Tag: planets

On lunar exploration

The Moon. Our closest celestial neighbor, the body that gives light to our nights. We’re coming up on the 50th anniversary of mankind’s greatest achievement: walking upon that body. And we’re losing the heroes who accomplished that feat. With the recent death of Alan Bean, only 4 of the 12 remain alive.

Something must be done on that front. We can’t let the direct, personal exploration of our natural satellite pass out of living memory. Some private corporations (e.g., SpaceX, Boeing) are looking into the matter. Next July would be a fantastic time to make a power move in that space race.

But let’s take a step back, look at exploring the Moon from a storytelling perspective. That is, after all, what we do here. For the budding author of science fiction, dear Luna presents an interesting setting not entirely unlike Earth’s deserts, the deepest ocean trenches, or the vast emptiness of space.

The right stuff

As you know (unless you’re one of those lunatics—note the pun there—who thinks the whole thing was a hoax, in which case I have nothing more to say to you), 12 American men walked on the surface of the Moon between 1969 and 1972. A total of 24 traveled there, including those who merely orbited it. Stays ranged from a few hours on Apollo 11 to over 3 days on the final mission, Apollo 17. EVAs (moonwalks) lasted as long as 7 hours. And they did it all with 60s-era technology, with so many corners cut that it’s a wonder nobody died in space.

Since then, and even during the golden years of the Space Age, the media has been enamored with lunar exploration and cis-lunar travel in general. But that fascination extends much deeper into history. Jules Verne’s From the Earth to the Moon, written about a century before Neil Armstrong’s small step, set the original standard for the subgenre. Pulp action from the early and mid 20th century painted a distinct picture of the Moon that today’s generation mostly knows from Looney Tunes and The Jetsons.

In the now five decades since Apollo 8’s “Earthrise” picture, we have the data to make much better fictional accounts. Some of the best, in my opinion, are actually biographical in nature: Apollo 13, as well as From the Earth to the Moon, the HBO miniseries named after Verne’s seminal work. More recently, we also have Moon from about a decade ago, the found-footage horror film Apollo 18, and many others. Advances in technology and cinematography can transport viewers straight to the Sea of Tranquility, Tycho crater, or any number of other lunar locations.

Literary fiction doesn’t have movie magic, but the same fire burns in the book world. Andy Weir’s Artemis, for instance, shows that writers’ love for the ball of rock next door has not waned completely. Mars might get more airtime, but the Moon is so much closer. It’s the perfect stepping stone, both for a species and an author.

Magnificent desolation

But the Moon also presents problems. In that, it’s both a setting and a source of environmental conflict, much like the “middle” Mars in my post about the Red Planet. Take out the dust storms (because there’s no significant atmosphere) and the months-long travel time, and you don’t have all that much difference.

The Moon has about half of Mars’ gravity, 1/6 g instead of 3/8, which can present more physiological and medical problems. Lunar dust is a well-known source of trouble. Without air—what little atmosphere the Moon has seems to come from solar wind interacting with dust particles—you have to search for consumables. Radiation is a much greater concern, more like the trip to Mars rather than living on its surface. All told, it’s not a place friendly to life in the least.

Yet there are upsides to the Moon. Besides its proximity to Earth, you have the simple fact that it’s tide-locked to us. Anywhere on the near side will always be in radio contact with some part of our planet. (Conversely, the far side is in total radio silence, one reason why so many astronomers want a telescope out there.) Building material is cheap and plentiful; lunar regolith has the potential to make decent concrete, according to some studies, and recent surveys indicate that our satellite, like so many in the outer system, may have a massive storehouse of water lurking beneath the surface. Also, unlike Mars, Europa, and the asteroids, the Moon is in Earth’s orbit, and thus close enough to the Sun for solar power to be reasonably efficient, so no need for perfectly safe, yet politically unviable, nuclear options.

Sailing the seas

The Moon might not make a good home for humanity. The hazards are too great. In the single sci-fi setting I’ve created, with the present day set in the 26th century, all that progress has seen only limited colonization of Luna. It’s treated more like a combination of Antarctica and an offshore oil platform. Space opera and science fantasy fans might differ on that point, and that’s okay. It’s your call.

Whatever your moon ultimately becomes, it’ll start as an exploration target. Somebody has to continue the story Apollo left unfinished. And that will likely be sometime relatively soon. Definitely in the 21st century, unless you’ve written some serious disaster that forces a period of technological regression, and very possibly in the next decade or two. (A good date for the first lunar colony, if you’re following a realistic timeline, is 2069, of course.) Robotic surveys will come first, as they do, but then you’ll get the flags and footprints, the serious scientific investigations, and all that great stuff.

What those first explorers will find is anyone’s guess; I’m just here to tell you how I would write it. For the Moon, given its hostile environment, its lifeless nature, and its desolate appearance, I can certainly see a scientific thriller aspect. Every step takes you farther from the safety of your capsule/module/whatever. One wrong move can send you tumbling down the slope of a crater. Abrasive dust wears away the seals on your suit, not to mention the damage it might do to your lungs. (It smells like gunpowder, according to eyewitness accounts.)

It’s not hard to create terror on a lunar excursion, and that’s without invoking alien artifacts and the like. If that’s what you’re going for, then play it to the hilt. Yes, this is dangerous work. Yes, anything can go wrong, and the consequences are dire. But it’s a job that has to be done, whether for the good of humanity, scientific progress, or cold, hard cash.

On the other hand, part of the allure of exploration is, well, the allure. You’re exploring a whole new world. Maybe not a planet, but it’s still virgin territory for the most part, and the next wave of lunar excursions may take place hundreds of miles from the nearest human footprints. Wonder is the order of the day. As barren and bland as the lunar surface is, many of the moonwalkers would later wax philosophically about its “stark beauty”. For a story about the exploration itself, about painting a picture with the Moon as backdrop, that’s probably the aspect you want to emphasize. The craters, the rills, the lava tubes and other strange sights.

Exploration is fun. So many of my own works feature it, because I truly believe that humanity’s greatest moments come when we explore. Space is the final frontier, and the Moon is the first step into that frontier, the very border of an endless land of opportunity. It may be inhospitable. It may be inimical to life as we know it. That doesn’t mean it isn’t worth experiencing.

Exoplanets for builders

In just over two decades, we’ve gone from knowing about nine planets (shut up, Pluto haters) to recognizing the existence of thousands of them. Almost all of those are completely unsuitable for life as we know it, but researchers say it’s only a matter of time before we find “Earth 2.0”. Like any other 2.0 version, I’m sure that one will have fewer features and be harder to use, but never mind that.

As so many science fiction writers like to add in a large helping of verisimilitude, I thought I’d write a post summarizing what we know about planets outside our solar system, or exoplanets, as we enter 2017. Keep in mind that there’s a lot even I don’t know, although I’ve been following the field as a lay observer since 2000. Nonetheless, I hope there’s enough in here to stimulate your imagination. Also, this will necessarily be a technical post, so fantasy authors beware.

What we know

We know planets exist beyond our solar system. They’ve been detected by the way they pull on their stars as they orbit (the Doppler or radial velocity method), and that’s how we found most of the early ones. The majority of those known today, thanks to the Kepler mission, have been discovered by searching for the change in their stars’ light intensity as the planets pass before them: the transit method. In addition, we have a few examples of microlensing, where the gravity of a planet bends the light of a “background” star ever so slightly. And we’ve got a handful of cases where we’ve directly imaged the planets themselves, though these tend to be very, very large planets, many times the size of Jupiter.

However we see them, we’re sure they’re out there. They can’t all be false positives. And thanks to Kepler, we’ve got enough data to start drawing some conclusions. Of course, these must be considered subject to change, but that’s the way of science.

First, our solar system, with its G-type star orbited by anywhere from eight to twenty planets (depending on who’s counting) starting at about 0.3 AU, looks very much like an outlier. We don’t have a “hot Jupiter”, a gas giant exceedingly close to the star, with an orbit on the order of days. Nor do we have a “warm Neptune” (a mid-range gaseous planet somewhere in the inner system) or a “super-Earth” (a larger terrestrial world, possibly with a thick atmosphere). This doesn’t mean we’re unique, though, only that we can’t assume our situation is the norm.

Second, we’ve got a pretty good idea about which stars have planets. To a first approximation, that’s all of them, but the reality is a little more nuanced. Bright giants don’t have time to form planets. Small red dwarfs don’t have the material to create Jupiter-size giants. Neither of these statements is an absolute—we’ve got examples of gas giants around M-class stars—but they’re tendencies. Everything else, seemingly, is up in the air.

What we can guess

Planets do appear to be everywhere we look. There are more of them around M stars, but that’s largely because there are so many more M stars to begin with. A lot of stars have planets with much closer orbits, so close that you wouldn’t expect them to form. Gas giants aren’t restricted to the outer system, like they are here. And there’s a whole class, the super-Earths, that we never knew existed.

We can make some educated guesses about some of these planets. For example, many of the super-Earths, according to computer simulations, may actually be tiny versions of Neptune, so-called “gas dwarfs”. If that’s true, it severely cuts our number of potentially habitable worlds. On the other hand, the definition of the habitable zone has only expanded since we started finding exoplanets. (Even in our own solar system, what once was merely Earth and maybe the Martian underground now includes Europe, Titan, Enceladus, Ganymede, Ceres, the cloud tops of Venus, and about a dozen more exotic locales.) Likewise, studies suggest that a tide-locked planet around a red dwarf star doesn’t have to be frozen on one side and scorched on the other.

We’ve got a few points where we don’t even have data, though. One of these, possibly the most important for a writer, is the frequency of Earthlike worlds. By “Earthlike”, I don’t simply mean terrestrial, but terrestrial and capable of having liquid water on the surface. Where’s the closest one of those? Until about a year ago, the answer might have been anywhere from 15 to 500 light-years away. But then came Proxima b. If it turns out to be potentially habitable—in the month and a half between my writing this post and it going up, we may very well know—then that almost ensures that Earthlike worlds are everywhere. Because what are the chances that the next-closest star to the Sun has one, too?

Creating a planet

For the speculative writer, this lack of knowledge is a boon. We have the freedom to create, and there are few definite boundaries. Want to put a gas giant in the center of a star’s habitable zone, with multiple Earthlike moons? We can’t prove it’s impossible, and the real-life counterpart might really be out there, waiting to be found.

Basically, here’s a rundown of some of the factors that go into creating an exoplanet:

  • Star size: Bigger stars are shorter-lived, but smaller ones require their “classically” habitable planets to be much closer, to the point where they’ll likely be tide-locked. G-type dwarfs like ours are a happy medium, but not a common one: something like 1% of stars are in the G class, and there’s not much data saying that planets are more likely around them.

  • Star number: Most stars, it seems, are in multiple systems. Binaries can host planets, though; we’ve detected a class of “Tatooine” planets (named after the one in Star Wars, because scientists are nerds) circling binary systems. For close binaries, this is a fairly stable arrangement, but with huge complexities in working out parameters like temperature. Distant binaries like Alpha Centauri can instead have individual planetary systems.

  • Planet size: We used to think there was a sharp cutoff between terrestrial and gaseous planets, based on the difference between the largest terrestrial we knew (Earth) and the smallest gas planets (Uranus and Neptune). Now we know that’s simply not true. It’s more of a continuum, and there may be super-Earths much larger than the smallest mini-Neptunes. And those gas dwarfs appear to be the most common type of planet, but that could be nothing more than observation bias, the way we thought hot Jupiters were incredibly common ten years ago. On the smaller end of the scale, we haven’t found much, but there’s no reason to expect that exoplanet analogues of Mars, Mercury, Pluto, and Ganymede don’t exist.

  • Surface temperature: This is a big one, as it’s critical for life as we know it. We know that liquid water exists between 0° and 100°C (32–212°F), with the upper bound being a bit fluid due to atmospheric pressure. That 100 (or 180) degrees is a lot of room to play with, but remember that it’s not all available. DNA, for example, can break down above about 50°C. Below freezing, of course, you get into subsurface oceans, which might be fun for exploration purposes.

  • Atmosphere: Except for a couple of gas giants, we’ve got nothing here. We have no idea if the nitrogen-oxygen mix of Earth is common, or if most planets we find would be CO2 pressure cookers like Venus. Or they could retain their primordial hydrogen-helium atmospheres, or be nearly airless like Mars. Something tells me that we’ll find all of those soon enough.

  • Life: And so we come to this. Life, we know, changes a planet, just as the planet changes it. A biosphere will be detectable, even from the distance of light-years. It will get noticed, once telescopes and instruments are sensitive enough to see it. And it will stand out. Some chemicals just don’t show up without life, or at least not in the quantities that it brings. Methane, O2, and a few others are considered likely biotic markers. The million-dollar question is just how likely life really is. Is it everywhere? Are there aliens on Proxima b right now? If so, are they single-celled, or possibly advanced enough to be looking back at us? Here is the writers’ playground.

What’s to come

Assuming the status quo—never a safe assumption—our capability for detecting and classifying exoplanets is only expected to increase in the coming years. But I’ve heard that one before. Once upon a time, the timeline looked like this: Kepler in 2004 or 2005, the Space Interferometry Mission (SIM) in 2009, and the Terrestrial Planet Finder (TPF) in 2012. In reality, we got Kepler in 2009 (it’s now busted and on a secondary mission). TPF was “indefinitely deferred”, and SIM was left to languish before being mercy-killed some years ago. The Europeans did no better; their Darwin mission suffered the same let’s-not-call-it-cancelled fate as TPF. Now, both missions might get launched in the 2030s…but they probably won’t.

On the bright side, we’ve got a small crop of upcoming developments. TESS (Transiting Exoplanet Sky Survey, I think) is slated to launch this year—I’ll believe it when I see it. The James Webb Space Telescope, the Hubble’s less-capable brother, might go up in 2018, but its schedule is going to be too crowded to allow it to do more than confirm detections made by other means.

Ground-based telescopes are about at their limit, but that hasn’t stopped us from trying. The E-ELT is expected to start operations in 2024, the Giant Magellan Telescope in 2025, and these are exoplanet-capable. The Thirty Meter Telescope was supposed to join them in about the same timeframe, but politically motivated protests stopped that plan, and the world is poorer for it.

Instead of focusing on the doom and gloom, though, let’s look on the bright side. Even with all the problems exoplanet research has faced, it’s made wonderful progress. When I was born, we didn’t know for sure if there were any planets outside our own solar system. Now, we’re finding them everywhere we look. They may not be the ones science fiction has trained us to imagine, but truth is always stranger than fiction. Forget about “Earth 2”. In a few years, we might have more Earths than we know what to do with. And wouldn’t that make a good story?

Mars: fantasy and reality

Mars is in the public consciousness right now. The day I’m writing this, in fact, NASA has just announced new findings that indicate flowing water on the Red Planet. Of course, that’s not what most people are thinking about; the average person is thinking of Mars because of the new movie The Martian, a film based on a realistic account of a hypothetical Mars mission from the novel of the same name.

We go through this kind of thing every few years. A while back, it was John Carter. A few years before that, we had Mission to Mars and Red Planet. Go back even further, and you get to Total Recall. It’s not really that Mars is just now appearing on the public’s radar. No, this goes in cycles. The last crop of Martian movies really came about from the runaway success of the Spirit and Opportunity rovers. Those at the turn of the century were inspired by earlier missions like Mars Pathfinder. And The Martian owes at least some of its present hype to Curiosity and Phoenix, the latest generation of planetary landers.

Move outside the world of mainstream film and into written fiction, though, and that’s where you’ll see red. Mars is a fixture of science fiction, especially the “harder” sci-fi that strives for realism and physical accuracy. The reasons for this should be obvious. Mars is relatively close, far nearer to Earth than any other body that could be called a planet. Of the bodies in the solar system besides our own world, it’s probably the least inhospitable, too.

Not necessarily hospitable, mind you, but Mars is the least bad of all our options. I mean, the other candidates look about as habitable as the current Republican hopefuls are electable. Mercury is too hot (mostly) and much too difficult to actually get to. Venus is a greenhouse pressure cooker. Titan is way too cold, and it’s about a billion miles away, to boot. Most everything else is an airless rock or a gas giant, neither of which scream “habitable” to me. No, if you want to send people somewhere useful in the next couple of decades, you’ve got two options: the moon and Mars. And we’ve been to the moon. (Personally, I think we should go back there before heading to Mars, but that seems to be a minority opinion.)

But say you want to write a story about people leaving Earth and venturing out into the solar system. Well, for the same reasons, Mars is an obvious destination. But the role it plays in a fictional story depends on a few factors. The main one of these is the timeframe. When is your story set? In 2050? A hundred years from now? A thousand? In this post, we’ll look at how Mars changes as we move our starting point ahead in time.

The near future

Thanks to political posturing and the general anti-intellectual tendencies of Americans in the last generation, manned spaceflight has taken a backseat to essentially everything else. As of right now, the US doesn’t even have a manned craft, and the only one on the drawing board—the Orion capsule—is intentionally doomed to failure through budget cuts and appropriations adjustments. The rest of the world isn’t much better. Russia has the Soyuz, but it’s only really useful for low-Earth orbit. China doesn’t have much, and they aren’t sharing, anyway. Private companies like SpaceX are trying, but it’s a long, hard road.

So, barring a reason for a Mars rush, the nearest future (say, the next 15-20 years) has our planetary neighbor as a goal rather than a place. It’s up there, and it’s a target, but not one we can hit anytime soon. The problem is, that doesn’t make for a very interesting story.

Move up to the middle of this century, starting around 2040, and even conservative estimates give us the first manned mission to Mars. Now, Mars becomes like the moon in the 1960s, a destination, a place to be conquered. We can have stories about the first astronauts to make the long trip, the first to blaze the trail through interplanetary space.

With current technology, it’ll take a few months to get from Earth to Mars. The best times happen once every couple of years; any other time would increase the travel duration dramatically. The best analogy for this is the early transoceanic voyages. You have people stuck in a confined space together for a very long time, going to a place that few (or none) have ever visited, with a low probability of survival. Returning early isn’t an option, and returning at all might be nearly impossible. They will run low on food, they will get sick, they will fight. Psychology, not science, can take center stage for a lot of this kind of story. A trip to Mars can become a character study.

The landing—assuming they survive—moves science and exploration back to the fore. It won’t be the same as the Apollo program. The vagaries of orbital mechanics mean that the first Mars missions won’t be able to pack up and leave after mere hours, as Apollo 11 did. Instead, they’ll be stuck for weeks, even months. That’s plenty of time to get the lay of the land, to do proper scientific experiments, to explore from ground level, and maybe even to find evidence of Martian life.

The middle

In the second half of this century, assuming the first trips are successful, we can envision the second stage of Mars exploration. This is what we should have had for the moon around 1980; the most optimistic projections from days gone by (Zubrin’s Mars Direct, for example) put it on Mars around the present day. Here, we’ve moved into a semi-permanent or permanent presence on Mars for scientific purposes, a bit like Antarctica today. Shortly after that, it’s not hard to envision the first true colonists.

Both of these groups will face the same troubles. Stories set in this time would be of building, expanding, and learning to live together. Mars is actively hostile to humans, and this stage sees it becoming a source of environmental conflict, an outside pressure acting against the protagonists. Antarctica, again, is a good analogy, but so are the stories of the first Europeans to settle in America.

The trip to Mars won’t get any shorter (barring leaps in propulsion technology), so it’s still like crossing the Atlantic a few centuries ago. The transportation will likely be a bit roomier, although it might also carry more people, offsetting the additional capacity. The psychological implications exist as before, but it’s reasonable to gloss over them in a story that doesn’t want to focus on them.

On the Red Planet itself, interpersonal conflicts can develop. Disasters—the Martian dust storm is a popular one—can strike. If there is native life in your version of Mars, then studying it becomes a priority. (Protecting it or even destroying it can also be a theme.) And, in a space opera setting, this can be the perfect time to inject an alien artifact into the mix.

Generally speaking, the second stage of Mars exploration, as a human outpost with a continued presence, is the first step in a kind of literary terraforming. By making Mars a setting, rather than a destination, the journey is made less important, and the world becomes the focus.

A century of settlement

Assuming our somewhat optimistic timeline, the 22nd century would be the time of the land grab. Propulsion or other advances at home make the interplanetary trip cheaper, safer, and more accessible. As a result, more people have the ability to venture forth. Our analogy is now America, whether the early days of colonization in the 17th century or the westward push of manifest destiny in the 19th.

In this time, as Mars becomes a more permanent human settlement, a new crop of plot hooks emerges. Social sciences become important once again. Religion and government, including self-government, would be on everyone’s minds. Offshoot towns might spring up.

And then we get to the harder sciences, particularly biology. Once people are living significant portions of their lives on a different planet, they’ll be growing their own food. They’ll be dying, their bodies the first to be buried in Martian soil. And they’ll be reproducing.

Evolution will affect every living thing born on Mars, and we simply don’t know how. The lower gravity, the higher radiation, the protective enclosure necessary for survival, how will these changes affect a child? It won’t be an immediate change, for sure, but the second or third generation to be born on Mars might not be able to visit the birthplace of humanity. Human beings would truly split into two races—a distinction that would go far beyond mere black and white—and the word Martian would take on a new meaning.

Mars remains just as hostile as before, but it’s a known danger now. It’s the wilderness. It’s a whole world awaiting human eyes and boots.

Deeper and deeper

As time goes by, and as Mars becomes more and more inhabited, the natural conclusion is that we would try to make it more habitable. In other words, terraforming. That’s been a presence in science fiction for decades; one of the classics is Kim Stanley Robinson’s Mars trilogy, starting with Red Mars.

In the far future, call it about 200 years from now, Mars can truly begin to become a second planet for humanity. At this point, people would live their whole lives there, never once leaving. Towns and cities could expand, and an ultimate goal might arise: planetary independence.

But the terraforming is the big deal in this late time. Even the best guesses make this a millennia-long process, but the first steps can begin once enough people want them to. Thickening the atmosphere, raising the worldwide temperature, getting water to flow in more than the salty tears NASA announced on September 28, these will all take longer than a human lifetime, even granting extensive life-lengthening processes that might be available to future medicine.

For stories set in this time, Mars can again become a backdrop, the set upon which your story will take place. The later the setting, the more Earth-like the world becomes, and the less important it is that you’re on Mars.

The problems these people would face are the same as always. Racial tensions between Earthlings and Martians. The perils of travel in a still-hostile land. The scientific implications of changing an entire world. Everything to do with building a new society. And the list goes on, limited only by your imagination.

Look up

Through the failings of our leaders, the dream of Mars has been delayed. But all is not lost. We can go there in our minds, in the visuals of film, the words of fiction. What we might find when we arrive, no one can say. The future is what we make of it, and that is never more true than when you’re writing a story set in it.

Exoplanets: an introduction for worldbuilders

With the recent discovery of Kepler-452b, planets beyond our solar system—called extrasolar planets or exoplanets—have come into the news again. This has already happened a few times: the Gliese 581 system in 2007 (and again a couple of years ago); the early discoveries of 51 Pegasi b and 70 Virginis b in the mid 1990s; and Alpha Centauri, our nearest known celestial neighbor, in 2012.

For an author of science fiction, it’s a great time to be alive, reminiscent of the forties and fifties, when the whole solar system was all but unknown and writers were only limited by their imaginations. Planets, we now know, are just about everywhere you look. We haven’t found an identical match to Earth (yet), and there’s still no conclusive evidence of habitation on any of these newfound worlds, but we can say for certain that other planets are out there. So, as we continue the interminable wait for the new planet-hunters like TESS, the James Webb Space Telescope, Gaia, and all those that have yet to leave the drawing board, let’s take a quick look at what we know, and how we got here.

Before it all began: the 1980s

I was born in 1983, so I’ve lived in four different decades now, and I’ve been able to witness the birth and maturity of the study of exoplanets. But younger people, those who have lived their whole lives knowing that other solar systems exist beyond our own, don’t realize how little we actually knew not that long ago.

Thirty years ago, there were nine known planets. (I’ll completely sidestep the Pluto argument in this post.) Obviously, we know Earth quite well. Mars was a frontier, and there was still talk about near-term manned missions to go there. Venus had been uncovered as the pressure cooker that it is. Jupiter was on the radar, but largely unknown. Mercury was the target of flybys, but no orbiter—it was just too hard, too expensive. The Voyager mission gave us our first up-close looks at Saturn and Uranus, and Neptune would join them by the end of the decade.

Every star besides the Sun, though, was a blank slate. Peter van de Kamp claimed he had detected planets around Barnard’s Star in the 1960s, but his results weren’t repeatable. In any case, the instruments of three decades past simply weren’t precise enough or powerful enough to give us data we could trust.

What this meant, though, was that the field was fertile ground for science fiction. Want to put an Earthlike planet around Vega or Arcturus? Nobody could prove it didn’t exist, so nobody could say you were wrong. Solar systems were assumed to be there, if below our detection threshold, and they were assumed to be like ours: terrestrial planets on the inside, gas giant in the outer reaches, with one or more asteroid belts here or there.

The discoveries: the 1990s

As the 80s gave way to the 90s, technology progressed. Computers got faster, instruments better. Telescopes got bigger or got put into space. And this opened the door for a new find: the extrasolar planet. The first one, a huge gas giant (or small brown dwarf, in which case it doesn’t count), was detected in 1989 around the star HD 114762, but it took two years to be confirmed.

And then it gets weird. In 1992, Aleksander Wolszczan and Dale Frail discovered irregularities in the emissions of a pulsar designated PSR B1257+12. There’s not much out there that can mess up a pulsar’s, well, pulsing, but planets could do it, and that is indeed what they found. Two of them, in fact, with a third following a couple of years later, and the innermost is still the smallest exoplanet known. (I hope that will be changed in the not-too-distant future.) Of course, the creation of a pulsar is a wild, crazy, and deadly event, and the pulsar planets brought about a ton of questions, but that need not concern us here. The important point is that they were found, and this was concrete proof that other planets existed beyond our solar system.

Then, in the middle of the decade, the floodgates opened a crack. Planets began to be discovered around stars on the main sequence, stars like our sun. These were all gas giants, most of them far larger than Jupiter, and many of them were in odd orbits, either highly eccentric or much too close to their star. Either way, our solar system clearly wasn’t a model for those.

As these “hot Jupiters” became more and more numerous, the old model had to be updated. Sure, our solar system’s progression of terrestrial, gaseous, and icy (with occasional asteroids thrown in) could still work. Maybe other stars had familiar systems. After all, the hot Jupiters were an artifact of selection bias: the best method we had to detect planets—radial velocity, which relies on the Doppler effect—was most sensitive to large planets orbiting close to a star. But the fact that we had so many of them, with almost no evidence of anything resembling our own, meant that they had to be accounted for in fiction. Thus, the idea of a gas giant having habitable moons begins to grow in popularity. Again, there’s no way to disprove it.

Acceptance: the 2000s

With the turn of the millennium, extrasolar planets—soon to be shortened to the “exoplanet” moniker in popular use today—continued to come in. Advances in technology, along with the longer observation times, brought the “floor” of size further and further down. Jupiter analogues became fairly common, then Saturn-alikes. Soon, Uranus and Neptune had their clones in distant systems.

And Earth 2 was in sight, as the major space agencies had a plan. NASA had a series of three instruments, all space-based, each increasingly larger, that would usher in a new era of planetary research. Kepler would be launched around 2005-2007, and it would give us hard statistics on the population of planets in our galaxy. The Space Interferometry Mission (SIM) would follow a few years later, and it would find the first true Earthlike planets. Later, in the early to mid 2010s, the Terrestrial Planet Finder (TPF) would locate and characterize planets like Earth, showing us their atmospheres and maybe even ocean coverage. In Europe, ESA had a similar path, with CoRoT, Gaia, and Darwin.

And we know how that turned out. Kepler was delayed until 2009, and it stopped working a couple of years ago. SIM was defunded, then canceled. TPF never got out of the planning stages. Across the ocean, CoRoT launched, but it was nowhere near as precise as they thought; it’s given us a steady stream of gas giants, but not much else. Gaia is currently working, but also at a reduced capacity. Darwin met the same sad fate as TPF.

But after all that doom and gloom had passed, something incredible happened. The smallest of the new discoveries were smaller than Neptune, but still larger than Earth. That gap in mass (a factor of about 17) is an area with no known representatives in our solar system. Logically, this new category of planet quickly got the name “super-Earth”. And some of these super-Earths turned up in interesting places: Gliese 581 c was possibly within its star’s habitable zone, as was its sister planet, Gliese 581 d. Sure, Gliese 581 itself was a red dwarf, and “c” has a year that lasts less than one of our months, but it was a rocky planet in an orbit where liquid water was possible. And that’s huge.

By the end of 2009, super-Earths were starting to come into their own, and Kepler finally launched, promising to give us even more of them. Hot Jupiters suddenly became oddballs again. And science fiction has adapted. Now there were inhabited red dwarf planets, some five to ten times Earth’s mass, with double the gravity. New theories gave rise to imagined “carbon planets”— bigger, warmer versions of Titan, with lakes of oil and mountains of diamond—or “ocean worlds” of superheated water, atmospheric hydrogen and helium, and the occasional bit of rocky land.

Worldbuilding became an art of imagining something as different from the known as possible, as all evidence now pointed to Earth, and indeed the whole solar system, as being an outlier. For starters, it’s a yellow dwarf, a curious part of the main sequence. Just long-lived enough for planets to form and life to evolve, yet rare enough that they probably shouldn’t. Red dwarfs, by contrast, are everywhere, they live effectively forever, and we know a lot of them have planets.

Here and now: the 2010s

Through the first half of this decade, that’s pretty much the status quo. Super-Earths seem to be ubiquitous, “gas dwarfs” like Neptune numerous, and hot Jupiters comparatively rare. There’s still a lot of Kepler data to sift through, however.

But now we’ve almost come full circle. At the start of my lifetime, planets could be anything. They could be anywhere. And planetary systems probably looked a lot like ours.

Then, we started finding them, and that began to constrain our vision. The solar system was now rare, statistically improbable or even impossible. Super-Earths, though, were ascendant, and they offered a new inspiration.

And, finally, we come to Kepler-452b. It’s still a super-Earth. There’s no doubt about that, as even the smallest estimate puts it at 1.6 Earth masses. But it’s orbiting a star like ours, in a spot like ours, and it joins a very select group by doing that. In the coming years, that group should expand, hopefully by leaps and bounds. But it’s what 452b states that’s important: Earthlike planets are out there, in Earthlike orbits around Sunlike stars.

For worldbuilders, that means we can go back to the good old days. We can make our fictional worlds match our own, and nobody can tell us that they’re unlikely to occur. Thirty years ago, we could write whatever we wanted because there was no way to disprove it. Now, we can write what we want because it just might be proven.

What a time to build a world.