Is there space dust in rain?

And if so, how did it get there?
20 September 2022


Raindrops hitting the ground



Katie writes in to ask: I heard that there’s a drop of space dust in every raindrop. If that’s true, how does it get there and is it harmful to us?


Peter Haynes answered this question...

Peter - So I think the simple answer is there is not a piece of space dust in every raindrop, but there is dust in every raindrop — because the formation of drops is basically helped significantly by solid particles. And it's much, much easier if you like for water, to condense some form of drop or ice also on a particle, than it is simply without that. So there's an element of truth. There's no space, but there's certainly dust.

Chris - We interviewed the guys on this show. It was about 20 years ago, but they flew collectors through clouds to see what was living in clouds. And they were very surprised to find lots of bacteria in the clouds, including bacteria that seemed to make holes in trees. So that the bacteria get blown up off the tree, into the cloud and they make rainfall in the cloud by doing exactly what you say, with making water droplets form around themselves. Then they rained down on a new plant that they can infest and infect. They also said there was dandruff. They found evidence for dandruff in clouds doing again the job well .

Peter - Your answer is consistent with what I said , that any, any dust is good.

Chris - Dust. Right? And it wasn't just human dandruff. I mean, there's a lot of animal dandruff as well, but it was just intriguing to me to think that, you know, you shake a cloud and you get some — it's not just snow that comes out and there's some other white flaky stuff in there and it might be some old dandruff. Can you help this person out though, Peter? Because this person's wondering how we detect what's in the atmosphere, not of our own planet, but other planets around other stars. So, if we look out into space and we are now at the stage where we've got telescopes, powerful enough to see not just distance stars, but planets around them. Scientists are reporting what's in the atmospheres of those planets. How do they know?

Peter - Well, the first thing to say is it's actually, to me as a bit of an old guy, it's actually, this is kind of amazing, right? Because it's only sort of 30 years ago, probably less, that we saw the first planet outside the solar system. So the idea that now we can actually start to say, what's in the atmosphere is actually pretty amazing. But we're seeing this basically through radiation, that if you look at the spectrum of radiation, the distribution of radiation over different wavelengths that you see coming reflected from a planet or perhaps the radiation has come from a star near the planet, then through the planet's atmosphere. And then to us then, by looking at the spectrum, you can deduce something about the chemical species that are in the atmosphere.


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