Field Trip: Venus, Earth, Mars

CARTER EMMART (Director of Astrovisualization): --50. 50 years since the first Earth Day, a celebration of the Earth because of the pictures brought back from the explorers, the Apollo mission astronauts on their way to the moon took pictures of the Earth.

And I'm Dr. Carter Emmart. I'm Director of Astrovisualization for the American Museum of Natural History, and we're pleased to bring you a program tonight we had originally planned to do in the Hayden Planetarium. But we're going to be bringing it to you tonight on software called OpenSpace. It is NASA supported that we're developing at the museum and several academic partners. If you are interested in obtaining this free software, our team is in the chat and ready to take your questions about it.

It's a great honor tonight to have the presentation by Dr. Martha Gilmore from Wesleyan University, and Dr. Gilmore is one of the world's leading authorities in the planet Venus. And understanding Earth, we've come to find out in outer space explorations is to understand the Earth in context to other planets.

Dr. Gilmore was one of our scientific advisors for our new space show at the planetarium called "Worlds Beyond Earth." And so Dr. Gilmore got her PhD at Brown University working with Dr. Jim Head, who was one of the leading geologists in developing the exploration of the moon and teaching the astronauts geology. So with great pleasure, we're going to turn this over now to Dr. Gilmore.

MARTHA GILMORE (George I. Seney Professor of Geology, Wesleyan University): Thank you, Carter. It's so nice to be here, and Happy Earth Day, everyone. I'm sorry that I can't see your faces in person, but I'm so glad that you tuned in today just to take a spin around the solar system with me on this amazing software that the American Museum has supported.

But I thought we'd start our journey by talking about starting at home. So this is an image of the Earth as we see it now all the time, right? Or images from space of the Earth. And for me, I suspect perhaps you as well, this image is a little emotional. It produces several feelings for me.

One feeling is just the awe of how beautiful the Earth is, the colors, this oceans, the clouds, and with that, the feeling of familiarity that this is the planet that we call home, right? That warmth of feeling like this is where we live. This is our place in the universe. And the third feeling, I think-- I feel, at least-- is a little bit of fear in that when you see Earth from this perspective, you realize how fragile our planet is, how small it is amongst the background of space.

Despite all this, the Earth is special. I mean because of all this, the Earth is incredibly special because even though we live in a universe that has trillions of galaxies and in all of those galaxies are trillions of stars, and we know now that in all-- around all those stars are trillions of planets. At this moment, the only evidence of life in the universe is us, right here on Earth. So as we think about our place, the question we ask is, we know that we're not the-- we know now that we're not the only Earth-sized planet, but are we-- is there only one Earth?

To address that question, we are lucky enough to have sent spacecraft amongst the planets of our solar system and have explored several of our neighbors. So as we back out here, we're looking at the Earth with the moon in orbit around it. And we're going to back out to see the orbits of our two neighbors-- Venus, which is closest to us, and Mars, away from us. What we've learned from the study of these worlds-- there's the orbit of Venus, and here's Mars.

What we've learned from the studies of these worlds is that although we are unique in the solar system today, our nearest neighbors, Venus and Mars, were once like us in that they were worlds of volcanism, they were worlds with atmospheres, and they were worlds with water. So what we understand now is that the early solar system contained three habitable worlds, each with an ocean, at the same time that life evolved on Earth. Did life evolve on those worlds as well? What happened to make those-- what happened to those once-habitable worlds?

One of the ways that we address whether a world is habitable has to do with its size. Mars is half the size of Venus and Earth-- Earth and Venus. And size dictates the length of time over which a planet is geologically active. Volcanism is the mechanism by which water gets into the atmosphere of a planet, and we know that life requires an atmosphere. And so Earth-size planets that support life should be-- Earth-- sorry. Planets that support life we expect to be geologically active. And if we look in our own solar system, the planet that is closest in size to us is the planet that's also closest to us, which is Venus.

We would like to discover Earth-like planets and explore them around other solar systems-- in other solar systems, but we have the opportunity to touch an Earth-size planet in our own solar system. And so what I'd like to do is travel to the planet next door, which is Venus. And we're going to show you a visualization from the planetarium show "Worlds Beyond Earth."

So what you're seeing on your screen right now is a-- shows the inner solar system, with the asteroid belt on the exterior. And now we're going to fly into Venus, which is the brightest planet in the sky. Venus, like Earth, has a substantial atmosphere. And as we zoom in, you can see that the brightness of this atmosphere is what causes it to look so bright to our eye.

What's being overlaid here in red is a visualization-- the interaction of the solar wind with the atmosphere of Venus. And because Venus lacks a magnetic field, one of the things that happens is that the solar wind is able to pull material off the atmosphere of Venus, material like hydrogen and oxygen, and strip them into space. So Venus gives us an idea about how water is lost on other Earth-size worlds, particularly exoplanets that lie closer to their host star.

The atmosphere of Venus is very thick and mostly CO2, so to see through it, we had to visualize it using radar. And what you're seeing here is the path of the Magellan spacecraft that was in orbit in Venus in the early '90s and mapped the surface of the planet so that we could understand the history of this world.

So what we're going to do now is we're going to descend through the atmosphere of Venus, and we're going to look at some of the images of the surface materials that we can see from the radar images of Magellan. So we're going to switch now back to Venus. There we go.

And as we approach, I want to appreciate the fact that Venus has a very thick CO2, carbon-dioxide-rich atmosphere-- so about 100 times thicker than the atmosphere of the Earth that you feel right now. That carbon dioxide produces a huge greenhouse effect, raising the temperature of the surface to about 450 degrees Celsius, which is 840-something degrees Fahrenheit. It's really hot.

So much can be learned about the greenhouse effect and how atmospheres evolve from the study of Venus. The effect of increasing CO2, the importance of a magnetic field, the maintenance of oxygen and atmospheres and ozone all can be learned by studying the thick atmosphere of Venus.

So as we descend, we're going to visit some volcanoes. The surface of-- what you're seeing here underneath the atmosphere are radar images, where the color that you see correlates to roughness. So things that are bright are rough on the centimeter scale, and things that are smooth are-- things that are dark are smooth. Magellan mapped the whole of the Venus surface, and what we see is that almost everything that is on the surface is volcanic.

We're descending now over the large volcanoes of Alpha Regio and looking now at the volcano Sapas Mons, who is named-- Sapas is named after the Phoenician goddess of travel and commerce and messages. She's a messenger. The size of this volcano, which we can recognize because it looks similar to volcanoes on Earth, is as large as the entire chain of the Hawaiian Islands. So it attests to a suite of repeated volcanic eruptions and lava flows that built up this volcano over time.

As we move to the south, past the different textured flows of Sapas, we recognize a couple other large volcanoes. So we're going to move over the plains of Venus, which are also made of lava flows, and head toward the two actually tallest volcanoes on Venus-- Ozza Mons on the left, and we're heading toward Maat Mons right here. Ma'at is the Egyptian goddess of truth and justice. So for you kids, you can think of her as a member of the Justice League, Ma'at. And this volcano also shows a long history of beautiful volcanic eruptions.

We can see in the foreground some dark, smaller volcanoes on top of the main mountain. We see individual lava flows in the different colors associated with individual eruptions. And we can see features indicative of collapse. So we call these features calderas. We see pits. These are things where magma was underneath the ground, and then it moved out of the ground, onto the surface, during a volcanic eruption.

We recognize these features because we see these exact features on Earth. All of these features we can see on Kilauea and are associated with the eruption that Kilauea volcano in Hawaii sustained last year, emptying its magma chambers and erupting lava flows over the surface of the Big Island of Hawaii.

As we move across the surface, we can look at these flows on our way to impact craters. So we're going to follow the flows of Maat Mons and visualize the tool that we use to measure the surface age of planets. So what you see in the foreground, what we're approaching is a round impact crater with its ejecta after a meteorite hit the surface. We see this beautiful white lava flow that is in-between it and yet another crater in the distance.

We can tell from the ages-- we can tell from the number of the craters what the ages of these surfaces, are and what we can see by counting up the craters on Venus is that there are only 900 of them, far less than the moon, far less than Mercury or Mars. And they tell us that the entire surface of Venus was formed about 500 million years ago. At the same time that complex life was generating like gangbusters on Earth, Venus was erupting volcanoes over most of its surface.

As we cross the plains of Venus, we realize that that means that in the last 500 million years, Venus has not been a great place for life. It's been hot and volcanic, but there are a couple of places on Venus that survived and predated that event.

We're going to-- we're flying toward one of those oases. These are mountainous regions that compose about 10% of the planet, and the reason they survived is because they're high-standing. While the volcanoes were erupting, these surfaces, these mountains stood high and were witness to the volcanic cataclysm that occurred about half a billion years ago.

These are called tessera terrain, Greek for tile, which attests to the complex pattern of folds and faults on the surface. We're approaching Thetis Regio, her name lent by the Greek titan Thetis. And as we get closer, we can begin to see this complex pattern of faults and folds.

The tessera terrain have a different history than the volcanic plains and the most ancient history available to us. These are the oldest rocks on Venus, and we don't actually know what they are. We haven't landed here yet. They could be-- are they volcanic? Are they made of sediments? Were they formed in the presence of water?

Some of the most recent data from the Venus Express spacecraft at Venus suggests that they did form in the presence of water. And if so, do these rocks record an ocean on a once-habitable planet? So as we pull away from Venus, I'd like us to consider that these ancient rocks may hold the record of the ancient ocean on Venus, and it's time to revisit Venus to understand what became of our sister world. So the record of habitability is preserved in the oldest rocks on Venus, the oldest rocks on Earth, and the oldest rocks on Mars.

As we leave Venus, we can now turn to another planet, where a flotilla of spacecraft have been launched in the last couple of decades to explore a little planet that has evidence of a habitable environment in its early history. So we're pulling away from Venus. There is the orbit of the Earth, and we're going to travel now to Mars, our little neighbor, the little neighbor that could.

A wonderful thing about all of the spacecraft that we've been able to send to Mars in orbit and on the surface is that it allows us to build upon the discoveries of the former. Each spacecraft helps. It helps build on our understanding.

So as we approach Mars, we see that it's red. It's rusty. And we're going to focus on the part of Mars that is the oldest. So we're going to turn the planet. I love how you can do this in real time. You can see volcanoes on the right side, Elysium Mons, and we're heading right toward that sort of pale impact basin called Isidis.

To its southeast are some of the most ancient rocks on Mars, recognized again by the age of and the number of craters that they contain. And what we've recognized since the Viking orbiters of the '70s is that these ancient rocks are rocks upon which rain fell, rain that formed streams that merged together to form rivers and rivers that flowed into lakes and an ocean for millennia on Mars. So what you're seeing here is the beginning of a river that flowed on Mars a couple billion years ago, three and a half, that lies amongst some volcanoes and volcanic plains and through which water flowed, carving out the rocks and depositing sediments over time.

We're getting closer and closer to the river, which is right below us. The meandering river, the snake-like river, is crossing some faults associated with volcanism, and it continues, carving through the rock, flowing downhill, as water always does, across the ancient terrains of Mars until it reaches the edge of a large impact crater. And the water-- just like how the Mississippi enters the Gulf of Mexico, this river enters into this impact crater called Jezero, which contained a lake, and drops all of its sediment on the bottom of that lake over time.

So what we're seeing here is what we call a delta, the sediments of the river that have fallen out into the lake. It's just like the Mississippi Delta or the Nile Delta. And these sediments carry the minerals and the sediments of a wet Mars 3 billion years ago.

This Jezero crater is-- it is the site of our next mission to Mars. So as we speak, the Insight Lander listens to the heartbeat of Mars as recorded in marsquakes, and in Florida, we are lovingly tending to the Mars 2020 rover, Perseverance, preparing her to go to Mars this summer-- this summer-- with the most sophisticated suite of instruments we've ever sent to Mars, including a helicopter-- helicopter! And its landing site, chosen by the community, will be explored by the rover.

And what she will do, what Perseverance will do, is something that's never been done before. She will collect rocks. She'll choose rocks from this delta, and she'll put them aside. And in the future, another spacecraft will land here, say hello to Perseverance, collect those rocks, and return them home to us. So we can think about bringing those rocks home and then analyzing them to tell us about the potential of life in this other habitable world.

So as we leave Mars, we're going to turn back to a clip of the Earth from the "Worlds Beyond Earth" space show. Thank you, Micah. There is the sun, the orbits of the inner planets, and now we're coming home.

So here we are, the Earth with our moon. And this visualization is going to show you, similar to Venus, the impact of the solar wind on the Earth. But this time, you can see that the Earth is protected by these beautiful aqua lines of the magnetic field. The magnetic field forms a protective bubble around us, diverting the solar wind particles, which have high energy and can strip our atmosphere as well as irradiate our surface. You can see the satellites that lie around the Earth that we've put there in the last less than 100 years.

So the Earth is special. We live on a planet that supports us so well. Why? Why us? This magnetic field is generated by motions of the liquid outer core of the Earth that propel a magnetic field that protects us. We need a hot planet to generate the magnetic field. Is this magnetic field a requisite for life as we know it?

The study of other planets allows us to better understand and study the things we take for granted on Earth-- the magnetic fields, plate tectonics, the water cycle, and the early evolution and persistence of life. We are a planet now where life occupies the highest mountains, the deepest crevices on Earth that we can reach, a planet where life has persisted-- there we are-- over 4 billion years.

So on this Earth Day, I'd like us to remember that we owe the Earth our lives. Happy Earth Day, everybody. Yeah. There we go.

EMMART: Great. Martha, thank you very much. This is a wonderful tour of the inner solar system in these three potentially habitable planets across time. There have been a number of really great questions that have been coming in, and before, I just mention that I had neglected to mention that OpenSpace is being piloted by Micah Acinapura, who's one of our developers-- he's developer for and with us at the museum. And so nice flying, Micah, and thank you for that.

GILMORE: Thank you, Micah.

EMMART: First question comes from Dave [INAUDIBLE]. Why does Venus have such a weak magnetic field? And this relates to a couple other questions we've gotten.

GILMORE: Yeah, so one of the first ideas was that it was because Venus rotates very slowly. It rotates once every 243 Earth days, so that it couldn't spin up the convection in the outer core. But the thinking now is that it actually spins quickly enough to do that. There's something else suppressing the convection in the outer core, and one way to do that is to actually have a very hot interior.

To make something convex, it has to be hot on one side and cold on the other. And if the mantle of the interior of Venus is hot, then maybe there's not enough temperature difference to drive that convection. So it's a very complicated and interesting problem, and it doesn't mean-- just because Venus doesn't have a magnetic field today does not mean it didn't have one in the past. So that's something we'd also like to measure.

EMMART: Well, great. So we have another question regarding composition from Claudia Vega. And I'll just mention, the picture that's actually behind me is from Venera 13. It was one of the several Soviet probes that actually made it to the surface and landed. NASA had never actually attempted a landing on Venus, but the Soviet Union did with several. And we can see, I guess-- Martha being the expert-- but the talk about that we're actually seeing a volcanic landscape of rocks. So Claudia Vega asks, does the fact that other planets have volcanic eruptions mean they have a similar inner composition to Earth?

GILMORE: Oh, my goodness. That was just-- if any of my students are online right now, they know the answer to that question. We just talked about in our class for planetary geology. Yes, it absolutely means that. We are all from-- all the planets are formed from the dust of ring around the sun, which is solar composition.

So we all start from the same stuff, and then as the planets evolve, that starting composition yields a certain type of lava. So the plains of Venus, the plains of Mars, the maria of the moon, the sea floor of the Earth, Hawaii-- they're made of the same stuff because we start from solar dust.

EMMART: Another question from [INAUDIBLE], if I'm saying your name properly. How can you tell the age of rocks without landing and collecting rocks? That's a great question.

GILMORE: Well, you have the astronauts to thank for that. You can, in a relative way, tell just by the number of craters on a surface because impacts come in-- the longer you sit on the surface, the more impacts you receive. It's like I tell my students. It's like your leaves in the fall. You rake your leaves, and you reset the surface, and then the leaves keep falling. And the length-- the longer you leave your leaves, the more you'll get.

But to actually attach a date to that number of leaves or impacts is a direct result of the Apollo program, because the moon is the only place where we've gone and picked up a rock from the surface of the moon that had X number of craters on it, and took that rock home and dated that rock with age-dating techniques. So we can correlate that this 3-billion-year-old rock equals this many craters, and we extrapolate that to the rest of the solar system. So I think that's one of the unsung advances from Apollo, actually, is that calibration of planetary chronology.

EMMART: And from Mica Lyons, was there any time that these three planets contained water at the same time?

GILMORE: I think that they contained water-- OK, I'll bet you $5 that Earth, Mars, and Venus all had water in the first billion years of the solar system. They all had oceans. So hopefully, we can see if that's the case. But we know that's the case. We see the water flowing on Mars. We have chemical evidence that Venus was wetter.

And so the next suite of missions that have been proposed for Venus will attempt to try to see if the rocks of the tessera in particular are a relic or have a signature of that ocean. And that's critical because in the first billion years, life evolved on Earth in a heartbeat. I mean, life had already started. So if we have three planets all with oceans and life is starting on one, then maybe it started on the others.

EMMART: So kind of a related question is from Michelle Stevens. Was the fact that these planets have water and don't at different times related to closeness to the sun or related to their atmospheres?

GILMORE: Oh, these are such great questions. Yes. OK. So the closer you are to the sun, the hotter you are, just from solar heat. But your atmosphere is a blanket, and the thickness of your blanket is a function of whether you have volcanoes that are puffing up your blanket with more water and carbon dioxide, how big a planet you are. You can hold onto your blanket better if you're a bigger planet. So both things have an effect. The first order is that you have to be close enough to the sun to have liquid water, but the atmosphere then adds another wrinkle to that story.

EMMART: Well, perhaps the final two here, but a nice one from Kate [INAUDIBLE]. Could you make Venus or Mars habitable for us?

GILMORE: Oh. [LAUGHS] Well, there have been several movies that talk about terraforming Mars. So you'd have to do the opposite thing for both. For the Mars case, the atmosphere is so thin that you'd have to increase the atmosphere by adding volatiles or water or increase the pressure somehow. And so there have been ideas to melt the ice caps or melt ground ice in order to thicken the atmosphere to make it warmer, OK?

Venus is the opposite problem. You have this huge atmosphere, and that carbon on Earth is actually stored in the rocks of limestone. So it's-- take the oceans, take the carbon dioxide out of the atmosphere and store it in rock. So you'd have to do something pretty dramatic to be able to scrub the CO2 out of the atmosphere of Venus artificially. So that would be a tough one.

EMMART: Well, and then perhaps a very nice last question for you, Martha. Adrianna [INAUDIBLE] was asking, are there any future missions planned for Venus?

GILMORE: Oh, yes. Yes. So I am proud to be a science team member on two missions that are in consideration by NASA right now-- the Veritas mission to Venus, which would take the best pictures of Venus we've ever had and help us understand what's happening at the scales that we see on Mars, and the Da Vinci Plus Probe, which would do the hard work of going down through the atmosphere of Venus and measuring the chemistry as we go to learn more about the water and see the surface with our own eyeballs, as it were.

There are also missions in contention in Europe and India that are being considered for going to Venus. So there is-- with luck-- I have everything crossed-- in the next year, we'll learn whether a Venus mission gets selected by NASA or the European Space Agency for flight. And that would do a lot to advance our understanding not just of Venus but of how planets evolve. The major questions about what makes an Earth-size planet habitable can be answered by Venus.

EMMART: Well, wonderful. This has been a wonderful attempt to bring you a program that otherwise would be in the Hayden Planetarium, and again, from OpenSpace. Martha, thank you very much, and we hope that we can get you back into the Hayden in the not-too-distant future and we can tour more of Mars and see it as though we're just right there orbiting it ourselves.

GILMORE: Oh, thank you, Carter. It was my pleasure, and I hope to see you all there in the planetarium.

EMMART: Great. Well, thank you. And I'll just mention once again, if you're interested in the OpenSpace software, you can go to openspaceproject.com. Also, if you're interested, every evening, I'm flying on Facebook Live, if you look my name up. But I'm flying over Earth with musicians playing live, just to see the Earth and beauty, especially on Earth Day, as we can appreciate the planet that we are. As we're all at home, we all are on one large home together.

Thank you very much from the American Museum of Natural History. Thank you again, Martha Gilmore.