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| − | {{comic
| + | pinis lol |
| − | | number = 2908
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| − | | date = March 18, 2024
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| − | | title = Moon Armor Index
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| − | | image = moon_armor_index_2x.png
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| − | | imagesize = 740x390px
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| − | | noexpand = true
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| − | | titletext = Astronomers are a little unsure of the applicability of this index, but NASA's Planetary Protection Officer is all in favor.
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| − | }}
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| − | | |
| − | ==Explanation==
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| − | {{incomplete|Created by a BOT COATING PLANETS WITH MOON ARMOR - Please change this comment when editing this page. Do NOT delete this tag too soon.}}
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| − | In this comic, [[Randall]] hypothesizes a situation in which each planet's moons were converted into protective armor to coat their respective planets. For example, the {{w|Moon}} would coat {{w|Earth}} in a 43 kilometer layer if it were molded into protective armor for the planet. It is unknown how the moons would be converted into armor, but with current technology, this would be highly impractical, if not impossible.{{citation needed}} It is also unclear how planets such as Jupiter, Saturn, Uranus, and Neptune, which are gas giants and thus have no solid surface, would sustain such a layer of armor, nor is it immediately evident what threat might necessitate such drastic measures. A 43km moon rock layer might in fact endanger life on Earth by blocking out the sun and impacting ecosystems, rather than protecting it.
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| − | Mars's moons {{w|Phobos_(moon)|Phobos}} and {{w|Deimos_(moon)|Deimos}}, being very small compared to Mars, would make a very thin layer over Mars. Huge Jupiter would be covered with almost 3km of "moon", which indicates just how much moon mass there is around Jupiter. This is, to a smaller degree, similar for Saturn, Uranus and Neptune.
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| − | Some trans-Neptunian {{w|Dwarf_planet|dwarf planets}} and dwarf planet candidates are included, as well: Only Pluto, having a moon ({{w|Charon_(moon)|Charon}}) of a comparable size to its planet, would have a layer thicker than Earth's. {{w|120347 Salacia|Salacia}}, {{w|Haumea}}, {{w|50000 Quaoar|Quaoar}}, {{w|225088 Gonggong|Gonggong}} and {{w|Eris (dwarf planet)|Eris}} are among the {{w|List_of_trans-Neptunian_objects#List|ten largest such objects}}. However, {{w|Makemake}} and {{w|90482 Orcus|Orcus}} are not included in this comic, despite both being known to have an available moon.
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| − | The comic uses the ≈ sign to show that the formula is only an approximation: it does not take account of the increase in armor surface area as it gets thicker. This approximation would be perfect for a shield of thickness zero, but for the thickest shield (Pluto) around a small celestial body the error is around 4% (52.5 km by approximation, but 50.4 km by calculation). To find the correct value, we can use the formula for the volume of a sphere, V = 4/3 * pi * r^3 (where V is the volume and r is the radius). Using this formula, we can find and add together the volumes of each moon, as well as the volume of the planet, to get a total volume of the new shielded planet. Then we can find its radius using the formula r = (V / (4/3 * pi))^1/3, derived from the previous formula. Subtracting the radius of the previous planet from the radius of the new planet gives us the thickness of the armor.
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| − | This process described above assumes that all objects involved are completely spherical, which may not be the case. Gravitational compression effects are not taken into account either; the planet's gravitational pull could settle some of the moon's material into a slightly smaller volume than the one it occupies in its separate lunar gravitational field. (And the planet below could be marginally affected by the change in its total planet + armor mass, too.)
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| − | The title text states that astronomers are "unsure" about the applicability of protective armor made from moons, possibly because they are wary of {{w|Giant-impact_hypothesis|moons and planets getting too close}}. It is dubious whether there would be an actual increase in planet safety due to the procedure. Moons as they are already serve a protective purpose by deflecting incoming asteroids, and by covering a small portion of sky.
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| − | The title text continues that NASA's [https://what-if.xkcd.com/117/ Planetary Protection Officer], whose job it is indeed to protect planets, is purportedly in favor of the idea. However, they are in fact responsible for keeping other celestial bodies safe from Earth's contamination, not for shielding planets in armor, as the title text suggests. There is no known method of shielding other planets from contamination by physically armoring them. {{citation needed}}
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| − | {| class="wikitable"
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| − | |-
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| − | ! Planet/<br>dwarf planet !! Surface area (km²) || Moons || Volume (km³) || Moon shield thickness <!-- please add more info -->
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| − | |-
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| − | | {{w|Earth}} || 5.1007*10^8 || {{w|Moon|1}} || 2.196*10^10 || 43 km (27 mi)
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| − | |-
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| − | | {{w|Mars}} || 1.4437*10^8 || {{w|Moons of Mars|2}} || {{w|Phobos (moon)|(5695±32)}}+{{w|Deimos (moon)|(1033±19)}} || 5 cm (2 in)
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| − | |-
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| − | | {{w|Jupiter}} || 6.1469*10^10 || {{w|Moons of Jupiter|95}} || 1.7646*10^11 || 2.87 km (1.78 mi)
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| − | |-
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| − | | {{w|Saturn}} || 4.27*10^10 || {{w|Moons of Saturn|146}} || 7.651*10^10 || 1.79 km (1.11 mi)
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| − | |-
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| − | | {{w|Uranus}} || 8.1156*10^9 || {{w|Moons of Uranus|28}} || ||
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| − | |-
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| − | | {{w|Neptune}} || 7.6187*10^9 || {{w|Moons of Neptune|16}} || ||
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| − | |-
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| − | | {{w|Pluto}} || 1.7744*10^7 || {{w|Moons of Pluto|5}} || {{w|Charon (moon)|(9.322×10^8)}}+{{w|Moons of Pluto|(approx 87100+38800+900+200)}} || 52.5 km (32.6 mi) (by XKCD)
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| − | 50.4 km (31.3 mi) (by full calculation)
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| − | |-
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| − | | {{w|120347 Salacia|Salacia}} || 2.27*10^6 || {{w|Actaea (moon)|1}} || 1.41*10^7 || 6.21 km (3.85 mi)
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| − | |-
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| − | | {{w|Haumea}} || 8.14*10^6 || {{w|Moons of Haumea|2}} || {{w|Hiʻiaka (moon)
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| − | |(17.2*10^6)}}+{{w|Namaka (moon)|(2.57*10^6)}} || 2.43 km (1.51 mi)
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| − | |-
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| − | | {{w|50000 Quaoar|Quaoar}} || 3.78*10^6 || {{w|Weywot|1}} || 4.19*10^6 || 1.11 km (0.69 mi)
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| − | |-
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| − | | {{w|225088 Gonggong|Gonggong}} || || {{w|Xiangliu (moon)|1}} || ||
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| − | |-
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| − | | {{w|Eris (dwarf planet)|Eris}} || (1.70±0.02)*10^7 || {{w|Dysnomia (moon)|1}} || ||
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| − | |}
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| − | | |
| − | ==Transcript==
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| − | {{incomplete transcript|Do NOT delete this tag too soon.}}
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| − | :[Text above diagram:]
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| − | :Moon armor index:
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| − | :How thick the shells around various worlds would be if their moon(s) were converted into protective armor
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| − | :≈Total moon volume/Planet surface area
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| − | | |
| − | :[Above the diagram, there is a depiction of two moons orbiting a planet, an arrow pointing right, and the same planet with an additional layer around it without orbiting moons.]
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| − | :[The diagram consists of vertical bars showing "moon armor" thicknesses for the Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto, Salacia, Haumea, Quaoar, Gonggong and Eris. Earth's bar has a label named "43 km thick" and is compared to the height of a comparatively small Mt Everest, with randomly drawn features indicating a cross section of the additional layer's rocky material. Most of the other armor thickness bars are not very tall compared to Earth. Some bars, notably Jupiter's, are embellished with various strata-like lines that possibly correspond to different contributing moons. Most bars show some small dots and patterns. A circular viewport shows the zoomed in detail of the top of Mars's otherwise not visible bar that reveals a thin layer with the label of 2", and also the bottom of a Mars rover wheel on top of the new surface. Pluto's bar is slightly taller than Earth's and has a label "(Mostly Charon)" inside, with arrows pointing into the bar area, which looks similar to that of Earth's Moon.]
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| − | {{comic discussion}}
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| − | [[Category:Astronomy]]
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| − | [[Category:Bar charts]]
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