In this episode, Courtney shares a talk she developed for the Science Museum about the planet Mercury, what we’ve learned about it so far and what we have yet to discover.
Find images to accompany this episode on Instagram, @ineedspacepodcast.
Here are a couple of images I wasn’t able to share via Instagram:
- The Structural Thermal Model of BepiColombo at the Science Museum in London
- BepiColombo’s trajectory from the Earth to Mercury via a series of flybys
Intro and outro music: “Ticking Away” by Cranston (used under an Attribution-Noncommercial-Share Alike 3.0 United States License)
Hello, and welcome to I Need Space, the podcast for people who… just need a bit more space. My name’s Courtney, and in today’s episode I’m going to share with you a talk that I originally developed as part of the Science Museum in London’s Summer of Space, which coincided with the fiftieth anniversary of Apollo 11. Do I mean fiftieth? [pause] Yes, sorry, I just had to do some very basic maths in my head there. Just to remind you I do have a degree in Physics.
Anyway… let’s get on with the talk, so, to just introduce again a bit, as I said, I developed this really in the summer of 2019, before you-know-what happened, and I recently… so, I’m talking now in November 2021, I recently started delivering this talk again in person in the Space Gallery in the Science Museum, and it’s been really good. So I have, you know, delivered it both during the day, when there were lots of kids and families and schools, but also I delivered it at the Lates, which is an all adults event and, yeah, had some really great feedback, had a really nice audience… But, I thought, for this first, sort of, proper episode of the podcast, I would just share that talk with you and, yeah, let’s… I guess let’s get on with it.
Unfortunately, obviously, I don’t have a beautiful big sphere that I can indicate some lovely pictures with, but I’ll leave some notes… some links, rather… down in the show notes just so you can have a look at some of these visual aids for this episode.
So, today, I’m gonna talk to you about a planet in our Solar System that we really don’t know that much about. But the thing is, the fact we don’t know that much about it is what makes it really exciting, because it means there’s always gonna be more to discover.
We’re gonna start our journey today at the Sun, the star at the centre of our Solar System. Can you imagine what it would be like to be much closer to the Sun than we are here on Earth? So I can think of three things that would be different. Number one, it will be so much hotter than we are here on Earth, particularly today, it’s a very cold November day. Number two, there would be a very strong pull of gravity. So, the Sun is so massive, it’s so huge that its gravitational force would be pulling us ever closer into the centre of the Sun. And number three, the Sun is very active, there are a lot of reactions going on on its surface constantly. There are these big solar flares, all sorts of other things going on, and when those occur, they tend to create a lot of tiny particles that are really dangerous that are just kind of flung out into the Solar System.
So, that’s what it would be like to be much closer to the Sun, but back here on Earth, if we look at the Sun – obviously we want to use binoculars or we want to use a telescope, both with a special filter so we don’t damage our eyes. (Don’t look at the Sun, kids: bad idea.) Anyway, as we look at the Sun thirteen times every century a tiny, tiny, tiny little shadow will go across the surface of the Sun. That tiny shadow is the topic of today’s episode, and it is the planet Mercury.
Now, Mercury got its name, sadly not after Freddie Mercury, but after the Roman messenger god, Mercury. The reason for that is that it moves across the sky faster than any other planet, so the Romans saw that and they thought, “yes, we are absolutely gonna call that after our messenger god”.
Now, Mercury’s the smallest planet in our Solar System, and it’s the closest to the Sun. Both of these things combine to mean that Mercury has barely any atmosphere at all, because the gravity of Mercury is just not strong enough to hold it in place and you’ve also got that heat from the Sun that’s just kind of boiling it off. In fact, the atmosphere of Mercury is one hundred trillion times less dense than Earth’s, so that’s a one with fourteen zeroes, that’s how many times less dense atmosphere of Mercury is compared to Earth.
Mercury also moves around the Sun very quickly, which means that a year on Mercury is quite short, so it’s about 88 Earth days. But Mercury actually spins on its axis really slowly, which means that a day on Mercury is very long, and in fact a day on Mercury is about twice as long as a year on Mercury which… Whenever I say that, I think it’s kind of hard to get what that means from the numbers, so what, how I like to think of it is: imagine here on Earth, you woke up this morning and then the Sun didn’t set for a whole year and then the Sun set after a year, but then it took another full year to rise again, and that’s kind of what it’s like to be on Mercury, with these very, very long days but these very – relatively – short years.
So, you might expect that Mercury gets super hot because it’s so close to the Sun and it does. It goes all the way up to 427 degrees Celsius, which is hot enough to melt lead, but what you might not expect is that actually Mercury gets very cold as well, and the reason for this is because there’s always, you know, there’s a side that’s facing away from the Sun and because there’s no atmosphere to keep heat in, that side is going to get super cold. So it goes all the way down to minus 173 degrees Celsius, and that is colder than anything that’s ever been naturally recorded on Earth.
So, this is the part of the presentation where I usually ask for a show of hands to see, “who wants to go to Mercury for a visit?”, and there’s usually, like, a couple of people maybe putting their hands up, usually the kids are much more enthusiastic, but luckily most people are very sensible and realize that no, going to Mercury, sending astronauts there, is really not a good idea. And I’ve already mentioned that because of the Sun’s rays, because Mercury’s so small, it’s really difficult to see from Earth, even if we have a special telescope with special filters.
So what this means is that our best bet is really to send an uncrewed spacecraft, so a spacecraft that is just robotic, it doesn’t have any people in it, to go and explore for us. And in fact, because this is such a difficult thing to do, only two spacecraft have managed to make that journey all the way to Mercury. So there was Mariner 10 in the 1970s, and then there was MESSENGER between 2011 and 2015.
So what I’m gonna link in the description is some the visuals that I, when I’m delivering this talk in the Science Museum, I have a beautiful big sphere which has images projected onto it, that I can indicate. Essentially, I start off by showing just Mercury, the sort of grey, crater-y planet that it is. And then what I say is, you know, this is what Mercury would look like to the naked eye, but something that scientists really like to do is to enhance images like this using colour and data to make it a bit more meaningful. And so what I show next is an enhanced colour image of Mercury that indicates the different types of rocks that make up its surface.
Mercury is a rocky planet just like the Earth, and it has a huge iron core in the middle, and this actually causes Mercury to have a magnetic field. That was something that was discovered by Mariner 10 that we actually didn’t really expect, so it’s something that is still kind of a bit of a mystery about Mercury. It’s one of the many mysteries that we still have to solve. And because Mercury doesn’t have an atmosphere, that means that it doesn’t have any protection from impacts, so anything can fly through space and hit its surface. And what this causes is Mercury has a really cratered, very rough surface.
And so you can actually see from this enhanced colour image that there are craters that sort of, they appear very bright white and you can see lines going out radially from the crater, kind like sunbeams almost. And what this is, is, if you can imagine, something like a big rock flying through space, hitting Mercury on the surface, and then rock from the impact is flung out, all across the surface, and you can see that when you enhance the image of Mercury.
And there’s another particularly interesting feature of Mercury, which is plains – as in P-L-A-I-N-S, not planes as in aeroplanes – but these plains are the result of ancient volcanic eruptions on Mercury. So, what happened was, there was these volcanic eruptions, and then lava from these volcanoes sort of spread out over huge areas and created these plains.
And so, one really interesting feature on Mercury is called the Caloris Basin, and what this is, is actually a plain within an impact crater, so, you know, there was clearly volcanic eruption that spread lava through this impact crater. It actually has a diameter of over 950 miles, which is about the distance from London to Copenhagen, so that is an absolutely gigantic crater. It’s one of the biggest in the Solar System, in fact.
And so, next, what we do is we kind of move on to another colour-enhanced image of Mercury, and this is actually my favourite one, so I really hope you check the link in the description to see it. And it’s a topographical map, which means that it uses different colours to indicate different heights on Mercury, different elevations, so, like, the mountains and the craters and all that kind of thing, and I love it because it’s so incredibly, obnoxiously colourful. I like to think of it as a colour scheme that only a scientist could love, because it’s got so much information, but it’s so ugly. [laughs]
So, as I said, this map indicates different heights with different colours so from the, sort of, white, red colours are the sort of highest parts, the mountains, and then the lowest parts are kind of black, going into sort of purple and blue. And you’ll see from the picture that Mercury has a very, very rough surface, as I mentioned previously. And there’s a particular feature that you’ll be able to see that is, I always think it looks a bit like an iris, and it’s on the sort of top half. It’s a very, very pronounced purply-pinky-blacky circle. This indicates that it’s a really deep down area of Mercury, and in fact it’s the deepest crater on Mercury. It is five kilometres deep. So, this crater is called Rachmaninoff because all of the craters on Mercury are named after musicians, composers, artists, creative people like that, and of course Rachmaninoff, the great composer and pianist. So, one of my favourite films, “Brief Encounter”, features his second piano concerto very prominently – definitely recommend that, nothing to do with space, just a really good film. Anyway, so, yes, as I said, Rachmaninoff crater, super deep, again, Mercury just doesn’t have that atmosphere to protect it from those really, really intense impacts from things flying through space.
Now, I’ve told you quite a lot about Mercury so far, but there’s also quite a lot that we don’t know and, as I said, this makes it really exciting, because there’s so many mysteries that we have yet to uncover. And I mentioned Mariner 10 and MESSENGER, which were two probes that have been sent to Mercury previously. Both of these were sent by NASA, in America, but what’s really exciting is that now Europe and Japan are working together to send their own mission to Mercury. So ESA and JAXA, which are the European and Japanese space agencies, respectively, are working together on a mission called BepiColombo, and this is named after an Italian scientist, whose name was Giuseppe Colombo, but his nickname was Bepi, and everyone called him Bepi, and therefore the spacecraft was named after him. I’m actually gonna talk a little bit more about his work in a sec.
So, Bepi was launched in October 2018, and it consists of three parts: two Orbiters which are gonna orbit, as the name suggests, they’re gonna orbit around Mercury, and there’s also the Transfer Module, which is the bit that, kind of, has all the power to get Bepi to where it needs to be. So you can’t just have the Orbiters, you need that Transfer Module as well, to get it up into Mercury orbit.
So, when Bepi is finally orbiting Mercury, it’s going to do all sorts of things, really, so it’s gonna study Mercury’s magnetic field, that mysterious thing that we discovered but still don’t understand. It’s gonna look at that atmosphere of Mercury, that really, really thin atmosphere that we just don’t understand. We always thought that Mercury just didn’t have an atmosphere, but somehow it does, and that’s really interesting. And Bepi’s also gonna look at things like what Mercury is made of, and how it was formed originally.
So how do we get to Mercury? We could just fly straight there, you know, it seems like a good idea. But the problem with that: if we were to fly straight from the Earth, what would happen is we would fly straight into the Sun, because the Sun’s gravity is so strong, it just loves pulling things into it. And that’s actually one of the reasons why there haven’t been many missions to Mercury, because it’s so challenging to maintain an orbit around Mercury, because of the Sun.
So what Bepi is doing instead, using an idea from the scientist Bepi Colombo, is it’s using a method where, instead of flying in a straight line, it kind of does loads of spirals. So, it’s sort of, if you imagine back in 2018 Bepi set off from Earth, it did one huge orbit around the Earth, called a fly-by, and then what it did was it kind of started spiralling inward, so it met up with the planet Venus, and it did two huge circles all the way around Venus. And each time the past one of these planets, it’s sort of borrowed some of the gravity to kind of boost it along its way, along the way to its final destination which is, of course, the planet Mercury.
But it’s not exactly where we want to be, because Bepi needs to get into the correct orbit to do all of the great science that we want it to do. And so it’s going to finally meet up with Mercury, but before it can start doing what it’s designed to do it needs to do six flybys of Mercury. And in fact, as I’m talking, last month – October 2021 – BepiColombo completed its first flyby of Mercury, but it’s got five more to go before it finally reaches where it needs to be, that final orbit. And so it’s not actually going to reach that orbit until 2025 so, in total, that is a seven year mission from launch to finally getting to start doing what it needs to do. I mean, that’s not even considering all the years of planning beforehand.
So you can probably see, it takes a lot of patience to be a space scientist. But, hopefully, with everything I’ve told you so far, I’ve convinced you that the wait is absolutely going to be worth it.
To finish the episode, I’m gonna come back down to Earth, which of course is where all space missions start. And if we’re sending something into space, generally, we can’t go up and fix it. If something’s in Earth orbit, sometimes we can send up an astronaut on the International Space Station to fix it, but that’s not guaranteed. And, of course, if something is on its way to Mercury, like Bepi is, we can’t send something up to fix it, that’s just not doable.
So it’s really important, if we’re going to send something into space, that we do a lot of testing beforehand, to ensure that it’s going to be able to survive and do what it needs to do once it gets into the harsh climate of space. And, of course, Bepi is no exception, particularly because going near Mercury means it’s going to have to contend with both really hot and really cold temperatures. And something else that Bepi and other spacecraft have to deal with is what happens when they’re launched on a rocket into space. Because, when this happens, if you think about astronauts, when they’re sent into space, they have to go through all these tests to check that they can withstand the forces, the vibration that’s gonna occur when that happens. And with a spacecraft, it’s similar, you have to check that- okay, your spacecraft isn’t going to have an upset stomach, but it has all sorts of delicate equipment in it, and if that equipment is going to be broken by really heavy vibrations then, again, you’ve wasted billions of pounds, decades of work, because you haven’t tested.
So, of course, Bepi went through all these tests before it was launched. So what the scientists and engineers who worked on Bepi did was, they built a model of it so, an exact replica, and they use this model, which is called a Structural Thermal Model. And you can tell from the two parts of that name, structural: they used it to test whether the structure would hold up to those vibrations that occur when a spacecraft is launched. And thermal: they tested whether the spacecraft could survive being heated up really, really hot and really, really cold. So, they did these tests here on Earth, spent years and years and years on this testing and then, once they were satisfied that in fact Bepi would be able to survive those conditions, they were confident to finally send it into space to complete its mission.
Now what’s really exciting, if you live here in London, is that this Structural Thermal Model is in the Science Museum, and it’s on the ground floor, it’s near the IMAX, so you can actually go and see it, and learn a bit more about Mercury and about BepiColombo. It’s really great when I’m delivering this talk in the Science Museum, because it means I can show people straight to another thing that takes them through some other galleries as well.
I’m not sure how this is going to have translated to a podcast, but I just, honestly, just really wanted to record something to kind of help me on my way to this podcast experiment that I’m doing. So I’m gonna end similarly to how I end my Science Museum talk, by just saying thank you so much for listening. I won’t tell you to enjoy your day in the museum because you might not be in a museum, you might be on the treadmill, or doing the washing up, or… I dunno, what else do people do when they listen to podcasts? Who knows? But, you know, whatever you’re doing I hope you’re having a lovely day and I will speak to you soon.
I Need Space is written, hosted and edited by me, Courtney Williams. Links to the transcript, images and the music I’ve used in this episode can be found in the description. You can also visit my blog, astrocourt.space – it’s like “astronaut”, but it’s “Court”!
Thanks again for listening, and don’t forget to give yourself some space.
[Outtake] So it goes all the way down to minus 173 degrees Celsius and that is colder than anything that’s ever been naturally recorded on Earth. Sorry, I’m giving Celsius, if you use Fahrenheit… if you’re in America, sorry, you’re just gonna have to Google it, just welcome- welcome to the rest of the world’s struggles, guys. I’m sorry, that might have been needlessly aggressive. Moving on… [Laughs]