Dr Ellen Stofan says that missions to the red planet are a priority of the US space agency – and that the best way to search for extraterrestrial life is by setting up a permanent presence

Is Nasa looking for intelligent life?

Nasa, right now, is really taking a step-wise approach: let's look at our own solar system and the most likely places where we might find life. That's why we are so focused on Mars, because we know Mars had liquid water on the surface and we think that is essential to life. What we expect to find, certainly in our own solar system, are probably simple single or multiple-cell forms of life. To get to intelligent life takes stability of conditions over huge long periods of time. [We're] not sure that condition exists anywhere else in our solar system. But certainly when we go out and look for habitable planets around other stars it's something that we can start thinking about.

The Kepler mission has found planets orbiting stars other than our sun. What is the impact?

It's turned around our understanding of how our own solar system formed, because when you only have one solar system to study you make assumptions that are based on that information. [When] you have many solar systems to study, many planets to study, it is really making us rewrite textbooks. We're launching the James Webb space telescope in 2018 that is going to study the atmospheres of those planets around other stars.

Some might argue that it's a luxury to be spending money investigating other planets instead of solving Earth's problems …

I always like to say just think you were a doctor with only one patient. You might understand how that person gets sick, how they get better, but you understand nothing about the progression of disease or how humans in general get ill. Now take an Earth scientist: you only have one planet to study. Our studies of other planets are really what we call comparative planetology. Think of the other planets as being simpler versions of the Earth where you've tweaked the physical conditions, maybe the composition, the density of the atmosphere. It allows us to rip apart the physics of some of these problems and give us a better comparison.

Mars doesn't seem to be teeming with life. Aren't we better looking at planets where there might be something alive and kicking?

On Mars we are not totally sure – there could be something still living under the surface. Mars is close by, humans can operate and work on the surface – that's part of why we are so focused on [it]. Over the last few years we have started to formulate the next mission to [Jupiter's moon] Europa – we know there is an ocean under that icy crust. There are plumes of water coming out of the cracks in the south polar region. There's orange gunk all over the surface – what the heck is that stuff? Huge questions about Europa – it is clearly our next step. We have [also] flown the Cassini spacecraft through the geysers erupting off [Saturn's moon] Enceladus – we know there are organics in those water plumes but we don't know how complex those organics are. So here we have three really rich targets.

Is Nasa going to send humans to Mars just to show that it can?

Well, I'm biased because I'm a field geologist. Humans can actually read a landscape, go through a lot of rocks – crack them open, throw them, pick up the next one. Rovers are great, they do amazing science, but it is a lot more tedious process – they go much less far than a human can cover in a day. Having humans on the surface is how I think we are going to be able to demonstrate totally conclusively that life did evolve on Mars.

There is a lot of talk about settling Mars. Will Nasa be bringing its astronauts back?

We would definitely plan on bringing them back. We like to talk about pioneering Mars rather than just exploring Mars, because once we get to Mars we will set up some sort of permanent presence.

Given Nasa's shuttle programme ended in 2011, are the astronauts going to have to hitch a ride?

We are working right now to return our capability of launching astronauts from the US through a programme we call "commercial crew". Right now there are three companies that are still interested in developing the capability to launch humans from US soil. We are also, at the same time, developing our own rocket called the "space launch system", which is a new Nasa rocket that will be a heavy lift vehicle that will be able to get humans out to the lunar vicinity to do this asteroid work, and then it will eventually have the capability to get humans on the path to Mars.

I heard there are plans to send humans to an asteroid that has been kidnapped and put in orbit around the moon. Seems pretty radical …

We are actually looking at two different mission concepts and trying to decide between them. One would be to find a small asteroid – so less than 10 metres across – basically encase it in a bag and bring it back with us. That enables us to test a type of propulsion system called solar-electric propulsion that we would need to use to take large amounts of cargo to Mars. The other option is to go to a larger asteroid and grab a boulder and bring the boulder back. All of the asteroid mission is actually testing capabilities and technologies that we need for the Mars mission.

Isn't there a risk that we will contaminate Mars?

It's a huge concern. First, of all you wouldn't want to bring any weird microbes from Mars to the Earth that could potentially be harmful to people here. In the future when we have Mars samples come back, they will go through an incredible procedure basically equivalent to an ebola level quarantine facility to make sure they are not going to contaminate Earth. Then there is contamination of Mars. We are looking for life on Mars so we don't want to carry microbes with us, "discover them" and declare victory. All spacecraft that go to Mars go through an incredible level of decontamination, they get swabbed all the time for microbes before they leave – also for spacecraft that go anywhere near Europa, anywhere near Enceladus, because we are really concerned about contaminating these watery worlds. Obviously when we send people, it's going to be a huge concern. We're kind of dirty things so keeping Mars uncontaminated at that point is going to take some work.

You were principal investigator on Titan Mare Explorer (TiME), a "boat" designed to land on the hydrocarbon seas of Saturn's moon, Titan. Has that idea been sunk?

It was like a little floating buoy that would make measurements, not that different from what ocean buoys here on Earth make. We made it through the final round of a competition and then got defeated [in 2012] by a mission to Mars called "InSight" that's going to measure seismic activity on Mars. The [TiME] has now been turned over to one of my colleagues – a guy named Ralph Lorenz at Applied Physics Lab – so what happens to the mission in the future will be up to Ralph.

Is a tight budget compromising Nasa's position as a leading space agency?

We have a really vigorous space programme with the budget that we have, and we've actually gotten extremely favourable budgets in the last few years. So I feel like we are in great shape.

So having a tight budget focuses the mind?

I think it focuses your mind on priorities and, frankly, I also think it fosters innovation. I'm not out there asking for budget cuts to create innovation, but on the other hand Nasa's budget is always going to be limited – it is one of many priorities of the US federal government. In that limited-budget situation we want to do amazing things so what we need are innovations – using technology in creative ways, approaching problems sideways. That's why we need [a] diverse workforce – you need people coming in with all kinds of backgrounds, multiple points of view, to look at problems sideways.

How does Nasa view the space race between India and China?

I think it is really exciting when we see how many countries are coming into space programmes. When you look at the global exploration roadmap – this path to Mars – we have 12 countries involved in that. These things we are trying to do are hard, going to Mars is hard. It's not a US thing, it's not a US and Europe thing, it's a worldwide effort to try and accomplish these things.

All these missions create space junk – is that a problem?

We move the international space station (ISS) every year, several times a year, to have it avoid debris in space so it's certainly something we keep an eye on.

Is there any doubt about the future of the ISS given tensions between Russia and America over the Ukraine situation?

We have excellent relationships on the working level with the Russians. We have not received any official notification that anything other than what is occurring now is going to occur. Our feeling is Russia has been a great partner on the ISS, and we hope that will continue.

Do you have a Nasa space pen?

I don't, actually. We get little badges, that's about it.