NASA selects UChicago scientist to analyze extraterrestrial samples from Martian moon

In Q&A, Prof. Nicolas Dauphas discusses what we can learn from mission to Phobos

The University of Chicago's Nicolas Dauphas was one of three scientists selected by NASA to receive extraterrestrial samples from the Martian Moons eXploration mission. The mission, led by the Japan Aerospace Exploration Agency JAXA, is scheduled to launch in the mid-2020s and will send a probe to Phobos – the Martian moon with mysterious origins. The probe is set to return in 2029 clutching a precious scoop of rock from the surface of Phobos. From these samples, Dauphas and his team will investigate the origins of the moon.

In a Q&A with UChicago News, Dauphas discusses the current theories on the formation of Phobos, how his work on the Martian Moons eXploration mission will inform those theories, and what it could mean for the habitability of Mars.

A 3D model of Phobos, one of two moons of Mars. Credit: NASA Visualization Technology Applications and Development.

Tell us a little bit about the mission and how you were selected for it.

Yes, it's great news, really! The selection was a competitive process by NASA. Of the selected ten scientists, seven will work on instrument data on the spacecraft. The other three [including me] will get the samples from Phobos and will be able to study them.

It's exploratory work; you feel like you're transported to the Apollo era or even before, like the first people who climbed the tallest mountains, or the first people who visited the deepest trenches. They did not know what they were going to find.

What are the highest priority questions regarding Phobos?

Mars has two moons, Phobos and Deimos – Phobos is the larger moon, though it's not still not very big. It's like 20 kilometers in size.

We do not know how Phobos was formed, but scientists have two main theories. The first theory is that it's a captured asteroid. The second hypothesis is that it was formed by an impact, which is closer to what we think about the formation of our moon. We think that our moon was spawned by the impact of something that was the size of Mars that collided with the Earth and formed a disk around our planet, and from that disk, the moon formed.

So very, very different scenarios of formation. It's difficult to tell remotely just by looking at the spectroscopy – that is, by looking at the light that is reflected from the surface of Phobos – whether it's an asteroid or something that was produced by an impact. But, once we have the sample in hand, it should be very clear. Once we've established that, we will be able to do many more studies.

How will your research tackle these questions?

So some of the most exciting things that we will be able to do: if it's an impact –we might be able to date the impact.

We are establishing a new methodology to get the age of rocks using in situ rubidium-strontium dating. If Phobos was formed by an impact, it's quite likely that the age that we get from the rock will actually date the impact on Mars. That's a very exciting thing.

If it's an impact, we can ask the same kinds of questions that we ask about our moon. The question of the age of Earth's moon is a big one. When we look at our moon, it's very close from an isotopic point of view and chemical point of view to rocks from the Earth. That's very puzzling, because we think that much of our moon should come from the impactor, which could be different from Earth. Why we do not see any difference is a puzzle.

We've never recovered samples [directly] from Mars, but we have meteorites that we are quite sure come from Mars, so we will be able to compare Phobos with those. We will see if we find evidence in the composition of Phobos that tells us something about the nature of the impactor. Was it something that looked like Mars—smaller-sized of course—or was it something very different? We might be able to tell.

If Phobos instead seems to be a captured asteroid, we will be able to study where the asteroid comes from, because we have meteorites that come from asteroids – so we'll be able to compare it with what we know and say something about where it came from.

What techniques that you will use?

Here in Chicago, we will measure the isotopic composition of the samples. So we will shine a laser and do measurements with the atoms that are released. We will also measure the iron isotopic composition, which involves dissolving a tiny bit of the sample.

How much rock do you need for those techniques?

You can do a lot with a little – there have been twenty papers published in the last year on the samples from Hayabusa. We can do it with such little material because the labs have developed expertise to measure precious extraterrestrial samples over decades. My lab has been involved in the studies of Ryugu, we've studied lunar rocks from the Apollo mission, we've studied meteorites, some of them extremely precious. So, we have the know-how to do that.

But much of the returned samples will be kept for future generations to study with hopefully better instrumentation. That is what NASA did with the samples from the Apollo moon missions, and we are still making discoveries by subjecting them to new measurement techniques.

What would be the most exciting outcome?

I think I'd like it to be an impact. If it's an asteroid, it'd still be interesting. But if it's an impact, it's just like our moon. We've been scratching our heads since the Apollo mission as to why it has the composition that it does. The impact would also give us some information about Mars; we will be able to get a sense of the size of the impact, and the nature of the impact. What will that tell us as to the habitability of Mars?