A soft lander to carry them out seems to Briggs and McKay as probably the top priority for our 2005 Mars mission, especially since it could also carry more scientific experiments that would be very useful even if the lander did not carry any kind of rover.

For instance, the cancelled 2003 lander would also have carried an extremely sensitive device to grind up Mars rocks and check them for traces of organic compounds -- an instrument which has now been combined with the "TEGA" soil analysis instrument that was lost on Mars Polar Lander.

By the way, NASA is now in the process of selecting the next "New Millennium" mission to test useful new space technologies in 2003-04 -- and one of the candidates is an Earth-orbit test of a miniature unmanned satellite that can automatically locate, rendezvous and dock with a tiny simulated sample return canister.

If ISPP turns out to be not feasible, such automatic rendezvous and docking in Mars orbit -- which had been planned for the earlier sample-return mission, with France providing the Mars retrieval orbiter -- will indeed be crucial for sample-return missions.

Another early part of the Briggs-McKay plan is to further extend reconnaissance of promising landing sites located from orbit, for both scientific value and landing safety.

NASA's overall plan for doing this is to drop a flock of a dozen or more "Mars Scouts" -- tiny, cheap landers to photograph potential sites in much more detail than is possible from orbit, and perhaps also to examine them in more scientific detail.

Its initial concept for the Scouts involved little landers modeled after the "Beagle 2" lander tentatively scheduled to be carried by Mars Express with a set of sensors to look for biological evidence; these would not only have taken aerial photos on the way down, but survived after landing to do more photography and mineral mapping.

Briggs and McKay, however, wonder whether it's really necessary for Mars Scouts to survive their landings; they think that their most important task is to take aerial photos with resolutions as low as 10 cm.

If so, the Scouts could be made much lighter, cheaper and more numerous if sent as crash-landing capsules. Alternatively, it might be possible to equip small balloons or gliders with cameras and send them sailing for long distances across Mars.

Briggs told TerraDaily that he regards the Mars Scouts as one area where it would be effective to solicit concepts from individual scientific groups and then select the best of them, as in the Discovery Program for solar system exploration.

One possibility would be to combine crash-landing photographic Scouts with tiny instrument capsules that could survive landing -- such as the "Deep Space 2" penetrator probes that were lost on Polar Lander, or a network of weather-station capsules - which they regard as being an important accompaniment for orbital Mars weather mapping.

At any rate, it may be better not to plan and fly the Mars Scouts until after the upcoming orbiters have completed their overall survey of Mars' surface -- perhaps in 2007.

Only when these preliminary missions for reconnaissance, landing-site selection and technology development have been completed will it be realistic to try the first unmanned sample-return mission from Mars.

The Briggs-McKay plan envisions such an attempt at 2007 at the earliest -- but JPL's Ken Nealson regards 2009 as a much more realistic earliest possible launch date.

Personally, given the amount of advance preparation needed to carry out such a mission properly, my own guess for the launch date of the first Mars sample-return mission would be late 2011 -- with the sample being returned to Earth in 2014.