As planets go, Mercury is a world of extremes – and one that doesn’t always make a great deal of sense. Its iron core is absurdly and inexplicably huge. Despite its searing temperature, it has ice trapped at its poles. It is also pummelled every day by wild solar storms – the likes of which Earth only experiences once a century.
Suzie Imber hopes she can help us get to know the planet a little better through her work as a co-investigator with Europe and Japan’s BepiColombo mission, which last week made its final and closest flyby of Mercury, helping it to slow down before it enters orbit in 2026. Imber, based at the University of Leicester, UK, is an expert on space weather and says her studies of Mercury could help us prepare for the worst solar storms here on Earth. She was also, in 2017, the winner of the BBC’s Astronauts: Do you have what it takes?, a gauntlet that pitted contestants against the rigours of space travel.
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Imber told Â鶹´«Ă˝ why she is so excited about sending a mission to Mercury, what we hope to learn about this intriguing planet and whether she might one day venture out to the final frontier herself.
Jonathan O’Callaghan: Why are we returning to Mercury now?
Suzie Imber: There are loads of reasons. From a high-level perspective, it’s a pretty unexplored planet. We’ve had three flybys and one orbital mission – NASA’s MESSENGER, which orbited between 2011 and 2015 – but the more we learn, the more questions come up. We think there’s water ice deep in the permanently shadowed craters near the poles, but we don’t know how it’s still there. There seem to be some mystery substances called low-reflectance materials covering this ice; these appear to be carbon-based, but we don’t fully understand them. It’s also the only planet we know of that we think has contracted considerably.
You’re saying Mercury has shrunk? Tell me more…
The MESSENGER mission discovered these interesting surface features called lobate scarps and that we don’t see anywhere else. We think they formed as the planet’s surface contracted in size, creating this bunching up of the surface rock. As far as we know, Mercury contracted in diameter. It doesn’t sound like much for a planet nearly 5000 kilometres across, but it’s quite considerable.
Your own particular interest is in space weather. Why is Mercury so fascinating from that perspective?
When we talk about space weather, we mean the “wind” of particles and magnetic fields streaming from the sun that washes over the planets. On Earth, if the conditions are right, this can cause problems with electrical systems. The worst-case space weather scenarios that we see on Earth – which can damage satellites and knock out power grids – happen once a century. But on Mercury you get extremely powerful solar storms every day. We’re still trying to figure out what that does to the planet. It has a weak magnetic field, and it’s very close to the sun. Is there a direct, observable effect on the surface? We’re interested in whether that could be the case. And if you’re wondering, by the way, there is an aurora on Mercury, but it’s only visible in X-rays coming off the planet.
Will studying space weather on Mercury teach us about similar phenomena on Earth?
The BepiColombo mission consists of two spacecraft; we’ll have one close to the planet and one far away, so that we can get a measurement of the magnetic field close in and then at a greater distance. We’ll see the solar wind, and then a few seconds later it’ll hit the planet. So this will be like getting a view of an extreme example of the solar wind hitting Earth’s magnetosphere.
The physical process that drives space weather on Earth is called magnetic reconnection, where magnetic field lines store energy and momentum from the solar wind, which is then released and results in the aurora that we see. This process is the same on Mercury, but the rate is crazy. We’re trying to understand the fundamental physics behind this solar wind-to-magnetosphere coupling. On Earth, the biggest space weather events happen so seldom that I’m never going to have a chance to measure one – though if one does happen it could be really catastrophic to our electronic infrastructure. So yes, by studying Mercury I’m trying to understand what would happen with a big space event on Earth.
Will the instruments you worked on help us solve any of the big mysteries about Mercury?
They might. The spacecraft has two special instruments, one of which we built at the University of Leicester called MIXS, the Mercury Imaging X-ray Spectrometer. One of these instruments points towards the sun, the other points towards the planet. The idea is that the sun gives off X-rays all the time, and when a solar X-ray hits the surface of the planet, it causes the surface layer of atoms to fluoresce. Our instrument picks up those X-rays and they can be used to tell us about the composition of the surface. This might help us unmask the identity of those mystery materials covering the ice at the poles.
Then there’s this issue about Mercury’s core. We know that Mercury’s core is 85 per cent of its radius. That’s massive; this planet is almost all core! For comparison, Earth’s core is maybe 30 per cent of its radius. Why Mercury has so much core compared with the other planets is a really big open question, so we hope we’ll get more information. One of the ways we’re trying to work out what happened to Mercury is by using the ratio of different elements on the surface, like potassium and thorium, because this could help us deduce the collision history of the planet – in other words, what kinds of things have hit it in the past. That might help us figure out why Mercury looks the way it does.
So do we think Mercury might have been smashed about aeons ago?
There is a that it was originally much larger and some massive collisions early in its life blasted away the outer layers. That would explain the apparently oversized core. But other people suggest that perhaps it looks unusual because it actually formed somewhere else in the solar system and then migrated inwards. It has more metal than it has a right to given its size and location – but maybe that’s because this isn’t its original position. Part of the reason this has come up is because we often see planets around other stars in locations where they cannot have formed – so we know in principle that planets can move and migrate.
Why Mercury has so much core compared with the other planets is an open question
Coming back down to Earth, tell me about competing in the BBC show ? That must have been a wild ride.
I didn’t know what to expect. In one of the tests, we had to take our own blood, and I’m pretty squeamish! Stabbing yourself in the arm is pretty stressful. There was a test to drive a Mars rover, which I massively failed at because I got the rover stuck in a cave. And there was a test where they submerged us in a swimming pool while inside a capsule that we had to escape from. Having a camera on you at all times for six weeks was interesting in its own right. We did over 40 challenges that spanned a huge range of disciplines, from psychology to fitness, teamwork to logical problem solving. We never knew what was coming and there was no feedback. It was a crazy experience!
But you won! How did it feel?
It was amazing. I wasn’t the best at everything, but I won because I was a fairly steady pair of hands. At the end, I was convinced someone else was going to win. We were standing in a row and they announced my name, and I just absolutely froze. My jaw dropped and they had to film it again. I kept thinking I didn’t do well in the tasks, so that gave me an interesting insight into my own psychology.
Would you go to space now?
If someone wants to buy me a ticket, I’d definitely go.
You’ve also been a high-altitude mountaineer for many years. Where have you climbed?
When you start climbing, you tend to start with popular mountains because you don’t really know what you’re doing. I started out in the Andes, and then I went to the Himalayas. I realized that I really enjoy complete remoteness, and I really don’t like being in a situation like Everest, where there’s a queue of people going up the mountain. So I started climbing more and more in the Andes.
I hear there was an algorithm involved at some stage…
I have access to a supercomputer here at the university. I asked some colleagues for a digital elevation model of the Andes and I wrote some code that would come up with a list of mountains over 5000 metres. There were dozens of unnamed and unclimbed peaks: there are 1042 mountains above 5000 metres in the Andes. So I started going to climb these unclimbed mountains.
How many have you bagged so far?
About 30 above 6000 metres and the same above 5000 metres. These mountains are difficult to get to and hard to climb, but sometimes we’d get to the summit and we’d find Incan remnants. The Inca had climbed these mountains and built small structures, little towers a metre high, and no one knows why they built them. We weren’t the first to climb some of these after all. We’d get to the top and find the Inca had been there centuries ago, which is really cool.
When did you last climb one of these mountains in the Andes?
A few years ago. Covid put an end to it because there was no travelling. Then I joined mountain rescue as a volunteer, and now I spend a lot of my time living in the Peak District rescuing other people who’ve come to grief in the mountains. I’m putting those skills to good use.
Tell me more about the rescue side of things. It is worlds apart from studying Mercury.
We get called out up to 200 times a year. Last weekend, we had a girl who fell bouldering and almost ripped her foot off and someone who had a serious head injury in a really remote place. I mentioned I’m really squeamish, so the one thing I always try to do is think about the areas I need to improve. I wouldn’t have believed it would be possible for me to deal with injuries like these, but now I’m much more confident. I love my job and I love studying Mercury, but I don’t feel like I’m actively helping anybody. So it’s a really meaningful thing to spend time doing.
