\n<\/p>\n
The multibillion-year story of life on Earth is defined by a handful of epochal transformations, such as the emergence of the cell, the rise of multicellular organisms and the biosphere\u2019s expansion from the primordial seas to the land and sky. Today, with life having crept into practically every possible niche on Earth, it may seem that there\u2019s nowhere else to go. But there is, of course, still one place that beckons as life\u2019s next evolutionary frontier: space. And humans are uniquely poised to propel this great transition by pushing out from our planetary cradle.<\/p>\n
That\u2019s the case Caleb Scharf makes in his latest book, The Giant Leap (Basic Books, 2025). Drawing on his expertise as senior scientist for astrobiology at NASA\u2019s Ames Research Center, he argues that our modern spacefaring era is not just a matter of geopolitical competition and technological innovation but also part of a deeper, more fundamental evolutionary imperative. For the first time in Earth\u2019s history, life\u2014with human technology as its agent\u2014can permanently expand from one lonely planet out into the rest of the solar system. Scharf calls this new trajectory the \u201cDispersal\u201d and notes it\u2019s becoming possible just as our ever growing dominion over Earth pushes the planet toward disruptive tipping points in climate change, biodiversity loss and resource use. This next great evolutionary transition, it seems, can\u2019t come too soon\u2014because the fate of life on Earth may ultimately depend on leaving our planet behind.<\/p>\n
Scientific American spoke with Scharf about some implications of this cosmic outlook\u2014from the physical limits of human expansion across the solar system to the dubious quest to build settlement on Mars and the political uncertainties that could stifle the Dispersal before it even starts.<\/p>\n
If you’re enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.<\/p>\n
[An edited transcript of the interview follows.]<\/p>\n
What was the genesis of this book?<\/p>\n
I\u2019d be dishonest if I didn\u2019t admit that it partly came about because I wanted to nerd out about space. But the deeper genesis was about examining the question of what it looks like, and what it means, when life moves beyond its planetary origins. There are lots of visions out there for our future in space and what happens when we\u2019ve built, you know, space elevators, and so on. They can get more and more fantastical. But they usually don\u2019t tell us about the big picture; they\u2019re attempts to imagine specifics of the future, which is really difficult, and so they\u2019re probably going to get things wrong. So I wondered if, instead, we could look at what might be called the natural history of space exploration\u2014of spaceflight as a sort of planetary phenomenon\u2014and what that would tell us.<\/p>\n
Let\u2019s talk about the Dispersal. What is that, exactly?<\/p>\n
As an astrobiologist who spends my days chewing over the nature of living systems at many different levels, in both abstract and practical terms, I\u2019m coming to this from a much broader perspective, thinking of our unfolding space age as another sort of evolutionary leap. Forget, for a minute, about the specifics of humans or even the specifics of how we\u2019re getting to space. If you think about it, gravity is glomming stuff together all across the universe to make stars and planets\u2014and eventually more and more complex chemistry. And, at least here on Earth, life arose and evolved. And now, billions of years later, we\u2019ve reached a point where our planet is throwing some sort of perverse tantrum and tossing\u2014dispersing!\u2014materials, machines and organisms back out into space. And I\u2019m interested in extrapolating this process and examining how far it can go.<\/p>\n
So the Dispersal is about what might happen to us, and all life, when it encounters scales of space and of resources that are unimaginably large. And just as you can imagine speciation happening when organisms are suddenly scattered across different terrains\u2014like the Gal\u00e1pagos Islands, for instance\u2014when life disperses beyond Earth, it can follow increasingly divergent trajectories. This means, among other things, that we\u2019re not necessarily talking about modern humans anymore in our extrapolations but whatever comes after us. It can seem kind of terrifying and awful that we might not fully recognize or identify with future \u201cdispersed\u201d versions of us, but those transformations aren\u2019t necessarily bad things.<\/p>\n
That means, I guess, that whatever the Dispersal is, it\u2019s not only about rocket science\u2014and it\u2019s not really about fantastic visions of space elevators or warp drives or the specific details of any posthuman future either. One thing I like about the book is how you\u2019re approaching this huge topic from a \u201cfirst principles\u201d perspective, initially focusing on fundamental things such as orbital mechanics that set various sorts of boundary conditions and shape the landscape of possibilities that may exist for us beyond Earth.<\/p>\n
Yeah, this concept of boundary conditions is really important\u2014the idea that certain phenomena can only happen within certain constraints, beyond which they can no longer take place. You need that to scope out the \u201clandscape,\u201d as you called it. Imagine a continent where humans have never set foot, and you\u2019re trying to predict what\u2019ll happen when they do\u2014you might say, for instance, they\u2019ll build a city, and that city will have a subway system. But if the whole continent is a waterlogged swamp, no one\u2019s going to build a subway there, and the planning for any city will have to account for the swampy conditions, and so the possibilities are different. It\u2019s the same for the solar system.<\/p>\n
There\u2019s a chapter in the book talking about all this, looking at the range of possibilities and challenges that exist for places close in to the sun, such as Mercury, to the other extreme, far-out places such as Neptune and even further afield. The obvious difference is sunlight, which is about seven times stronger at Mercury and more than 1,000 times fainter out at Pluto than at Earth. Usually, when an astrobiologist like me is talking about this, it\u2019s in the context of habitable zones, the physics- and chemistry-based potential for a world to have conditions such as an atmosphere, surface liquid water and other things that would allow life as we know it. But there are additional \u201czones\u201d to consider if you\u2019re thinking about how technological life might disperse itself in a planetary system. They are similarly related to availability of sunlight, of energy, but also things such as how much radiation you\u2019re exposed to and how easy any destination is to reach.<\/p>\n
It\u2019s actually really difficult to get to Mercury, for example, because it\u2019s so deep in the sun\u2019s gravity well\u2014the amount of energy you need to get there from Earth is on par with what you need to get to Jupiter and beyond. And because Mercury is so much closer up to the sun, you can be more vulnerable to nasty flares, and so on, whereas the further you get from the sun, the less you have to worry about solar activity but the more exposed you\u2019ll be to cosmic radiation, which has its own hazards.<\/p>\n
Accounting for all these, you might imagine a \u201czone of easiest exploration\u201d that will help you understand where we\u2019re likely to go elsewhere in the solar system and how we\u2019ll get there. That\u2019s how you get clues to what the Dispersal will look like.<\/p>\n
So, for most folks, this may be a really novel way of thinking about exploration and expansion in the solar system. But of course, for space nerds like us, lots of old, classic factions and debates pop out of this new framework.<\/p>\n
For instance, there\u2019s the choice of prioritizing sending humans to the moon\u2014as the U.S. and other nations are planning\u2014versus doing crewed missions to Mars. And there\u2019s also an argument that humans shouldn\u2019t be going to planets and moons at all and should instead stick to building space stations and other sorts of artificial orbital habitats. You discuss all this at length in the book, but I had trouble discerning which route you actually prefer.<\/p>\n
Well, in writing the book, I came to the conclusion that planets can be a real pain in the ass!<\/p>\n
We definitely need to study Mars and the moon, and maybe some of us should even try to live there. I mean, there\u2019s all sorts of genuine reasons for doing that. But in the long term, it\u2019s far better to engineer what you really need\u2014to create environments that place fewer stressors on life that evolved on Earth over four billion years. Even if you build fabulous habitats on the moon or Mars, you\u2019ll never have Earth-normal gravity in those places, for example.<\/p>\n
Whether you make use of a natural object such as an asteroid or just construct an entirely artificial habitat out there, both would give you far more options than a planetary surface. You can spin your habitat to get Earth-like artificial gravity; you can engineer a lovely atmosphere that precisely fits our biological needs. You can set up seasons, choose where to orbit and have robust protection from cosmic radiation.<\/p>\n
Relatedly, I get the sense you\u2019re not enamored with Elon Musk\u2019s dream of building cities on Mars. You even write in the book that if the rationale for Mars settlement is to safeguard humanity against existential risks, it would probably make more sense to skip Mars entirely in favor of building settlements deep underground on Earth. Why don\u2019t you find the \u201coccupy Mars\u201d arguments convincing?<\/p>\n
I think it\u2019s too easy to be the sort of the space enthusiast who sits in an armchair puffing on a cigar and saying, \u201cOh, yes, of course we\u2019ll go conquer and colonize space.\u201d Apart from feeling discomfort at all the sociopolitical baggage and privilege associated with that attitude, I think we simply can\u2019t afford to be so blinkered and blas\u00e9\u2014because these are unbelievably difficult and expensive things to do. And they can seem extremely disconnected from the problems that most humans face every day. So you\u2019ve got to have a really sensible, sane, reasonable motivation and explanation for why anyone should want to do this, and I don\u2019t think building a city on Mars is sufficient.<\/p>\n
Mars is a very interesting test bed for querying why we humans today, amid all our problems, should be thinking about any of this stuff. But I find today\u2019s focus on the Silicon Valley\u2013style \u201clet\u2019s make a backup for humanity\u201d outlook lacking. The way it\u2019s presented reeks of a utopian \u201cwe know best\u201d attitude\u2014\u201cWe\u2019re going to build some glorious new society on Mars!\u201d\u2014when, hey, living on Mars would probably be pretty dystopian no matter what.<\/p>\n
At the same time, yeah, no one with a big-picture view would seriously argue that life on Earth isn\u2019t subject to a variety of existential risks. So of course it makes sense to have some sort of backup\u2014and one way to do that would indeed be to create a self-sustaining permanent settlement on Mars populated with enough people to avoid everyone becoming inbred idiots. But I don\u2019t think this can be the sole motivating factor.<\/p>\n
So what\u2019s your preferred approach to Mars, then?<\/p>\n
In the book I tried to examine Mars exploration by ideological camps. There\u2019s the stance we just mentioned, you know, of \u201clet\u2019s immediately get lots of humans to Mars as an existential backup. To hell with the Martian environment or anything like that; this whole planet is just there for us to conquer and take.\u201d Then there\u2019s the pure science camp that says we really should be incredibly cautious but not entirely hands-off about sending humans or anything else to Mars, because we don\u2019t want to disrupt this near-pristine environment where there might be clues we simply can\u2019t get on Earth to the origins and fundamental nature of life. And then there\u2019s this sort of \u201cEarth first\u201d extreme, which says even the scientific stuff is too expensive, and space exploration as a whole is diverting attention from all the very pressing problems we have right here on Earth, so we should just stop doing it. Most debates about space policy tend to revolve around these views and usually end up in a stalemate.<\/p>\n
I advocate for a fourth kind of approach that, in some ways, is about reinventing how we do human exploration. We know how to \u201cconnect up\u201d and digitize a planet with sensors and satellites, and so on, because we\u2019ve done that on Earth, and we\u2019re learning how to work with our machines in new, incredibly tight-knit ways. If we really put all that to work on Mars, I think there\u2019s an opportunity to do all the things we want and to learn new ways to exist.<\/p>\n
And I guess the reason this same logic wouldn\u2019t apply to, say, the moon is that, in comparison with Mars, it offers dismal prospects for breakthroughs in our search for the origins of life.<\/p>\n
Right. The moon is also incredibly interesting and beautiful, and it\u2019s certainly much more accessible in terms of its proximity to us. And there are resources there such as water ice that could support interplanetary exploration needs. We could also learn about processes of biological contamination there. But the moon doesn\u2019t quite tick all the boxes the same way as Mars does, yeah.<\/p>\n
So, you know, it\u2019s not that the moon should be ignored\u2014and it may play a pivotal role in the next several decades\u2014but it\u2019s definitely a downgrade from Mars in my opinion.<\/p>\n
I ask about the moon for practical reasons. As you mention, it\u2019s much easier to reach, so in some respects maybe it\u2019s like a set of training wheels for more ambitious trips to Mars, and so on. This is, of course, another resurrection of a timeless debate\u2014some people would say it makes more sense to go to the moon first before making the bigger leap to Mars.<\/p>\n
That is to say, it feels like, in the book, you\u2019re laying out the wonders of the solar system\u2014 \u201clook at all these amazing worlds that await us!\u201d\u2014without much focus on what the path could be to get there. You\u2019re talking about the boundary conditions that exist, and the resulting zones where we might explore or even live, but less about the plausible routes by which those situations can become reality.<\/p>\n
You mentioned evolutionary leaps earlier, and I guess that\u2019s what I\u2019m getting at: it\u2019s not really clear to me how we\u2019re going to go from our comfortable, well-adapted lives here on Earth into, say, dwelling in city-sized space stations carved out of asteroids between Mars and Jupiter. That seems like, well\u2014a giant leap!<\/p>\n
That\u2019s a good observation. And it comes back to me not wanting to fall into the trap that\u2019s gotten so many people before, where someone will declare, \u201cClearly, this is the trajectory that things are going, and so this and that will absolutely happen!\u201d<\/p>\n
Imagine, for a moment, being back in 1968, watching three NASA astronauts on their way home to Earth after orbiting the moon for Apollo 8. You\u2019d think that the future was becoming clearer, right? We were about to send more astronauts back there\u2014to land. Maybe the Soviets would do it as well. There\u2019s going to be a lunar land rush, passenger flights to the moon and a flurry of new rockets and space stations, and then we\u2019ll be going to Mars in the 1970s. But of course, the complicated reality of human civilization got in the way, and most of that stuff didn\u2019t happen. We left that imagined trajectory for a different one\u2014if we were ever really on it in the first place.<\/p>\n
It\u2019s undeniable that \u201cspace\u201d is at another inflection point today. We\u2019re rapidly approaching the point where there will be at least one rocket launch per day into orbit, which is astonishing. There are now around 10,000 space-oriented companies around the world, which definitely wasn\u2019t the case 10 years ago. And I think it\u2019s fair to say even the growth in the value of Earth data obtained from space has shot up. So all the curves seem to be following this exponential upward slope. That\u2019s not a guarantee it keeps going. Regression is possible. Or maybe just a flattening of the curves into a plateau might happen\u2014which would still be interesting because then the question would be: Is there still something in the future that could occur to create more exponential growth?<\/p>\n
I don\u2019t know if that gets to your question exactly, but I feel there\u2019s sufficient evidence that something new is happening right now that we should pay attention to\u2014and it may presage the beginnings of the Dispersal. The point is: I don\u2019t think it\u2019s likely that we\u2019ll just repeat history, right? There will be surprises. It\u2019s no longer as simple as it was in the Apollo era, when you could really see most everything through the lens of \u201cthe U.S. versus the Soviets\u201d in space.<\/p>\n
The situation we have today is a much richer, more complicated set of motivations, actors and capabilities. So it becomes more relevant to consider the ultimate end points in those vast scales and resources of the solar system and what those limits might mean\u2014rather than the limits of earthly thinking about what will happen next week.<\/p>\n
Overall, it seems you\u2019re presenting a pretty optimistic big picture of where we\u2019re going from here. But to zoom in on smaller details for a moment, you\u2019re also saying this while being furloughed from your NASA work because of the latest U.S. government shutdown while the space agency is facing steep budget cuts and workforce reductions\u2014things that I\u2019d imagine someone like you would be pessimistic about. How do you reconcile this?<\/p>\n
Let me start by saying that finding the bigger perspective always helps in times of uncertainty! In that context, I think the Dispersal is a hugely positive idea, with relevance no matter what the current earthly circumstances are. What life often does when it disperses is find opportunities to do better. The human species is no different. And the universe seems to be tilted towards making that happen. So, to some degree, I think it\u2019s out of any one group\u2019s control.<\/p>\n
Space exploration is happening; there\u2019s just a critical mass of financial interests, of people\u2019s pet interests, of individuals with resources who are interested in this, of countries that still see the enormous value in having access to space for all sorts of reasons\u2014economic reasons, security reasons or maybe just for national pride. With all these players, I think we\u2019re crossing a threshold that we didn\u2019t quite get to in the 1960s and 1970s. And having so many players in the mix also means that who gets to do what first is an open question.<\/p>\n
That is relevant to your point about NASA\u2014I\u2019m speaking personally here and not for the agency in any way. It\u2019s irrefutable that the pioneering efforts of NASA have been key for getting space exploration to where it is today. We\u2019ve learned that when you solve the hard problems of space with long-term investments in science, engineering and people, it paves the way for others to further innovate. That\u2019s great because the hard problems will keep coming. We just need to figure out how to keep this special recipe working.<\/p>\n
Where I\u2019m not optimistic is the idea that we\u2019ll get together as a species and draw up some unified master plan for humanity and space. Forget it. That\u2019s not happening, right? But I think that\u2019s okay. What we\u2019re going to see are multiple ideas and efforts and innovations all at once at a level that hasn\u2019t existed ever before. And in retrospect, it makes a lot of sense that it\u2019s happening like this rather than how it looked like it might for most of the 20th century. Throughout human history, there have been moments where advances just \u201ccome together,\u201d whether it was the printing press or mass transport or telecommunications or computing and the Internet. These are invariably fueled by science, as well as by competing interests in realms of economic or commercial opportunity, driving investments in multiple places.<\/p>\n
I feel like that\u2019s where we\u2019re at now with space. And that, to me, is new and pretty amazing.<\/p>\n","protected":false},"excerpt":{"rendered":"
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