11 reasons we haven’t found aliens22/07/2020

It’s one of the first big questions someone learning about space, especially a young scientist, will ask: Why haven’t aliens visited?

This article contains a lot of speculation based on the ideas of leading scientists. At any time, we could discover a new scientific fact or idea that will completely change the whole way we think about the cosmos. However, this is a summary of the most popular ideas so far.

Why do we think aliens would exist?

This is a good starting question. The reason many scientists think aliens – that is to say, life like the animals on Earth, but on other planets – must exist is because of probability. Even if they’re extremely rare, the universe is so big, and there are so many planets like the Earth, that it seems reasonable to assume that extra-terrestrial (alien) life will have evolved somewhere. In fact, if the universe is infinite, then they must have!

Aliens may have evolved like animals – alive and complex, but not advanced enough to try contacting our planet. When we talk about aliens that we think are like us, we describe them as “intelligent life”.

We don’t think aliens exist in our solar system – we’ve explored our planets quite closely, and haven’t found a shred of evidence. While it’s possible we may discover something unexpected, most scientists work off of the assumption that we need to look elsewhere for our neighbours.

How would intelligent life contact us?

There are a number of ways that aliens might get in touch with the human race. They could visit Earth in spaceships, much like in movies.

Or, if they’re anything like us, they might send space probes, just as we have sent rovers to Mars or satellites to Jupiter and Saturn. There are a couple of types they might use. A “Von Neumann” probe uses resources it finds to replicate itself – in a few years you might have a whole flock of them reproducing across a solar system. A “Bracewell” probe, meanwhile, is sent out into space and designed to talk to aliens on behalf of whoever designed it.

The Voyager 2 probe from Earth took forty years to leave our solar system; it’s a long way from discovering any new worlds yet.

Alternatively, they may try to get in touch by sending radio signals. The important thing to remember is that space is big; even if aliens orbited the closest star to us, and travelled at the fastest speed allowed by physics, it would still take them four years to reach us.

For that reason, they may try to send us a radio signal instead. An alien civilization wouldn’t really be able to gain anything from sending us a radio signal. It’s just a way to say “hello!” to us from a huge distance. They may try to describe themselves, or share some of their knowledge or history, depending how complex the signal is.

The “Very Large Array” in New Mexico.

The organisation SETI (Search for Extra-Terrestrial Intelligence) exists for this reason. They listen out for signals from space using huge satellite dishes. Occasionally, they send out signals from Earth too – us saying “hello!” to anyone who might be listening. We haven’t heard anything yet, but who knows what the future may bring?

The Fermi Paradox, and its solutions:

Italian-American physicist Enrico Fermi pointed this out in the 1950s. There are half a trillion stars in our galaxy alone, and billions of galaxies with similar numbers of stars throughout the universe. Many of these stars have planets that would be suitable for aliens to live on; water, a good temperature, a similar size, and so on. So why haven’t they got in touch?

There are a number of possible solutions that have been put forward over the years:

They might not be clever enough

It may be the case that even though alien animals evolve in many places, none become intelligent enough to build things like radio telescopes; or even if they have, they simply haven’t thought of the idea yet.

Alternatively, we might not be clever enough. After all, we’re assuming that aliens will try to contact us using radio signals. However, they might have discovered a new way to communicate across the universe – and assume we’re using that too.

They might not be loud enough

The reason we think we should be able to hear alien civilizations is because we use radio signals, which leak out into space. We think they probably use the same. However, as a species, we have been moving towards other, “less leaky” ways of talking to each other, such as fibre optic cables. Perhaps aliens have been doing the same, so very little noise is coming from them; imagine trying to work out what song someone was listening to if they were using headphones across the street.

They might not have enough resources

There are many times when we have discovered a new barrier to exploration of space – for instance, the speed of light. It may be that we have simply underestimated the amount of material it takes to effectively get in touch with another world, a bit like not having enough credit on your phone to call your parents.

Theoretical models for launching Von Neumann probes involve mining Mercury, shown in this image from, for resources. Perhaps alien civilizations don’t have planets like Mercury at their disposal.

They might have been destroyed by natural disaster

The human race is bombarded by floods, earthquakes, tornadoes and hurricanes every day. It’s possible that aliens have been wiped out by natural disaster – or even destroyed by a meteor, like the dinosaurs.

They might have been destroyed by themselves

Nuclear war, demonstrated in this image by a mushroom cloud, is one of the more dramatic events that might lead to a species’ extinction.

Some thinkers have proposed that aliens might be doomed to destroy themselves when they reach a certain level of advancement; and with climate change, nuclear weapons, and discrimination on our own planet, you can see why. Don’t panic, though – it’s equally possible that that isn’t true, and that alien species live for an extremely long time!

They might live underwater

Despite so much of our planet being water, our planet’s 32% landmass could theoretically be unusually large. Perhaps on other planets, it’s usual for more or less the entire surface to be covered in water, and aliens haven’t developed features that suit space travel, such as hands and large brains.

Alternatively, perhaps alien intelligent mostly occupies subsurface oceans, such as those theorised to exist under the icy surface of Europa. Radio signals would struggle to escape these surfaces, and civilizations would effectively be invisible. They would, however, be largely protected from impacts and stellar radiation.

Jupiter’s moon Europa is theorised to have subsurface oceans. Though we’re sure that life like ours doesn’t exist there, it’s possible single-celled organisms or even small animals have managed to evolve under the protection of the ice!

They might live on too big a planet

It’s already difficult to accumulate enough power to get off of Earth. If aliens live on a bigger planet, they might not be able to escape its larger gravity. That wouldn’t prevent them from sending radio signals, but it would mean they couldn’t travel in a spaceship or send a space probe.

They might have deliberately left us alone

The “zoo hypothesis” is the idea that aliens have left us alone on purpose. It’s like how when people explore other countries, they are asked to leave the animals alone, and not interfere in their ecosystems. However, it would only take one species of many to change their mind for this to break down, so this seems unlikely.

They might just not want to meet us

We assume that because we want to contact aliens, they’ll want to contact us. But perhaps they don’t like other planets as part of their culture. Perhaps they don’t want to colonize or explore elsewhere in the way that we do. Perhaps they don’t even have scientific curiosity.

We might be too young

We’ve only been broadcasting radio signals since the very end of the 1800s. We might not have made enough of an impact on the universe to be detected yet; we’ve done the cosmic equivalent of clearing out throats before the speech begins.

We might be extremely rare

This is Professor Brian Cox’s theory, and one I find convincing. The process of evolution is extremely complex, and to some extent relies on chance. For that reason, intelligent life developing in the way we did may be extremely unlikely; perhaps as little as one-per-galaxy. While there may be the slim chance of picking up on communication from them, we’d never be able to visit due to the literally astronomical distances involved – it would take many millions of years at the very least.

So which is the answer?

All of the ideas here necessarily make a huge number of assumptions about the way an aliens species would communicate, operate, and evolve. With no evidence available to tell us about aliens or their absence, we cannot be sure why we haven’t met aliens yet. If they don’t exist, that’s a reminder how special life on Earth is. If they do, it would be extremely exciting to communicate with them and perhaps learn more about the cosmos.

Either way, the very idea of aliens means that we should always try to keep learning, whether to protect our own species or discover new ones.

See Jupiter (CosWatch Blog 2)08/06/2020

Welcome to the second of Fun Science‘s CosWatch blog posts, which you can read through with your young scientist and learn how to see Jupiter.

What is CosWatch?

There’s so much to see in the night sky! You may have seen Brian Cox on TV describing the “wonders of the universe”, or Carl Sagan talking about the “awesome machinery of nature”, and they’re absolutely right. But while huge rockets and observatories can help, space isn’t just for people with expensive equipment. You can see amazing things from millions of miles away from your very own back garden. Each week, I’m going to talk about one of these incredible objects, and how you can find them.

This amazing shot of Jupiter was taken with the Hubble Space Telescope that orbits the Earth.

This time, we’re going to be talking about how to see Jupiter, the largest planet in the solar system!

Tell me about Jupiter

Jupiter is the fifth planet from the Sun, and takes just under twelve years to go around it. It is a gas giant; unlike our planet, which has a solid surface and a relatively small atmosphere, Jupiter is almost nothing else but atmosphere. Like all the gas giants, it has rings, though unlike Saturn’s, they’re very faint.

This amazing image from the spacecraft Juno is useful for two reasons; we can see the swirls of Jupiter’s atmosphere, and we can also see the shadow of one its moons!

Jupiter is a powerful planet; it is the third-brightest thing in the night sky after the Moon and Venus, and, despite being so large, it is the fastest-spinning planet, with its days only ten hours long. It also has a huge magnetic field, fifteen times bigger than the Sun’s! You may have heard of the great red spot, which is a storm in Jupiter’s atmosphere that has been raging for four centuries, and is very slowly diminishing. You could fit three Earths inside it, such is its size.

There are many, many moons of Jupiter. The human race has confirmed at least 79, but there could be quite a few more. The most famous are the four “Galilean” moons: Callisto, Europa, Ganymede, and Io. These are much larger than Earth’s moon, and are named after the Astronomer who first spotted them, Galileo Galilei. They have many interesting qualities; Io is teeming with volcanoes because its surface is torn apart by the gravity of the other planets, while Europa may hold life in its Icy oceans, twice the volume of Earth’s!

The Jupiter mystery

A photo from NASA of the four Galilean moons, edited so they sit together. From top to bottom: Io, Europa, Ganymede, and Callisto.

When scientists look at planets that go around stars that aren’t our sun, the largest gas giants – that is to say, the ones like Jupiter – tend to orbit very close to their star. They aren’t quite sure, then, why Jupiter orbits from so far away, past four solid planets. They think a young Jupiter may have collided with several other early planets, then been catapulted back to where it is now – this theory is called the “Grand Tack”.

The eight planets that make up our solar system. What this graph from NASA doesn’t show is at least five dwarf planets and thousands and thousands of other objects, including satellites we’ve made outselves. To get a model of the Solar System, check out the link to Fun Science’s home kit in the notes at the bottom of this CosWatch!

How can I see Jupiter?

As I mentioned, Jupiter is at times the third brightest object in the night sky. This means that, like the ISS, it can be observed with the naked eye, and indeed it has been; people as far back as the Ancient Egyptians tracked its movements across the sky.

However, unlike the ISS, which is simply too fast to catch with most equipment, you can see Jupiter with any telescope or pair of binoculars if you’d like to. You don’t necessarily need any special filters or lenses, and you may be able to see the Galilean moons in your device!

A handy graph from SchoolsObservatory.Org shows UK stargazers how to spot Jupiter, next to Saturn, Mars and the Moon, in the south this month.

You can try to memorise the movements of all the planets, but given that this is quite complicated, I like to use the National Schools’ Observatory, which provides a daily forecast for the UK sky at night. To see Jupiter at the moment you’d need to be up at 2-6am – but there are plenty of times in the year where it is visible much earlier, so don’t be disheartened!

In conclusion:

  • Jupiter is the powerful fifth planet from the Sun, with a huge magnetic field and a fast spin.
  • A gas giant, very little of Jupiter is solid, instead mostly being liquid and gas.
  • Jupiter has at least seventy-nine moons, of which four are very famous. One of these may hold life!
  • Jupiter is in an unusual place for a planet of its size, and scientists still aren’t certain why.
  • You can see it with the naked eye, but get an extra-special view through equipment.

What’s next on CosWatch?

Next time, I’ll be talking about Orion’s Belt. See you soon!


Fun Science recently created a “Planets and Space” home kit, pre-orderable now for only £5.00. Check it out here!

Younger scientists, or older ones with good taste, may want to check out The Magic School Bus Lost in the Solar System in Joanna Cole’s Magic School Bus series to help them remember and learn about the different planets – though note that this book has Pluto classified as a planet, which is of course out of date..