Naturally, a very large number of the papers involved very detailed geological analyses of the only returned samples of other worlds we have so far: meteorites and the Apollo moon rocks.

These, frankly, really are unlikely to be of interest to anyone but geological specialists, and so I'll give them short shrift. But there were many papers on more interesting subjects.

The most important of these was Mars. Despite the embarassing fiasco of the 1998 Mars probes, there is a flood of important new information coming in from Mars Global Surveyor, the one working Mars spacecraft -- and so Mars, along with the Moon and meteorites, was one of the Conference's three major subjects.

The most interesting aspects of Mars remains the two big questions: was there ever life on it, and was there enough liquid water on the surface of ancient Mars that it was an environment in which Martian life could have evolved?

Lacking more than a very few Martian meteorites as samples, we still don't have much data on the question of life itself. But we have a steadily accumulating supply of data on the question of whether ancient Mars -- which we already know possessed a dense atmosphere of carbon dioxide -- was warm enough that it also had a significant supply of liquid water on or near its surface.

Unfortunately, that data is still too ambiguous to give us a really firm answer. In a few more years, we certainly will be able to answer the question of water -- but at this LPSC meeting, there has still been room for a great deal of scientific wrangling over just how clear the marks of ancient liquid water on Mars' surface really are.

First, there is the matter of the branching, dried-up "valley networks" scattered over Mars' surface. These were clearly carved by water running during a protracted period of time; but we aren't sure whether that water actually ran across the surface of Mars, or whether it trickled along more slowly just beneath a frozen ancient surface and gradually tunneled out underground channels that enlarged until their roofs finally fell in -- a process which is called "groundwater sapping", and which is surprisingly common here on Earth.

Up to now, the general feeling has been that the Martian valley networks look more as though they were carved by groundwater sapping. They seem to lack the fine networks of sources which rivers and streams carved by surface runoff have; instead, they often seem to commence abruptly at some point on the surface, as though their sources were underground springs where more deeply buried water was gushing outwards on to the surface.

But this year's LPSC papers shows both sides have much to debate yet. Some authors take the optimistic view. James M. Moore, for example, says that in the Libya Mountains -- the rugged highlands just south of the Isidis Basin which was the favored landing area for the now canceled next U.S. Mars Surveyor Lander in 2001. Here, the local features provide clear evidence of surface runoff: "If groundwater was involved, it must have been locally derived (within a few km) and implies very high recharge rates from the surface (i.e., precipitation, either snow or rain).

"Groundwater sapping, either fed by a decaying regional groundwater system or by hydrothermal [hot spring] circulation, is an insufficient explanation for [the features seen]; recharge by precipitation and local runoff-groundwater throughflow must have occurred."

And Robert Strom describes Mars' Loire Valley as "the Grand Canyon of Mars": "Since the [geological characteristics] of the dissected Loire Vallis is so similar to the Grand Canyon, it is probable that water runoff (e.g., precipitation) was important in its formation."

However, other geologists are more pessimistic. MGS' closeup photo of the Nanedi Valley has drawn great public attention because it clearly shows a smaller channel running along the bottom of the main water-carved valley -- indicating that water later ran along the surface of the valley floor, even if the initial valley had been carved by subsurface sapping.

But Michael Malin and Ken Edgett, in their study, conclude that "Inner channels within other valley networks are extremely rare... In over a thousand [MGS] images of networks, only one other valley [the Nirgal] shows an inner channel."

This suggests that prolonged surface water runoff on Mars, while it may have existed in a few places, was very uncommon -- but Malin and Edgett point out that MGS' photos also show that the valley networks have been highly eroded and largely filled up with dust and sand during the billions of years since Mars lost its surface water, which may obscure most evidence of surface runoff.

R.M. Williams and R.J. Phillips suggest that there may have been a mixture of the two processes: Mars "would transcend from an early warm phase to the current arid, cold conditions by a freeze-out which moves from pole to equator over a time-scale of a few hundred million years.

Thus, the oldest valley networks presumably would form due to surface runoff... As the surface temperature began to drop, the formation mechanism would transition first to water-lubricated sapping and finally to ice-lubricated sapping...

Thus the near-equatorial valley networks would continue forming due to [runoff] for a longer period of time than their polar valley network counterparts" -- which they say is in accord with the visible evidence, including the fact that many valley networks seem to share characteristics of the two formation processes.

And Pascal Lee makes still another suggestion: that the valley networks resemble northern Canadian channels formed by meltwater trickling along under glaciers. However, for Mars to have had glaciers -- which some authors (including G. Komatsu at the current Conference) have claimed also left recognizable gouges in some of Mars' mountains -- ancient Mars must have had snowfall.

More recently, a more spectacular concept of early Mars has been advanced by some researchers: the idea that it may have actually had a large ocean (the "Borealis Ocean") filling up the smooth-floored lowlands that cover most of its northern hemisphere.

Robert Strom and Victor Baker go further: they have proposed for some time that Mars, throughout its history, may have had volcanic outbreaks every few tens or hundreds of millions of years that have thawed enough frozen water and carbon dioxide in the soil to briefly restore its original dense atmosphere and northern ocean, even into fairly recent geological times. They repeated that theory at this conference.

Regardless of the truth of that, the Borealis Ocean (perhaps ice-covered) may at least have existed during Mars' ancient days, and several Conference speakers claimed additional evidence of that.

A team led by David Smith stated that their analysis of the very detailed measurements of Mars' surface topography made by MGS' laser altimeter "has revealed intricate details of channels into the northern plains, particularly in the Chryse region, that represent strong evidence that at one time large quantities of water flowed into the northern plains, and that to do so would have required fluid depths to have been at least a kilometer in places."

And, as other speakers (such as M.A. Kreslavsky and J.B. Garvin) pointed out, the floors of Mars' northern lowlands have turned out to be astonishingly smooth, further suggesting that they may have been covered with a layer of ocean-floor sediment at one time.

Again, though, there are alternative theories: K.L. Tanaka and William Banerdt suggested that the apparent lack of shorelines of this "ocean", and some odd features of its seafloor altitude, indicate that it may have been an ocean not of water, but of sediment-rich mud.

Finally, even if there was never a Martian ocean, there may have been early Martian lakes -- perhaps ice-covered for most of their history. Quite a few Martian craters seem to have had local valley networks drain into them; some of these are likely to serve as landing sites for Mars sample-return missions in the near future.

Kathryn Fishbaugh, H. Hiesinger and G.E. McGill suggested at the Conference that two basins hundreds of kilometers across -- the Prometheus Basin and the Utopia Plain -- may have served as giant versions of such lakes.

C.M. Weitz repeated earlier suggestions that the odd-looking layered deposits that cover the bottom of some parts of the giant Marineris Valley may be lakefloor sediments -- and R.A. Beyer said that some other strange, swirling features on the Valley's floors look tantalizingly like ancient salt domes.

And Nathalie Cabrol and Robert Haberle said that they had seen intriguing signs that some lakes may have endured into recent geological ages, "with some of the most recent lakes (the Ares Group) being constrained between only 400 to 200 million years [in age]" -- long after standard theories say that Mars lost most of its surface air and froze.

If true, this would seem to support Baker's theory of occasional periods in which Mars becomes briefly hospitable again, although Cabrol and Haberle point out that it might also be due to outbursts of water thawed out by brief local volcanic episodes.

Not to be outdone, Tanaka and M.G. Chapman proposed that almost all of Mars' water-carved features -- including Tanaka's "mud ocean" -- may have been due to outflows of subsurface ice water thawed by volcanic eruptions.

LIFE
What all this apparently boils down is that we still don't know just how much surface liquid water (perhaps covered by a thin layer of ice) ancient Mars had, and thus how hospitable it might have been for the evolution of life.

But, again, there is no doubt that we now have a lot more evidence to judge with than we had just a few years ago -- and, with any luck, within three or four years we will have a definite answer to the question.

In the meantime, though, one remarkable new theory about Mars came to the front in several LPSC papers: the possibility that the planet may be a kind of giant Fizzie!

Mars is sprinkled with an entirely different type of water-carved feature: the "catastrophic outburst channels", which were carved by brief but gigantic eruptions of subsurface liquid water which lasted for only a few days, but were literally hundreds of times bigger than the biggest floods for which we have any evidence of on Earth.

These constitute perhaps the biggest geological mystery about Mars: where did such a seemingly dry planet come up with such huge outbursts of water, even up to 2 billion years ago - long after Mars had lost most of its air and frozen over?

Jeffrey Kargel suggested that the Martian subsurface, below the kilometer-thick permafrost layer that most scientists think it now possesses, may also contain a lot of carbon dioxide mixed with the water ice to form a "clathrate" -- and when heated by an episode of geothermal warmth, this may boil back into gas with tremendous force, cracking the thick permafrost to create a gigantic fountain of seltzer!

M.D. Max proposed that this subsurface CO2 may have been augmented by pockets of methane hydrate. And Baker and Strom proposed that this could be the mechanism behind their hypothesized occasional planet-wide eruptions of water and carbon dioxide which, they believe, may make Mars briefly hospitable again, although for only a few tens of thousands of years before the planet turns frozen and airless again for tens -- or hundreds -- of millions of years.

In short, the LPSC talks have made it clear that Mars may still have some astonishing surprises to offer us in the near future -- and the Conference is only half over.

But Mars was not the only subject of the Conference -- and in Part Two of this report, I'll review some of the papers covering other planetary targets.

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