Science

Kateryna Frantseva studies space debris

It’s raining asteroids

Every day, cosmic dust, asteroids and comets rain down on planets in our solar system. But what comes down with them? And should we be worried about their impact?
By Christien Boomsma

Every once in a while, she gets to hold one: a heavy lump of iron, millions of years old, that was once the heart of an asteroid soaring through space. ‘They are really, really cool!’ says Kapteyn Institute astronomer Kateryna Frantseva.

Frantseva borrows one such rock from the University Museum whenever she teaches a class on astrobiology or planetary sciences. There’s something special about touching an object that’s older than the Earth itself, she says: these pieces of rock and ice transport secrets – and life – all throughout the galaxy.

She has been studying comets and asteroids for years. But all the fascination and wonder of them is reduced to dots on her computer screen, or to bits of information on mass, speed, and configuration. She’s a simulation whizz, trying to determine what role asteroids and comets play in delivering certain key substances essential for creating life.

Organic compounds

‘We know that these rocks flying through space contain water and organic compounds’, says Frantseva. ‘And we know that from time to time, they impact with planets. But what we don’t know is how often that happens, or how important they really are for enriching the surface of planets.’ That information is important for understanding whether life is possible elsewhere.

This Friday, Frantseva will receive her PhD for her research into the consequences of comet and asteroid impacts on Mars, Mercury, and a distant star system called HR8799. HR8799 is located 129 light years from Earth and is visible in the constellation of Pegasus, which contains four huge planets, each nine times bigger than our Jupiter.

We don’t know how important these rocks are for enriching the surface of planets

‘A lot of research has been done on the search for life on Mars’, Frantseva says. ‘First, there were the Viking missions in the seventies; more recently, there were the Curiosity Mars Rover missions to collect soil samples. However, we have never found any organic materials on the surface of Mars.’ The only finding that did contain organics was a rock that was around 3,5 billion years old. So, the question was: how is that possible? Why are organics so hard to find?

And then there was Mercury – where the Messenger spacecraft found something in the shadowed craters on the surface that is almost certainly water, though it’s hard to see how that’s the case. ‘It’s really interesting, because it is so close to the Sun.’

Computer models

To learn more, Frantseva made extensive computer models containing information on all 700,000 asteroids that have been detected so far. She added information on 4,000 comets, each cloned by 5,000 times to compensate for the thousands of comets that have not yet been discovered and entered information on the known masses of the sun and planets.

Knowing what’s in a space rock is one thing – the next thing is calculating how the gravitational pull of the sun and planets influences their courses. Finally, she let the enormous cluster of computers on Zernike called Peregrine ponder her dataset for a couple of weeks.

‘Every ten million years, Mars is hit by asteroids around forty times. Those asteroids range from between tens of metres in diameter to a couple of kilometres.’ An impact from an object that big on earth would destroy life as we know it.

The radiation from the Sun may be destroying organic material on Mars

All these impacts leave behind the equivalent of eight truckloads of organic materials on the surface of the planet. Most of it – around 67 percent – comes from cosmic dust. Asteroids account for 26 percent, and comets are responsible for the last 7 percent. ‘So that is clearly a non-negligible amount’, she says.

The fact that no Mars rover has ever found organic material probably has to do with the thin atmosphere on the Red Planet. ‘The ultraviolet radiation from the Sun may very well be destroying it, so it doesn’t pile up at the surface.’

The water found on Mercury can also be explained by the impact of dust, asteroids and comets. Over 90 percent of it comes from space dust and only 10 percent from comets and asteroids.

Meteor showers

According to Frantseva’s research, the gas giants in the distant exoplanetary system HR8799 are also regularly bombarded and enriched by space rocks. ‘These impacts are happening all the time’, Frantseva says. ‘And they happen on Earth too. Sometimes we see meteor showers, but usually we don’t notice how space dust evaporates in the atmosphere or falls into the sea.’

But every once in a while, somwe do. Every hundred million years an asteroid of around ten kilometres will make impact with Earth. The last one killed the dinosaurs. Frantseva smiles: ‘The impact was so huge, it probably hurled pieces of the Earth into space. You might even be able to calculate where they are now’, she says. ‘And maybe, just maybe, one of those pieces contained a bacteria or microbe or two, and eventually slammed into another planet far away.’

Maybe a piece of Earth containing bacteria or microbes eventually slammed into another planet

The Earth takes smaller hits more often; every 10,000 years or so, smaller objects – usually over 140 meters in diameter – make impact. ‘That’s big enough to cause unprecedented, regional devastation to human settlements in the case of a land impact, or a major tsunami in the case of an ocean impact.’

And the ‘tiny’ objects hit even more often. They aren’t big enough to wipe out civilisation, but they can definitely cause a lot of damage. ‘Long story short, I would not say that we have to be worried, but I would definitely say that we have to be prepared.’

The animation above was based on Frantseva’s dissertation cover illustration, made by Marysya Rudska (marysya.com). The animated infographics are based on work by Nickolas Oberg.

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