I haven’t written much about it on here, but lately I’ve been brainstorming about Earth climatology…and in true “me” fashion, this eventually has me wandering back to thinking about how one of my alien planets would behave. In particular, my Earth-like (but very much not Earth-twin) planet that I’ve placed around Sirius B in my universe. Yes, Sirius B, the white-dwarf star. Oh, it’s unlikely that a new generation of planets would have formed after the star reached the end of its main-sequence lifespan and no doubt destroyed any planets close enough to be habitable around a white dwarf, but supposing a vagrant planetary-mass moon around a gas giant orbiting Sirius A…it’s possible one could migrate in to a suitable orbit.
It would even explain much; I’m supposing a Mercury-style 3:2 spin-orbit resonance for my planet instead of the Moon-style 1:1 tidal lock that would usually be expected for a planet orbiting as close to Sirius B as it would have to to be habitably warm around a white-dwarf sun. Usually the cause is a more eccentric orbit than “normal” (as Mercury possesses; its orbit is the most eccentric of any planet in the inner solar system!), and captured bodies’ orbits are usually more eccentric. So that checks out. This leads to fun effects like the sun at certain times of year appearing to stall in the sky and reverse direction before resuming its “normal” course.
Anyway, the basic setup for my planet around Sirius B, which I’ve coined “Cerberus”, after the association in Greek mythology, is that it was originally an icy world, a la a moon like Europa or Enceladus, but when it migrated in to Sirius B’s clutches it was fried by radiation, losing most but not all of its water inventory, with the net result of a deep but still fundamentally Earth-like ocean, along with an atmosphere consisting of oxygen that was split off from water vapor by high radiation from Sirius B, the hydrogen released escaping into space. This is a real mechanism that has been proposed around red-dwarf stars in scientific studies, and modeling suggests that up to several thousand bars of oxygen could be generated this way…without the need for any photosynthetic life-forms to make it. Freaky, isn’t it? In the case of my planet I take the opposite approach and suppose that for whatever reason only a small relic oxygen atmosphere is left behind, perhaps 0.1 bars; enough oxygen for human beings to breathe unaided (its similar to the oxygen content found on high plateaus of our planet), but with the total ambient pressure being far lower than Earth (a tenth as much!).
The last time I brainstormed for this world I was supposing that it would be mostly ocean, but with continents consisting of huge volcanic plug-like formations that resemble Devil’s Tower…only supersized in height due to low gravity and vigorous volcanism. To the tune of plateaus that rise to 60,000 feet high, twice as high as Mount Everest on Earth. With canyons that are chasms reaching right down to sea level. Katabatic winds on such a planet might be extreme; with the massive altitude difference and the thin atmosphere, the total kinetic energy involved would be respectable compared to a katabatic windstorm off the Antarctic or Greenland ice sheets…only the thin air permits much faster wind speeds. The geometry of the terrain also means that wind-tunnel-style effects where air is squeezed through and accelerates even faster would be much more pronounced. Instead of 200 mph, you would easily see 600 mph gusts. Extreme events could even reach 1000 mph, well above the speed of sound, causing sonic booms and all manner of exotic effects.
Naturally these canyons would be polished and sculpted by the wind; superficially they might resemble the Colorado Plateau (think much of southern Utah’s deserts) crossed with Iceland, but with what one might call hyper-aeolian landscape features, along with tell-tale pock-marks perhaps resembling impact craters from glassy regolith lifted by the wind and impacted at supersonic speeds. The thin air means large heavy objects (like a human…) would not be blown down or lofted easily, but what is lofted up would be traveling extremely fast. You could be standing outside and the wind wouldn’t knock you down, but the glass storm would shred your skin off (maybe even your whole body down to your bones…). Yikes…
Aside from those wind tunnels of glassy death, the planet might actually be quite pleasant. Temperatures would hover around 0 Fahrenheit, albeit with a wide daily range, but the thin dry air coupled with the strong sunlight would keep it plenty warm for human comfort during the day: the same phenomena experienced by mountaineers, only carried to a fantastic extreme. The global climatology is such that the lands are primarily concentrated around the south pole, with the coast primarily experiencing a mild desert climate similar to the coast of Namibia: plenty of fog, but with much lower temperatures (but again, the strong sun and dry air make up for it).
And yes, there would be a coast, as in beaches with liquid-water waves crashing ashore, despite the very cold temperatures. I had in mind that the oceans are extremely salty, enriched with calcium salts to the tune of Dead-Sea-style salinity. Enough to register visually as seawater rather than brine, but extreme enough that the temperature could fall to -40 Fahrenheit and it would not freeze. Certain eutectics of water with these salts can stay liquid down to -60 Fahrenheit or so (Antarctica, naturally, has a few lakes that already exhibit this in its “dry valleys”). Delightfully alien.
But have I underestimated how alien this world might be? Somehow I caught onto this fact when worldbuilding Capella’s “skiers’ paradise” planet, but not Sirius B: like Capella’s, Sirius’s planets would be young, which, as we see in the most ancient geology of Earth, means a lot more geothermal activity…and georeactors. Yes, reactors. As in, naturally-occurring nuclear fission reactors. Earth had some at Oklo 2 billion years ago, and presumably had many more dating back to its earliest epochs; the reason we don’t see them heating up the ground beneath us everywhere today is because Earth’s uranium ores have become steadily depleted of the U-235 isotope, as opposed to U-238 (the latter decays much more slowly than the former). Uranium-235 can sustain a fission chain reaction, whereas uranium-238 cannot. Current-day uranium ores on Earth have 0.7% U-235, which is too low to start up a reaction, but 2 billion years ago, natural uranium ores contained 3% U-235. 4 billion years ago, shortly after the Earth formed but after it had already cooled enough to support oceans, U-235 represented 17% of natural uranium ore. That, for context, approaches the 20% fraction beyond which we don’t even consider it “low-enriched uranium” anymore, but rather “medium-enriched”! It’s peppy stuff…
So much so that on a planet Sirius’s age, 200-300 million years old (the same stage Earth was at 4 billion years ago, roughly), any uranium ore within a geological space that would provide a natural moderator and coolant (as Oklo did; 2 billion years ago these reactor sites were submarine caves) would run hot. In a planet like mine, a great many places where uranium ore would be found bathed under water, you would also find natural reactors running. Water attenuates radiation extremely well (to the point you can literally swim in a spent-fuel pool we store nuclear waste in and get less ambient radiation than you do outside the pool…yes, really), and by default all nuclear fission reactors produce is a lot of heat. The effect would be remarkably similar to a hydrothermal vent or a plain ordinary hot spring, just with more radiolytic reactions that generate free hydrogen and the like from the ambient water. Paradise for certain kinds of microbes, to the point that natural reactor pools have been proposed as an alternative to the now-prevalent hydrothermal vent hypothesis of Earth life’s original habitat.
The effect on my planet? Lots of geothermal hotspots. So rather than global Namibia, the thermal landscape might be more reminiscent of Iceland in winter: a very cold ambient climate, but with enough hotspots welling up from below that there’s always some warmth close at hand wherever you go…
Where it gets fancy is when you realize that these geothermal hot spots would undoubtedly influence local and regional weather. Sea smoke would be generated by the interaction of reactor-warmed water and freezing-cold air, along with lake-effect clouds and precipitation. The ambient climate as I envisioned it is bone-dry anyway (it’s not like water at -20 Fahrenheit or so is going to be putting out much moisture content…), but it could have a large regional influence, these plumes of enhanced moisture. Where they meet pressure waves that emanate out from these canyons, especially when there’s a convergence of wind streams from different katabatic wind sites, you could see some remarkably consistent zones of convection when the strong sun heats things up during the day. Not enough to make any kind of true overcast, but enough to cause notable local and regional patches of thunderstorm activity, perhaps even organizing into cyclones if the conditions are correct.
This of course would superficially resemble Earth’s hurricanes, though polar lows might actually be a better analogue…only, unlike on Earth, their zones of formation would be highly predictable: they’d tend to spin up in exactly the same spots across the planet, and at similar times of day, leading to precipitation-rich microclimates. Whereas surrounding regions might virtually never receive any precipitation. Precipitation that, by the way, would always arrive in frozen form: air temperatures might warm to as high as 80 Fahrenheit or so during the day, but the air is so dry as to keep “wet-bulb temperatures” well below freezing. In the sunlight it might be 80 degrees, but when the shadow of the storm cloud comes over you and the precipitation shaft falls, you’d see big fluffy snowflakes or even hailstones, and the temperature would quickly crash to 0 Fahrenheit or so.
Considerably more dynamic than the cold Namibia-style climate I had in mind originally; worldbuilding has a way of getting out of hand like that, hehehe.
Also dynamic is the question of stellar input. Namibia, like coastal California, the Atacama Desert, and similar zones, is remarkably stable thermally: summer and winter temperatures average about the same. This assuredly would not be true worldwide on my planet. There is no axial tilt, and the orbital period (which is in resonance with the rotation period) is short; on the order of a few Earth days, perhaps less. Nevertheless, it would have seasons. Why? Because of Sirius A! It would appear as another star in the sky as opposed to a full-blown Tatooine-style second sun, but its distance from Sirius B is subject to substantial variation. Over a cycle of 50 years, it reaches a maximum distance, where its heat input would be minimal, but at minimum distance Sirius A would shine bright enough to heat up a planet orbiting Sirius B by tens of degrees in Celsius terms. That’s a pretty substantial seasonal swing! Albeit on a much longer timescale than Earth’s seasons, and over the whole planet rather than just one hemisphere.
Nevertheless, if we suppose 80 Fahrenheit is as hot as it ever gets at “high summer” (and, since the low atmospheric pressure means the oceans would boil if temperatures got much above 100 Fahrenheit, it damn well had better be…), and 0 Fahrenheit is about the average even during summer, then with tens of degrees of cooling we’re looking at temperatures getting low enough during “winter” for even this hypersaline ocean to start to freeze over. At first I thought this would be something of a problem for what I had in mind, but today I realize that the enhanced geothermal and especially georeactor activity would open up huge “hot spots” across the surface. Together with the usual polynyas that you’d expect in an ice-dominated sea, there might be a lot of open ice-free terrain and ocean even at relatively high latitudes even during the peak of winter. Local life could go on as I envisioned! Albeit locally, more so than globally.
Seasonal variations also introduce the wrinkle of what the precipitation cycle looks like, and on this I’m not entirely sure. To preserve the California coast vibe (heh), I had in mind that storms would mostly gather strength and break out during the winter, but this seems at cross-purposes with heat and moisture being at their peak in summer. Though my understanding is it’s not so much the raw heat content, so much as how the energy cycle configures itself. Heat input would peak in summer, yes, but more goes into a storm than just raw heat and moisture; it needs to be released along with pressure gradients, temperature differences, wind shear, lift, and the like reaching a peak. Conveniently, the very configuration of my continents might suggest strong winter storms: land heats and cools faster than the water, and with rapidly cooling land and a still-warm ocean, temperature contrast and pressure gradients in my southern hemisphere would tend to be maximized in early winter. Heat and moisture (such as it is…) might build up during summer, but only in winter might it be released in the form of storm belts.
Unlike in California, on this world “storm belts” mean river-like sections of atmosphere where isolated thunderstorms bloom during the heat of the day, rather than vast seas of cloud and contiguous shields of precipitation. But the seasonal contrasts would be marked. As sea ice forms in the later part of the winter that provides yet more local contrast of sunlight absorption and temperature that could generate pressure waves, different wind fields, etc which, like the katabatic winds coming down the canyons, could converge in fairly predictable locations, driving small-scale storm activity or enhancing larger-scale patterns.
Meanwhile, the northern hemisphere might not even have the same pattern at all; its circulation is largely isolated from the southern hemisphere, so it wouldn’t have the land-vs-sea-driven contrasts that dominate the southern hemisphere’s circulation. Its storm season might be entirely different, perhaps centered on “autumn” as opposed to winter. Globally, therefore, late autumn and early winter might be the most active time for storm belts, with spring and summer being very quiet (aside from local microclimates where storms and even small-scale spin-ups could be active year-round).
Very patchy and driven by very alien mechanisms compared to what we’re accustomed to on Earth, but the physics check out…and I think it’s distinct enough from Earth, from Capella in my imagination, and also from my thick-air world orbiting Proxima Centauri to be a very memorable place to visit. Will we see a story from me someday about the first expedition to this strange new world? Perhaps…but for the nonce, I continue to marinate this idea in the stuff of dreams…stay tuned…