Ripples on the Cosmic Ocean

Sarah Al-Ahmed: How did space shape the story of our planet? We'll learn more this week on Planetary Radio.

I'm Sarah Al-Ahmed of The Planetary Society with more of the human adventure across our solar system and beyond. When we think about the environment, we often picture Earth, its oceans, forests, and blue skies. But historian Dagomar Degroot argues that our environment extends far beyond our planet. His new book called Ripples on the Cosmic Ocean, explores how events across our solar system from Martian dust storms to solar flares have transformed life and history on Earth. We'll talk about what he calls cosmic environmental history and why understanding our place in the wider system may help us protect our world today. And we'll wrap things up as always with Bruce Betts, our chief scientist for What's Up.

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Our relationship with space isn't limited to exploration rockets and telescopes. The worlds around us have been shaping life on Earth for billions of years. That includes everything from our sun to small asteroids. Historian Dr. Dagomar Degroot argues that understanding these cosmic influences is key to understanding our own planet's past, present, and future. His new book Ripples on the Cosmic Ocean: An Environmental History of our Place in the Solar System was published by Harvard University Press on October 28th, 2025. It invites us to see the solar system as an interconnected ecosystem, one that has always shaped life on Earth.

Dagomar traces how solar cycles, Venus' runaway greenhouse effect, Martian dust storms, and even Cold War fears of nuclear winter have influenced human civilization. From the asteroid that ended the dinosaurs to the science that helped us save the ozone layer, he shows how events in space have shaped our planet and the story of humanity.

Dr. Dagomar Degroot is a professor of environmental history at Georgetown University and holds the Baruch S. Blumberg chair in Astrobiology Exploration and Scientific Innovation at the Library of Congress. He's also the host of a podcast called The Climate Chronicles, where he explores the history of climate and civilization. I spoke with him about what he calls cosmic environmental history and why looking outward may be one of the best ways to protect our world and our people.

Hey Dagomar, thanks for joining me.

Dagomar Degroot: Oh, it's such a pleasure. Thank you for having me.

Sarah Al-Ahmed: I had a wonderful time reading this book. As part of this job, I have the privilege of being sent many, many space books, but I think there's a lot that we can learn from the study of environmental history here on Earth. But you've taken a really interesting tactic here in that you've expanded out this idea of what our environment is to include all the worlds around us. Can you define what environmental history is and why you made the decision to extend that beyond Earth to include our cosmic environment?

Dagomar Degroot: Absolutely. So environmental history can be defined in a bunch of different ways. I like to define it as the study of the reciprocal relationships between humanity and everything else in the universe. And that can range from single-celled organisms to galaxies.

It's kind of revisionary, history as a discipline, when it was professionalized in the 19th century, was all about great men and how their ideas and decisions influenced the past. And really for the 20th century, historians have tried to argue with different groups of historians that more and more people had an influence on humanity's past from blue-collar workers to women to non-white men. The list keeps growing. And eventually in the '60s and the '70s, a group of people said, "You know, humans don't just create their own past by themselves. We are part of environments, we're part of nature. And not only have our decisions, our history, not only has that shaped the natural world, but also the natural world has changed in ways that must have influenced us." So that gave rise then to the study of environmental history.

The study of environmental history has been Earth-focused. It's been about everything from earthquakes, to soils. You name it, but it's all focused on Earth. And you could say these environments that we focused on have been living and non-living. For me, I've been an amateur astronomer since I was a kid. That's why I've listened to your podcast for many years. I've just been passionate about amateur astronomy. I feel like maybe I had the insight, maybe I knew that there's stuff that happens beyond Earth as well, really important things. The sun is changing. There's constant flows of energy and even matter through the solar system, and I felt like, "Well, if we're going to think about the non-human Earth and its influence on humanity's past, we ought to think about environments in a much bigger way too. We can start thinking about how the solar system is the collection of environments and even dynamic environments that have changed." So from that idea came Ripples on the Cosmic Ocean.

Sarah Al-Ahmed: I did note that as I was reading your book. There are these beautiful little moments where you're talking about the kind of revelations that you have when you're outside with your telescope. So I love that you've woven in your own personal journey with astronomy and those moments into the book as well.

Dagomar Degroot: Thank you. That was actually really important for me. And it's a little bit different, I think, from a normal history book or from a normal... Well, it's a quasi-academic book I guess, but academic books usually are not first person. But for me, not only the motivation of the book, but also kind of the passion behind the book. And even kind of an important part of my life when I look at the cosmos here from downtown Washington, D.C., I feel like I'm connecting with something much bigger than myself. Of course, it's almost a spiritual kind of experience. And it connects me also to many, many people in the past who looked up at the night sky and saw its changes and responded to those changes sometimes in ways that made history. So it's helped to make me a better historian, I think, doing this kind of stargazing. It's also given me the passion that you need, I think, to write a book. And it's really made me, I think, a different kind of person than I would otherwise be.

Sarah Al-Ahmed: Well, that context allows you to see something that other people might not have, right? To actually take the step back and look at the ways that humanity has been impacted by space over time. I think it's really easy to think about... Well, not necessarily easy as it is a more modern field of history, but it's easy to think of the ways that humanity has been changed by our local environment. But unless you actually contextualize that with the things that change that outside of us, it is a very different perspective to say humanity has been altered by famines or ice ages versus solar activity drove systems on Earth that then led to human war and famines and broader systems. That's a very interesting way of thinking about it, and it's one more way of connecting ourselves to the space around us.

Dagomar Degroot: Yeah, I think so. And it took the book actually in a very unanticipated direction. When I started the book years ago, I thought I was going to write something that helps contextualize what I viewed and still view as kind of a new space age, right, where you've got these space companies like SpaceX, Blue Origin. But also new space agencies and newly capable space agencies all pushing out in different ways and beginning to realize those dreams of the 1960s of space exploitation maybe, space settlement, different ways of actually using space and maybe eventually living in space for human beings.

But as I started to write the book, I began to realize these environmental changes that happen in space and that have influenced our past kind of also make us precarious in a way that scholars have realized now, I guess, and written about for decades and centuries. And in fact, many of our ideas about risks to all of humanity, which we call existential risks, they've come to us through space exploration. So the book took on a different character. It began to consider these kinds of profound existential risks to humanity and how we began to realize those risks through space exploration, space discovery, and in some cases even how we were able to mitigate or begin mitigating some of these risks again as a result of what we do in space. So in a way, the book is also an argument for the importance of outer space, outer space research, space science, including astrobiology in human affairs.

Sarah Al-Ahmed: Well, you named this book Ripples on the Cosmic Ocean, which clearly I'm going to love. It's a reference to our co-founder Carl Sagan, who said that the surface of the Earth is the shore of the cosmic ocean. Why did you choose that name for this book and how has Carl Sagan impacted your work more broadly?

Dagomar Degroot: Oh, so I chose, I think, the name for the book... Well, I knew about Carl Sagan when I was a kid. I grew up in a tiny little town called Waynefleet, and actually an even tinier part of that town called Winger. This is a place with about 300 people. And my goodness, there was nothing to do. And I just remember growing up, obviously it's before the internet because I'm getting older, before the internet, and I just remember dreaming of things that were far away. That's how I got interested in history actually, because I kept imagining times far removed from my time when exciting things happened. And that's also then how I got interested in outer space because I kept thinking about what was happening elsewhere as far away from Winger as possible is what I cared about.

In getting interested in outer space, I visited libraries and I checked out books, which is what we did back in those days when we were interested in something. We checked out books instead of going on social media. And of course, that's how I encountered the work of Carl, Carl Sagan. I read Cosmos cover to cover multiple times. And eventually as I got older, also was introduced to some of his other work, including Pale Blue Dot, which I referenced in the beginning of Ripples on the Cosmic Ocean.

So I'm sure that somewhere in my brain I had this idea of the cosmic ocean, and that came from Carl Sagan. But also when I got started in environmental history, I was actually a historian of oceans on Earth and climate change. And one of the things I did in my early career was argue that natural climate changes before human caused global warming profoundly altered the oceans and changed how wind especially moved over the oceans. And that then actually altered how people could live on the oceans, how they could move across the oceans, which had an impact on economic history and military history hundreds of years ago. This comes up a little bit in Ripples on the Cosmic ocean, but that's actually how I started my career.

So the ocean was very much I think in my mind as I started working on Ripples on the Cosmic Ocean, which at first did have a different name. But then I guess gradually, may be this early Sagan influence and my own continuing work on oceans got me to change the title to something maybe that's a little bit more evocative.

Sarah Al-Ahmed: What are the ripples in this context?

Dagomar Degroot: Yeah, the ripples are the environmental changes or what I would call the environmental changes in cosmic environments. Everything from explosions on the sun, to dust storms on Mars, to radio signals coming from Jupiter and all the things that comets and asteroids do. All these things are disturbances, I would say, in cosmic environments. And the book is really about how these disturbances have influenced us the last 500 years of human history, also how people have imagined those disturbances, right, even if they weren't real. And even in some cases recently, how we might've been making our own disturbances in outer space environments, our own changes, some of which we didn't realize, and some of which are now on the drawing board like terraforming Mars.

Sarah Al-Ahmed: Well, our understanding and our interaction with the space environment fundamentally changed around the 17th century. What was it that altered the way that humanity began to interface with the universe around us?

Dagomar Degroot: So the easy and the incorrect, I think, answer is that the telescope was invented. So the telescope was invented in probably around the first few years of the 17th century, though the origins are a little murky. And it allowed natural philosophers, as they were then called, to see things that they couldn't see before, from sunspots to the rotation of Jupiter's moons around the planet, to craters on the moon. They could see these space environments. And it's a very beautiful thing because it's almost like you create this magical instrument. It's like magic basically, right? You can start to see across the veil that surrounds you and has long sort of hidden away the true nature of reality. So it's this incredibly powerful, almost magical device that lets you see things that hundreds of millions of people have never been able even to imagine.

So it is really profound, the invention of the telescope, but it's not the whole story. And in fact, even the invention of the telescope comes from other things. There is the reformation that's like this huge schism in the church. And the reformation allows for pockets to emerge in Europe where you can think freely and talk openly about the nature of reality. So that's really important. That happens in the 16th century.

Of course, what also happens is the dawn of an era of a discovery of colonialism in the 15th century. There are literally new worlds as they were called by Europeans discovered on Earth and new sciences, kind of new ways of knowing emerge around the discovery of those new worlds as before trying to make sense of them, trying to understand them and realizing that the Greeks and the Romans in fact did not know everything, right? They didn't know about a lot of the stuff that's actually happening on Earth. So that prompted kind of new ideas that enabled challenges of old ideas or encouraged people to combine ideas in different ways.

So there's all this kind of upheaval. The 16th and the 17th centuries in Europe at least are really about upheaval. It's a jarring time to be alive. And it's also the kind of time that encourages and permits new ways of understanding the universe, right? Obviously you've got this kind of change from an Earth-centered way of understanding the universe now increasingly to a sun-centered way of doing so, the Copernican Revolution, which slowly unfolds over a century or even longer. You've got the development of gravity, the theory of gravity, and you might call it the scientific revolution, sort of takes hold halfway through the 17th century.

So there's all these [inaudible 00:16:36] really complicated, all these entangled changes in culture, in economics, even in politics that come together in just the right way to enable the invention of the telescope, and then really the foundations of modern astronomy, and I would say also new conduits between environmental changes in outer space and human history on Earth.

Sarah Al-Ahmed: Well, in this book, you break down each environment as we go, starting with the sun, which clearly is the place that we should start. I mean, other than just what's going on here on Earth, the sun is one of the greatest dictators of our local climate. But it's interesting because you highlight that there are larger celestial cycles, the Milankovitch cycle, solar variability, axial tilts, and each of these influence the climate. But how do these forces all combine to shape larger systems like ice ages or ultimately human migration and civilization?

Dagomar Degroot: That's a great question. And I have to plug something. If your listeners are interested in this, I've started a kind of multimedia thing that I call the Climate Chronicles, so they can look through and really dive into some of these changes. It's like an audiobook.

But the big thing to know about Earth's climate over the past 40 to 50 million years is that we sit at the tail end of a prolonged cooling trend. And that cooling trend probably began with the collision of the Indian plate into the Eurasian plate, which pushed up the Himalayas and through precipitation began scraping carbon dioxide out of the atmosphere. That was kind of the initial push. And then from that, comes just an enormous and dramatic cooling trend unfolds again for tens of millions of years. And by the time you get to about two and a half million years ago, the Earth is probably cold enough for regular cycles in its rotation, so the wobble of its rotation and the tilt of its rotation and cycles in the ellipticity of its orbit around the sun to begin overlapping in ways that can actually reduce temperatures in some seasons and some parts of the Earth. And that begins to enable what we call in ice ages and what are more appropriately called glacial periods, right?

So then you start getting these alternating glacial periods and interglacial periods. But interrupting those periods are actually dramatic pulses of cooling or warming, which are caused by the shutdown and resumption of circulation systems in Earth's oceans. So it's a mess. It's a real big climatic mess. And in that mess, we evolve. And perhaps we evolve our big brains in part because they allowed us to adapt to all of these changes unfolding around us. So this is a period now that's called the Pleistocene, a period of these constantly climatic swings, cooling, and warming, and it's only about 11,700 years ago that things stabilize, get a little warmer. It's really just an interglacial period. And that we then develop agriculture, different groups around the world, develop agriculture, all in relatively warm, stable, and wet climate, which we call the Holocene. So that's kind of the big climate picture in about 30 seconds, but you can look at more at the Climate Chronicles.

Sarah Al-Ahmed: And I'll include a link for that on the web page for this episode of Planetary Radio so people can check it out.

Dagomar Degroot: Awesome.

Sarah Al-Ahmed: But before reading this book, I'd never really internalized that the sun was such a driving force behind human conflicts and even bigotry in some instances. It's kind of easy to think of famines and ice ages as these local events, but if we take that step back and really think about how they're driven by these larger factors, and then those things led to human migration and war, and in some cases blaming of marginalized groups, it's this larger cycle. And that gives a whole different flavor to human history for me.

Dagomar Degroot: I'm happy to hear that. Yeah. So if you think about the Holocene, so that's 11,700 years, ,globally, temperatures are relatively stable, but regionally things could still change quite a bit. And even small changes globally of several tenths of a degrees Celsius could have a big impact on pre-industrial communities, which in many cases were much more sensitive to shifts in weather than we are now.

Now, I should emphasize you're talking about these changes of several tenths of a degree Celsius. The Earth has now warmed by one and a half degrees Celsius since the late 19th century as a result of human greenhouse gas emissions. So we are changing the climate much more than has ever changed in the Holocene, and in a way bring us back to the chaos of the Pleistocene years that we were lucky to survive. In any case, those small changes in the Holocene do seem to have had a profound impact on human history. They, in some cases, reduced harvest dramatically causing famines, widespread starvation, political destabilization, rebellion, wars between countries. So especially then in a period that we call the little ice age from about the 13th century to the 19th century, when cooling really came in waves, waves driven by in part maybe changes in solar activity, but also by these spectacular explosive volcanic eruptions that released sulfur dioxide into the stratosphere. So a little ice age is a period where there's waves of cooling. They're relatively small compared to modern warming, but as you say, they definitely had an impact on human history.

Sarah Al-Ahmed: And you've also traced how our understanding of the sun has been shaped through science from Herschel and his early sunspot studies, to things like the Carrington event. What would you say are the biggest lessons we can take from these solar events that are probably most urgent for us to address these days?

Dagomar Degroot: Yeah. So the one thing I'll say about Herschel and his solar discoveries and kind of a finding I had while working on this book that really struck me is that William Herschel, [inaudible 00:23:02] astronomer in the late 18th century, discoverer of the planet that he called George that was later renamed Uranus, right? So he really laid the foundations for a lot of climate research today because he used his telescopes to chart changes in the number of sunspots on the sun, which got him to think that, "Well, if the sun is changing its appearance, Earth's climate must be changing as well." And that got him to do research into the history of grain yields and to kind of try and reconstruct, as we call them, as we call it, reconstruct climate changes in the past, and to figure out the ways which those climate changes might have influenced human affairs. So William Herschel I think is one of the unheralded founders of climate science. And how did discover it? Well, it's by observing the sun and its changes.

In terms of solar storms, so coronal mass ejections and solar flares, the biggest lesson I think we should learn from that is that we might be at risk, right? Solar storms have influenced our history in some pretty profound ways, none more so than when spectacular solar flare sent radio waves towards Earth that jammed radar stations, American radar stations, and seemed to reveal that a nuclear attack was underway. A Soviet nuclear attack just barely avoided total nuclear war, potentially human extinction because solar forecasters were able to NORAD, so American officers, that in fact, this was a solar storm, not a Soviet jamming effort. So huge impacts in the past, potentially really catastrophic impacts in the past.

But now again, there's a lot of uncertainty about how profoundly a solar storm could influence us. There's been really interesting research using tree rings. It seems to suggest that there were massive solar storms in the past, much bigger than those of today, those that we've experienced in recent centuries. But also there've been studies of sun-like stars across the galaxy, which may indicate that sun-like stars are capable of much bigger storms than we've experienced. So it's entirely possible that we are overdue for a megastorm. And we've just become more and more dependent on electrical systems and electrified systems from satellite constellations, obviously to AI, to even pipelines which use electricity. Transmission lines are getting bigger as we shift to renewable power in many parts of the world. So it's, in some respects at least, an increasingly vulnerable world. And we should heed the lessons of the past to, first of all, continue to fund solar research and to experiment with things like AI systems for predicting solar storm events and then develop ways of protecting our electrical grid, which is the key vulnerability, I think, to solar storms.

Sarah Al-Ahmed: It's so interesting that the sun sparked all of these new ideas and science that allowed us to create this technology that is now made vulnerable by the thing that led to its invention in the first place. It's just-

Dagomar Degroot: Yeah, exactly.

Sarah Al-Ahmed: ... really interesting. But after the sun, you take us into the history of Venusian exploration and how that shaped our understanding of Earth and life in the universe, but also climate change more broadly.

How would you say that Venus played a role in, specifically, human's understanding of climate change, not just here on Earth, but on worlds all across our solar system?

Dagomar Degroot: Well, Venus was thought to be a temperate world in the late 19th century. And one of the great shocks of the early space age in the 1950s was the discovery of evidence, the accumulation of evidence, that Venus was in fact the hottest world in the solar system and probably the world you would least like to be on. It was a hellscape, fascinating hellscape, but the hellscape nonetheless, as long as you were on the surface of Venus. The cloud tops of Venus are considerably better, but you do not want to be on the surface of Venus.

So how did Venus, which is a planet that is in some respects so similar to Earth, it's about the same size as Earth, it's made of about the same stuff, it's relatively close to Earth, technically on the inner, inner, inner edge of the habitable zone around our sun, how did Venus come to be so very different from Earth? That was one of the great mysteries then also of the early space age. And of course Carl Sagan helped to solve that mystery by developing models and the ideas that there could have been a runaway greenhouse effect on Venus that created today's planet that's supercharged the temperatures on Venus.

So if there was a runaway greenhouse effect on Venus, what did that say about the stability of Earth-like worlds, right? What did that say about Earth's future? This became a very urgent question after the confirmation in sometime between the '60s and the '80s that the world was warming. Our world was warming. Human greenhouse gas emissions were beginning to raise global temperatures. And so Venus became a kind of worst case scenario in the 1980s, a kind of warning of what could befall the Earth if we continue to burn fossil fuels. And in fact, we've subsequently found scientists that if we were really ambitious and we decided to burn every last atom of fossil fuels on Earth, we probably would set in motion the same kind of runaway greenhouse effect that might've warmed Venus because we would begin to boil the oceans. And water vapor is a greenhouse gas, so that would further warm the Earth and boil more of the oceans, and eventually maybe we turn out like Venus. So it is still a very effective warning.

Sarah Al-Ahmed: What's interesting is that it doesn't just pose this existential threat, but if we look at it the other direction, it also suggest that we could enact some kind of positive climate change or some kind of alteration of other world's climate systems, which then ultimately leads to this idea of terraforming. So it's both terrifying, but also suggests that someday it might be within our power, not just to fix our planet, but potentially make other worlds more habitable.

Dagomar Degroot: Yeah. And in fact, I mean, you could argue that research into the atmosphere of Venus is why we are able to have this podcast right now. Because research into chemical reactions in the atmosphere in the 1970s began to expose how the ozone layer could potentially break down. There is no ozone layer on Venus. Other strains of research confirmed that there was in fact a hole in Earth's ozone layer caused by CFCs, which were in refrigerants and spray cans, and that hole was growing dramatically.

And so in the 1980s, you get the Montreal Protocol, which limits the ability for companies to produce CFCs and the hole stops growing. But if that research into Venus's atmosphere, it never happened, you might argue that either you wouldn't have had the Montreal Protocol or you would've had it later when more damage is done. We now know that if the ozone hole had kept growing, there would've been just a tremendous wave of skin cancer all over the Earth. The DNA would've started to break down in plants and animals, so there would've been even worse wild diversity crisis.

And the ozone layer plays a big role in Earth's climate as well. So there could have been an intensification of global warming. It would've been potentially even apocalyptic or it not for the Montreal Protocol. So this is one of the good news stories in human history. It's evidence that we can actually do something about existential threats, and it's also one of the ultimate examples I think, of space research benefiting life on Earth.

Sarah Al-Ahmed: We'll be right back with the rest of my interview with Dagomar Degroot after the short break.

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Sarah Al-Ahmed: I don't remember how many years ago it was. I was speaking with Michelle Fowler who was at the time in charge of NASA's communications. I think she was director of NASA communications at the time, and we were speaking about something and I asked her whether or not we could save the world from these broader things, climate, but also asteroids and things like that. And her answer to me was, "We've already saved the world through science specifically because of the ozone layer," and told me a bit more of this history and the dire consequences of what would've happened if we didn't have the Montreal Protocol. And I think people generally kind of jokey joke about like, "Oh, that hole in the ozone there." I don't think it's commonly known just how close we came to devastation and how much we should all be celebrating the fact that we managed to turn this around.

Dagomar Degroot: I could not agree more with that. And I think actually these stories are incredibly important to tell because I'm a professor at Georgetown University, and so I teach young people. More and more young people are kind of hopeless about the future. They're worried about climate change, they're worried about nuclear war, they're worried about AI. There's no end of things that seem scary right now, but the past shows us that it's possible to confront even these biggest of challenges, and if not to completely stop them in their tracks, then at least to reduce the risk.

And it's a story of science. It's a story of politicians sometimes taking risks, of companies sometimes even acting in the public interest or at least finding ways to act in their own interests that don't harm the public. But it has been done before. So I think that's an uplifting story maybe for our young people.

Sarah Al-Ahmed: And clearly, humanity is capable of uniting to do wild things. After Venus, you go onto your chapter about the moon. And I mean this dream of putting humans on the moon has so drastically altered recent human history. But even now we're talking about returning humans to the moon and potentially sending humans to Mars, and that is a driving factor in how much funding we get for space. And I think we're in a really interesting time where there's this kind of discussion about whether or not we should be scaling back money for scientific exploration with robots and giving more money to things like human space exploration. And I think we should be able to walk and chew gum at the same time, right? Clearly, putting people on the moon has been a huge driver for both funding, but also human curiosity about space. But I don't know. It's an interesting situation we find ourselves in. What are your thoughts?

Dagomar Degroot: Well, I'm a supporter of The Planetary Society in part because my passionately believe in space science and the value of space science. I would say that belief goes back to my childhood, but it certainly has been strengthened by writing Ripples on the Cosmic Ocean. The space science has had all kinds of profound beneficial impacts for life on Earth, and I think it is a borderline suicidal to cut funding for space science, in part because it's helped to identify so many of these risks and others might be out there.

So I agree with you 100%. I actually do support efforts to direct more funding to crude space exploration, including to the Moon and Mars, but at the same time, I do not support cutting space science at all. There is one thing that I've been wrestling with lately, which is the role of the astronaut and space exploration. And this is something I get into towards the end of Ripples on the Cosmic Ocean, but we live in a time of rapid AI development, and it's now possible to imagine that artificially intelligent systems will be competent scientists on the Moon or Mars, and they'll be able to do many of the things that astronauts can do there. I think we're kind of challenged to start thinking of what can humans uniquely do in space and is space settlement something that we should be thinking of as an urgent priority?

There's a beauty and a romance in space settlement, I think, for me as well. There are arguments for it that I think are very interesting like humans being in space could have experiences that no humans could have on Earth. Human settlements in outer space could experiment with new forms of governance even that might go on to benefit people on Earth. But I think we are still challenged to think of whether the costs of sending people to Mars, for example, rather than robots, which are probably in the hundreds of billions of dollars, maybe even the trillions depending on much you tend to try and do there, if those costs are now worth it? Do we want to leave outer space to the machines or do we want to allow the machines to build things for us that we can then use? I think it's a really interesting moment where we're sort of challenged to think of what the human role in space should be at least in the next few decades.

Sarah Al-Ahmed: And it also brings up this need for more regulation and space law when we're thinking about these things, which you bring up throughout a lot of this book, but particularly when we're talking about Mars and other human settlements. I don't think when people were laying down things like the Outer Space Treaty back in 1967 that they imagined how rapidly our technology would advances. They weren't thinking about things like asteroid mining or Mars' tourism when they wrote those.

Dagomar Degroot: Yeah. Well, it's interesting to think about what they were thinking about and why their dreams might not have come to fruition in the 1960s because of course that was the first space age.

I like to think of two space ages. So I like to think of the first space age maybe beginning in the '50s and sort of petering out into the '90s, and now us being in legitimately a new space age. And I do actually think that a lot of what we now anticipate and the technologies we're now developing kind of take us back to those first years of the space age. The likes of Wernher von Braun or Korolev in the Soviet Union, they were expecting us to move on to Mars quickly after being done with the moon and to build space stations. They had a grand vision of human life and outer space, and they had an expectation that we would be developing space stations and space settlements into the '70s and the '80s. And if you had told them how things really turned out, they would've been crushingly disappointed.

And in a sense, we are in a similar moment where you've got these technological systems coming online like hopefully Starship and promising all of these breakthrough dramatically reduced costs for getting stuff into outer space. That now seem to be finally materializing. But it's possible to imagine that progress peters out in the future if there's less interest in doing things in outer space. If there's a war on Earth, God forbid. So even now, I think the future in space may be more precarious than we expect.

With that said, I think it is true that we have to start thinking more seriously about whether space environments need to be protected, whether there are environments on planets that are special, that deserve special respect, that need to be conserved. The classic example is the moon landing sites, the Apollo moon landing sites. But you could even argue that there are places on Mars that are more likely to have microbial life, and therefore astronauts should not go near those places. This is an argument that has been made for decades. Or perhaps we should be very careful about going into the cloud tops of Venus where there's very controversial phosphine detection maybe. But there's been long discussion about the possibility for microbial life there. What about the ocean worlds of the outer solar system? How should we engage with those places?

So now is the time, I think, for very serious discussion of space conservation, and even you can call it space environmentalism, not when we're actually already sending human beings to Mars, let's say.

Sarah Al-Ahmed: Well, I'm definitely seeing a rising interest in, both for planetary protection reasons, but also this idea of not polluting the space around us. I think images of things like back shells on Mars for some people are very inspiring. For others, lead to these ideas of, "We're just going to be spreading pollution around the solar system as we've done with our own world." So now it's definitely the time to begin having these conversations, especially as our search for life continues.

Dagomar Degroot: I think that actually also gets us into an interesting point, which is, should the space environments have rights, let's say, that terrestrial environments do not, we litter terrestrial environments, we bring our microbes all over the place, right? Why should we be careful about avoiding forward contamination? So avoiding microbial contamination on Mars, let alone on the moon, which almost certainly has no possibilities for life? I would actually argue that one thing we should be thinking about for the future of space exploitation, space settlement and exploration should be how to reduce humanity's burden on the Earth. Because I think terrestrial environments probably are uniquely important, valuable. They are after all teaming with life, and humanity for the foreseeable future will depend on them. So the kind of idea of offloading energy generation to space to the extent that's possible, or in the long run offloading industry into outer space, and maybe even in the very long run, human numbers, human population, I think that's a very important idea, and I think that's one that I would probably support.

Sarah Al-Ahmed: Well, we need to defend our world and in multiple ways, right? It is the only world that we know has life on it. And it's very interesting to point out that we have all these concerns about planetary protection when it comes to other places, but it's really easy to just throw your trash out the window if you're living here on Earth and not think about the consequences. But you also bring up comets and asteroids at the end of the book and how this other existential threat of defending the Earth has altered human history. I've had a lot of conversations about these moments like Shoemaker-Levy 9 and how that altered human history, but there's so much to be said there.

Dagomar Degroot: And this is another one of those good news stories, right? And it's a classical good news story where you have a plucky bunch of scientists and they're laboring in the darkness for decades and they're trying to track these asteroids that might pose a threat to Earth.

So Eugene and Carolyn Shoemaker are kind of the leaders in some of this work. Nobody takes them seriously. There's what they call the giggle factor. So no one actually expects that an asteroid or a comet could hit the Earth. And I think this is hugely important, and it gets right at the heart of what makes existential risk risks to human existence so difficult to deal with because by definition, we've never experienced them. And so they seem like something out of a science fiction book and there's a high giggle factor around them. And maybe more of us are taking the threat of AI seriously these days, but I think it's still kind of a niche idea that AI could bring about our destruction. More and more people are concerned about nuclear war, for example, but still, I don't think we would rank nuclear war as one of the most important things facing United States right now.

Same thing with climate change. I think a lot of people are concerned about it, but maybe the really apocalyptic stuff is still a fringe. You go down the list. Asteroids were the ultimate example of that in the 1980s, something straight out of science fiction and never could impact us. And then a few things happened. And one of those things, as you say, was the Shoemaker-Levy 9 comet fragment impacts on Jupiter, which I still remember vividly. I was nine years old, and I just remember all those flashes on astronomy magazines, the infrared flashes, and just being blown away by those impacts like so many people were, right? Here was proof that a planet could be just wrecked by a relatively small comet. I mean, my goodness, these comet fragments were not more than a kilometer or so across, right? And here you have the biggest planet in the solar system, and it looks like it just got in a fight and came out worse for it. So that was really a critical threshold.

But there were others too, and they pushed in different directions. I think that's something that really came out from my research for the asteroids and comets section of the book, is that there were things that were pushing people to take asteroid and comet impacts more seriously, and there were things that were pushing them away from that. So the end of the Cold War is something that pushed people away from what we might call impact mitigation. So you had all these weapons scientists who were suddenly out of a job, including ones who were working on the Strategic Defense Initiative or Star Wars, and they proposed these outlandish schemes to protect the Earth from asteroids and comets that helped to discredit the whole enterprise.

So it's always fascinating with history because there are so many different things pulling in different directions. But ultimately, the efforts by these plucky scientists started to get more and more funded. And ultimately for a very modest amount of money, scientists were able to detect and track thousands and thousands of near-Earth asteroids. And that actually ended up dramatically reducing the risk because risk is really all about perception. So by just cataloging an asteroid, tracking its orbit, and determining that it won't impact Earth, you end up reducing risk.

Then planetary defense entrenched inside of NASA by Congress, and you've got these wonderful asteroid redirection impact missions like DART most recently. And a kind of proof of concept that if we're able to detect an asteroid, we can see that it's spiraling towards Earth and we have enough lead time, we can actually alter its orbit. So the risk of an asteroid impact goes from being unknown, but potentially very serious in the 1980s, to now being much better known and very, very, very low. And I think that's just a wonderful example of existential risk mitigation reduction.

Sarah Al-Ahmed: There is so much left in this book that I wish we had time to speak of, but I'll leave that to the reader to get into it to learn some more of this wonderful history. And I hope it recontextualizes the way they think about our world and our connection with all the other worlds around us. But before I let you go, after tracing five centuries literally of cosmic environmental history, what is the biggest takeaway that you hope readers carry from this book with them into conversations in real life?

Dagomar Degroot: Well, the biggest takeaway and takes me back to Carl Sagan, that picture that is so central to the history of the planetary society and so central to how many of us think about outer space, which is the Pale Blue Dot. And Carl Sagan described the Pale Blue Dot with the most beautiful words that I think were ever written in connection to space exploration, but he mentions the dot as being alone, right? There's nothing around it. It's separated. There's no hope of relief from outside of the dot, which is probably true. Ripples on the Cosmic Ocean looks at the sunbeam that kind of cuts over the dot, right? And it argues that there's the vision that we see between Earth and the rest of the cosmos is in large part an illusion. Earth is again kind of a node in a much, much bigger set of environments. And that's partly why outer space research exploration matters so much. So I hope readers come away with that realization.

Sarah Al-Ahmed: Well, Ripples on the Cosmic Ocean: An Environmental History of our Place in the Solar System is out now. Thank you so much for writing this book and for coming on the show and for being a fan of Planetary Radio. I think I just learned just as much from you as maybe you've learned from me and our guests over the years.

Dagomar Degroot: I sincerely doubt that. It's been a dream for me to come on your show for a long time, so thank you so much.

Sarah Al-Ahmed: And now it's time for What's Up with Dr. Bruce Betts, our chief scientist at The Planetary Society.

Hey, Bruce.

Bruce Betts: Hello, Sarah.

Sarah Al-Ahmed: This show and next week's show are both about books. And anytime you get into them, I mean, I don't know, it's part of the privilege of my job that I get early access to these cool space books, but it also means that I read a lot of books. So it does take a lot of time, but then I learned all these awesome things. But in the first half of the conversation, we talked a lot about the ways that solar activity has impacted human history. And a lot of that was ice ages and these large scale things, but we've had a lot of big events in recent solar history.

So I wanted to ask you, what are some of the largest moments in recent solar history in the last, say, 150, 200 years?

Bruce Betts: And you're looking for things that disrupted things on Earth, not just [inaudible 00:51:05]-

Sarah Al-Ahmed: Yeah, specifically space weather that interacted with Earth.

Bruce Betts: Space weather. Well, the biggie of infamy is the Carrington event named after British astronomer where there was in, you remember it, 1859 there was a big solar flare which send some X-rays. Then they get here quickly. But also more significantly, there's an intense CME or coronal mass ejection. So when the sun belches this ginormous amounts of its atmosphere, of its charge particles headed out more than the usual solar wind, hit Earth 17 hours later and caused all sorts of chaos with catching fire, telegraph machines, auroras seen down in Caribbean, in Hawaii. I mean, so basically this caused an extreme version of all the usual solar wind we're getting hit with, and we see it in a smaller sense since then. But this was the big thing that continues to worry people today, which is it's not going to hurt you, but it can cause power grid failures, satellite damage, communication blackouts globally. It's a good time.

Skipping ahead. You had 1921, the New York Railroad storm, always a good name. Burned out and fires broke out control rooms of the New York Central Railroad, and they blamed space, a likely story. But March 1989 definitely got people's attention in Quebec, had another big CME, came in, caused chaos and knocked out the Hydro-Quebec power grid, leaving 6 million people without electricity for nine hours.

Sarah Al-Ahmed: God, that's terrifying. I could barely go three hours without power. And then without internet, I shrivel up. So I don't know how people survived.

Bruce Betts: Anyway, then there were the Halloween storms, which I think I slept through in October and November 2003, but other people did not. A series of solar flares with CMEs, including one of the largest ones ever measured and knocked out power in parts of Sweden. So sorry. There's also the danger that you damage satellites or at least knock them out. If we have warning of these things, you can do a couple things. You can turn your power grids if they have enough time. They can put them in a mode where they're not going to get damaged. If astronauts knew in this case, they buried themselves deeper in the ISS before the CME hit. So anyway, that's a long way of saying there's space weather and it can affect us, and in our modern world can affect us quite severely if we get one of those big CMEs.

Sarah Al-Ahmed: Fingers crossed that doesn't happen. I know Bill Nye had an episode about that in his show, The End is Nye, where everything gets completely messed up like some kind of giant solar storm. I mean, honestly, imagine what that would do to our modern society. And hopefully if it does happen, it's not a long-term effect because everything is so dependent on these systems. It's one more example of why understanding how the sun works and space exploration in general really honestly impacts life on Earth way more than people under understand. We love you, Sun. Please don't bake us alive.

Bruce Betts: So I'd like to, if it's okay with you, move on to Random Space Facts Rewind. That's right. Facts are so good we're visiting them again. Here it comes.

If the Earth were the size of a professional soccer ball, then Jupiter would be about the height of a professional soccer goal.

Sarah Al-Ahmed: Huh. Well, that's actually a great visual and also terrifying.

Bruce Betts: Yeah, no, it's impressive. Yeah. You can check out The Size of Space, one of my latest books with The Planetary Society, where I've shamelessly put a picture of my son from many years ago playing soccer, kicking the Earth towards Jupiter.

All right, everybody. Go out there, look up the night sky and think about whether you are bigger than a professional soccer ball or if you know anyone who is. I meant goal. Whatever. Thank you and good night.

Sarah Al-Ahmed: We've reached the end of this week's episode, but we'll be back next week with more space science and exploration. If you love the show, you can get Planetary Radio T-shirts at planetary.org/shop, along with lots of other cool spacey merchandise.

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Planetary Radio is produced by The Planetary Society in Pasadena, California and is made possible by our members from all over this beautiful planet whose lives have been touched by space exploration. You can join us as we work together to support space science and exploration around the world at planetary.org/join.

Mark Hilverda and Rae Paoletta are our associate producers. Casey Dreier is the host of our Monthly Space Policy edition, and Mat Kaplan hosts our Monthly Book Club edition. Andrew Lucas is our audio editor. Josh Doyle composed our theme, which is arranged and performed by Pieter Schlosser. My name is Sarah Al-Ahmed, the host and producer of Planetary Radio. And until next week, ad astra.