2258: Solar System Changes
|Solar System Changes
Title text: "Actually, Jupiter already has a very impressive ring system!" --someone who knows Jupiter is within earshot
This comic shows a drawing with a standard sketch of the Solar System, featuring the Sun, 8 planets, the asteroid belt, and Pluto. Randall then proposes eight changes to the solar system that he would make if he had the power to do so. Each change is drawn in red with explanatory labels. Performing these changes would be impossible in practice and would probably make the solar system unstable if actually performed.
This is another comic containing red annotations over a complex and established structure.
The title text is being spoken by "someone who knows [that] Jupiter is within earshot," implying that the speaker does not wish to offend Jupiter. While Jupiter does have its own ring system, it is so faint that it wasn't discovered until 1979. Considering that Jupiter is known to disrupt the asteroid belt and send asteroids towards the inner solar system (cf. Kirkwood gap) and completely destroy other celestial bodies (Comet Shoemaker–Levy 9), someone who is "within earshot" of Jupiter may wish to reassure the planet that they think its ring system is already very impressive when they really don't.
Table of proposed changes
|Add mysterious planets inside Mercury's orbit
| In the 19th century, scientists found discrepancies between Mercury's predicted orbit and observations. They proposed a hypothetical planet, Vulcan, to account for this discrepancy. After general relativity was discovered by Albert Einstein in the 20th century, it was found to account for these discrepancies.
Planets inside Mercury's orbit would be "mysterious" because they would be difficult to see (due to being above the horizon only during the day and a short period of twilight) or visit (spacecraft traveling inside Mercury's orbit are subject to enormous amounts of sunlight, causing them to overheat). If such planets existed, it's plausible that flybys wouldn't have occurred until very recently.
|After what it's been through, Venus deserves rings and a moon
| Billions of years ago, Venus and Earth are believed to have been almost identical objects orbiting the Sun. However, orbiting somewhat closer to the Sun, Venus became sufficiently hot that its oceans evaporated, cloaking the surface with gases that caused the Sun's heat to become trapped. This made the planet even hotter, causing a runaway greenhouse effect, and ultimately Venus became very much hotter than the Earth. In turn, the lack of water caused Venerean plate tectonics to fail, causing Venus to have periodic "resurfacing" events where the entire crust is recycled by volcanism. On top of that, Venus was almost certainly hit by an enormous object, hard enough that its spin was completely reversed. Randall may be saying that Venus has fared so badly throughout its life that it deserves some compensation, like rings or a moon.
Alternatively, Randall could be referring to how we see Venus now as opposed to in the past. A hundred years ago, scientists considered Venus and Mars to be equally likely candidates for life and future human exploration - one being a little warmer than Earth and the other a little colder. However, when we sent spacecraft to Venus and Mars in the 1960s, we quickly discovered that Venus is a terrible place. Its atmosphere is more than 90 times as dense as Earth's and its surface temperature is over 450° C (800° F), not to mention the sulfuric acid rain. Spacecraft that have landed on its surface have lasted a couple hours at most. As a result, missions to Venus have become far rarer since the 1960s, while missions to Mars have remained frequent. Randall might be saying that most people don't consider Venus to be nearly as fascinating place as they used to, and that it would be far more interesting with rings, or at least a moon like Earth or Mars.
In the 17th and 18th centuries, some astronomers (most notably Giovanni Cassini) claimed to have found a moon of Venus, but that was later determined to be an illusion.
Note that, due to the retrograde spin of Venus, any prograde-orbiting moon would inspiral due to tidal drag (the same effect causing the Moon to slowly move away from the Earth). It is unknown whether Venus used to have moons that were destroyed by this mechanism (possibly passing through a ring state in the process).
|Replace our moon with Mars. Mars is more interesting and we can consolidate missions.
| Mars has a lot more geological variety than the Moon, a much faster rotational period, and is much larger and has active weather patterns, and would therefore look far more interesting than the Moon when seen from Earth. In addition, by replacing Earth's current moon with Mars, sending spacecraft to the moon and Mars wouldn't require separate missions and could thus be consolidated into a single one. This would benefit NASA's space exploration efforts, which have suffered from presidents alternating targets for human exploration between "moon-to-Mars" versus "Mars direct" architectures.
Unfortunately, replacing our moon with Mars would have some negative side-effects for both worlds. Mars is 8.7 times more massive than the moon, which means that it would raise much stronger tides on Earth than our moon does now. As for Mars, it would now be significantly warmer than in its present orbit. The ice caps would likely sublimate, and what little water is left on the planet could boil away due to the lack of a thick atmosphere.
Incidentally, the Moon is thought to have been formed by an impact between the young Earth and a Mars-sized body. While Randall probably means well, the situation could get out of control very quickly.
|The solar system needs a super-Earth
|Super-Earths are a type of exoplanet -- a planet orbiting a star other than the Sun -- that are significantly larger than Earth but significantly smaller than the gas giant planets (Jupiter, Saturn, Uranus, and Neptune). While they are relatively common among systems in which smaller exoplanets have been found, our Solar System doesn't have any super-Earths, and with Mars being moved to replace the Moon, its location would be open to a new planet. With a super-Earth nearby, astronomers would be able to get a much better idea of what they are like. A super-Earth might also be an exciting place to colonize, although it would not be possible to return to orbit from such a planet with current rocket technology.
|Asteroid belts are usually portrayed in fiction as being incredibly crowded with asteroids, so much so that they pose a significant hazard for spaceships. In reality, the asteroid belt is much more boring, as most large asteroids are millions of miles from their nearest neighbor. The number of asteroids in the asteroid belt is indeterminate, as they range in size from dwarf planets down to about a meter across, and more than 100,000 have been found. Despite this, the density of asteroids in the belt is low enough that spacecraft have no problem flying through the belt untouched. Randall wants more asteroids.
|Merge the big planet and the ringed planet into a big ringed planet ("Jaturn")
|Jupiter is the largest planet, with a volume larger than all other planets combined, and it displays striking weather patterns such as the Great Red Spot. Saturn, with its prominent ring system, is perhaps the most spectacular, but the planet itself looks very bland with the exception of an enormous hexagonal storm at the north pole. Randall would merge the two, creating one planet that would dominate by both size and appearance. This new planet has Jupiter's cloud features, but Saturn's rings and polar hexagon. The two planets' moons would also be combined: the "Jaturn" diagram shows both the Galilean moons (the four largest moons of Jupiter) and Titan (the largest moon of Saturn) orbiting outside of Jaturn's rings.
|Cut Uranus. Uranus and Neptune are redundant and Neptune is better. Tough but fair.
|Uranus and Neptune are often regarded as being planetary "fraternal twins." Both have approximately the same size, the same mass, and the same composition - they even have similarly bizarre magnetic fields. Uranus's most notable trait is that its axial tilt is almost 98°, meaning it lies on its side and has a seasonal cycle unlike that of any other planet. However, this causes Uranus to look completely featureless most of the time, which makes it less interesting, while Neptune has more active weather patterns, including, episodically, a Great Dark Spot similar to Jupiter's Great Red Spot. The name "Uranus" is also subject to ridicule by English speakers. Randall also characterized Neptune as the slightly more interesting planet of the two in what if 30.
|Settle the planet thing by making Pluto a moon of Neptune
| Pluto was considered a planet from its discovery in 1930 until 2006, when the International Astronomical Union changed its definition of "planet" and reclassified Pluto as a dwarf planet. However, many people who grew up with Pluto listed as the ninth planet of the solar system were unhappy with the change, a topic that has been the topic of several other xkcd comics (473: Still Raw, 1551: Pluto, 1555: Exoplanet Names 2, etc.). Randall proposes a Solomonic compromise to "satisfy" both the camps who prefer to think of Pluto as "not a dwarf planet" and "not a planet" by making it into a moon. The diagram shows that Charon will also be made a moon of Neptune, and presumably Pluto's other moons as well. Even if the entire Pluto system were transplanted all at once, tidal forces would cause the bodies to drift apart and orbit Neptune independently.
Interestingly, one of the original hypotheses for Pluto's origin is that it and Triton were originally both moons of Neptune, but Triton knocked Pluto out of its orbit into a new orbit around the sun, while Triton remained with Neptune.
- [A not-to-scale diagram of the solar system is shown with the right edge of the sun on the left side, featuring all eight planets along with their major moons, Pluto (along with its major moon), and the asteroid belt. The original solar system is drawn in black, but several changes have been proposed. If some of the existing planets are removed or changed, they are greyed out, possibly with red crosses over them or red circles or arrows. New planets, moons, rings and asteroids have been added all in red. Each change has been labeled with red text. Only the Sun and Mercury are completely unchanged, Earth and Neptune are not changed directly but their moons have changed. The only black text is a caption at the top:]
- Changes I Would Make to the Solar System
- [Below each of the changes to the solar system is mentioned from left to right, with their labels, that are all in red text. Except for the label under Jupiter and Saturn, there is a line going from the changes to the relevant label.]
- [Three additional planets, one Mercury sized and two smaller on either side very close to each other, have been drawn in between Mercury and the Sun. A bracket marks all three of them and a long line goes from that to the label above, which is even above the next label positioned above the planets.]
- Add mysterious planets inside Mercury's orbit
- [A ring has been drawn around Venus, and a dot representing a moon has been added on its left. A small line goes from the label beneath to Venus.]
- After what it's been through, Venus deserves rings and a moon
- [Next to Earth, drawn with four of the major continents visible, the Moon has been grayed out and crossed out with a red X. Also Mars has been grayed out and it is inside a red circle. An arrow goes from the circle around Mars to the Moon. a small line goes from the arrow between the Moon and Mars to the label above the planets.]
- Replace our moon with Mars. Mars is more interesting and we can consolidate missions.
- [An additional planet, all in red, has been added between Mars and the asteroid belt, about halfway in size between Earth and Neptune. Four continents are visible in a large ocean, along with weather patterns as in an atmosphere. A small line goes from the planet to the label beneath.]
- The Solar System needs a super-Earth
- [Numerous asteroids have been drawn, half in black, with the other half in red added to the existing asteroids that were already there. A small line goes from the asteroids to the label beneath.]
- More asteroids!
- [Jupiter and Saturn have both been greyed out and also crossed out with two red X'es. Two arrows points from each of the original planets to a new larger red planet drawn above the two. This new planet has the belts, zones, Red Spot, and size of Jupiter, and the hexagon on the north pole and rings of Saturn. It also has the four largest moons from Jupiter on one side and the largest moon from Saturn on the other side, with all five drawn similarly to the original moons. Below the two original planets is a label.]
- Merge the big planet and the ringed planet into a big ringed planet ("Jaturn")
- [Uranus is greyed out and also crossed out with a red X. A line goes down to the label beneath it.]
- Cut Uranus. Uranus and Neptune are redundant and Neptune is better. Tough but fair.
- [Pluto and Charon have both been greyed out and are inside a red circle. An arrow points from Pluto and Charon to the right side of Neptune, where Pluto and Charon have been redrawn in red. Neptune's own largest moon is on the other side of Neptune. A line goes from the arrow up to a label above the planet.]
- Settle the planet thing by making Pluto a moon of Neptune
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