Hi. Sorry about the silence: I've been busy redrafting the current-newest novel in progress (it's back with my agent), and now I just flipped over to rewrite the much-rewritten novel before that (which ran into a brick wall in late 2025 for structural reasons, and which I set aside while I was working on the next book, figured out a fix for in late 2026, and am now fixing).
As you can imagine, slaving over manuscripts isn't the only thing I do on a computer. Along the way I'm browsing the web--or what's left of it these days that isn't clickbait nonsense and LLM-generated slop--and slowly accumulating a mass of perpetually open browser tabs with stuff that bears future consideration. These are not story ideas, but they're elements of background or texture that I think might conceivably come in handy in a future project. And because I'm currently working on a pair of space operas, this list is astrophysics-oriented ...
(Hint: click the links, there's some truly crazy stuff here, most of it new since 1990.)
This century is a golden age of exoplanetography. Back in 1990 there were zero tentatively identified exoplanets. But the advent of orbiting telescopes with significant light gathering power (most famously, the Hubble Space Telescope which launched that year) has shown us that not only are solar systems with multiple planets quite common, but that our own solar system is that weird kid in the corner of the playground who nobody wants to hang out with: there is an absolute zoo of exoplanet types out there. While Hubble wasn't specifically an exoplanet-hunting tool it was follwed by NASA's Kepler and Spitzer space telescopes, and just-launched Nancy Grace Roman Space Telescope, ESA's Cheops and coming PLATO) and ARIEL space telescopes, and of course the very large joint NASA/ESA James Webb Space Telescope.
Exoplanets are identified by perturbations they induce in the light curve emitted by their primary, either because they pass in front of the star or cause it to wobble slightly as the massive object orbits around its centre of mass. The consequence of having a bunch of infrared telescopes outside the atmosphere is that the count of known exoplanets as of October 2026 hit 6,445 confirmed in 4,834 planetary systems, of which 1,070 solar systems contain more than one planet. And this is only scratching the surface: to be detectable in this way, an exoplanet needs to be very massive and orbit very close--a Hot Jupiter. So of course Hot Jupiters are what we have mostly found so far. "In general their prevalence decreases exponentially as a function of the absolute stellar magnitude:" they're most common around F- and G-type stars, somewhat rarer around K-type, and very rare around red dwarfs.
While Hot Jupiters aren't of direct interest in writing human-centered SF--they're profoundly hostile environments for interstellar canned monkeys to explore--they have weird sequellae. If they end up too close to their primary star, they might undergo atmospheric stripping, leaving behind a Chthonian Planet, a rocky or metallic super-Earth such as TOI-849 b, which is about 40 times as massive as Earth but only 3.4 times Earth's radius. Alternatively, TOI-849 b might be a Mega-Earth rather than an eroded gas giant. Other Mega-Earths are a lot weirder: PSR J1719−1438 b is a pulsar planet, orbiting the millisecond pulsar PSR J1719−1438. what makes it weird is not only the fact that it orbits a millisecond pulsar (pulsars being supernova remnants, their original planets should have been vapourized during the stellar explosion that gave birth to it), but that it might be a planet that evolved from another star: the outer layers of the star were siphoned off by the more massive pulsar, leaving behind a core roughly as massive as Jupiter but a fraction of its diameter, seemingly composed mainly of crystalline carbon at a much higher density than diamond, with some oxygen concentrated in its surface.
(Don't bother writing this into your fic as a place for your hero to be exiled to mine hyperdiamond, though: it orbits its pulsar primary about twice as far out as our moon orbits the Earth, so it's probably baked by hard radiation: PSR J2719-1438 is spinning at roughly 10,000 rpm so inducing insane electrical currents in anything nearby, and your hero would be squished flat by Jupiter-adjacent surface gravity.)
A Hot Neptune is another type of common-so-far exoplanet, an Ice Giant (like, oh, our own Neptune and Uranus--a gas giant composed of elements heavier than hydrogen and helium) orbiting within 1AU of its primary. They're easier to find than actual Ice Giants because they transit their primary far more often than planets in distant orbits (Neptune's orbital period, for example, is 164.8 Earth years). Some Ultra-Hot Neptunes orbit so close to their primary that temperatures on the day side exceed 2000 celsius, and their atmosphere is probably metal-rich, with clouds of silicate: LTT 9779 b completes an orbit of its star in less than a day. At noon, it's hot enough to boil lead: it probably rains molten iron.
We also have some promising candidate Super-Earths (Earth-like but more massive planets, too small to be gas giants, probably possessing a rocky surface or hydrosphere as well as an atmosphere) and Hycean Planets, super-Earths with liquid water beneath a hydrogen ocean. (Note that water undergoes some whacky and exciting phase changes at increasing pressure: in particular, above 1,000 to 10,000 times atmospheric pressure solid phases predominate, and the high density phases don't float on liquid water (being dense). So below a certain depth the oceans will probably turn to slush, then extremely weird ice. But don't worry, our kind of life is based on enzymes that can be denatured by that kind of pressure regime.) Hycean worlds are nevertheless promising candidates for supporting life, although it'd probably be entirely aquatic.
Exomoons are a possibility, but as of 2026 none have been confirmed. If exoplanets are themselves hard to detect using current methods, exomoons are worse: Doppler spectroscopy doesn't work, although there's a list of exomoon candidates. One thing's for sure, there are a lot more moons in our solar system than was previously thought (Saturn alone has 293 moons). So it seems reasonable to posit the existence of many exomoons, of many types not found in our own system.
Rogue Planets or iPMOs (isolated Planetary Mass Objects) are planets that have formed in isolation or been ejected from a solar system; they're not bound to any star, and are less massive than a Brown Dwarf--failed stars too small to fuse hydrogen into helium, but massive enough to support deuterium fusion or even lithium fusion. There are hundreds of known candidate iPMOs, many of them ranging in mass between Earth and the lower end of Brown Dwarfs: some of them appear to be binaries, and it's reasonable to expect iPMOs with their own moon systems to exist.
(Do not seek out an iPMO as a setting for a spa resort: they're likely extremely dark and very cold, although they may retain a thick hydrogen atmosphere and enough residual core radioisotope decay to maintain a surface temperature above the melting point of water.)
Finally these are just the commoner types of planet in the exoplanet bestiary! Once we stop looking at boring old stars things begin to get really weird. Just as iPMOs don't necessarily form in the protoplanetary disk surrounding a new star but may form in substellar nurseries that birth brown dwarfs, we have to consider the Blanet or black hole planet.
Galaxies such as our own nucleate around a supermassive black hole such as Sagittarius A*, at the core of our own galaxy, which has a mass of around 4.3 million solar masses. (Other supermassive black holes may range up to billions of solar masses.) We know these objects exist, from observation of their radio emissions and studies of the orbits of stars passing close to them, and the holes at the heart of an Active Galactic Nucleus are believed to generate their emissions from the accretion disk around the hole.
Blanets are planets that form in the accretion disk around a sufficiently large black hole, provided the disk is dim enough not to disrupt the process (posited, more than 0.01 parsecs out from the event horizon--about 2000 astronomical units, roughly 50 times further out than Pluto). They're posited to be at least 20 Earth masses, and may be stable in orbits with periods of up to hundreds of thousands of years. They're believed to be unlikely to accumulate an atmosphere and become a gas giant due to the black hole scavenging gases. And they can be heated by either radiation from the black hole's accretion disk, or (this is whacky) the blueshifted cosmic microwave background if they're close enough to the hole. Best part: the outer regions of AGN disks may be prolific birthplaces for planets.
(Blanets aren't the only things that can form in an AGN accretion disk. Stars are likely to be common as well, including massive ones that rapidly undergo core collapse and result in smaller-than-supermassive stellar black holes. And where you get star formation, you get protoplanetary disks and therefore planets as well.)
Anyway, just sticking a peg in the ground: a good chunk of the action of my work-in-progress Starter Pack is set on a terraformed Earth-mass moon orbiting a Hycean planet of roughly Neptune's mass orbiting its star in the triple phase zone for water (i.e. where water can exist as ice, liquid, or vapour). The moon in question has spin (presumably it got kicked off by a collision with another proto-moon while the moon system was forming), so a magnetosphere, and tides to keep plate tectonics going--but this time tides from its primary planet, not a large sub-moon of its own.
But that's enough about me. What insane exoplanet facts can you add to this pool?
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