Selecting the Mars landing site for Curiosity

Saturday 29 September 2012 12:27PM (view full episode)

Joseph Michalski worked on selecting the best landing site for the rover Curiosity on Mars. He explains what made Gale Crater the ideal site.

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Robyn Williams: Brian Schmidt suggests we may discover life in space within his lifetime. It's been an ambition for generations, especially focused on Mars. This is Carl Sagan a few years back.

Carl Sagan: I see the exploration of Mars by human beings as an enhancement of the human spirit, as the de-provincialisation of the Earth. I see a great deal of science coming from it, including the search for life past or present on Mars, I see a great deal in favour of it. I also recognise that the cost will be very large and that the United States has an extremely long list of urgent social problems that are going to require a great deal of money. And so it seems to me fair that exploring Mars, especially with humans, be considered in competition with these other drains on the discretionary federal budget. I'd like to see a national debate.

Robyn Williams: Carl Sagan. And since then we've had probes like Curiosity just weeks ago, and this at the Natural History Museum in London. I am with Dr Joe Michalski.

And what are we looking at in this wonderfully darkened fault with the illuminated rock?

Joseph Michalski: This is the latest in meteorite to be found that has been ejected off the surface of Mars and has landed on Earth, this is Tissint meteorite. It is technically called a shergottite, and what that means is that it's made of basalt which is a dark volcanic rock that is common on Earth and on Mars as well.

Robyn Williams: The thing that amazes me is it's so huge. I would have imagined that a piece of Mars travelling all that way would be the size of an egg at the most, but that's the size of a double pack of butter.

Joseph Michalski: That's one reason why this particular rock is so valuable. We don't know exactly what's inside of it, but people have begun to do things like CT scanning and so on to look for density differences within it, but that provides a large amount of material to research moving forward, especially considering that as you curate materials, especially very valuable ones, you want to be very cautious in how you slice it up and do any sort of destructive analysis. So having a big mass of material is excellent for the research community.

Robyn Williams: You knew it was coming down because there were great big bangs and noises in the sky, and presumably it was found...was it in Morocco?

Joseph Michalski: I believe so, yes, in Morocco.

Robyn Williams: The most important thing is, how do you know it's coming from Mars and not just the asteroid belt or the Moon or something?

Joseph Michalski: There's a long story to that actually, but, in brief, some years ago, I would say about 25 years ago we knew that there was a category of meteorite in which all of the meteorites in that category were different from everything else that has been found, and the reason we knew that was from the oxygen isotopes, so differences in the weight of oxygen that are measured within the sample. And what that means when you find a grouping of the oxygen isotope ratios within all the different meteorites, when you find a grouping of that, that means that the meteorites in that category all came from the same source, the same parent body, but we had no idea what that source is. Now, as years had gone by, people were investigating the composition of the gas bubbles trapped within the meteorite. And the gases that occur in those bubbles correspond exactly to those in the Martian atmosphere that had been measured by landed spacecraft.

Robyn Williams: Yes, indeed, it's quite extraordinary when you actually look at that, that that was actually on Mars. Presumably when people want to examine it they open the vault and they take it out very carefully with gloves. Have you done that yourself?

Joseph Michalski: I have with other meteorites, not with this. Yes, it's amazing to hold a piece of rock in your hand and imagine the life that that rock has been through, being launched off the planet, travelling through space, landing on Earth, and eventually being found, being curated and so on. It's a magnificent thing.

Robyn Williams: Let's walk around to where you've got some of your own specimens going. You've come from the JPL, the Jet Propulsion Lab in Pasadena California. What were you doing there?

Joseph Michalski: At that time I was working on the Curiosity mission, helping to select the landing site. Although it was many years in advance, we had already begun that process because it's really a one-shot deal. You have to land in one spot on Mars, and you'd better select wisely, for a number of reasons; in terms of safety and hazard avoidance, and also in terms of maximising the science value of the site.

Robyn Williams: And so you were actually working on that up to six years ago.

Joseph Michalski: Exactly. You know, the process is a really complex one that is dependent on the engineering specifications of the rover, the EDL team, that is the Entry Descent Landing team, the team responsible for putting the asset on Mars, and the evolving science during the whole process. So you can imagine there's a lot of interdependence there, and there are even parts of the rover that weren't totally developed at that time, so they had the capability of adding or subtracting different things in order to enable it to land safely in different types of terrain.

Robyn Williams: And when it landed a few weeks ago, you were here. What did you think?

Joseph Michalski: It was such a sigh of relief to see that such a complex feat of engineering, to land successfully using this sky crane manoeuvre which, to be honest with you, a lot of people in the community, no matter how much faith they have in each other, no matter how much hope they have, everybody had a little bit of doubt somewhere deep down that this thing could actually work. And it worked flawlessly, it was such a great thing.

Robyn Williams: For those of us who can't do reverse parking, it was pretty impressive. The pictures have been coming back, fabulous, the best ever pictures from Mars, aren't they.

Joseph Michalski: Absolutely, and one of the most interesting things about this landing site is that it provides landscapes that people can connect to. If you've ever driven through Western Australia or through western USA you find similar types of landscapes with layered mountains containing sedimentary rocks, red rocks that are really reminiscent of what we see back home.

Robyn Williams: As to your other research, well, it's all connected, looking at the types of rock and sands that are found on Mars, show me part of what you're working on now in this great big hall in the South Kensington Museum, it is I suppose about 200 metres long with display after display of wonderful minerals.

Joseph Michalski: In the last 10 years of Mars exploration we've really blown the doors off the barn in terms of understanding the mineralogy of the planet, and that has come through infrared measurements of the surface through a number of European and American missions. By using the infrared we can see spectroscopic fingerprints of particular minerals on the surface remotely. And of all the minerals that you can measure, the most interesting ones from Mars are in three different categories; clay minerals, those are the things you're used to seeing in mud, muddy rocks, things that people make pottery out of, for example, but those are important because they indicate the sustained presence of water. Another type is sulphate minerals, and those are things that people are used to seeing in evaporite setting, very dry settings, desert lakes that have dried up and you see those white crusts that form all over the ground, those are evaporites and commonly sulphates. You see those on Mars as well.

The third one is carbonates. Those are the types of minerals that compose coral reefs and occur as layered materials in oceans and lakes. If we see carbonates on Mars, that doesn't mean that we see coral reefs, but that means that we see another piece of evidence for aqueous activity. So those three things have been the holy grail of Mars for a long time. And now we have thousands and thousands of discoveries of clays and sulphates, and a handful of discoveries of carbonates on Mars.

Robyn Williams: And you were saying before, there's the question of where the atmosphere of Mars went, because there is so little of it now.

Joseph Michalski: Absolutely. The atmospheric pressure of Mars is less than 1% of the Earth. And it is composed largely of carbon dioxide. And in the past we see evidence for dried-up river channels that indicate that the atmospheric pressure was probably higher, allowing higher surface temperatures and precipitation. But we don't know how was that atmosphere thicker, and if it was, when did it become thinner and where did it go? Because the atmosphere is made of CO2, the way to store up a lot of that material into rocks is to put them into carbonates, and that is one reason why carbonates have long been the, as I said, holy grail of Mars exploration.

Now we have a handful of discoveries, and I can show you here in this case some examples of them. On Mars we see mostly magnesium carbonates, and they occur just as a tiny little rind or in weathering environments that correspond to the ancient surface. But in a few cases we see something else, something really extraordinary in my opinion. Within meteor impacts there is a central peak that rises up in the centre of this large crater, and that central peak is material that has been exhumed from deep in the crust. So we know from how deep these materials typically come. On Mars this is our best chance to probe into the subsurface, is to measure the mineralogy of those central peaks. We see central peaks that contain material that has come from the subsurface and we find carbonates in there, including iron and calcium carbonates that may have formed from hydrothermal conditions deep in the crust. And that indicates there may be a lot of carbonate at depth, there may be habitable conditions at depth, and there may have been a lot of the atmosphere stored deep in the crust.

Robyn Williams: With Curiosity on Mars, it's got this lovely laser which goes zapping into the soil and brings back an analysis and tells you what's there. Are you waiting for information coming through that way?

Joseph Michalski: Absolutely. This is an instrument that is likely to deliver some major discoveries. For example, this landing site was not chosen for the occurrence of carbonates, it's not something we see from orbit. However, history has always showed us to expect the unexpected, and nobody will be terribly surprised if we reveal the presence of carbonates or some other strange mineral that we had never anticipated in this particular site.

Robyn Williams: Dr Joe Michalski, planetary geologist at the Natural History Museum in London, formerly at the JPL, that's the Jet Propulsion Lab in Pasadena, California, where he helped select the site for the Curiosity lander, now on Mars.


Joseph Michalski
Planetary Geologist
Natural History Museum London


Robyn Williams
David Fisher

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  • Max Bancroft :

    03 Oct 2012 7:19:35pm

    Has Curiosity been designed to give it the capability to walk 'spider fashion' out of soft sand in the event its wheels becomes bogged like Spirit?