IRA FLATOW: This is Science Friday. I’m Ira Flatow. Mercury is the smallest planet in the solar system and closest to the sun, so close that the temperature there can reach up to 800 degrees. You would think that the extreme heat would bake the planet into an inert, dry rock. But different groups of scientists have found signs of the basic chemical building blocks of life.

One team found possible evidence for these chemicals underneath Mercury’s, quote, “chaotic, rocky terrain, a landscape pitted with impact craters and haphazardly strewn hills.” Another study found even evidence for water on that hot, rocky planet. Some of the findings were published recently in the journal Scientific Reports. Deborah Domingue is an author on that study. And she’s also deputy director and senior scientist at the Planetary Science Institute. Welcome to Science Friday.

DEBORAH DOMINGUE: Well, thank you for having me.

IRA FLATOW: Give us an idea of what Mercury is really like. Can you describe what it would be like to stand on the planet, how long you would last standing there?

DEBORAH DOMINGUE: You wouldn’t last standing there. This is an object without an atmosphere. So there’s nothing to conduct heat. There’s nothing to change the heat flow. So when you’re on the day side, you bake, like you said. You can melt lead there. It’s very hot. When you’re on the night side, it’s extremely cold. You’re exposed to the vacuum of space. And you have nothing heating you. So it’s a place of extremes.

IRA FLATOW: How does being so close to the sun affect Mercury? Are there certain features? You say that’s so hot on one side and cold on the other side. Does that creates specific features to the planet because of its proximity?

DEBORAH DOMINGUE: Not so much in terms of altering the geology, but it does affect the chemistry that you see on the surface. There are interactions with the solar wind that are made more efficient by the heating on the day side. The night side can be a repository for what we call volatiles. These are materials that can transfer from solid liquid to gas within a small temperature range. So the night side can provide them a harbor, whereas on the day side they vaporize and they travel. They leave the surface.

IRA FLATOW: They travel. What do you mean by that?

DEBORAH DOMINGUE: Well, they leave the surface. They are in search of a place that is more stable for them, a little cooler, where they can reside. Some of them get swept up by the solar wind and carried off. Others stay in the proximity– there’s what’s called an exosphere. That means maybe have one molecule for every cubic centimeter. And they’ll reside in this exosphere or atmosphere for a while. But they migrate to places where it’s cooler, where they can be stable on the surface. That’s one of the reasons why we have ice at the poles of mercury.

IRA FLATOW: You’ve got to stop there for a second. There’s really– I mean, that blew my mind when I was reading these papers, that it’s 800 degrees on the surface, but you can’t have ice at the poles.

DEBORAH DOMINGUE: OK. So at the poles, you have craters. You have impact craters. And the bottoms of these craters never see the light of day. They never see any sunshine. So they’re cold. They are never heated. So these are nice little niches for volatiles, especially water, to find a home. It’s stable there. They can reside as a solid. They’re not heated sufficiently to turn into liquid or gas. So they migrate there. That’s their stable, happy place, so to speak.

IRA FLATOW: So these stable, happy places must be far away from the hot side, so that the conduction of the rock doesn’t even melt them.

DEBORAH DOMINGUE: That’s correct. So these craters are deep enough that, like I said, they’re permanently shadowed. They’re towards the bottom of the craters. And the heat conducted through the surface isn’t sufficient to melt.

IRA FLATOW: Wow, I love that. I love that idea, that picture. Give me a better picture of Mercury, of how it formed. I know that the inner planets are rocky, right? The outer planets are gaseous giants. How did Mercury form? Did it form something like our moon? Because it’s like the same size, right?

DEBORAH DOMINGUE: So our moon formed after a giant impact with the Earth. And so the formation of Mercury is a little different than that. It formed basically like all the terrestial planets. You had a little speck of dust that attracted another speck of dust. And they attracted more. And it accumulated. The composition is based on where, or the distance from the sun, it accumulated.

And one of the things from our study that we’re finding unique is that there were volatiles that accumulated with Mercury. And these volatiles, over its history, remained in some respect. And the chaotic terrain that you mentioned in your introduction is an example of what the surface looks like when you remove volatiles from underneath. And one of the biggest surprising discoveries from the Messenger mission– and this is NASA’s orbital mission to Mercury.

They placed a spacecraft in orbit– was the high volatile content that the elemental chemistry instruments discovered, the amounts of sulfur, the amounts of sodium, magnesium on the surface. That was a big surprise for us, is that how– once again, this is a hot place. How can you retain such a high volatile content? So this is one of the questions we are still continuing or still trying to answer.

IRA FLATOW: Is the planet locked in its orbit, like always facing the sun, like the moon is always facing the Earth?

DEBORAH DOMINGUE: It is not. It’s in two to three resonance. So it’s slowly orbiting, rotating as it goes around the sun. But it does not always show the same face to the sun.

IRA FLATOW: And yet, when it rotates, and those little pockets in the caves where the volatile ice is located, they’re still shielded enough that they don’t melt away when it’s their turn to face the sun?

DEBORAH DOMINGUE: They never face the sun. Remember, you’re at the poles. These are deep enough that the sides of the craters cast shadows over the bottom. So they are never illuminated. They never see sunlight. And that’s how come the ice can accumulate there.

IRA FLATOW: In your study, you looked at this chaotic terrain of Mercury that you talk about. And it is a bit jumbled up, as you say. What was the original idea of how the planet got this way?

DEBORAH DOMINGUE: OK. So the original idea was there was a big impact that came. And it formed an impact basin known as Caloris Basin. And these chaotic terrains are found on the opposite side of the planet from that impact basin. And the hypothesis was that the energy from the impact traveled around. So it’s coming from one side, coming from the other side. They meet. And all that energy disrupted the surface.

All right. When our team took a look at this and they did an age dating of the chaotic terrain, they found that it did not form at the same time. For this hypothesis to work, the chaotic terrain would have had to form pretty much the same time the Caloris Basin had formed. And we found that, well, wait a minute, it did not.

The lead author on this paper, Alexis Rodriguez, he has spent a great deal of time studying the Martian surface. And when I showed him this terrain, he’s like, I recognize that. On Mars, the chaotic terrain was identified in the ’70s, when it first imaged, as indicators of a hydrological system on Mars. This is evidence of water being removed from the surface, volatiles being removed from underneath to form the jumbled, chaotic terrain.

You see craters that have been misplaced. You see half of it moved one way, half of it dropped down. You see tectonic features displaced in such a manner that says, hey, these blocks just dropped. And he looked at the chaotic terrain on Mercury and said, this is the same cause and effect. We had volatiles from below removed. That’s how the chaotic terrain formed. It formed the same way as it did on Mars.

IRA FLATOW: Probably with the same timescale, do you think?

DEBORAH DOMINGUE: Relative timescale, I do not know. One more mystery to try and solve.

IRA FLATOW: A lot of mysteries. And you know we keep talking about the volatiles, meaning– besides water, what other volatiles are there on Mercury?

DEBORAH DOMINGUE: So the big one for us is sulfur, and sulfur-containing compounds, like sulfur magnesium, calcium sulfide, magnesium sulfide. So those are the ones that we are hypothesizing that are present on Mercury at the moment. That’s based on measurements from the elemental chemistry. That’s based on color observations, spectral observations. That’s our going-in hypothesis at the moment with the data set we have.

IRA FLATOW: What has Messenger, the spacecraft, Messenger, that observed Mercury– what has it taught you about the planet?

DEBORAH DOMINGUE: So much, so much. So Mercury is just this really complex, intricate system between the exosphere, the surface, the core, the mantle, how it all interacts, how it all interfaces. What’s it made of? How did it form? We’ve got a long way to answer a lot of these questions.

And in trying to answer those, we’ve unveiled a plethora of more questions. The interplay between the atmosphere and the surface, how are we forming that exosphere? How are we replenishing it? How come we haven’t exhausted the amount of sodium from the surface? How is that coming into play? So these are a lot of things that were answered. Volcanism– the surface was active at one time. And we see from our little study that there’s more than just volcanism going on.

There’s more than just tectonism going on. We have other things going on there. There’s a volatile system. How active was that? When was it active? Is it still active? We discovered very unique features on Mercury called hollows. And they’re some of the youngest features. And they’re associated with volatile loss from the surface.

How is that connected with the volatile loss we’re seeing in the chaotic terrain? Are they linked? Do we have a global inventory of volatiles? Or are volatiles very localized? These are the kinds of questions we can only start asking because of what Messenger discovered.

IRA FLATOW: OK. So you you’ve made this study. You’ve found out these things that you want to know more about. Where do you go from here on this?

DEBORAH DOMINGUE: Well, the Messenger mission provided a huge resource of data, huge resource of information. And while we’ve been mining it, there’s so much more work to do on the Messenger data set. There’s so much left to discover. In addition to that, the Europeans have launched their mission to Mercury that will– I forget the date that it will arrive. But it has a different suite of instruments on board, which will be able to answer some questions that Messenger wasn’t able to address.

IRA FLATOW: It’s so fascinating, this plane.t I understand that you have virtually visited all the planets in our solar system. Would that be a fair statement?

DEBORAH DOMINGUE: That would be a fair statement.

IRA FLATOW: And how does Mercury– and also some of the asteroids, places like that. How does Mercury rate in mystery– Mercury mystery– in our solar system?

DEBORAH DOMINGUE: Well, that’s the one thing about exploration is there’s always a surprise around the corner. No matter where you go, you go in with a set of expectations. And those are turned over. It doesn’t matter where in the solar system you go. There’s a mystery waiting to be revealed. There’s a mystery waiting to be discovered.

Mercury had its fair share of surprises. It had its fair share of intrigue. Being one of the missions I’ve been involved with, it holds a soft spot for me. But I don’t think there’s anywhere in the solar system you can’t go and be excited about.

IRA FLATOW: I’m Ira Flatow. This is Science Friday from WNYC Studios, talking with Dr. Deborah Domingue, talking about Mercury. OK. Then if you’re that excited about Mercury and the planets, I’m going to give you the famous Science Friday blank check question. If I had a blank check and you could spend any amount of money– oh, I don’t have one here in my pocket right now. But if I did, what would you do with it to learn more about Mercury?

DEBORAH DOMINGUE: Lander.

IRA FLATOW: A lander. We’ve never landed there before.

DEBORAH DOMINGUE: We’ve never landed there before. So usually, the steps in exploration is send– you look at it through a telescope from the Earth. That’s the first step in learning about anything. And then you send a spacecraft to fly by and get a feel for what the place is like.

And after you’ve done that, you send one to orbit, to hang around a while, and to really do a reconnaissance. And after that reconnaissance is done, that’s when you want to go and you want to land. And you want to have a more in-depth study, where you can only do that by being as in contact with that planet as you can be. So if I had my druthers, I would land something. Or I’d land more– if it’s a blank check where I can spend as much as I want–

IRA FLATOW: Sure, go crazy.

DEBORAH DOMINGUE: Let’s go crazy. I’d send more than one. And I would send it with some very unique instrumentation. I would do seismology, so I could understand what’s underneath. I would do chemistry to understand the mineralogy. I would want to understand how that magnetic field works and how that solar wind– how does it really interact with that surface? And how does it really alter that surface? I’d like to understand the geology of the terrains. And I’d go to that chaotic terrain. I’d go to those hollows. Hey, why not? I’ve got a blank check.

IRA FLATOW: Very jealous of your job, Deborah.

DEBORAH DOMINGUE: Thank you, thank you. And it’s the thrill of discovery. It’s an adventure. And that’s what I like so much about it. And the people I get to work with and the people I get to meet– that’s been the icing on the cake as well.

IRA FLATOW: Dr. Deborah Domingue is deputy director and senior scientist at the Planetary Science Institute. Thank you for taking time to be with us today. And good luck on your next voyage to Mercury.

DEBORAH DOMINGUE: Thank you so much. It’s been a pleasure.

IRA FLATOW: When we come back, some scientific research projects that you can contribute to while you’re staying home during this Citizen Science Month. Stay with us. We’ll be right back after this short break.

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