Maggie Aderin-Pocock on asteroid impacts – and how we can avoid them

At the moment, the Japanese spacecraft Hayabusa2 is orbiting around the asteroid Ryugu, while the NASA spacecraft OSIRIS-REx closes in on its target Bennu. 

Both missions have the same aim, to sample the asteroid before returning back to Earth with their precious cargo. While this is not the first time this has been done (Japanese scientists managed it back in 2010), the volume of rock to be returned from the asteroids will be unprecedented. 

Dr Maggie Aderin-Pocock, space scientist and co-presenter on the The Sky at Night, says, 'We've got two missions coming up that are both doing sample returns. So not only are they going to an asteroid and landing on it, but they're also going to bring samples back.'

There are a number of reasons why scientists want to bring physical bits of asteroid down to Earth, despite the incredible complexity it adds to a mission.

Largely, it comes down to the simple fact that scientists will be able to use much more sophisticated technology - and carry out far more detailed analysis - on these samples in labs on Earth.

'The space industry is very good at miniaturisation,' explains Maggie, 'because what you tend to do is take the lab to whatever you're looking at. But that means you're very limited by what you can do.'

'The joy of a sample return is that we don't have to do any of that. Labs across the world will get these samples and examine them in great detail, giving us the best analysis we've ever had of what asteroids are made of. It should reveal a lot about our own origins.'

Asteroids are some of the oldest bodies in our solar system, formed when the planets were only just beginning to come together as the Sun formed at the centre. For the last 4.567 billion years these time capsules have been whizzing around almost unchanged.

This means that asteroids can act as a window into the early solar system. As the origin of most of the water that is currently on Earth, they could even help answer questions about how life kicked off on our young planet.

Simple tech

While both these missions to rendezvous with asteroids involve innovative science, the technology that actually makes up the spacecraft is often deceptively simple.

'Most people think that we're using cutting edge technology and the latest equipment, but generally we don’t,' says Maggie. 'If something came out a month ago, you wouldn't want to put it into space.'

Scientists need to use slightly older technology to be certain that a piece of equipment won't fail.

'When we build a spacecraft or satellite, we generally use equipment that has been tried and tested. You don't want to send out a £300 million satellite that then doesn't work because we didn’t test it enough,' says Maggie.

'We put the satellites through hell, because space is quite a harsh environment.'

Each component is tested on its own, subjected to vacuums, extremes of temperature and vibrations, before the modules are pieced together. 'Once we've built the spacecraft, we then need to know that everything interacts and sits happily together,' says Maggie, 'so we do similar tests  but on a larger scale.'

Impact imminent

It is not just for the esoteric reasons that we need be studying these objects though.

Asteroid impacts are not a rare event. Scientists have predicted that a meteorite between 30 and 50 metres across should smash into Earth on average every 1,000 years. The last one of this size to strike Earth was 55,000 years ago.

'History tells us an asteroid impact is a significant risk,' explains Maggie. 'We know asteroids can have a huge impact on life on Earth - after all the dinosaurs are thought to have gone extinct due to one.

'On Earth we have bigger and better telescopes with some that are designed specifically to look for asteroids, so anything larger than a fist can be tracked. We have the ability to follow these objects over time, because the interesting thing is how they are moving.'

The reason why Bennu was chosen by NASA to visit is because its orbit is so close to our own planet's that the asteroid even crosses it. Yet this is the very same reason why astronomers have been keeping an eye on it.

Every six years or so, Bennu passes within 300,000 kilometres of Earth, closer even than the Moon. That would be fine if its orbit was stable, but we know that Bennu is in fact drifting. This is thought to be down to a phenomenon known as the Yarkovsky effect.

During the day small asteroids absorb the Sun's heat, which at night is then emitted as radiation, this gives the asteroida small boost. This helps explain how the heating of the surface of small, dark objects can subtly shift the rotation and direction in which they are going.

While this is thought to have a limited impact on larger asteroids, for smaller asteroids the Yarkovsky effect can be quite significant. With Bennu it is thought to have shifted the asteroid's position by 185 kilometres over a 12 year period.

The chance that this will cause Bennu to hit Earth remains incredibly slim, but that may not be the case with all Near-Earth Objects.

For that reason, one of the aims for OSIRIS-REx is to study this Yarkovsky effect in more detail. This will allow scientists back on Earth refine their predictions for how other asteroids are moving and which direction they are likely to take. 

Asteroid defence

When it comes to assessing the impact risk of any asteroid, figuring out exactly what orbit it is in and how this might change is critical, giving scientists an advanced warning. When it comes to the potential threat of asteroids, time is of the essence. 

'The sooner you realise it is coming towards Earth, the better,' says Maggie. 'This is because the earlier we know that there is a potential danger, the more we can do about it.'

'If the asteroid is a long way out, for example, then a small push is enough to move it out of the away. But if the asteroid is much closer then a lot more force is needed to deflect it into a safe path.' 

With both the OSIRIS-REx and Hayabusa2 missions still in their early days, anticipation – and nervousness - is growing. Within the next few months, as the spacecraft start sending more data back to Earth, experts will begin to get glimpses of what to expect over the coming years.

And when asteroids inevitably head for Earth, scientists are hoping to be ready for them.

With the impact from an asteroid long overdue, NASA has been drawing up plans for how they might deal with the imminent threat of a rogue asteroid heading for Earth. This includes the Asteroid Impact and Deflection Assessment (AIDA) mission, tentatively scheduled to launch in 2020.

The space agency hopes to send a spacecraft to Didymos, a large asteroid which has a smaller one orbiting around it, and then slam the craft into the little 'moon'. This will allow scientists to measure what effect this impact might have on the small asteroid's path. It will also inform scientists about the feasibility of doing something similar, if an asteroid were to make a beeline for Earth.

It means that species of the future will hopefully avoid the same fate as the dinosaurs.