1547: Solar System Questions

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Solar System Questions
My country's World Cup win was exciting and all, but c'mon, what if the players wore nylon wings and COULD LITERALLY FLY?
Title text: My country's World Cup win was exciting and all, but c'mon, what if the players wore nylon wings and COULD LITERALLY FLY?


This comic is a list of questions which Randall has about the Solar System, which at first glance may appear to be things that Randall would like to learn about. In actuality, most of the questions have not been satisfactorily answered or proven by anyone in the scientific community. These open questions may serve to intrigue readers and prompt further interest in astronomy and austronautics.

Question given Answered? Answer given by Randall (in red in the original) Comments
Why is the the Moon so blotchy? Yes Lava The Moon is in synchronous rotation with Earth, which means that we always can see only one half of the surface of the Moon. And on that side we can see large lunar maria formed by lava from big volcanoes. This surface is very different from all other celestial bodies we know in our Solar system. The double "the the" could be a Randallism — intended or unintended.
Why are all the blotches on the near side? No ... The nearside of the Moon is dominated by the blotchy 'seas' or maria, the far side by craters. Several explanations for this have been proposed, including an overabundance of impacts obliterating the blotches on the more exposed far side, different compositions of heat-producing elements, large collisions, or heat produced by the still-cooling Earth.
Did Mars have seas? Yes Yes (briefly?) Recent explorations have confirmed there was once standing (and also flowing) water on Mars. Many rovers and orbiters on Mars give us the evidence on this early development of that planet, but it is still unknown how long such conditions existed in its history. Two of these probes have been the subject of comics before: 695: Spirit and 1504: Opportunity.
Was there life on Mars? No ... One of the big mysteries, not yet answered.
What's Titan like? Partly Cold, yellow, lakes + rivers (methane) The Cassini–Huygens mission confirmed the presence of lakes and rivers on Titan. The Huygens lander itself returned some very yellow images of a dry lake bed from Titan's surface. The possibility of life on Titan was mentioned in 829: Arsenic-Based Life.
What was Earth like during the Hadean? Partly ... The Hadean was the first geologic era on Earth, the planet had just formed and not much is known of that period of Earth. But since it was the time when Earth was formed it was mainly very hot with extreme volcanic activity, with the entire surface melted. This is why the era is named after Hades the ancient Greek god of the underworld, even though Hades was never associated with fire.
Is the Oort Cloud a real thing? Partly ... The Oort Cloud is a theoretical spherical cloud of icy planetesimals, maybe dust, and also larger objects at a distance of up to around 60,000 AU from our Sun. Although the Oort Cloud has never been directly observed (and likely will not be seen directly for a very long while), a large number of comets have been measured to have orbits that could only originate from many thousands of AU from the Sun, especially between 20,000 and 60,000 AU in particular.
Why is the Sun's corona so hot? Maybe Something about magnets? The corona of the Sun is hotter than it theoretically should be. Tiny solar flares called nanoflares might be responsible. The Sun's magnetic field is almost certainly relevant.
What are comets like? Yes Precipitous A comet can be dangerously steep: the Philae lander finally stopped tumbling when it ran into a cliff.
Where's Philae, exactly? Yes ... ...but we were not sure which cliff until September 5, 2016, when the European Space Agency announced that Philae had been found and photographed by Rosetta on the previous Friday (September 2). The landing of Philae was depicted in real time in the dynamic comic 1446: Landing. This lasted for several hours. Later the comic was updated with a new image where Philae is resting on the edge of a cliff.
What's Pluto like? Partly [Soon!] Pluto is so far from Earth and so small that traditional telescopes couldn't discern much about it. When this comic was released, the probe New Horizons was eight days away from its closest approach to Pluto and its moon Charon; Randall was naturally excited about it. The probe was the subject of the comic 1532: New Horizons.
What's Charon like?
Why don't we have in-between-sized planets? No ... There is a size-gap between the rocky terrestrial planets up to Earth size and the gas giants very much larger than Earth in our Solar System.

There are many known exoplanets (planets in other solar systems) filling in the range between our rocky planets and our gas giants, known as Super-earths However, there is an observed but unexplained scarcity of planets of this size category even among exoplanets.

What's Ceres like? Yes [Working on it!] The Dawn probe was currently exploring the dwarf planet Ceres at the time that this comic was written and released. Since the spacecraft's mission, it was determined that Ceres's surface is a mixture of ice and hydrated materials, like clay. The crust is at most thirty percent ice by volume, and though it likely lacks an internal ocean of water, highly-concentrated saltwater can still reach the surface from the outer mantle, allowing cryovolcanoes to form.
Why is Europa so weird-looking and pretty? Yes Ice over a water ocean Europa is a moon of Jupiter and the surface is basically thick pack ice covered in lineae.
Why is Io so weird-looking? Partly Sulfur volcanoes (? in the wrong places?) The moon Io is also orbiting Jupiter and is close enough that tidal forces make it the most volcanic object in the solar system. The moon is mainly yellow but there are several other colors on the surface, for instance spots and streaks of bright red that comes from sulfur ejected by the volcanoes. The "wrong places" refer to some volcanoes discovered by the Voyager missions and believed to erupt sulfur. But more recent measurements showed that the temperature inside those volcanoes is about 2000 °C where this element is not liquid anymore but gas.
Why are so many Kuiper Belt objects red? Yes ... Many objects in the Kuiper Belt have a reddish hue. A possible explanation is that they are covered in organic molecules called tholins formed by the irradiation of their surface ices. The New Horizons probe showed these to indeed be tholins.
What are those spots on Ceres? Yes ... The Dawn probe found some mysterious spots on Ceres. These white spots were confidently explained in 2020 as being hydrated magnesium sulfate salts percolated to the surface by deep brine reservoirs in the interior of Ceres. These spots became the punch line of the joke in 1476: Ceres.
What's in the seas under Europa's ice? No ... The ESA selected the mission Jupiter Icy Moon Explorer (JUICE) to Jupiter. The moon Europa is one target for that mission. But we have to wait, because, even though it has already launched on 14 April 2023, its arrival at Jupiter is planned for 2031. But that's not uncommon for missions like this. New Horizons and Rosetta also traveled approximately ten years to reach their targets. And before such a mission can start many preparations have to be done. 2010: Odyssey Two is a 1982 science fiction novel by Arthur C. Clarke in which he envisions life under the ice on Europa. This life becomes a major plot point both in this and in the two sequels.
Which of the other moons have seas? Partly Several Randall has already mentioned above that there are liquids on two moons. The moon Titan at Saturn has lakes on its surface formed by liquid ethane, methane, and propane and the Jupiter's moon Europa has a sea of water covered by a thick sheet of ice. Depending on the definition of 'sea', other less obviously 'frozen water world' moons such as Ganymede at Jupiter may have subsurface oceans of liquid water and on other moons it could be other substances that are liquid at the relevant temperature, like on Titan.
What are the big white things in Titan's lakes? Yes ... This refers to the bright transient features seen by Cassini appearing and disappearing in Titan's lakes, nicknamed "magic islands". These have since been largely explained as an organic-compound equivalent of icebergs.
What do Jupiter's clouds look like up close? Partly ... The Jupiter mission Galileo, operated by NASA and the German Aerospace Center (DLR), arrived at Jupiter in 1995 and was sent to impact the planet at the end of that mission in 2003 to eliminate the possibility of contaminating local moons with terrestrial bacteria. Several measurements were done on the atmosphere but no pictures were sent back to Earth. The Juno Spacecraft arrived at Jupiter in 2016 to study the planet's clouds up close, and has sent many high resolution pictures of Jupiter's clouds from just a few thousand kilometers above the planet's surface
What's all that red stuff in the Great Red Spot? Partly ... The Great Red Spot is a storm south of Jupiter's equator. Observations from Earth show a lifespan of more than 150 years. It's unknown why it's stable for that long a time and it's also not clear why the color is red. The probe Juno has arrived in July 2016 at Jupiter but has not answered Randall's question. One working hypothesis is that (like the cause for red Kuiper Belt objects) these are tholins produced from the sun irradiating ammonium hydrosulfide and acetylene.
What's pushing the Pioneer probes? Yes Heat from the RTG Discussed as the Pioneer anomaly. RTG stands for Radioisotope Thermoelectric Generator. This effect was mentioned (and explained a little differently) in the title text of 502: Dark Flow.
What pushes spacecraft slightly during flybys? No ... Several spacecraft experienced unexplained speed increases during Earth flybys. This is called the flyby anomaly.
Where are all the Sun's neutrinos? Maybe partly Oscillating There are fewer observed electron neutrinos from the Sun than the standard model predicts. This is called the Solar neutrino problem. Since the sum of all the neutrinos, regardless of type, that come from the Sun add up to the predicted number of electron neutrinos it is theorized that neutrinos can change their type. This is called Neutrino oscillation, and can occur only if neutrinos have mass. Neutrino oscillation is considered a proof that the mass of a neutrino is non-zero. The mass of a neutrino is not yet measured and is one of the problems on the list of unsolved problems in physics on Wikipedia.
Why is there so much air on Titan? No ... Titan has an atmospheric pressure 1.45 times that of Earth, but only 1/7th of the surface gravity which is less than Earth's own airless Moon has, hence the confusion. In fact, Titan actually has almost 20% more atmosphere by mass than Earth, and seven times more atmosphere across a given surface area! Less influence from the more distant Sun probably helps retain more of the atmosphere's gases (for instance, Mars saw most of its atmosphere blasted away by the Sun), and cryovolcanoes may replenish the methane fraction which should by now have all been converted into the other hydrocarbons present from subsurface reservoirs. Further studies are required to properly answer this question.
Why does the Kuiper Belt stop? Partly ... A reference to the Kuiper Cliff. Most Kuiper Belt Objects are found between 42 and 48 AU; calculations predicted that there would be more and larger KBOs beyond 50 AU, but instead very few objects have been found in that region. As of 2024, a partial explanation is that the Kuiper Belt has a large number of objects beyond 50 AU, but previous surveys were biased against seeing the fainter, more distant objects. Additionally, if the hypothesized Planet Nine exists, simulations show it may have destabilized some objects orbiting beyond 50 AU, throwing them into much higher or lower orbits.
Why is Iapetus weird-colored? Partly ... Iapetus is an icy moon of Saturn and always keeps the same face towards Saturn. The trailing hemisphere is bright, with the leading one notably darker. From Wikipedia, the darker side of Iapetus is currently believed to have been caused by a combination of outside sources of matter (particularly meteors) and lag deposits from melting ice, via exposure to the Sun. It appears to consist of carbon compounds and frozen hydrogen cyanide polymers.
Why does Iapetus have a belt? No ... Iapetus has a 13 km high ridge around most of the equator, and a number of 10-km-high mountains where the ridge is interrupted.
What's the deal with Miranda? No ... Miranda is the smallest of Uranus' five round satellites, and it's a bit rough around the edges and also has an unusually high orbital inclination that is difficult to explain. Also possibly a Firefly reference since Miranda is also the name of a planet in Serenity, a film based on the Firefly TV series.
Did Uranus and Neptune change places? No ... The Nice model is a theory of how our solar system formed, which suggests the possibility of Uranus and Neptune having swapped places before reaching their current positions. Work by Professor S. Desch also came to this result.
Did the Late Heavy Bombardment happen? No ... The Late Heavy Bombardment is the name given to a theorized bombardment of the planet Earth during its early history, along with the other rocky planets around the Sun. It's believed that during that time many large objects still existed and are likely to have impacted the planets. On Earth the evidence for those impacts would have been destroyed, but on the Moon or Mercury some evidence may be available.
Did life start before it? No ... For some speculation on this topic, see Life Could Have Survived Earth's Early Bombardment. It is still a mystery if life was formed on Earth first or if it came from outer space.
Is Europa covered in ice spikes? No ... Dr Daniel Hobley has put forward a theory that Jupiter's icy moon Europa has the right conditions to form ice spikes called penitentes of up to 10m in height.
Why haven't we built a big inflatable Extreme Sports Complex on The Moon? Partly ... The only silly item besides the "white on Titan's lakes" question, this question is less about science than about human priorities. It would be fun to watch sports in such a stadium - see the title text. Building a sports complex on the Moon would be prohibitively expensive in the context of government budgets, and transporting athletes to such a venue regularly would be logistically and financially complex. But it would be extremely cool.

See also What If # 124, which gives great detail to the topic of lunar swimming. The Menace From Earth, a 1957 short story by Robert Heinlein, describes another potential moon-based extreme sport.

The title text refers to the 2015 FIFA Women's World Cup which was won by the USA the day before. The nylon wings and flying may be a reference to two passages from 3001: The Final Odyssey, one where Frank Poole tries out various wings while in an extremely low gravity environment, and one where he remarks while watching Swan Lake that Tchaikovsky could never have imagined a performance where the dancers were actually flying (due to aforementioned low gravity). This is also a reference to the last point on the list, because if we had such a stadium on the Moon, maybe it would be possible to use such wings to make very long floating leaps.


Questions I have
about the solar system
(some answered)
Why is the the Moon so blotchy? Lava
Why are all the blotches on the near side?
Did Mars have seas? Yes (briefly?)
Was there life on Mars?
What's Titan like? Cold, yellow, lakes + rivers (methane)
What was Earth like during the Hadean?
Is the Oort Cloud a real thing?
Why is the Sun's corona so hot? Something about magnets?
What are comets like? Precipitous
Where's Philae, exactly?
What's Pluto like? [Soon!]
What's Charon like?
Why don't we have in-between-sized planets?
What's Ceres like? [Working on it!]
Why is Europa so weird-looking and pretty? Ice over a water ocean
Why is Io so weird-looking? Sulfur volcanoes (? in the wrong places?)
Why are so many Kuiper Belt objects red?
What are those spots on Ceres?
What's in the seas under Europa's ice?
Which of the other moons have seas? Several
What are the big white things in Titan's Lakes?
What do Jupiter's clouds look like up close?
What's all that red stuff in the Great Red Spot?
What's pushing the Pioneer Probes? Heat from the RTG
What pushes spacecraft slightly during flybys?
Where are all the Sun's Neutrinos? Oscillating
Why is there so much air on Titan?
Why does the Kuiper Belt Stop?
Why is Iapetus weird-colored?
Why does Iapetus have a belt?
What's the deal with Miranda?
Did Uranus and Neptune change places?
Did the Late Heavy Bombardment happen?
Did life start before it?
Is Europa covered in ice spikes?
Why haven't we built a big inflatable
extreme sports complex on the moon?

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I wonder if "What's the deal with Miranda?" is talking about one of Uranus's satellites or if it's a Firefly/Serenity reference? Keavon (talk) 15:31, 6 July 2015 (UTC)

  • That was my reaction too. Randall is (as he should be) slightly obsessed with Firefly. Cosmogoblin (talk) 19:12, 6 July 2015 (UTC)
    • There are other Mirandas... Miranda Sings, Miranda Hobbes, etc. Smperron (talk) 13:36, 8 July 2015 (UTC)
      • Given that the title of the comic is "Solar System Questions", and Miranda in firefly is not in the solar system, this is clearly a reference to the Uranus moon. Niffe 00:09, 10 July, 2015
        • If it's a reference to Miranda from Sex And The City, it's still a valid question. 12:42, 13 July 2015 (UTC)

Many of the entries can be found at https://en.wikipedia.org/wiki/List_of_unsolved_problems_in_physics Cschwenz (talk) 16:16, 6 July 2015 (UTC)

The title text is a reference to the Futurama episode "Butterjunk effect" http://theinfosphere.org/The_Butterjunk_Effect. (talk) (please sign your comments with ~~~~)

What's Titan like? Refernece to Gattaca (https://www.youtube.com/watch?v=lZa83dTf4JA)? The Twenty-second. The Not So Only. The Nathan/Nk22 (talk) 16:23, 6 July 2015 (UTC)

I wonder if Randal is using us as unpaid researchers to answer his questions for him? 16:53, 6 July 2015 (UTC)

  • Crowd-sourcing space probes? I certainly hope so!! Cosmogoblin (talk) 19:12, 6 July 2015 (UTC)
    • I was also thinking that, or at least he might have been thinking, "This oughtta keep those silly people on the ExplainXKCD wiki busy!". ;) KieferSkunk (talk) 20:42, 6 July 2015 (UTC)

Timing is good as it has recently been shown that red organics (Tholins) are produced by the particular UV wavelength called 'Lyman-Alpha' which is almost as bright on Pluto's night-side due to starshine as it is from the Sun during its daytime... the Edgeworth-Kuiper Belt may be the original Red-light District. Go New Horizons! Squirreltape (talk) 15:13, 7 July 2015 (UTC)

Ice Spikes could be a reference to the Ice Spikes biome in Minecraft: http://minecraft.gamepedia.com/File:Ice_Plains_Spikes.png Daedalus (talk) 10:12, 7 July 2015 (UTC)

The last question/the title text could also refer to Robert A. Heinleins "The Menace from Earth": https://en.wikipedia.org/wiki/The_Menace_from_Earth Bichlesi (talk) 01:13, 8 July 2015 (UTC)

The "big white things in Titan's lakes" may also refer to the magic islands that were observed by Cassini.-- 02:56, 8 July 2015 (UTC)

If they wore wings and could fly you would end up with the Butterfly Derby on the moon from the Futurama Episode "The Butterjunk Effect" 06:23, 14 July 2015 (UTC)

Ideas about the "What pushes spaceships slightly during flybys?": (1) Gravity is slightly stronger near the equator due to the faster relative motion of the planet surface (which is why the plane of orbits of moons, planets, rings, galaxies try to align near the equator of the central mass). (2) Earth's mass is not 100% evenly distributed within it's volume causing minor gravitational distortions. (3) Flybys "behind" the Earth as it moves in its orbit gravitationally slow the Earth (very very slightly) robbing it of KE and giving it to the craft. Flybys "in front" of the Earth in orbit do the reverse. - Ezfzx (talk) 17:46, 1 December 2021 (UTC)

I think this page, perhaps more than any I've run across so far, can really use a few more sets of eyes. I would even suggest that the page is incomplete, because of all the new science we've done in the past decade. It would be nice if we could label the status of these questions. "Which other moons have seas" answer is clearly incomplete, as it doesn't list "several" contenders. Maplestrip (talk) 10:41, 14 February 2024 (UTC)

I just added the color-coded column, which might be of interest and helpful when looking at this as a checklist. Maplestrip (talk) 11:02, 14 February 2024 (UTC)
Thank you, anonymous IP editor, for adding so much information to this page! That was exactly what I was hoping when I marked this page as incomplete, and it's amazing to see how much new knowledge we've gained in the past decade. The floating islands of Titan particularly wowed me. I'm beyond pleased! Maplestrip (talk) 13:23, 23 April 2024 (UTC)

Why are so many Things where there is clearly absolutely no answer give not marked as no, but either partly, maybe, or even yes? how did this happen? -- Xkcd explainer (talk) 08:09, 15 May 2024 (please sign your comments with ~~~~)

Please change those items to "no" if you are unhappy with the answer given. I'm not entirely happy with some of the answers too, but I gave a few of them the benefit of the doubt. A "no" in this chart is an invitation for people to find better answers! Maplestrip (talk) 12:01, 15 May 2024 (UTC)