We have to go to these places where we know that there is liquid water on Mars today, and that is exclusively underground.

Does Mars have a history of glaciation? And why the heck did they think there were canals on Mars?

Hello, welcome to the Supermassive podcast from the Royal Astronomical Society with me, science journalist, Izzy Clark

and astrophysicist Dr Becky Smithurst. We thought it was about time that we did a deep dive

into water on Mars. So grab your space swimsuit, everybody. Yeah. So when did Mars have water? What was a

wet Mars like and where did all the water go?

We'll be speaking with Joe McNeil from the Natural History Museum and taking a look into the Royal Astronomical Society's archives.

And obviously Dr Robert Massey, the deputy director of the Royal Astronomical Society, is here.

So, Robert, when did Mars have water?

Well, a long, long time ago in the sense of

lots of liquid water on the surface, we think. So the idea is maybe 3.8 billion years ago,

which if you think the solar system is 4.5 billion years old, that's a really long time ago.

Mars had a much thicker atmosphere, probably a carbon dioxide one. And that higher

surface pressure means that water could be present as liquid because if you have, say, water in a

vacuum, it can or very low pressure. It can only either be ice or gas. To have a liquid, you have

to have a certain pressure. And that was present apparently in early in Martian history. And it's

what makes it possible on

Earth today as well. You know, if you went very high up in the atmosphere of the earth, you can't have liquid water there either. And we see evidence of its action on the surface, you know, evidence of giant flood shorelines, materials cemented together, and in some minerals that can only be made with the help of liquid water that the rovers have found, the various rovers going around the surface. And actually, of course, the only caveat on this is that it still has water today and on the surface in the form of ice. And we sometimes see the evidence of these little transient flows, you know, maybe something's bubbling up from underneath, but it doesn't last very long. Just because the soil is super dry, the atmosphere is too thin for it to stick around.

So it just disappears again.

But there's a lot of interest in how much that was there in the past.

So this is hopefully a great episode to talk about that.

Yeah, absolutely.

...