Human Journey

Mars Science Lab ISO Best-fitting Site

One of the perks of coming to a scientific meeting is that, in addition to press briefings and poster sessions, you get to sit down and just chat with some of the bright minds working on solving the mysteries of the universe.

In my case, I ran into planetary scientist James Wray of Cornell University here at AAS/DPS in Pasadena, and he gave me an insider’s view of what went down at a meeting held last week to decide where to land NASA’s next big mission to Mars.

The Mars Science Laboratory, nicknamed Curiosity, is a robotic rover the size of a small car that’s due to launch in fall 2011—one Martian year from now. The probe’s stated mission is to “assess whether Mars ever was, or is still today, an environment able to support microbial life.”


Curiosity stretches its robotic arm during September 3 tests in a clean room at NASA’s Jet Propulsion Laboratory.

—Image courtesy NASA/JPL-Caltech

Well, Mars may be smaller than Earth, but it’s still pretty huge compared to a lone robot, so how do you pick the best landing site to achieve this goal?

Scientists have been making their individual cases for years, and the pool of candidate sites got narrowed to four back in 2008, when MSL was slated to launch in 2009.

But then the mission got delayed, leaving lots of time for supporters of a given site to collect new data and continue championing their causes.

Last week’s MSL confab was the last one to be held before a final decision gets made next spring.

Ever diplomatic, James wasn’t ready to say which site looks like it’ll be the front-runner. But he did walk me through why each of the four candidate sites has its community of advocates, and why certain ones may be a better fit for MSL’s now locked-in capabilities.

What follows is a transcript, lightly edited, of our hallway conversation:

So, what are the differences between the four candidate sites?

All of them have both hydrated minerals—mineralogic indications from orbital spectroscopy that water once interacted with the rocks and altered their chemistry—and they also all have evidence for liquid water flowing across the surface at some point in the history of the region.

(See “Martian ‘Lake Michigan’ Filled Crater, Minerals Hint.”)

The big differences are in the strength and diversity of the mineral signatures. Some have both clay minerals and sulfate minerals that were inferred to form in different kinds of environments, so you could study chemical changes over time. That’s true especially at the Gale Crater and Mawrth Vallis landing sites. Mawrth Vallis also has strong mineral signatures that the rocks really are mostly clay.

The challenge is telling how the rocks formed. We know water altered them, but how did the rocks get there in the first place? Was it deposition from wind in standing water? Was it airfall from the atmosphere? We don’t know.

At other sites such as Eberswalde Crater, where the mineral signatures aren’t quite as strong or diverse, you have very good evidence that the rocks the rover would access were deposited in a standing body of water. So it’s a tradeoff between diversity and strength of mineral evidence for water rock alteration versus confidence in the conditions that formed the rocks that we would study.

All of the sites still have advocates in the science community. I think they all have their pros and cons, and I think it’ll be difficult to chose just one. The organizers of the workshop have emphasized these are all very compelling sites … and ultimately we’d like to land at all four, if we can, with future missions.

Will picking a final landing site have any bearing on the types of instruments that MSL will carry to Mars?

No, it’s too late to make changes to the science payload. The mission was originally slated to launch last year in fall 2009, so most of the instruments are delivered and on the rover already.

Even though we can’t change them at this point, given that we know what the payload is going to be, that may be a consideration in making the choice of site. Which site will we learn the most about with the set of instruments we have on MSL?

Do you plan to be at the MSL launch next fall?

I hope to be there! The launch window is scheduled for late November 2011, so I have to figure out how to get from Thanksgiving dinner to the Cape [aka Cape Canaveral in Florida] the next morning, but we’ll see.

What do you think of the rover’s new name, Curiosity?

I think it’s an appropriate nickname, because curiosity about each of these sites is what will ultimately drive us to them. But many of the scientists and engineers who have worked on the project have continued to call it MSL, and that’s also true of the Mars Exploration Rovers: The pubic obviously knows them as Opportunity and Spirit, but the science team day to day still refers to them as MER-A and MER-B.

You are here at DPS presenting new results on one of the Mars sites. Can you tell me a bit about your findings?

I presented on two different new mineral detections, and the one that’s related to the landing site decision is at Mawrth Vallis, which is one of the sites where we see both clay minerals and sulfates. I was presenting evidence for sulfates … within a few kilometers—at most ten kilometers—outside of the landing ellipse. [If MSL lands at Mawrth Vallis] you could access this new class of minerals distinct from the clays that have been found there previously.


The proposed MSL landing site at Mawrth Vallis, seen by the Mars Reconnaissance Orbiter.

—Image courtesy NASA/JPL/University of Arizona

The mineral at Mawrth Vallis is called bassanite, a calcium sulfate. The mineral is known on Earth but it’s in fact quite rare on Earth because it wouldn’t exist stably at the surface conditions. It would either dehydrate or become more hydrated, depending on specific conditions. But on Mars, where it’s much colder, it’s harder for minerals to go through these changes, so you might expect this bassanite to be more common on Mars.

Regardless of where MSL lands, what do you think will be some of the highlights of what it finds?

I think without question it would be if the mass spectrometer instrument found organic carbon compounds in rocks or in soils. [That will be exciting], whether it’s actually from modern or ancient Martian life, or from some other less exciting source: For example, cometary impacts should deliver organics to Mars.

Just the fact that comets should deliver organics to Mars but Viking didn’t find any is scary, when you think about. Could ancient organic matter [on Mars] be preserved? Well, maybe the surface of Mars is so harsh it’s hard to preserve anything. So even just finding cometary organic matter would be reassuring for future additional searches for evidence of past Mars life.

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