Given some time to digest yesterday's press conference I am struck with the overall strategy for Mars exploration. A couple things that keep coming back are:
1. An overall vision of Mars exploration with the backing of the President. At the press conference there was repeated references to the "President's vision".
2. Discovery-driven science. No plan is good enough that there shouldn't be corrections. Now that they know what minerals to look for they will be expanding that using satellite-based observations. Given they found a high concentration of sulphur they are thinking of adding an isotope analyzer to the next probe. The reason: life processes sulphur differently than non-life. This appears to be a challenge to get a device that is small enough on the next rover. This will result in a delicate interplay between engineering and science as described by Dr. Squyers to Nova. He said, "Once you get all the engineering constraints and safety stuff out of the way, then it boils down to science." There is really a good team of engineers and scientists who have been able to work together towards a common goal, and it appears that it will continue to do so.
The discovery announced yesterday was not luck but the result of good plannning. I will close with a quote made by Dr. Squyers before the discovery. Note how much of it came true. Congratulations to all involved.
Once you get all the engineering constraints and safety stuff out of the way, then it boils down to science. The science of this mission involves going to places where there was liquid water in the past, so I want to go to places where there is absolutely compelling evidence that liquid water was present. The problem with that is that evidence for liquid water on Mars is never going to be 100 percent convincing, and it comes in different types.NOVA: Such as?
Squyres: I'll give you two examples. One form of evidence that we find is what I'll call chemical evidence. The best evidence that we have for that is a mineral called hematite. On Earth, hematite mostly forms in places where there's liquid water, in big standing bodies like lakes or oceans, or in hot springs. Or it forms where cold water percolates through the ground and dissolves stuff.
There are a few places on Mars, including one called Meridiani Planum that we can probably land on, where hematite is present. So that's a place where the chemistry of the surface, as viewed from orbit, tells you that maybe water was there. The problem with that is that there are other ways to make hematite too, and some of them don't involve water. So it's kind of an ambiguous signal that says water was here.
The other kind of evidence for water comes from landforms. I'll give you a good example. There's a place called Gusev Crater, an impact crater maybe 100 miles across. It's got this huge, dried-up river valley flowing into it. It had to have been carved by water: water flows through the river valley, flows downhill, gets into this big hole in the ground. It's hard to believe that this thing didn't have a great big lake in it at some point in martian history. Sediments were surely deposited in that lake, so you should have a good sedimentary record of liquid water and whatever was going on there. Gusev Crater is a fabulous place to go.
The problem with Gusev is that whatever happened there happened a long time ago. We're talking billions of years. Since then, other stuff could have happened. Impact craters could have chewed things up, lava may have flowed down onto the sediments. And we can't dig big holes with this rover.
So there's no slam-dunk winner here. There's no place where you can go and say, Oh yeah, that will be a place where there will be absolutely conclusive evidence for liquid water. There are a number of very, very tantalizing ones, and I hope we pick wisely.
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