"What does Space sound like?" and other impossible to answer questions from 5 year olds.

This is an article about space, in the context of questions a 5 year old might ask (and some of which 90 5YOs have asked me). It’s also an ode to the achievements of science and engineering, and the excitement of exploring the unknown. I’m publishing it in honour of John Young, NASA's most experienced astronaut who passed away a few days ago (Godspeed, John). As well as the upcoming launch of SpaceX’s Falcon Heavy, which is planned to blast off in a few weeks from the same launch pad that was used by the Saturn V moon rockets (39A at Cape Kennedy). Amazing space.    

It seemed like a good idea. Initially.

LAST YEAR, my wife signed me up for a visit to my daughter’s primary school. Their term topic was space, and she thought that as a trained aerospace engineer with a passion for exploring the unknown, I’d be perfectly suited to do this sort of thing (and make my daughter proud in the process).

While I was honoured by my wife’s trust in my knowledge (at least of space), I had an instant flash of that scene from Kindergarten Cop where Arnold Schwarzenegger - playing a tough hero cop, what else – takes on an undercover role and walks into a pre-school with a room full of, well a few-year olds, and comes out crying (if you’re a millennial, don’t worry; if you’re Generation X, you will know exactly what I’m talking about).

You know, THAT scene.

On the day itself, it turned out I wasn’t just talking to my daughter’s class, but all the children in Year 1. Me vs. 90 five-year olds. What could possibly go wrong?

The children were allowed to ask me anything (an early-development AMA, for sure), and so it went...

1. How big is the universe?

Ok, we're starting with the "basics". Right... Well, the short answer is, we don't really know. But it's big. Very big! Infinitely big, possibly... Now, how do you explain infinitely big to anyone?

Let's look at this in a slightly more scientific way: we know that the universe is about 13.8 billion years old (How do we know this? By measuring the cosmic background radiation and the expansion rate of the universe, but that’s another story). Given that nothing can travel faster than light (at 300,000 km/s, which is very, very fast), the maximum distance between the centre of the universe (if it has one) and the edge would be 13.8 billion light years. In other words, the universe would be about 28 billion light years in diameter. Or at least, the "observable universe" would be, as we don't really know if anything is beyond what we can physically see.

That's a lot, but we also know that the universe is expanding (because of an effect called red shift, which can be compared to the change in pitch of the siren of an ambulance passing by), and that it has done that ever since the big bang. So, add in the stretching effect, and the number that scientists today regard as the approximate size of the universe is about 46 billion light years. But that's merely from the Earth to the edge of what we can observe (to a large extent with the Hubble telescope out in space, but there are also others). Which means that the universe is about 100 billion light years across! Now that's big. Really big.

How can you even start to imagine how big this is? Try this - if our entire solar system was the size of a grain of sand, the Milky Way alone would be 1,000 times bigger than St Paul’s cathedral in comparison. And if the entire Milky Way instead were the size of a grain of sand, the universe would be about the size of St. Paul’s (Want to experience for yourself what it's like to scroll through our solar system? Click here)

2. How many moons are there in the solar system?

I totally failed this one. Totally. Like, if there was a score of 1-10 for how well I answered this question, I would have been at -1. Seriously. Turns out I’m more interested in deep space than our solar system, which I consider largely explored and not very exciting overall (colonisation of Mars notwithstanding, but even that is just a very tiny step towards deep space). Yeah sure, I knew other planets had moons, too, and some planets have several moons. And there’s Europa (but was that Saturn or Jupiter?) and Ganymede (probably Jupiter? – seems to have all the best moons out there). And some moons are larger than Pluto, some maybe even larger than Mercury. But that was about it.

Little did I know.

The kids, however, totally aced this one. They seemed to know everything there was to know about our solar system. They even had a SONG for it (which they didn’t hesitate a light second to sing for me while I was on my way out).

Did you know there are a whopping 181 moons in our solar system?! And we’re still finding new ones. I could not believe it. Jupiter leads the pack with 67 moons, closely followed by Saturn with 62. Our single companion seems like it’s lost in space. Literally. Ok, so Venus has none at all, which is a bit weird and hard to explain. Mercury also has none, but then again it's so close to the sun that any moon it might have had in the past would have most certainly been more attracted by the giant ball of fire right next door, and ended up plunging into it at some point. That's gravity for you.

Some of these moons are truly amazing, and we should one day be able to mine them for resources, or even settle on them. After all, there are only three potentially inhabitable planets in our solar system, but many more moons. Titan (a large Saturn moon) even has its own atmosphere! Wowzers! Note to self: moons = exciting.

Result after round two: 5YOs: 1 – Ben: 1.

3. Why is Pluto not a planet?

Gawd, this wasn’t going well. Did you just say Pluto was not a planet? Who said that? Last time I checked, it still was one. And surely I learned ?Mein Vater Erklaert Mir Jeden Sonntag Unsere Neun Planeten“ when I was a child. That’s P für Pluto right there at the end of it.

Oh well, things move on, and so does celestial science. Pluto, which was only discovered in 1930 by Clyde Tombaugh, has always been special in some ways due to its smallish size and tilted orbital plane compared to the rest of the solar system. And in 2006 the International Astronomical Union ruled that Pluto would now be referred to as a “dwarf planet”. Which reduces the count of (regular) planets in our solar system to a mere eight. Their reasoning? Pluto doesn’t “dominate” or "clear" its surroundings, e.g. by attracting other, smaller objects (even though it has a whopping five moons... hmmm...). I knew there was some discussion about Pluto not being a planet anymore, but I didn't know that this was the reason why. You really never stop learning.

While this decision hasn’t been undisputed (call me a Plutoist!), as a a matter of fact there are several other minor-planet-size objects in the solar system, some of which even larger than Pluto – take Eris for example, discovered only in 2005. But this didn’t keep the New Horizons spacecraft from doing a close fly-by last year, and take some amazing shots. How’s that for fame, old Pluto?

Did you know?

Over the past few hundred years, more than 100 planet-like objects were identified by astronomers, including all sorts of large asteroids, many of which reside in the two asteroid belts around the sun (one belt is located between Mars and Jupiter, the other one past Pluto). Over time they were downgraded from planet status, in much the same way as Pluto.

5YOs: 2 – Ben: 1.

That scene from Kindergarten Cop kept flashing back now...

4. How did the astronauts get into the moon rocket?

The kids must have sensed my growing exasperation and gave me an easy one. Thanks children, thanks. I love you.

So yes, this one is straightforward. Sort of. Via an elevator, of course. But do you know why they had to get to the very top of the rocket to get in? Because the bottom is packed with engines and fuel, ok. But why? The kids knew the answer to that (see 5), incredibly.

Did you know?

The Vehicle Assembly Building (VAB) where the Saturn V rocket was put together before it was moved to the launch pad (the one with the very tall elevator), is still the largest single story building in the US at 150 meters high. And its doors are the largest and heaviest sliding doors ever built. Now there’s a thought. And you thought elevators were easy stuff.

5. Why do rockets have multiple stages?

Ah. We’re getting to the engineering side of things now. Colour me impressed. I did sort of expect this question, but still it’s quite advanced stuff for 5YOs, don’t you think. Good stuff – if they continue on this path they’ll be calculating Mars approach trajectories before they reach double digits in age.

The answer has a lot to do with gravity. The Earth’s gravity in this case. It’s incredibly hard to lift things off the ground, let alone a Saturn V rocket (the one that took the astronauts to the moon and back) which weighed 3,000 tons, or as much as 600 Asian elephants! And all that to lift a mere 50 tons of useful stuff and the astronauts (together called the payload) into an orbit around the moon! So you can see that most of the weight of the launcher is essentially fuel. And fuel tanks and engines. Most of which resides in the first stage that gets you out of the strongest gravitational pull closest to the Earth’s surface. Then there are two more stages before you make it to the moon.

But why not keep the stage and bring it back when you return from your trip? Turns out this is a really good question, but one which for decades people didn’t really consider. Until a certain Elon Musk came along and fixed it by building a rocket that would send the spent stages safely back to Earth for re-use. And it works! But more on this another time.

The burnt-out stages are traditionally shed – either into the ocean, or into space. The reason is that weight and fuel are paramount in space (even in zero gravity, yes), because you need to be able to manoeuvre and land on / lift off from other celestial bodies. Carrying extra weight around on that journey isn’t a good idea, so space engineers build spacecraft in a way that they shed any extra weight that’s not absolutely necessary for the mission. And the most efficient way of doing this is, or has been for a long time, by building rockets in different stages.

6. Why did the astronauts leave the buggy on the moon?

I did not expect this question, but it makes total sense. The moon buggy looks like it’s so useful and a lot of fun to drive. So surely you’d want to hang on to it when you go back and not leave it on the moon?

Well, we already know it’s important to save weight when travelling through space, as more weight means you have to carry more fuel, which in turn means bigger rockets, more costs, and - let me tell you - generally more complexity (and risk) overall. So the buggy had to stay behind to allow the astronauts to return safely to Earth in the little module at the very top of the massive Saturn V rocket. Also, it’s a moon buggy, which is not going to be much use on Earth. But yes, it would be fun to drive around in one I am sure. Ideally on the moon!

However, the astronauts brought hundreds of kilograms of rocks and soil back from the moon (and left a lot more of their equipment behind, like the lower stage of the lunar module, parts of their moon suits and so on). They had just about enough fuel to do this, but it was tight every single time.

7. What sound does space make?

I did not expect this question, at all. I should have though (these are 5 year olds, after all), but I was a little dumbfounded when someone asked this. Then I remembered my astronaut training. Sort of.

So, we can assume space is a vacuum (that’s almost true, apart from a few hydrogen atoms and, you, the planets and comets and stuff – but 99.9%+ of it is empty space). And as we know, sound needs a medium to travel from the source (say, your friend) to the recipient (say, your ear). Here on Earth that medium is the atmosphere; in other words basically the air we breathe. In space, there’s nothing. No air, no nothing. So there is also no sound. Sad, but true.

Imagine you were an astronaut taking off your helmet on a spacewalk to hail a fellow team member who’s out fixing a solar panel on the International Space Station. Never mind the lack of oxygen or the freezing / scorching temperatures, but stay with me for a moment here. If you were able to shout at them, they wouldn’t hear anything, even if they were only, say, a meter away from you (and with the helmet off and not frozen / scorched, obviously).

Did you know?

There is something in space however that we can measure, and that is a form of energy. It’s everywhere, and it’s very faint. It’s called the Cosmic Background Radiation, and you can think of it as a left-over form of radiation - or noise - from the Big Bang. It’s very faint because the Big Bang was so long ago (13.8 billion years ago, remember?). But we can still measure it. If you think of sound on Earth as a form of energy, then this is the “sound” you will be able to hear in space.

Incidentally, this background radiation is also responsible for the temperature in “dark” space (ie, not in a spot with direct or indirect solar radiation), to be a few degrees above absolute zero (-273 degrees Celsius). Which is how cold it is everywhere in space far from a hot object like a sun, or one that is radiating heat at you. But that’s another story, for another time...

I will never forget that song about our solar system though. Simply brilliant. Thank you!