explain xkcd - User contributions [en]

3103: Exoplanet System

2025-06-17T12:26:26Z

Bertrc: /* Explanation */

{{comic
| number = 3103
| date = June 16, 2025
| title = Exoplanet System
| image = exoplanet_system_2x.png
| imagesize = 623x447px
| noexpand = true
| titletext = Sure, this exoplanet we discovered may seem hostile to life, but our calculations suggest it's actually in the accretion disc's habitable zone.
}}

==Explanation==
{{incomplete|Explanations for the planets are incomplete and some categories are missing. [[explain xkcd:Editor FAQ#table|Do NOT create a table]], unless it is impossible to convey that information without it.}}
{{w|Exoplanet}}s are planets outside the Sun's {{w|Solar System}}. Astronomers are constantly on the lookout for planets that have {{w|Earth-like_planet|Earth-like}} conditions, especially Earth-like planets that might support life. Unfortunately for many hopefuls, the conditions that made Earth suitable for life are believed to be extremely rare.{{acn}} [[Randall]] draws a hypothetical star system containing many exoplanets that describe (in an exaggerated fashion) 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
: {{w|Giant planet}}s 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 {{w|Hot Jupiter}} is typical terminology used in analyzing exoplanets, generally depicting a {{w|gas giant}} (of a size similar to our {{w|Jupiter}} or {{w|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 their gravitational effect on their stars.

;  Planet that may actually be in the habitable zone, according to a very optimistic modeling paper by some desperate postdocs
: The {{w|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 {{w|pulsar}} is a {{w|neutron star}}, emitting beams of radiation while spinning very fast. Contrary to the label, the presence of a neutron star in the system is probably not fine, since a second star would be source of {{w|gravitational instability}}, a lot of extra heat, and the beams of radiation pose substantial danger to the planets, rendering their surface uninhabitable. Also, it means that this system is technically a {{w|binary star}}.

;  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 {{w|steam world}}. An example of this can be found in our own solar system with {{w|Venus}}, which was speculated to be habitable when its clouds were first discovered long before those clouds were found to be made of steaming hot {{w|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? (blog)|what if?]]'' article ''{{what if|30|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 {{w|Neptune}}/{{w|Uranus}}. A {{w|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.

;  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. Possibly in reference to headlines about exoplanets whose atmospheres contain molecules that may indicate biological life, but extrapolated to comedic levels of vagueness.

;  Earthlike data artifact
: An {{w|Artifact (error)|artifact}} in this context is any error where it looks like something exists when it actually doesn't. This is usually caused by faults in the equipment. In this case the astronomers thought they detected an Earth-like planet, only to discover it was a data artifact. Either that, or it has turned out that {{w|Simulation_hypothesis|Earth itself is a data artifact}}, which would raise {{w|Epistemology|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.

;  Potentially habitable void
: It seems that the ideal orbital distance 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.

;  Hot {{w|Mars}}
: Continuing the joke on Hot Jupiter. This assumes that if there's hot Jupiters, there must be a "hot" variant of every planet.

;  Faint dust cloud that will cause several papers to be retracted
: This could refer to either {{w|Fomalhaut b}}, a former proposed exoplanet that turned out to be a dust cloud, or {{w|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.{{acn}}

;  Either a gas giant or a fist-sized rock, depending upon which calibration method you use
: Even if a "fist-sized rock" were detectable around a distant star (it would be difficult to spot {{w|Russell's teapot|something of this size}} around ''our own'' star), this represents a considerable range of uncertainty between tens of thousands of kilometres and a few centimetres, being perhaps five orders of magnitude. This is not particularly precise, even for a [[2205: Types of Approximation|cosmologist]].

;  Mini Pluto
: {{w|Pluto}} is already significantly smaller than most planets, thus its designation as a "{{w|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" {{w|Saturn#Physical characteristics|due to its density}}. The difficulties of finding a practical way to test this out, notwithstanding, perhaps someone managed it with this planet.

;  Planet whose surface may host conditions suitable for rocks
: As with planet number 9, this planet is too difficult to get a read on, and the measurements are still so vague it's so far unknown if this planet is a rocky planet or a gas/{{w|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''.

;  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 solar 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, {{w|Mercury}}.

; Title text
: The title text mentions a planet within an {{w|accretion disk}}, which means that the planet is in the orbit of a {{w|black hole}} and will be bombarded with X-rays and stars orbiting at close range. Nevertheless, the researcher speaking assures that the planet is in the disk's habitable zone, implying it is a worthwhile option for colonization.

==Transcript==
{{incomplete transcript|Don't remove this notice too soon.}}

{{comic discussion}}<noinclude>
[[Category:Astronomy]]
[[Category:Exoplanets]]

3051: Hardwood

2025-02-17T05:28:54Z

Bertrc: /* Explanation */ they are not discussing remodeling a house. They are applying house remodeling ideas to the earth’s crust

{{comic
| number = 3051
| date = February 14, 2025
| title = Hardwood
| image = hardwood_2x.png
| imagesize = 273x350px
| noexpand = true
| titletext = They may technically have been softwoods at some point, but they definitely aren't now.
}}

==Explanation==
{{incomplete|Created by a DIRT FLOOR INSTALLER - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
Home remodelers, whether contractors or do-it-yourselfers, sometimes seek to remove layers of modifications to restore some previous condition. An example is to remove carpeting or other covering to restore an earlier, perhaps original, floor. Flooring made of hardwood (oak, maple, etc.) panels, perhaps deprecated by earlier homeowners for comfort or style reasons, can be prized by later homeowners as tastes or fashions change. Hardwood floors are currently considered desirable in homes for durability, aesthetic appeal and other reasons, and may have been the original choice for the building, but aspirations constantly change and intermediate decoration may have overlaid carpetting or {{w|linoleum}}/{{w|Sheet vinyl flooring|vinyl}} at a time that this was considered more fashionable or practical.

In this comic Cueball has learned about geological strata and refers to finding a hardwood floor under these layers. The joke is that the characters are talking about the earth’s crust, rather than about a house. The ‘hardwood floor' is actually a fossiliferous coal seam from {{w|Carboniferous|300-350 million years before present}} that originated as plants and other woody material. The “layers” are subsequent geological strata, making it impractical, if not impossible, to tear them up. (Additionally, there is unlikely to be any ascetic reason to expose the “hardwood” layer)

The title text refers to the fact that the {{w|Carboniferous#Plants|plants}} typical of the Carboniferous period of Earth's history would all be classified as {{w|Softwood|"softwoods"}} at best; flowering plants ({{w|Flowering plants|angiosperms}}), the principal source of "{{w|hardwoods}}", would not appear on Earth in any significant numbers for another 220 million years. However, whatever it would be classified as in the beginning, it is hardwood in the literal sense of wood that is hard, as it is now all coal and rock.

[https://www.explainxkcd.com/wiki/index.php/Category:Geology Geology]-themed comics appear in xkcd with increasing frequency, with 19 of the 51 comics in the category published since the beginning of 2023.

==Transcript==
:[Cueball is looking down and pointing with a finger towards the floor in front of Blondie who is facing him. Behind her is a picture on the wall showing seven sedimentary layers above each other, assuming the top of the picture is air. Each layer has a different texture than the ones it borders but two are as white as the air at the top, including the bottom-most layer.]
:Cueball: So you're saying that if we tear up these layers, there's hardwood flooring under here?
:Blondie: ...I mean, sort of...

:[Caption below the panel:]
:Home remodelers learn about the Carboniferous

{{comic discussion}}

[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Blondie]]
[[Category:Geology]]

2972: Helium Synthesis

2024-08-16T12:58:25Z

Bertrc: /* Explanation */

{{comic
| number = 2972
| date = August 14, 2024
| title = Helium Synthesis
| image = helium_synthesis_2x.png
| imagesize = 740x312px
| noexpand = true
| titletext = Our lawyers were worried because it turns out the company inherits its debt from the parent universe, but luckily cosmic inflation reduced it to nearly zero.
}}

==Explanation==
{{incomplete|Created by a BIG BANG NUCLEOSYNTHESIZER - Please change this comment when editing this page. Do NOT delete this tag too soon.}}

This comic explores the challenges of obtaining {{w|helium}}. [[Hairy]] is leading a company meeting with [[Megan]], [[Cueball]], and [[Hairbun]], who are discussing the recurring problem of {{w|helium shortage}}s, a real-world issue due to helium's limited availability on Earth. Helium is a non-renewable resource extracted from {{w|natural gas}} deposits, and its scarcity can affect industries such as medical imaging, semiconductor manufacturing, scientific research, and party balloon supplies.[https://www.marketplace.org/2023/01/19/heliums-been-rising-in-price-and-its-bringing-businesses-down/] (See also [[2766: Helium Reserve]].)

Hairbun suggests investigating the origin of helium. Cueball's research reveals that most helium in the universe came from {{w|Big Bang nucleosynthesis}}, which occurred shortly after the {{w|Big Bang}} when the first elements were formed. (However, 99% of the helium here on Earth has been produced from the {{w|radioactive decay}} of {{w|uranium-238}} and {{w|thorium-232}} — which in turn came from {{w|r-process}} {{w|Supernova nucleosynthesis|nucleosynthesis}} inside merging {{w|neutron star}}s;[https://svs.gsfc.nasa.gov/13873/] see [[2826: Gold]] — into {{w|alpha particles}} identical to temporarily ionized helium, with only the remaining one percent originating from the Big Bang.)

Hairy assigns the team to figure out how to recreate Big Bang nucleosynthesis, which is not actually possible for a contemporary business organization.{{cn}} Nonetheless, the team builds a machine capable of it. While one might hope they would realize activating it may carry risks of obliterating them, along with at least all the closest galaxies, that disadvantage seems to grimly escape their attention in the tightly-focused drive towards their ill-fated mission.

The final panels show the creation of a second Big Bang followed by the next 14 billion years of that new universe, culminating with the same characters in an identical meeting, presumably having arisen from the same series of post-Big Bang events as in the original universe. They are facing the same predicament: helium shortages are still a problem, and they still need a reliable source. That such an extreme solution didn't actually solve the problem shows the impracticality of their plan, suggesting that some problems are too complex or vast to solve through uncritical brainstorming by corporations.

The title text is a wordplay on the two concepts of {{w|cosmic inflation}} and {{w|monetary inflation}}. The joke imagines the company as having inherited a debt from the parent universe (A play on how a child might inherit the debt of their parents upon their parents' death). In economics, monetary inflation is the rate at which the cost of things increases over time (one can also think of this as the value of money falling). If a debt is arranged on favorable terms, such that the interest on it turns out to be less than this rate, the value of that debt reduces over time. Cosmic inflation is a theory in cosmology that describes the rapid expansion of the universe just after the Big Bang. Somehow, thanks to this effect, this company's debt was diluted (perhaps ''physically'' across the effectively infinite vastness of space), reducing it to [https://www.accum.se/~ola/hitchhik.htm nothing]. (See also [[2688: Bubble Universes]].) This is not really how debt works.

==Transcript==
{{incomplete transcript|Do NOT delete this tag too soon.}}
:[Hairy sits on an office chair at the head of a conference table and has his hands on the table, with Cueball and Megan also at the table.]
:Hairy: These helium shortages every few years are such a pain.
:Hairy: Our company needs a reliable source of helium.

:[The same situation, but now Hairbun is also seen at the table on the left side of Cueball. Cueball holds a cellphone in his left hand, which Megan looks at.]
:Hairbun: Where does helium come from, anyway?
:Cueball: Hmm, apparently most of it is from "Big Bang nucleosynthesis"?
:Hairy: Well, let's figure out how to do that.

:[Hairy, Megan and Hairbun are working on a large machine labeled "Big Bang Nucleosynthesis," with Megan holding its wired control device in her left hand.]

:[Two panels depict another Big Bang, followed by various stages of cosmic development, including galaxies and planets forming, shown in white on a black background.]

:[The scene returns to the same conference room setup as before, with the characters in the same positions. Text at the top reads: "14 Billion Years Later."]
:Hairy: These helium shortages every few years are such a pain.
:Hairy: Our company needs a reliable source of helium.

{{comic discussion}}
[[Category:Comics featuring Hairy]]
[[Category:Comics featuring Cueball]]
[[Category:Comics featuring Megan]]
[[Category:Comics featuring Hairbun]]
[[Category:Comics with inverted brightness]]
[[Category:Cosmology]]
[[Category:Physics]]
[[Category:Recursion]]