Editing 2908: Moon Armor Index
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==Explanation== | ==Explanation== | ||
− | + | {{incomplete|Created by a MARS ROVER THAT GREW 2 INCHES OVERNIGHT - Please change this comment when editing this page. Do NOT delete this tag too soon.}} | |
− | + | In this “What If?”-style comic, [[Randall]] hypothesizes an imaginative 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. | |
− | + | The comic helpfully illustrates that Earth and Pluto both have remarkably large moons for their size. The large relative size of Earth’s moon — and its protective role in deflecting asteroids — is one reason that’s been suggested by astronomers for why intelligent life successfully evolved on Earth. | |
− | Six trans-Neptunian {{w|dwarf | + | Mars's moons {{w|Phobos_(moon)|Phobos}} and {{w|Deimos_(moon)|Deimos}} are small compared to Mars, so they would contribute a thin 2-inch layer of armor around 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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+ | Six 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}}. (Two dwarf planets with moons — {{w|Makemake}} and {{w|90482 Orcus|Orcus}} — are not mentioned in the comic, but their index values would be similar.) | ||
The title text states that astronomers are "unsure" about the applicability of this index, a joking understatement that imagines this comic as being a serious contribution to astronomical academic knowledge. Astronomers might also point out additional issues: | The title text states that astronomers are "unsure" about the applicability of this index, a joking understatement that imagines this comic as being a serious contribution to astronomical academic knowledge. Astronomers might also point out additional issues: | ||
− | * wariness of {{w|Giant- | + | * wariness of {{w|Giant-impact_hypothesis|moons and planets getting too close}}. |
− | * moons already serve a protective purpose by deflecting | + | * moons already serve a protective purpose by deflecting some incoming asteroids. |
− | * the four gas giants — Jupiter, Saturn, Uranus, and Neptune — lack a solid surface to practically sustain a layer of armor | + | * the four gas giants — Jupiter, Saturn, Uranus, and Neptune — lack a solid surface to practically sustain a layer of armor. |
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− | The title text continues that NASA's [https://what-if.xkcd.com/117/ Planetary Protection Officer] is purportedly in favor of the idea. In reality, this officer is actually responsible for keeping other celestial bodies safe from Earth's contamination, not for shielding planets in armor. Theoretically, though, armoring other planets could indeed protect them from | + | The title text continues that NASA's [https://what-if.xkcd.com/117/ Planetary Protection Officer] is purportedly in favor of the idea. In reality, this officer is actually responsible for keeping other celestial bodies safe from Earth's contamination, not for shielding planets in armor. Theoretically, though, armoring other planets could indeed protect them from Earth-sourced contamination, and armoring Earth would also theoretically protect other planets by blocking out the sun, thus apocalyptically destroying all human life — a common result in many of Randall’s “What If?” explorations. |
{| class="wikitable" | {| class="wikitable" | ||
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− | ! Planet/<br>dwarf planet !! Surface area (km²) || Moons || | + | ! Planet/<br>dwarf planet !! Surface area (km²) || Moons || Volume (km³) || Moon shield thickness <!-- please add more info --> |
|- | |- | ||
− | | {{w|Earth}} || 5. | + | | {{w|Earth}} || 5.1007*10^8 || {{w|Moon|1}} || 2.196*10^10 || 43 km (27 mi) |
|- | |- | ||
− | | {{w|Mars}} || 1. | + | | {{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) |
|- | |- | ||
− | | {{w|Jupiter}} || 6. | + | | {{w|Jupiter}} || 6.1469*10^10 || {{w|Moons of Jupiter|95}} || 1.7646*10^11 || 2.87 km (1.78 mi) |
|- | |- | ||
− | | {{w|Saturn}} || 4. | + | | {{w|Saturn}} || 4.27*10^10 || {{w|Moons of Saturn|146}} || 7.651*10^10 || 1.79 km (1.11 mi) |
|- | |- | ||
− | | {{w|Uranus}} || 8. | + | | {{w|Uranus}} || 8.1156*10^9 || {{w|Moons of Uranus|28}} || || |
|- | |- | ||
− | | {{w|Neptune}} || 7. | + | | {{w|Neptune}} || 7.6187*10^9 || {{w|Moons of Neptune|16}} || || |
|- | |- | ||
− | | {{w|Pluto}} || 1. | + | | {{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) |
− | 50.4 | + | 50.4 km (31.3 mi) (by full calculation) |
|- | |- | ||
− | | {{w|120347 Salacia|Salacia}} || 2. | + | | {{w|120347 Salacia|Salacia}} || 2.27*10^6 || {{w|Actaea (moon)|1}} || 1.41*10^7 || 6.21 km (3.85 mi) |
|- | |- | ||
− | | {{w|Haumea}} || 8. | + | | {{w|Haumea}} || 8.14*10^6 || {{w|Moons of Haumea|2}} || {{w|Hiʻiaka (moon) |
+ | |(17.2*10^6)}}+{{w|Namaka (moon)|(2.57*10^6)}} || 2.43 km (1.51 mi) | ||
|- | |- | ||
− | | {{w|50000 Quaoar|Quaoar}} || 3. | + | | {{w|50000 Quaoar|Quaoar}} || 3.78*10^6 || {{w|Weywot|1}} || 4.19*10^6 || 1.11 km (0.69 mi) |
|- | |- | ||
− | | {{w|225088 Gonggong|Gonggong}} || | + | | {{w|225088 Gonggong|Gonggong}} || || {{w|Xiangliu (moon)|1}} || || |
|- | |- | ||
− | | {{w|Eris (dwarf planet)|Eris}} || (1.70±0.02) | + | | {{w|Eris (dwarf planet)|Eris}} || (1.70±0.02)*10^7 || {{w|Dysnomia (moon)|1}} || || |
|} | |} | ||
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===The complexities of armor thickness calculations=== | ===The complexities of armor thickness calculations=== | ||
− | The comic uses the ≈ sign to show that the formula is only an approximation: it does not take account 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 | + | The comic uses the ≈ sign to show that the formula is only an approximation: it does not take account 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.) | |
==Transcript== | ==Transcript== | ||
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[[Category:Astronomy]] | [[Category:Astronomy]] | ||
[[Category:Bar charts]] | [[Category:Bar charts]] | ||
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