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Clues to Life on Mars Are Hidden In The History of Ancient Lakes


Fifty years ago this month, Apollo 11 landed on the moon. Amid all the celebrations - new discoveries about space are happening all the time. Many of them are now centered on Mars. Marisa C. Palucis, assistant professor of Planetary Geology at Dartmouth College, has been researching ancient lakes and other bodies of water on Mars using data from the Curiosity Rover, which has been exploring the red planet for the last seven years. 

NHPR's All Things Considered Host Peter Biello sat down with Palucis to learn more.

Transcript has been lightly edited for clarity.

So when Curiosity landed in 2012, it landed in a crater. You've been studying this crater. What have you learned about it?

Curiosity landed in Gale Crater. We’ve learned that Gale Crater has hosted at least one large lake, but potentially a series of lakes.

Credit NASA/JPL-Caltech / NASA
This image is an interpretation from the MSL team of what Gale Crater (where Curiosity landed) once looked like - researches think that water from the crater rim transported sediments (like the ones in the image above) onto the crater floor in a large lake that existed billions of years ago.

Lakes that have filled and then evaporated somehow?

Yeah. So we think that these lakes were probably active about 2.5 billion years ago. So basically the big thing that we're interested in is, did Mars ever host life? For life, we know that water is a major ingredient. One of the things we look for though, is not only is water on Mars, but was there water for a very long period of time? For in order for life to evolve, we need to have water for potentially millions to a billion years.

So I think a lot of listeners tuning in right now will wonder, "OK, if there was water there before, could there be water again?" And is Mars hospitable, perhaps for human life at some point?

Yes. So there is still liquid water. We know in the poles that there is water that's frozen. There are very small amounts of water that are in vapor form in the atmosphere. And there are hypotheses that there is a lot of water that's trapped in the subsurface. And so all of those would be sources of water if we actually put humans on the surface of the planet.

So the water that did exist on Mars, not the frozen stuff that's there now, but the water from the past, what can you tell us about it?

So we think based on the mineralogy, the clay minerals that the rovers discovered, that this water would have had a neutral P.H, meaning the type of water that we could drink; not too salty, not too acidic, not too basic. And so this is really good if you're thinking about trying to find a place that would be hospitable for early life.

So how do you go about studying Mars from where you sit in New Hampshire?

Yeah. So we use a lot of orbital imagery, images that are taken by satellites that are continuously rotating around the planet. And we also use the images that are brought back from the Curiosity rover. We do a lot of analysis of these images. We can actually create topographic maps just like the ones when you go hiking. And we can use the topography and the imagery together to model what we think the environment was like in the past.

Credit NASA/JPL-Caltech/MSSS / NASA
This was taken with the MAHLI instrument on Curiosity early in the mission and shows sand and pebbles that were once transported by flowing water - as a geomorphologist, Palucis can use the size of the pebbles to calculate the depth and velocity of that flowing water based on the size of the pebbles.

And there's a plan for another rover to go to Mars next year, right?

Yes. So next July, we're going to send a rover, I don't think has a name yet, that's going to be very similar in scale and size to Curiosity. It's going to be going to Jezero crater.

And what's this rover going to do that's new? What will it enable you to do that you can't yet do?

So one of the cool things about the Mars 2020 rover is that it's going to actually be landing right next to a large delta. I study delta deposits and alluvial fans and use those as analogues to understand past water on Mars. So this rover is going to be able to get up close and look at all of the rocks and minerals and things like that. What the Mars 2020 rover has that the Curiosity rover doesn't, is that as it explores the delta deposit, part of its mission will be to actually take drill samples of where we think there might be preserved organics or interesting rocks that we want to study on Earth. Because it's sort of the first step of a three stage mission. We're going to send this rover there and it collects samples. Then we have to get another rover to collect those samples. And then we have to do what we've never done before, which is actually get a rover off of another planet back to Earth. And so that's a pretty big deal. If all of that works according to plan to actually bring back Mars rocks, which we've never done.

So with respect to the 2020 rover and the technology you're using now, how much possibility is there for opening up explorations of deeper space?

I think there's a lot of interest in the planetary community to going out past Mars and further out in the solar system. There are planets like Titan that have a very active hydrologic cycle. But instead of water, it's methane. And so there are places in our solar system that I think have all of the ingredients that life would need. And so by preparing and testing out these different rovers in different missions on Mars, we're getting better and better. And we can then design instruments and rovers and orbiters to orbit these other icy satellites and planets.                  

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