How do toads predict earthquakes?

Chris Smith put this to Marian Holness, geologist from the University of Cambridge...

Marian - At first sight, it sounds like a really crazy question. But in fact, it's a subject of a really serious research effort particularly in China and Japan because everyone is very, very anxious to know when the next earthquake is going to go off. And so, people are exploring all avenues. In fact, a very, very long time ago, 373 BC, there's the first report of strange animal behaviour immediately preceding an earthquake. This is an earthquake that wiped out really important Greek city of Helike. Apparently, five days before the earthquake, rats, weasels, centipedes, and snakes all left the area and ran away. And so, ever since then, people have thought that animals know much more than we do about whether earthquakes are on their way. But the question is, how on Earth do they do it? there's a very obvious way of doing it for animals particularly those that live in burrows and that's because when earthquakes go off, they send off two types of waves. There's P-waves which are like sound waves and there's S-waves which are more like light waves. The P-waves come much, much faster than the S-waves. If you're the sort of animal like gerbils for example that communicate by thumping, you're really, really tuned to vibrations. So you can hear these things coming before humans can and that's when you leave your burrow because otherwise, it will collapse in on you.

Chris - You're sort of suggesting then that the animals are picking up on either the earthquake itself or maybe some of the rumbles that presage or predate an earthquake because earthquakes sometimes giveaway signature rumbles before they actually move, don't they?

Marian - Yeah. They'll be picking up on pre-shocks but any earthquake will send out these two sorts of waves - one of which comes much faster than the other and they'll pick up these fast ones. Earthquakes are caused by the movement of faults and faults are generally all sort of jammed up and they're accumulating strain, and then suddenly the strain will be too great and they'll sort of go and pop open. But as they start to slide, it's going to affect the water table. So, you get water movements changing, you'll get springs stopping flowing, or starting flowing. So the toads might have been picking up on something to do with water, with humidity in the soil, something like that but picking up something five days before, now that's a real mystery.

Chris - So there are lots of potential environmental clues that they could be picking up on. Thank you, Marian.

Kat - It's totally fascinating. Andrew, here's a query for you. We've got a question from (Alisna Arun) asking how signals sent from space probes get back to Earth. Do you know it's about to reach Jupiter? We had loads of those amazing pictures coming back from the New Horizons mission that's out like Pluto. How are they getting back to us?

Andrew - Well, the simple answer is it's just a radiowave. It's a radio transmitter on the spacecraft that sends a signal to Earth.

Kat - So, it's basically like a snapchat.

Andrew - Kind of. The thing is.

Chris - Instagram.

Andrew - If only it were that simple. The thing is that the transmitters on these space probes, they're so low power. The power requirements of the spacecraft are just a few watts so that the transmitter is only beaming a tiny, tiny weak signal back to us. And so, it's literally sending the data back a bit at a time. So, you don't get a whole picture at once. You get each pixel one by one. And so, you have to build up the pictures over time. And that's why it takes so long for the data to get particularly from that New Horizons probe out of Pluto.

Chris - Sounds like my home internet connection. (Tucker Oilinkee) has twitted @nakedscientists and says, "What kind of camera can take photos of Pluto where light is very limited?" he wants to know things like the sensor, the ISO rate in the proper time, the f value if you know it.

Andrew - I'm afraid I don't know the details like that, but it is literally a digital camera. That's what it is onboard these spacecraft taking pictures in low light levels, perhaps in the infrared rather than visible light. But yeah, it's working just like the camera on your phone. But working in those low light levels.

Kat - It is incredible to think that those amazing pictures that we saw of Pluto, the sort of the heart shaped on its surface, one pixel at a time over thousands and thousands of miles.

Andrew - I know. It really is incredible. We tend to think, "Oh, it's just a space probe out there in the solar system sending back the pictures" but yeah, it's taken years to get there. And even the signals themselves will take hours to get back to Earth.

Chris - It's 6 billion kilometres to Pluto. Light goes about a billion kilometres an hour so it's 6 hours for all the messages to come out. Marian.

Marian - So, how long is it going to take for all the data to eventually get back to us?

Andrew - Well, I guess they'll keep going until the power runs out really. Yeah, it could be many, many months yet.

Kat - So in many ways, it is like a mobile phone. You just keep taking those photos, keep posting them on instagram until your phone dies.

Andrew - Exactly.