Liquid water on Mars discovered by InSight Lander

But first, scientists in the United States have discovered a reservoir of liquid water on Mars. It follows analysis of data from Nasa’s Mars Insight Lander, which touched down on the planet in 2018. I’ve been speaking to Michael Manga from the University of California, Berkeley. I began by asking him where the water might have come from…

Michael - Mars was wet, at least episodically, 3, 4 billion years ago. So much of the drawing happened over the last 3 billion years. Where did water on the rocky planets come from? It's still the subject of active debate and controversy. Even for the Earth, we don't know where our water came from, but presumably Mars' water came from the same place: some of it when it first formed, and some from comets later on in its history. But deciphering that question is a really tough one.

Chris - So why do you think, or what sort of hypotheses have you got for where it went? Because if it had similar amounts of water to the Earth, which is not an unreasonable supposition is it? Why have we got so much and Mars is now a prune of a planet, relatively speaking?

Michael - Well, our conclusion is in fact that Mars may actually have as much liquid water in proportion to its size as the Earth. If we look at the surface of Mars right now, there's a large ice sheet at the North and South Pole, and we conclude that there's probably one to two kilometres depth of water in the mid crust of Mars, so not a dry planet by any means.

Chris - How have you been trying to get to the bottom of this or scratch beneath the surface to see where all this water is and if you are right, that there's ice and water within the substance of the surface of the planet.

Michael - Looking deep is difficult because we can't use light, but we can use other types of waves. When Mars quakes happened, they shake the ground, and the Insight Lander had an instrument called a seismometer that measures vibrations of the ground and the speed at which those seismic waves, those vibrations, travel depends on the properties of the material the waves are travelling through: the composition of the rock, whether the rocks are full of fractures, and then what's sitting inside those fractures. We find that they're best explained by having a crust full of cracks and then filling those cracks with liquid water.

Chris - What temperature would it be at then, do you estimate?

Michael - We're talking about depths of about 10 kilometres to 20 kilometres. At those high pressures, the boiling temperature of water is higher than 100 degrees Celsius. And I'm guessing that we're basically seeing temperatures from the top of the water that are about a 100 degrees Celsius down to maybe 200 degrees Celsius at the bottom of the water.

Chris - Was the water always there like that then, or has it retreated inside the planet at some point in its life?

Michael - If we think about how the water cycle and Earth works, we see water continually being exchanged between the atmosphere, the oceans, what we call groundwater, water that sits inside the crust, then water and lakes, rivers and streams. Water is continually being transferred between these different areas. There's no reason to think Mars was much different and what we're seeing now is just the leftover of that groundwater.

Chris - Do you think then the rest of it has boiled off, or been lost into space, for example?

Michael - For sure, some has been lost to space and we know that by measuring isotopes of the element hydrogen in both rocks excavated by impacts, meteorites, as well as the atmosphere. But the amount of water that would've been lost is very small compared to how much water we think we're seeing.

Chris - Now, if there is liquid water there, that obviously has a lot of implications, both geologically but also biologically if there were at some point or still are life processes happening on Mars. If the water's retreated into the crust, is it possible that life processes, life, could have retreated there with it and therefore could it still be in existence in there somewhere?

Michael - I want to make clear of course that we have not found any evidence for life, nor have we established that that water is a habitable environment. But at least on the Earth, where we see water deep underground, we also see microbial life. So if there was once life on Mars, and the subsurface is habitable, meaning there's also an energy source, then this could be one of the settings in which you might want to look for life.

Chris - When you say an energy source, what sorts of things could power life down at those sorts of depths?

Michael - One possibility would be gases such as methane that can reproduce by geochemical reactions, or hydrogen gas. These are some of the energy sources that microbial communities on earth take advantage of underground. Deep underground, you don't have access to light, so photosynthesis is not a great way to get energy.

Chris - We have seen also extreme bacteria deep underground, found in mines under South Africa, for example, that were thriving on radiation, uranium in the rocks. Is that a possible model on Mars as well?

Michael - I don't see any reason why not. We think the rocks on Mars are not that different from the rocks on the earth. And you're absolutely right, when we go deep underground in deep mines in South Africa and Canada, we do find evidence for life, microbial life.

Chris - So how are you going to take this forward then? You've got these observations, they seem to fit with the explanation that there is deep liquid water, it's at high temperature down there, but you've got all this water down there. What are you going to do next to flush out how this got there, whether it really is there and what it's doing?
Michael - One of the puzzles was that, as we go to more shallow depths, the crust gets colder and the liquid water would be frozen as ice. We did try and use the seismic data to look for evidence for the ice and we don't see it. I'm quite curious as to why there's no ice sitting on top of this water. I think the next step is to try and understand better the history of this water, how it connects to the surface environments, and how Mars could have evolved to a state that we see. I'm sure there's much to be learned from continued analysis of that data.