3103: Exoplanet System

Exoplanet System

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Title text: Sure, this exoplanet we discovered may seem hostile to life, but our calculations suggest it's actually in the accretion disc's habitable zone.

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Explanation

This is one of 52 incomplete explanations: Explanations for the planets are incomplete and some categories are missing. Do NOT create a table, unless it is impossible to convey that information without it. If you can fix this issue, edit the page!

Exoplanets are planets outside the Sun's Solar System. As astronomers discover more and more of these, they are finding all kinds of weird and unexpected examples, often with unusual and interesting physical properties, necessitating the introduction of new categorisations to describe them. Here, Randall presents a depiction of a hypothetical star system containing many exoplanets of different exotic types. Most of these are entirely imaginary, and some are outright nonsensical.

A number of the planet descriptions reference the potential habitability. This attracts a lot of attention, particularly in the media and popular imagination, both because it suggests a higher potential for finding extraterrestrial life of a form we might more easily recognise, and because such planets might potentially be examined as candidates for future space colonization. Unfortunately, for many hopefuls, there are a number of specific conditions required for Earth life to survive, and there are many possible ways for space to be inhospitable to life. As a result, most exoplanets that have been discovered have conditions that make it nearly impossible for humans to survive, and difficult for any life form as we know it to exist. The examples here illustrate (in an exaggerated fashion) some of the many frustrations astronomers face when analyzing planets and getting their hopes up, only to discover the planets they found are, sadly, nothing like Earth.

There are a total of 19 planets in the comic. Here are the explanations for each planet, in order of how far they are from the star:

Giant planet orbiting so close that it's actually rolling on the star's surface

Giant planets are often gravitationally pulled close to their star. Here, the planet is literally touching the star, which, given both bodies' gaseous makeup, should cause them to merge.

Hot Jupiter

A Hot Jupiter is typical terminology used in analyzing exoplanets, generally depicting a gas giant (of a size similar to our Jupiter or Saturn) which orbits in a much closer/hotter orbit than our own. Hot Jupiters are easier to detect than many other types of exoplanets, due to both their gravitational effect on their stars and their dimming effect on their stars when they pass in front of it.

Planet that may actually be in the habitable zone, according to a very optimistic modeling paper by some desperate postdocs

The habitable zone of a star is the range at which water is liquid. Notably, planets in the habitable zone are seen as options for colonization by humanity, which would mean greater funding for research. As such, researchers will go to great lengths to determine as many habitable planets as they can.

There's a pulsar here but it's probably fine

A pulsar is a neutron star which emits beams of radiation while spinning very fast. The intensity of this radiation makes it extremely difficult for any form of life to exist in the system. This is in addition to the gravitational instability, and excess heat that the pulsar would produce. The mass of a neutron star, this close to the visible star, means that any planets could not be simply in orbit around the latter. This lends a substantial level of irony to the "probably fine" comment. Also, it means that this system is technically a binary star. Also neutron stars are remanentes of a Supernova explosion, which means it is actually unlikely there would be any planets left this close to the stars. And even if they could have survived they would have been sterilized.

A waterworld paradise with beautiful oceans and warm— wait, no, we just got new measurements, it's a hellish steam oven

In any scientific field, new information may turn previously established knowledge on its head. Exoplanet research is no different, and a planet that at first seems to be habitable might turn out to be an incredibly deadly steam world. An example of this can be found in our own solar system with Venus, which was known to have clouds as early as the 1700s and was speculated to be habitable — but later, in the 1960s, those clouds were found to be made of steaming hot sulfuric acid.

Planet that could be habitable, if there's a form of life that hates water but loves acid and being on fire

Scientists remain open to the possibility that life might form from different conditions than those found on Earth. That said, the speculation that life on this planet must "love acid and being on fire" is more than a little sarcastic. Possibly to a reference to the what if? article Interplanetary Cessna, in which Randall points out that the atmosphere on Venus is pretty survivable at 55km, except for the sulfuric acid, and way too hot at the surface.

Mini Neptune

"Jupiter" and "Neptune" are rough size/mass categories for gas giants with a mass similar to Jupiter versus Neptune/Uranus. A mini-Neptune would be smaller than Neptune, possibly small enough not to be a gas giant at all.

Lukewarm Jupiter

A humorous extrapolation of Hot Jupiters, assuming that there are other named types of Jupiters. The French Wikipedia has an article on warm Jupiters.

Planet whose atmosphere is confirmed to contain atoms

With interstellar distances, it is inevitable that some planets will be hard to get a read on. Here, the astronomers can only confirm the planet has an atmosphere, not what it is made of or how thick it is. If it has an atmosphere at all, there are very few options except for that to be composed of atoms.

Possibly in reference to headlines about exoplanets whose atmospheres contain molecules that may indicate biological life, but extrapolated to comedic levels of vagueness. A similar 'too cautious' approach to the data can be seen in 2359: Evidence of Alien Life.

Earthlike data artifact

An artifact in this context is any error where it looks like something exists when it actually doesn't. This may be caused by faults in the equipment, or by other activity that looks similar to a planet signal. In this case the astronomers thought they detected an Earth-like planet, only to discover it was a data artifact. There have been several such cases already, for example Gliese 581g, which was considered to be the most Earthlike planet discovered at the time, before more detailed analysis concluded it didn't exist. Either that, or it has turned out that Earth itself is a data artifact, which would raise epistemological questions about the whole endeavour of studying the universe.

Cold Jupiter

Implicitly the opposite of a "Hot Jupiter" described above. Used here as another extension of the "Hot Jupiters" running gag, "Cold Jupiters" is occasionally used in real astronomy but is fairly informal. The French Wikipedia has an article on cold Jupiters.

Potentially habitable void

It seems that the part of this system that would be ideal for habitable planetary conditions does not actually contain any planets. This would make it much harder to actually inhabit (the notional inhabitants would have to build a world to live on, and would have nowhere to easily locate themselves while the building was in progress), to the implied frustration of the astronomers. Confusingly, the illustration of the void is as a patch that crosses several of the planetary orbits. Since it cannot remain a void if a planet passes through it, this suggests it is an object (or rather a lack of objects) that orbits in its own right. This is not normally how habitable zones work — they are usually a span of potential orbits, forming a ring (or shell) around the star. Additionally, this region is positioned right between Cold Jupiter and Hot Mars, implying that it is in between hot and cold, and between gaseous and rocky, being closer to Earth conditions.

Hot Mars

Continuing the joke on Hot Jupiter. This assumes that if there's hot Jupiters, there must be a "hot" variant of every planet, including Mars.

Faint dust cloud that will cause several papers to be retracted

This is in reference to the astronomical transit method of discovering planets by measuring periodic dips in brightness of the central star, done by missions like the Kepler space telescope. It turns out that not all variations in brightness are caused by planets, much to the disappointment of overeager data analysts and science news reporters; see, for example, Fomalhaut b, a former proposed exoplanet that turned out to be a dust cloud, or Tabby's Star, a star with odd irregular dimming pattern likely due to a dust cloud which was briefly thought by some to be an alien megastructure.

Either a gas giant or a fist-sized rock, depending upon which calibration method you use

Scientific instruments, including telescopes, must be calibrated in various ways, and different calibration methods can lead to different corrections applied to raw data and hence different values for calibrated data. This is exaggerated in the comic to make a raw observation emerge from the calibration correction process as two objects of vastly different size - a range of uncertainty between tens of thousands of kilometers and a few centimeters, perhaps nine orders of magnitude. This is not particularly precise, even for a cosmologist. Also, a "fist-sized rock" would be impossible to detect around a distant star using current technology; it would be difficult to spot something of this size around our own star.

Mini Pluto

Pluto is already significantly smaller than most planets, thus its designation as a "dwarf planet". A "mini Pluto" suggests an exoplanet that shares most of Pluto's features, but is somehow even smaller.

Wet Saturn

May be a reference to the 'fact' that "Saturn would float in water" due to its density. The difficulty of finding a practical way to test this notwithstanding, perhaps someone managed it with this planet.

Planet whose surface may host conditions suitable for rocks

As with the above planet whose atmosphere "contains atoms," this planet is too difficult to get a read on, and the measurements are still so vague that it's unknown whether this planet is a rocky planet or a gas/ice giant. This is also a play on the holy grail of exo-planet research -- finding a planet whose surface hosts conditions suitable for life. It's not impossible that that would involve living rocks, but that would impose a different set of environmental restrictions from those for the carbon-based life we're familiar with.

Somehow this whole system is smaller than the orbit of Mercury?!

No planet, or anything other than an orbital path, shown. But apparently an indicator that all the rest of the given orbits (for Jupiter-likes, Mars-likes, dust clouds, etc., and even semi-inconvenient pulsars) exist within a planetary system that is extremely compact, fitting into a volume of space the size of that between our Sun and the orbit of its nearest planet, Mercury.

This is likely a reference to the fact that many exoplanets located so far have been in even tighter orbits around their star than Mercury is with the Sun. It is worth noting, however, that this is likely to be observational bias, as large and tightly orbiting planets have a significantly larger (and hence easier to identify) effect on their parent star. There are likely many small and more distantly orbiting exoplanets that we are simply unable to observe effectively at this time.

This is also likely a reference to the fact that the majority of stars in our galaxy are red dwarf stars, which are much cooler and dimmer than our sun. This means that the habitable zone and a wide range of solar irradiance can be found within a smaller radius from the star.

Title text

The title text mentions a planet within an accretion disk, which means that the planet is passing through material inspiraling into some significantly more massive object and is likely inspiraling itself from resistive effects of passing through said material. Nevertheless, the researcher speaking assures us that the planet is in the disk's habitable zone, implying it is a worthwhile option for colonization. This is despite the observed location being likely temporary as the planet's orbit inspirals closer and closer to the central object, to say nothing of the likely constant bombardment of debris and potential radiation depending on how massive the central object is and how dense the accretion disk is.

Transcript

This is one of 27 incomplete transcripts: This transcript sucks because I used AI, but it's a start. Feel free to discard it. If you can fix this issue, edit the page!

[Central diagram showing a star with various planets and objects orbiting around it, with labels and descriptions connected by dotted lines:]

[Label pointing to a large planet very close to the star:]

Giant planet orbiting so close that it's actually rolling on the star's surface

[Label pointing to a small object near the star:]

Hot Jupiter

[Label pointing to a small object:]

Mini Neptune

[Label pointing to a planet in the middle distance:]

Planet that could be habitable, if there's a form of life that hates water but loves acid and being on fire

[Label pointing to another object:]

Cold Jupiter

[Label pointing to a circled area:]

Potentially habitable void

[Label pointing to another planet:]

Hot Mars

[Label pointing to a planet:]

Planet that may actually be in the habitable zone, according to a very optimistic modeling paper by some desperate postdocs

[Label pointing to a small object:]

There's a pulsar here but it's probably fine

[Label pointing to another object:]

A waterworld paradise with beautiful oceans and warm-- wait, no, we just got new measurements, it's a hellish steam oven

[Label pointing to a small object:]

Mini Pluto

[Label pointing to another object:]

Lukewarm Jupiter

[Label pointing to a planet:]

Planet whose atmosphere is confirmed to contain atoms

[Label pointing to another object:]

Earthlike data artifact

[Label pointing to another object:]

Wet Saturn

[Label pointing to another object:]

Either a gas giant or a fist-sized rock, depending which calibration method you use

[Label pointing to another object:]

Faint dust cloud that will cause several papers to be retracted

[Label pointing to another object:]

Somehow this whole system is smaller than the orbit of Mercury?!

[Label pointing to another object:]

Planet whose surface may host conditions suitable for rocks

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Discussion

"Faint dust cloud that will cause several papers to be retracted" could refer to either Fomalhaut b (former proposed exoplanet that turned out to be a dust cloud) or Tabby's Star (star with odd irregular dimming pattern likely due to a dust cloud, but was briefly thought by some to be an alien megastructure the speculation of which caused the media to lose their shit). Erika lovelace (talk) 19:53, 16 June 2025 (UTC)

Somebody should word it better but the idea of a black hole accretion disk having a habitable zone is pretty typical for Randall brand humor. 130.76.187.35 20:12, 16 June 2025 (UTC)

I think it's actually a reference to Interstellar. In that movie three planets are sort of in the habitable zone of a giant black hole's accretion disk. Whether that means they have to be in the accretion disk, or whether they can be outside it but still in the habitable zone of the disk's radiation, I'm not sure. -- Ken g6 (talk) 00:17, 17 June 2025 (UTC)

An alternative reading of #18 is that the planet may or may not be too hot for rocks to solidify at the surface. (Even if this turns out to be implausible, Randall does stretch the bounds of plausibility on occasion.) 87.75.45.216 08:36, 17 June 2025 (UTC)

An accretion disk is also found around a star. So the exoplanet may be in the zone where planets may actually form. (talking about the title text) 129.27.217.99 08:59, 17 June 2025 (UTC)

An accretion disk forms around my desk. Whether or not it counts as habitable is debatable, though. 82.13.184.33 09:15, 17 June 2025 (UTC)

Yeah, the Earth is thought to have formed from the accretion disk of the Sun 4.5b years ago. It probably has nothing to do with black holes. Robisodd (talk) 12:12, 17 June 2025 (UTC)

This is my reading of it too: the planet being within the habitable zone of the accretion disk is (IMO) referencing a very young solar system, discovered at some time before the planets have swept their orbits clear. Therefore although "habitable", it'll be a few hundred million years before even what we hypothesize as the "Late Heavy Bombardment", concomitant with the very earliest traces of life on Earth. In other words, great news for future colonization as long as your hopes for the future are not contingent on there being anyone remotely human still around... 2A01:CB08:E6:7000:910F:2296:2C6D:46C4 10:27, 18 June 2025 (UTC)

My read of this is that the planet is habitable but perhaps it "doesn't like" life. Galeindfal (talk) 13:36, 17 June 2025 (UTC)

Weird side note: isn't Anne McCaffrey's PERN technically a Habitable planet that passes trough an accretion disk? There's a whole subplot about doing some weird magic-science to stabilize the orbit and stop the inspiraling in the later books. 104.129.192.49 22:33, 17 June 2025 (UTC)

I'm a little unsure of this so could someone help me confirm my theory? There is a shape in xkcd: Escape Speed that looks quite similar to the "faint dust cloud that will cause several papers to be retracted" shape (in xkcd: Exoplanet System). I'm wondering if xkcd: Exoplanet System might be a map of the xkcd: Escape Speed world? RedDragon (talk) 14:53, 17 June 2025 (UTC)RedDragon

I assumed the "fist-sized rock" was something relatively close to the observatory, which is not calibrated properly so it seems to be at the star's distance. Barmar (talk) 16:09, 17 June 2025 (UTC)

https://www.youtube.com/watch?v=MMiKyfd6hA0 92.23.2.228 20:17, 17 June 2025 (UTC)

Could the ‘fist-sized rock’ be a reference to Welcome To Night Vale, in which a character, named Sarah Sultan is a ‘fist-sized river rock’? Broseph (talk) 06:18, 18 June 2025 (UTC)

The intro seems to major a little too heavily on the habitability aspect. Only four of the items in the comic mention habitability - five if you count the 'Earth-like data artifact' - plus the title text. That's not even a third of the total items. Astronomers aren't only interested by worlds that might be habitable - they're excited by the vast array of interesting things out there. 82.13.184.33 08:31, 18 June 2025 (UTC)

"Wet Saturn" and "Hot Mars" may also be a reference to Pliny the Elder's Historia Naturalis, Book 2 Chapter 18. https://www.perseus.tufts.edu/hopper/text?doc=Perseus%3Atext%3A1999.02.0137%3Abook%3D2%3Achapter%3D18

im sorry is this website using biased odds for random comics?? because i’ve got a comic in the last 200 published at least 20 times out of the last 25 i’ve rolled. and 2 of the others were the same non comic 92.40.197.124 17:11, 2 December 2025 (UTC)

Unfortunately, yes, and people have discovered that it's a wiki thing, not specifically anything to do how this site uses its Random button. Though it has been changed to include the set of non-comic page-explanations, as well as numbered/non-numbered comics, which is a fairly new (and deliberate) development. 82.132.237.203 17:45, 2 December 2025 (UTC)
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