The Fermi Paradox: Solar Flares
This video is sponsored by CuriosityStream. Get access to my streaming video service, Nebula, when you sign up for CuriosityStream using the link in the description. We view our sun as eternal and stable, the object around which the day revolves and which has been and always will be, and yet it is a whirling mass of chaos and storms of fire.
In September of 1859, a year-and-a-half before the American Civil War began, 162 years before this recording, Earth experienced the Carrington Event, the most powerful geomagnetic storm ever recorded. Telegraph systems all over North America and Europe went haywire. Telegraph line towers buzzed and arced, sending sparks to the ground. In some places, the arcing started fires in dry grass. Several telegraph operators received severe shocks, and in a few offices metal contacts melted and papers near the wires caught fire.
With telegraphers busy putting out fires and many lines shorting out, America’s only fast long-distance communication network was mostly shut down. And that meant trains had to be postponed too for safety. Most interestingly though, or perhaps most eerily to the bewildered operators, offices connected by the lines that hadn’t shorted out found that they could still send each other messages even after they’d disconnected their power supplies—and the signals were actually clearer than normal.
Electricity was literally in the air--and that’s not really where we want it. The mid-19th century was not an era very reliant on electricity or radio, so beyond those telegraph disruptions and folks being able to see Aurora for the first time in places it normally is never seen, this event was not disastrous. No event as powerful has happened since, and a good thing too, as it would wreak havoc on our modern high-tech infrastructure. It’s hard to solidly estimate such things in advance, but estimates of the worldwide cost of the direct damage and aftermath are in the $1 to $2 trillion range. Antarctic ice core samples contain traces of the Nitrogen Oxide produced in the atmosphere by such heavy electrical activity, and that data seems to indicate that the 1859 Carrington Event was at least twice as big as any other solar storm of the past 500 years.
Lesser but still significant events happen far more frequently, typically driven by solar flares, and we have good reason to think our own sun is atypically stable, though we’re not at all certain how common they are on other stars like our Sun. Indeed many fluctuate in their output so sharply and frequently that there is no plausible scenario for an Earth-like world to exist around them. And even where Earth-like planets do exist, frequent Carrington-like Events might severely hamper development of a high-tech civilization if not make it impossible. So today we will be examining how the stability of stars might affect the Fermi Paradox, the big question of why in a Universe so vast and ancient we don’t seem to detect vast numbers of ancient civilizations out among the stars. Needless to say, things that might make those stars less hospitable to life on worlds around them could impact that equation.
“That Equation” incidentally is Drake’s Equation, which is paired to the Fermi Paradox and tries to look at various factors that might make star systems able to host life, and life that could reach the point it was giving off signs of intelligent civilizations to astronomical observers. We refer to these sorts of hurdles to intelligence arising, these hurdles to going from random lifeless rocks to interstellar empires, as “Filters”. These might be minor ones that would only eliminate most candidates, what we often call a lesser filter, or enormous ones that a world has slimmer chances of passing through than you or I do of winning the Lottery, and we call these the “Great Filters”, and we discuss both types and everything in between in our Fermi Paradox Great Filters series. Great Filters are those events or conditions that would reduce the odds of an alien civilization developing by a million fold, and an example might be if it turned out the typical solar system had 100-kilometer-wide asteroid collisions with planets on an average of every few thousand years.
If we contemplate an event like that, which would kill all complex life on a planet hit by it, then we’re talking about something that at best would set back the evolutionary clock hundreds of millions of years if not sterilizing the whole planet. If we’re assuming there’s a period of time the average system has of that happening with a 50% likelihood, then if 10 such periods elapsed, the odds of it not happening become one-half to the 10th power, or one in a thousand, and at 20 iterations, one in a million, and at 30 iterations, one in a billion. Now planets really do often get smacked with asteroids or even dwarf planets, that’s probably how we got our giant moon – itself another commonly suggested Fermi Paradox Filter – and we don’t know how often such collisions happen in the typical system. If that period was once in a million years, then less than one in a thousand systems might host life, if it was a thousand years then the odds of even a single planet in the whole Universe going 4 billion years without being fatally smashed multiple times is pretty small. But that’s a critical aspect of filters of that type, a disaster that might happen on average every million years changes the odds by many orders of magnitude difference in the 4 billion year history of a possible life bearing planet. Small changes in the odds of filter events result in large changes to the odds of technological life arising, and unfortunately our understanding of the odds of most filters is still very imprecise.
And mind you, these cases are in addition to any other filters in play, and throughout the aforementioned Great Filter Series we discussed over 50 such conditions which each seemed likely to reduce the odds by at least 50% in each case, often vastly more. One of those areas was Solar stability and the general category of suitability of a given star, and it is one of the ones I expect to be a big filter on life emerging and evolving, as we’ll discuss today in terms of solar flares. Though Solar Flares are just one example of how, but let’s begin with that. What is a solar flare? The Sun gives off a fairly steady amount of sunlight – indeed it appears to be steadier than most stars – but it still has drops and rises in brightness, and the latter are called solar flares, eruptions on the Sun, which also increases the overall brightness of the Sun while they persist.
They usually are observed in close proximity to sunspots, which are temporary phenomena on the Sun that are actually darker than normal. Loosely speaking this can be thought of as a big bubble of activity manifesting as a clump of darker sunspots and a sudden flash of hot and bright activity, that flare. Sunspots range in size a lot, varying from the size of a city to bigger than a planet, even a big one like Jupiter.
They move around, often in groups, and change in size, and appear and disappear, and how common they are at any given moment changes and seems to loosely follow an 11-year cycle. They are often accompanied by other activities like solar flares. We have coronal loops, which are giant ribbons of plasma rising and falling with magnetic field lines off the sun, thousands of kilometers long, and we also have their big brother, solar prominences, which are bigger and last longer.
These can break up into a Coronal Mass Ejection, or CME, which is basically where one of these large protrusions of plasma breaks off, and our Sun has as many as 5 of these a day during the peak of that 11 year cycle to as few as one every five days near the minimum, a factor of 25 difference. These head out into space and only the ones that move in the direction of Earth are cause for concern – currently anyway, they could be more worrisome in a developing interplanetary civilization with infrastructure spread out around its star. Now as we often note on the show, Earth is very small compared to our Sun and even smaller compared to its orbit around the Sun, so it only gets about a billionth of its sunlight, and only gets about a billionth of its CME ejected material. They are big and spread out as they go, so a lot more than one in a billion strike Earth, but the vast majority of CME’s either come nowhere near us or hit us only with their fringe. At the same time not all Mass Ejections are made equal, some are bigger than others. The Carrington Event in 1859 was visible to the naked eye as a flare and a brightening of the solar disc, most are not nearly that intense.
But nor is that intensity super-rare either, we had a Carrington-Class solar superstorm back in the summer of 2012 that landed a glancing blow on Earth, and, had it been head on, we estimated it would have done around a trillion dollars in infrastructure damage, resulting in huge human and societal costs while we rebuild. We would expect cascading failures of the power grid, electric disruptions and grid damage, potentially leaving some areas without power for months, and where we kept power, huge problems in terms of electronic payments systems, crashes to the internet, and general chaos in banking in general. It’s hard to guess how much secondary chaos this might cause, but as we emerge from the Pandemic, it’s worth remembering all the stuff that came out of left field from that, like the great Toilet Paper Shortage of Spring 2020 or shortages of various food items simply from an inability to keep the processing plants open.
So don’t think of such an event as just a few days of rolling blackouts. We were actually hit by a smaller one in the Spring of 1989 that knocked out power in Quebec and the aurora was visible down in Florida and Texas. Hardly a doomsday event though.
I was eight at the time of the ‘89 event, living in northeast Ohio, not far from Quebec, and was already very into astronomy and also already a news junkie, but I can’t say I recall the news even mentioning it, that time Earth got smacked by a coronal mass ejection 36 times bigger than the planet. And this is critical because we have not observed any CMEs that would have brought on the apocalypse had they hit Earth directly. At worst the ones we have seen would have caused short term chaos and economic disruption of power outages and fried communication systems. There probably have been much worse ones, and yet they are nothing compared to what planets around many other stars experience. We have a category of stars called variable stars, with the variation referring to their brightness, and presumably they all vary in brightness but, for example, our own sun’s brightness only varies by about 0.1% over the eleven year solar cycle, just by a factor of a thousandth, and that variation is enough to cause a variation of 400% in the dangerous UV-B light reaching Earth through the Ozone layer, a possible planet wide temperature variation of about a fifth of degree Celsius, and possibly some alteration of weather patterns.
Alternatively Mira type Variable Stars can have variation of not a thousandth, but of a factor of a thousand or more. They’re an extreme case but most stars vary in brightness by a lot more than a tenth of a percent. Our sun is unusually stable, and I just mentioned a few of the effects even a 0.1% variation in brightness has.
A coronal mass ejection an order of magnitude more powerful than the Carrington-event is getting into that region where the effects aren’t just messing up electronics and making the sky have pretty auroras, it's getting into the area where it can start severely damaging the atmosphere. Remember a CME is a giant ball of plasma, we were just talking early this month about using plasma as a weapon for tearing stuff apart in our Lightsabers and Laser Pistols episode. Plasma is hot ionized atoms, the same kind that already hit Earth as Solar Wind but dialed up to 11, that’s the same solar wind that slowly strips off our atmosphere and which stripped them off every planet without a strong enough combination of magnetosphere and gravity to keep theirs. There are a lot of variable stars – and there are several types and causes for star variability, ranging from the internal mechanics of the star, what we call intrinsic variability, to extrinsic causes like passing through a dust cloud and gas cloud.
However a lot of variable stars are already so big that we rule them out for the Fermi Paradox, as we tend to assume a big but short lived star would not be around long enough to let complex life evolve near it. Indeed even Class F Stars, those just one category above our own G2 Sun, are pretty dubious candidates for longterm stable Earth-like worlds as we’ll discuss in a bit, and the most massive of those come in at only 1.4 times the mass of our sun, and yet 40% more mass should result in a main-sequence lifetime of only 4.3 billion years, our sun is 4.6 billion years old, and 300 millions years ago life had barely gotten onto land. Stars more massive than that, anything in the A, B, or O ranges live even shorter lives, often making their lifetimes in millions rather than billions of years.
To be sure, life might evolve faster on some worlds, but stars also get brighter as they age and hotter, and we worry if our world will even have an atmosphere a couple billions years from now if our Sun heats up a bit more. This sort of star variability, brightness from aging, is much slower but more potent in many ways too, as every star emits solar wind that strips atmosphere off worlds, and there’s a bit of snowball effect on that, once the stripping effect reaches a certain strength things move very fast, removing sea and sky. For instance a star living only half as long as our own sun is going to go through those age-related changes in brightness twice as fast, giving the ecologies under them half the time to adapt, assuming they even can.
Whichever the case, it makes it very dubious if stars even a decent bit more massive than ours could really offer a habitable zone to an Earth analogue planet for long enough that evolution could produce intelligence, even if that bigger and shorter-lived star was as stable as our sun. And again our sun is pretty stable even when compared to other stars in our type, at least for the last several thousand years, which is as far back as we can track it using means like ice cores and tree rings. With such a short record, it might be that the Sun has just been unusually calm during this era.
However the Sun is the major driving influence of our weather and climate, and we have had a lot of big climate shifts over that same period, largely driven by that solar activity which has varied minimally. When compared to a graph of brightness variability of other stars like our own, our sun is very sedate and stable, and if this is the norm, the instability of most Sun-like stars might be a major filter for the Fermi Paradox. Even if it were a temporary period though, we know how much damage the variability of our Sun could do to a technological civilization. You can bury and harden power lines and telephone wires against this sort of disruption but you have to put a lot of effort and expense into doing that – we’re not idiots, we haven’t proofed ourselves against this because it would take a major effort and its uncertain if the cost of doing and maintaining that would exceed the possible damage, especially since a lot of that would be because of chinks in our armor, like one country or region didn’t do it and all their networks drop.
We also might want to ask what Carrington Events happening every year or even more often or more severely might do to a developing civilization. One thing we need to understand is that even for very stable stars, the slow and steady stellar wind that all stars give off will slowly strip away the atmosphere of any planet—unless that planet is so large it can hold its atmosphere down with brute force gravity, or unless the planet is so far from its sun that the wind is weak, or unless the planet has a geomagnetic field to create magnetosphere that will guide all those charged wind particles safely away from the atmosphere. But huge planets and distant cold planets are unlikely to develop life, so life as we know it has the best chance of developing on planets that have a geomagnetic field protecting the atmosphere. Mars has a much thinner atmosphere than Earth’s partly because of its lighter gravity but mostly because it lack of a magnetic field, so the solar wind has stripped and is still stripping its atmosphere away. Life evolving on a planet with barely an atmosphere isn’t necessarily impossible, but it isn’t nearly as probable either.
And since our data on planetary atmospheres and magnetic fields is very limited, we can only make estimates as to how intense a geomagnetic field a planet really needs to protect its atmosphere from its sun at its orbital distance from that sun. But even if a planet has a strong enough magnetic field and magnetosphere to protect its atmosphere from the steady stellar wind, there are still the storms and flares to worry about. We can only make estimates of how much of the Earth’s atmosphere the Carrington Event blasted away, so while it would take frequent Carrington-class events to leave us airless, it’s not clear exactly how frequently. And there’s an interesting range in there, where the magnetic field might be strong enough to hold the atmosphere in place but we’d still have the intense erratic electrical activity to deal with. In a way, we’re actually very lucky the Carrington Event happened when it did. Had it come decades earlier, there would not have been astronomers monitoring the Sun daily and we might not have realized that all the strange events were connected with the gigantic sunspots that had just erupted.
Had it come much later, of course, we’d have already invested heavily and come to depend on an electrical grid that was completely unprepared for it. Though if it had happened early on in our electrification efforts, we may have re-evaluated and instituted more rigorous standards for our electric infrastructure. So an Earthlike planet that suffered a few Carringtons per decade couldn’t develop a worthwhile electrical grid until they learned to shield and harden it. On the one hand, this might drive them to work that much harder on their studies of solar physics and electronics. On the other hand, that extra hurdle might make the whole idea of a grid impractical and too expensive, leaving the planet’s civilization dependent on cruder, less adaptable, and more decentralized forms of power like water power, and by water power I mean water wheels driving gears, not hydroelectric power generation.
If they cleared that hurdle, there are plenty of others, like deploying a satellite network. You can shield satellites, but it’s expensive and difficult. And even then, they need antennas or they aren’t very useful. If you shield an antenna completely it stops being an antenna, but you can withdraw the antenna and other vulnerable structures into the shielding if you know a storm is coming.
So before this civilization could build their satellite network, they need a sufficiently advanced understanding of solar physics that they can monitor their sun and know when it’s about to act up. It’s possible, but every hurdle placed in a civilization’s way is a hurdle that some aren’t going to get over. And thinking for a moment about civilizations at a lower level of technology, there’s no telling what superstitions about metal might develop if a culture noticed that long pieces of metal got hot, gave off sparks, and started fires on the days before the night skies filled with green fire.
This could lead to a Game of Thrones-like scenario, where a planet reaches a certain level of technological development and just stays there for thousands of years. Some things are a lot more difficult to harden though, like space based hardware, be it probes, rovers, or manned stations. We already have to work to minimize mass to get things into space and arguably expose our astronauts to unhealthy amounts of radiation during their stays, it’s a lot worse during storms like this and if that was the norm, it might simply be viewed as an impossibly impractical endeavor.
Personally I think they’d eventually get the technology to do it anyway, but astronomy and scientific development might look very different on worlds where the sky was always lit up with an aurora. We don’t know how often major solar storms like this would need to occur, or at what intensity, to strip the atmosphere off Earth, but we can make some decent guesses and there’s a lot of stars that probably are too volatile. As mentioned any of the variable types stars, at least the intrinsically variable ones, probably are not good candidates for Earth Analogues. As I also mentioned, a lot of the variables are more massive stars too, ones too short lived to have modern Earth-like worlds, but these are tiny fraction of stars anyway.
The overwhelming super-majority of stars are less massive than our own Sun and much longer lived, and thus in terms of main-sequence brightening with age, would be even slower than our sun and give far longer for life to develop. However, these red and orange dwarfs that make up the vast majority of stars, M and K type stars, are basically all variable stars. Red Dwarfs are frequently covered in sunspots and can be dimmed by nearly half of normal for months at a time. Some months back we looked at colonizing red dwarfs and noted various ways they could have seasons, given that a planet close enough to them to have liquid water might orbit in mere days for the dimmest, and only a few months for the biggest and brightest. I didn’t mention it at the time as an option for seasons but it might well be periodic, and having your sun dim periodically by a decent fraction is one such option for seasons. For folks contemplating another Game-of-Thrones Westeros style world for a story or game, heavy sunspots is one more way to cause what we’d think of as atypical weather cycles.
Of course it’s also a reason a civilization might get stuck in an iron age for thousands of years, unable to move into modern electronics because there were too many solar storms for many electronics to be used safely and well and catch on, but let's focus on the world’s climate instead. In and of itself, this is not necessarily too problematic for life, most red dwarfs don’t dim by that much that regularly, dimming by nearly a half, even if it did that would not necessarily be a dealbreaker on having a livable planet. As an example a 20% percent drop in light hitting a planet would generally result in a temperature about 5% colder in absolute terms, or of an earthlike world, somewhere between 15-20 Kelvin or Celsius drop, or 20-30 degree Fahrenheit drop.
Now mind you that’s the whole planet slowly cooling, not just a seasonal change, and planets are big things slow to heat and cool, so it's not hard to imagine a lifecycle and ecosystem able to handle such drops and adapt to them being rather random for months at a time. On the other hand, given that tidal locking is often thought to be fairly common on such worlds, it wouldn’t be too shocking if a given star, especially the smallest of dwarfs and closest of planets, actually had a solar cycle that was periodic to that orbital period of that close and massive satellite, tidal forces go both ways after all, even if a planet effects a star less than a star a planet, much like us and our own moon. So the dimming is problematic but not necessarily fatal, however dimming isn’t the whole of it for smaller stars, and much like our sun they have flares that often accompany those sunspots, and these can as much as double the output of the star. Also, while our own sun has a vast region of space to spit coronal mass ejections without them coming anywhere near Earth, the volume and cross section habitable planets of red dwarfs take up is much higher, a habitable planet around the dimmest of red dwarfs, being 10,000 times dimmer than our Sun, would have 10,000 times the proportional cross-section for intercepting things flying away from that star, getting hit or clipped by them far more often, and they would only have had a fraction of the distance and time to disperse upon leaving their Sun. So smaller suns are a lot more volatile and a lot more likely for that volatility to whack habitable planets around them more frequently and more potently.
Indeed we often worry such worlds might not be able to maintain atmospheres at all, or lose them much easier and faster, which eliminates the big advantage of them as potential sources for advanced life, that such stars live far longer and allow more time for life to emerge and develop. On the one hand a conceivable variation of 10% in brightness should be manageable for an ecology, after all a planet on a mildly elliptical orbit could experience that much, Earth at its closest and furthest varies in total brightness by about 7%. On the other hand we see what even a 0.1% fluctuation in solar luminosity over an 11
year cycle can do, and in the wider timelines we tend to suspect there is a longer solar cycle or more than one even, many have been proposed in terms of ice ages. Other stars won’t have 11 year cycles, incidentally ours is the Sun’s north and south magnetic pole reversing, the sun has a very strong and wild magnetic field and is composed of ionized plasma, which is what is driving the eruptions, but we don’t know that this has always been an 11 year cycle and always will be, and it should be different for every star, based on its composition, age, spin rate and other factors. We are going to need much more detailed, long-term observations of our sun and nearby systems to better define the Drake Equation. Until then though, we need to consider the very real chance that planets like Earth might be rare for life to evolve on because stars as stable as our own Sun are much rarer than we think. I was mentioning today how stable our Sun is compared to many other stars but it’s still impossible to describe how explosive and volatile our Sun is, with the equivalent of millions of atomic bombs going off on its surface every moment, and there’s a great video examining this over on Curiositystream called “Our Violent Sun”, one of their many great astronomy and space episodes. That’s also a notion that comes up in science fiction a lot, with ships flying close to stars to lure enemies into being hit by solar eruptions or civilizations causing intentional flares as weapons, and we will be discussing the notion of using solar flares as a weapon in an extended edition of today’s episode over on Nebula, and for those watching on Nebula rather than Youtube you can see that extended version in place of our usual sponsor spot.
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