth became habitable.

But even this evidence has recently been clouded by the general acceptance that ancient Mars may very well have been habitable for life for a very long time before Earth cooled down enough to become habitable -- so it's possible that microbial life first appeared on Mars after a long period, as an unlikely chance event, and was then transferred to Earth by meteorites from Mars to colonize Earth the moment Earth cooled down enough for Martian microbes to survive here.

Indeed, it's now becoming disturbingly clear that -- even if we do find proof of life on Mars -- unless it's radically different biochemically from Earth life, we will have the Devil's own time proving that it didn't originate on only one of the two planets and then simply get transferred to the other world by their exchange of meteorites, after which it could have followed its own separate evolutionary path.

If so, even the discovery of Martian life will not prove that life isn't a fantastically unlikely chance event in the Universe. (Thus the discovery of life on Europa may actually be of far greater scientific importance than the discovery of Martian life, since it's far less likely that meteorites could have transferred microbes between Europa and the inner worlds, and so Europan life unquestionably would be a very strong indicator that life is common in the Universe as a whole.)

Conversely, if other worlds turn out to have been habitable for long periods in their history but life did NOT develop there, it will be a strong piece of evidence that life on our own world is the result of a long-shot stroke of pure biochemical chance.

At any rate, the conclusion stated by Jakosky and Sogin is that -- properly viewed -- "astrobiology" can justify almost the entire range of Solar System exploration; there's almost no scientific fact about the System that is irrelevant to it, and so it may be wise to use it as a public justification for the entire planetary program. But other members of the Committee pointed out that even in that case, some scientific studies of the planets and smaller bodies are far more relevant to astrobiology than others.

A network of seismometers to study a planet's internal structure -- or a spacecraft to study its magnetosphere, or the chemistry of its upper atmosphere -- will plainly be of less relevance biologically than a direct search for organic chemicals (let alone actual fossil life) on its surface.

And a world (such as Mercury), which has surely always been lifeless, is obviously much less important "astrobiologically" than a world that may have developed life or prebiotic chemistry, no matter how much you try to stretch the definition of astrobiology to call Mercury relevant to it.

When I left the Meeting, it was clear that this major debate was far from over among the Committee members, as is surely the case among planetary scientists in general.

But the same two OMB officials who announced the White House's desire to cancel the Pluto flyby and Europa Orbiter for now also made the power of astrobiology's appeal clear -- for one of their main reasons for canceling the Pluto mission was precisely that they saw it as having little biological importance.

They said that even though Pluto may have some complex organic compounds on its surface, a search for these in other places such as comets and Titan may be far more rewarding.

And it is a fact that NASA still intends to spend as much money on the exploration of Mars alone -- about half a billion dollars this year -- as it will spend on the study of all the rest of the Solar System put together, because of Mars' obvious biological appeal.

A second important theme bought up repeatedly at the Meeting was the fact that NASA -- while funding expensive planetary missions -- spends a good deal less than it should on the terrestrial aspects of Solar System exploration. These fall into a wide variety of categories.

To begin with, there is the fact that the "science cycle" of space exploration missions falls into three phases. The first -- "Research and Analysis" -- includes the wide range of studies that eventually lead to the design and proposal of new missions: theoretical studies of astronomical phenomena, development of new scientific instruments (and the improvement of existing ones), and terrestrial observations.

The second -- "Flight Mission Development" -- involves the actual design, construction, launch and operation of planetary spacecraft. The last -- "Data Analysis" -- involves the actual analysis and scientific interpretation of the data radioed back by such missions, which in turn naturally leads to more new theoretical predictions and thus back to the Research phase of the cycle -- and so on.

As you might expect, most of the money in NASA's Office of Space Sciences (OSS) -- fully 80 percent -- goes to Flight Mission Development, with only about 10 percent going to each of the other two phases. Yet they are equally crucial in space science exploration, and for some time there's been a strong feeling that NASA was underfunding them simply because they're less immediately glamorous to the general public.

In 1998 the OSS ordered a detailed study to look into the funding for the "Research and Analysis" (R&A) part of the cycle, and to see just what individual fields in space science might be over- or underfunded. Its final conclusions were released only last June.

It concluded that several specific areas in the space sciences -- theoretical work in astrophysics, instrument development for the "Sun-Earth Connection" program including NASA's studies in solar astronomy and the Sun's effect on Earth's magnetosphere and atmosphere, Earthbased attempts to detect planets of other stars, and the development of "information systems" for the overall nationwide interexchange of scientific data -- badly needed increased funding.

But it also expressed satisfaction with the fact that, starting only last year, NASA has begun to sharply increase the total amount it spends on Research and Analysis, to the tune of about $25 million more each year, thus keeping pace with inflation. (The increase in R&A is especially sharp for Solar System exploration, which is scheduled to double between 2000 and 2006 -- with most of the increase in astrobiology-related research.)

But while NASA's total spending on the third part of the science cycle -- the "Data Analysis" of science data telemetered back by spacecraft -- is also now being increased fast enough to outstrip the inflation rate, the vast majority of this money goes into the analysis of the increasingly huge volume of data from NASA's orbiting telescopes and astrophysics satellites, such as the Hubble Telescope and the Chandra X-ray telescope.

While NASA's planetary spacecraft up to now have sent back a good deal less total telemetry, this volume of radioed data will dramatically increase in the coming years, and the latest report from NASA's central Space Science Advisory Committee just this month urges that the spending on Data Analysis for Solar System spacecraft be dramatically increased quickly.

The Decadal Survey Meeting also heard descriptions of some specific instruments and programs needed for these purposes. For instance, earlier this year NASA's Solar System Exploration Subcommittee urgently warned about the need to quickly increase spending on the enlargement of the Deep Space Network of radio dishes scattered around the world to stay in touch with the rapidly growing population of probes scattered over the Solar System -- especially given a sudden chance accumulation of important missions in late 2003 and early 2004. It even said that this need for massively increased spending on the DSN might force cancellation of the planned 2007 "Mars Scout" mission.

To complicate matters further, the U.S. Senate commanded the start of the privatization of the DSN -- which may save money in the long run, but which most planetary scientists thought was disastrously ill-timed given the fact that it would throw DSN's management into disorder at just the time when the Network urgently needed to be expanded.

This crisis has now been alleviated -- Congress finally backed down for now on its demand for privatization, and the Decadal Survey Committee was told that reallocation of funds will definitely allow the DSN to be expanded fast enough to cope with the 2003-04 "data traffic jam" without endangering the 2007 Mars Scouts.

But the Committee was also told that the longer-run problem remains; the DSN still needs to undergo rapid expansion in the coming decade to deal with the expected further increases in the Solar System armada.

The Committee was also told about some new terrestrial facilities important or downright vital to the planetary exploration effort -- including some groundbased astronomical observatories, likely to be built over the next decade, which would be funded not by NASA but by the National Science Foundation (along with some private and international partners).

They are also intended to study stellar and galactic astronomy and cosmology in a major way, but are solidly useful for Solar System studies.

One is the Giant Segmented Mirror Telescope (GSMT) -- the biggest terrestrial telescope yet, with a mirror fully 30 meters wide (36 times the area of the Palomar Telescope's mirror!), which would be built with $350 million of U.S. money in collaboration with other nations.

Its use for observing the distant planets and asteroids is obvious -- for instance, it could sharply observe the weather patterns on Uranus and Neptune (taking regular photos of Neptune 400 pixels across), and with an adaptive-optics coronagraph it could directly photograph some giant planets of other stars.

Another is the Large Synoptic Survey Telescope -- a revolutionary new 6.5-meter telescope with a huge 3-degree viewfield which would map the entire sky for faint objects at hundreds of times the rate it has ever been done before, repeatedly sweeping the whole sky for objects down to the 24th magnitude every three or four days.

While LSST's usefulness for every kind of astronomy is obvious, its top two scientific uses have now been officially ranked as:

• the detection and accurate orbital mapping of at least 90% of all near-Earth objects in the inner Solar System down to a diameter of only 300 meters (allowing a long advance warning of any future collision by one of them with Earth); and
• (2) the detection of fully 10,000 objects in the Kuiper Belt -- the iceballs, ranging from only a few kilometers in diameter up to the planet Pluto (and perhaps bigger), which are now known to make up a whole new previously unknown major section of the Solar System which utterly dwarfs the Asteroid Belt and is extremely important in understanding the System's beginning and development.

LSST would cost $170 million, and it is only the lowest priority among the three "Major Initiatives" in terrestrial astronomy recommended for the next decade in last year's very important report by the National Research Council's Astronomy and Astrophysics Survey Committee. (GSMT ranked first).

But David Jewitt reported at last week's Steering Committee meeting that it is "very likely" to be built in this decade, partly because of the importance of tracking near-Earth objects' orbits, and partly because the Survey Committee's list of recommended new terrestrial observatories isn't ridiculously overpriced as a whole.

Already tentatively started, and also likely to be completed this decade, is the international Atacama Large Millimeter Array -- an array of 64 12-meter millimeter-wavelength radio astronomy dishes in Chile whose input would be interferometrically combined to create microwave images of the sky as high-resolution as the Hubble Space Telescope's visual photos, enabling very high-quality studies of the temperature patterns and trace gases of other planets' atmospheres.

Finally, one lower-price recommendation of the Astronomy and Astrophysics Survey Committee was also described at last week's meeting as a ertainty -- the $60 million "National Virtual Astronomy Observatory", an automated data storage and distribution facility which would store and intricately organize the trillions of bytes of data produced by both the coming terrestrial and orbiting observatories, allowing researchers to access it and "data-mine" it for relevant information at tremendously higher speeds than the current Internet system allows.

Another vital terrestrial facility will soon be needed to handle samples that will soon be returned from Mars and other worlds -- many of which could conceivably carry alien microbes that could be pesky or downright dangerous if accidentally released on Earth.

While this risk is small, it must not be completely ignored -- and any search for evidence of life in such samples also requires them to be protected from contamination by Earth microbes and organic substances.

A study by the National Research Council this year has concluded that two different kinds of facilities are really needed. The first would receive the samples as soon as they are returned to Earth, and give them a careful preliminary examination for evidence of living organisms.

If none were found (as is always probable), the samples could then be safely released to various "curatorial facilities" around the world, which could store them contamination-free for genuinely detailed scientific study.

Dimitri Papanastassiou told the Steering Committee that these curatorial facilities already either exist or are already funded for construction soon -- but the initial receiving facility (the "Sample Receiving Facility") is another matter.

It presents a unique problem because it must be a "two-layer" complex combining two different and contradictory functions. First, it must provide "Biosafety Level Four" protection against any risk of internal alien germs escaping into Earth's environment -- which, like all existing Level Four facilities to handle dangerous disease germs, requires internal air pressure lower than that outside to keep any germs from blowing out of the lab on air currents. (This lower pressure is maintained, in turn, by a circulating pump system which runs the air it sucks in through a series of superfine filters to remove all germs and viruses before expelling that air outside).

But the Facility must also include another facility INSIDE that one to protect the samples themselves from contamination, which requires the opposite: an air pressure higher inside the facility than outside to keep terrestrial particles in the air outside from wafting into the lab, like spacecraft "clean rooms" and the existing Lunar Receiving Laboratory in Houston.

If the Receiving Facility fails to find even any sign of organic compounds in the samples, they can safely be released immediately to outside labs. But if such compounds are found at all, any samples must be sterilized by heat or (better) intense gamma radiation before they are released to the outside world. And if unequivocal evidence of viable alien life is found by the Facility, the samples must be retained inside it until entirely new facilities can be built to safely study such microbes in detail -- which could take years.

A great deal of preliminary research will thus be necessary before the Receiving Facility can even be designed, and Papanastassiou said at last week's meeting that that planning work on the Facility must thus start 7 to 10 years before any Martian samples are returned to Earth (for which the current date is 2016). It will also be necessary to set up an international scientific advisory committee to be completely in charge of handling and allocating Martian and other astrobiologically interesting samples.

Finally, Jeffrey Rosendhal mentioned the important functions of Education and Public Outreach in the planetary program. NASA's Office of Space Science is virtually unique among government agencies in having its scientists directly involved in such efforts and their design -- which is understandable, given the fact that Rosendhal said the educational role is one of the main reasons why the Bush Administration supports the expensive space sciences at all.

Rosendhal brought up two particularly interesting points. First, he said -- certainly correctly, in this reporter's opinion -- that, before any Mars samples are returned to Earth, it will be absolutely necessary to properly educate and inform the public as to the real level of risk involved, in order to avoid a national or worldwide panic, given the extent to which we have all been steeped in "Andromeda Strain"-style horror stories about alien plagues for decades.

Second, he pointed out one eyebrow-raising fact: each year, the number of Americans who visit science museums or observatories is equal to the total number who attend professional football, baseball and basketball games combined. It would seem to be a serious mistake to underestimate the general public's level of interest in science -- IF it is clearly presented to them.

However, all these discussions about terrestrial activities at the Meeting -- despite their importance -- were really somewhat peripheral to the Committee's central function, which was to recommend the best sequence of the unavoidably expensive space missions needed to study the Solar System, around which the less expensive terrestrial studies and activities revolve like satellites. And while their detailed deliberations on this are still sealed off from the press, in the last part of this report I'll describe some of the very interesting potential missions that are under consideration.

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