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Now that Pluto and Ceres have been visited, the question then becomes, what now with space exploration? I think we should start thinking beyond sending more rovers and probes, although that does not mean we stop sending rovers and probes. Nevertheless I think it is about time we consider what our ultimate ambitions are. Essentially, this comes down to, do we want to send people into space or not? If all we want to do is to potter around on our own planet, then there is no need to do anything else, but if we want eventually to go into space, there is a lot to be done that involves nothing more than thinking, and thinking is relatively cheap.
There is a school of thought that all we need to do about planets is explore them with rovers. These are relatively cheap, and will not involve risk to human life. However, I disagree. I feel for a given technology, the law of diminishing returns applies. The very first missions that visit an object send back information that totally changes our view of the body. The relatively airless desert with huge erosion features that is Mars changed our view of Mars forever. The cracks on the surface of Europa, the volcanoes of Io, the image of Miranda, and more recently, Pluto. Before the missions, these bodies were faint smudges, so of course our view changed. But what happens now? We get a lot of rock analyses from Mars, but they are starting to look the same, varying only in location. I am not suggesting we know all there is to know about Mars, but I think we are starting to know enough that it is not worth while spending this amount of money to find out not much more. Basically, I feel we are reaching the limits of that sized rover. We know most of what is important about the top centimeter of the surface of Mars. We also know that that centimeter of rock is very highly oxidized, thanks to the interaction of ultraviolet light with water vapour, which results in the formation of highly reactive and oxidizing species such as the hydroxyl radical. The chloride ions appear to be converted to perchlorate. If we want to know about possible early life, about any organic chemistry, or for that matter, the initial conditions of Mars, we have to get below that layer of oxidized species, and if we want to know about anything associated with water, we have to go to depressions to where water would flow, and get below the wind-blown dust, and then to the depths to where the water would sink. That requires digging.
To illustrate, consider two of my predictions:
(a) there will be nitrogenous materials buried below the bottom of Hellas Planitia,
(b) where there should have been ponding in the Reull Vallis, there will be mineralization, the nature of which depends on the initial conditions.
To check the first, we need to drill, but because there could be a lot of wind-blown topsoil, it may take several tens of meters to find any deposits. What sort of rover can assemble a hundred meter drill pipe and drill to the full depth? What sort of rover could carry good lengths of drilling pipe and descend the walls to get to the bottom of the Reull Vallis? How many rovers could navigate with sufficient accuracy to get safely anywhere near an interesting section of the Reull Vallis?
My view is that to find out whether Mars is worth doing anything with we need to send people. We know enough about it to know what has to be done, even if we do not yet know how to do it. Then maybe we settle Mars. But if we wanted to do that, what has to be done? What do you think?