Where do all the meteors that hit Earth come from?

And a special comet to keep an eye out for...
18 October 2024

Interview with 

Matt Bothwell, University of Cambridge

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Meteor heading towards Earth

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Two new papers in the journal Nature suggest the most common types of meteorites that reach Earth are likely to have come from just a handful of parent asteroids. Commenting on the research, and with news of a new comet you can look out for, here’s public astronomer and space science author Matt Bothwell, from the University of Cambridge’s Institute of Astronomy…

Matt - Essentially they're trying to answer the question, where does all the stuff that lands on Earth come from? The Solar System is actually quite a busy packed place and something like 5,000 tonnes of cosmic material falls on earth every year. Lots of it is very, very small like space dust that slowly wafts down. But lots of it is quite big. It's like chunks of stuff causing fireballs and burning up very dramatically. And it's been a bit of a mystery for a long time. Like where does all this stuff come from? And researchers think they've finally identified a few major breakups of large asteroids that caused all this debris.

Chris - How did they do it?

Matt - So chemical composition, a lot of it. So a lot of the things that fall on earth are what we call chondrites, which means they have these small little kind of like blobby spheroids inside the meteorites. And we chemically analyse the stuff that lands on Earth and we do the same. We chemically analyse these families of asteroids we see out in space using reflection spectroscopy. Essentially we look at the light that reflects off them and infer what we can about their chemical composition and they found a match.

Chris - What's come from what and what does it explain?

Matt - We think that there was one major breakup around 450 million years ago, which resulted in one particular family of asteroids. And we think there was also a series of breakups between 5-7 million years ago that caused the rest. It's something like 80% of all the asteroids hitting Earth just came from a few very big things breaking up in the not too distant past.

Chris - And can we link those to any events that have happened on the Earth? Can we see any consequences?

Matt - We absolutely can. So the really, really big one that smashed up about 450 million years ago, as well as breaking up into chunks which have caused the asteroids that are now hitting Earth, also released a lot of dust. So the solar system would've become a very dusty place around 450 million years ago, and that dust settled on Earth and would've raised the opacity of the atmosphere blocking sunlight from the ground, which would've caused an Ice Age. So we know there was a couple of million years around 450 million years ago where there was a bit of an Ice Age and there was a bit of a die off, and we think now it was all caused by that big cosmic crash.

Chris - Do you know what I find really surprising is that that is the blink of an eye, really, the time you've just mentioned. Given the age of our Solar System, we measure that as close to sort of 5 billion years. And yet relatively recently, we're still seeing these sorts of breakup events. What's, what's actually causing them to still be jockeying for position in the solar system like this?

Matt - I think the answer is that just our solar system on what you might call medium timescales, is just still quite a dynamic place. Even on human timescales, right? I mean, listeners might remember Comet Shoemaker-Levy 9 slamming into Jupiter very dramatically, which I watched as a kid and it was very dramatic. I think just seeing over timescales of tens of millions of years, there's a lot of stuff in our solar system flying around and smashing into each other.

Chris - I think I saw that report. I remember watching Patrick Moore on The Sky At Night reporting on that. And I was also very lucky to see Comet Hale-Bopp when it came past here. That was really bright. That was the first time I'd properly seen a comet. But speaking of comets, it's pertinent that you raised this because if people look in the sky at the moment, they can see another one.

Matt - Yes. So there's a comet called Tsuchinshan, which is very close to the sun right now, which means you have to wait till after sunset. It peaked just a couple of days ago, but over the next week or two, the comet will be getting fainter and fainter and fainter, but also getting further and further away from the Sun. So hopefully those two things should slightly counteract and leave the comet visible till the end of October. So what you want to do, if you want to see it, is look to the west just after sunset and hopefully in the kind of the sunset glow, you should see a nice comet and a nice tail hanging there in the sky.

Chris - And that's true in both the northern and southern hemisphere. Is it?

Matt - Yes, absolutely true. So wherever you are in the world, as long as you have clear skies around sunsets, you have a good shot of seeing this.

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