1633: Possible Undiscovered Planets
|Possible Undiscovered Planets|
Title text: Superman lies near the bird/plane boundary over a range of distances, which explains the confusion.
| This explanation may be incomplete or incorrect: It there a peer reviewed paper? Or other place the data has been published? Links to this is needed. Wiki link in the table.|
If you can address this issue, please edit the page! Thanks.
This comic is about Planet Nine, a possible Neptune-sized planet far beyond the farthest planet Neptune. Astronomers Mike Brown and Konstantin Batygin published a paper on 2016-01-20, only two days before the release of this comic. The paper is called Evidence for a Distant Giant Planet in the Solar System and it shows indirect evidence that such a planet may exist, inferred from an otherwise unlikely correlation between the unusual orbits of several dwarf planets. See for instance also an explanation, for the layman, of the results here: Astronomers say a Neptune-sized planet lurks beyond Pluto.
As this paper came out on the day of the previous comics release (1632: Palindrome), this comics release day, was the first release day after the news came out. This explains why this comic was released in the late afternoon rather than just past midnight as is often the case with normal releases. Once Randall heard this news, he had to decide to do this comic instead of the scheduled comic, and then invent and draw a completely new and actually very complicated comic about "Planet X", (now Planet IX, with Pluto degraded to a dwarf planet), before he could release this comic. Note that Mike is the astronomer that killed Pluto, or at least reduced Pluto to a dwarf planet, something that has been a subject in xkcd before, (see 473: Still Raw.)
Stating the obvious, this log–log plot shows that for an object to be an unknown planet it has to be very far away, since planets are big, to explain why we haven't seen it yet. With the log scale it is possible to go from less than 1 mm to an astronomical unit (AU) on the Y-axis and from 1 cm to thousands of AU on the X-axis.
Randall's chart is very egocentric as it categorizes objects based on size but also on their distance from himself ("from me"). This distance starts at 1 cm, and an item on the chart reads "skin flora", thus distance is measured from the surface of Randall's body (skin/eyes) rather than from his center of mass. As all the discovered planets are much farther away than their diameters, then their real size would hardly take up any space due to the log-scale. The dots marking these 7 planets are thus not drawn to scale that should represent they actual size compared with the other planets. However, for Earth, which is marked with the largest of the dots, it seems he has used the opposite side of the Earth, as his distance from Earth is equal to its diameter. This is clear as the Earth dot is situated on the line that has the planets he would be inside to the left. It is just left of the 10,000 km line on both axis, and Earth has a diameter of 12,000 km, which will fit fine with the center of the dot.
The chart uses a generous definition of planet (from the Greek word for "wanderer"), especially towards the lower-right corner, and allows any distinct solid object as a possible planet, whereas the IAU definition of planet requires a solar orbit, gravitational rounding, and "clearing the neighborhood", a controversial (at the time of its introduction) calculation of relative size that excludes Kuiper Belt Objects such as Pluto. The calculation regarding Planet Nine would make it large enough to meet the IAU definition.
That said, despite jokes such as "planets that are actually birds" the actual planets are prominently marked on the chart: they are the solid black dots. Besides Earth and Planet Nine?, the bottom row of three is Mercury, Venus (the largest of those three, but the three dots are of equal size) and Mars. It is unclear how Randall is calculating the distance to these three since neither of these options work: closest approach, average, mean, current or max. It is thus also unclear which of the three represents which planet. In the comic 482: Height Randall shows (among other) the distance from the Earths surface to all the planets. For especially Venus and Mars he shows that their distance changes a lot based on theirs and Earth's orbital positions. He has also not used these loops to base the dot size or position, as these loops clearly go closer than 1 AU and only one of the planets are drawn closer than that. In the table below there is made some reasoning that the planets are listed in the order of their distance to the sun, as this will give least deviations from the position of the dots and the data for the planets.
The top row of four is (from left to right) Jupiter and Saturn (visible to the naked eye) and Uranus and Neptune (visible through a telescope). Pluto, no longer considered a planet, is not marked on the chart, but it would be below Neptune in the corner of the pink region. (There is one dwarf planet that doesn't appear in the pink region, because it is visible with a telescope: Ceres, which would appear roughly below Mars and Jupiter.)
The Moon is marked on the chart, parenthetically and in gray since it's not a planet (because Earth is clogging up its neighborhood), but it was considered one of the classical planets by the ancient Greeks who invented the word. (Randall has messed up the positioning and the diameter of the Moon (see the table below). The Sun, however, is not marked at all (not even in grey), even though it is extremely prominent and was also one of the classical planets. It should be right above Mercury, inside the region of things that we can see during the day (note that objects this big will always be shining, Jupiter is already brighter than if it would reflect 100% of Sun's light. In general, "planets ruled out because we would see them during the day" refers to objects big enough to be stars, but the only star system, other than Sun, that would fit on the chart is Alpha Centauri, which at 4.37 light-years (ly) is well withing the right boundary that falls at 5,68 ly, just before the distance to the next nearest star Barnard's Star at 5,96 ly from the Sun. (A light year is 63,241 AU, and with the 10,000 AU mark far from the right edge of this log-log plot, it is clear that also 100,000 AU and thus a light year is within the chart. And this also goes for 5 ly).
Randall correctly states that if there was a planet that was at a distance from him smaller than its radius, he would be inside it (although at the bottom of that region, it's more like the planet that would be inside him, as this line goes down to a diameter of 1 cm).
"Planets ruled out by the WISE survey" refers to the Wide-field Infrared Survey Explorer (WISE), a space telescope designed to look for warm objects such as brown dwarfs, which generate heat at their centers. It was capable of detecting Saturn-sized or larger planets in the outer reaches of our solar system, but did not find any. WISE would not have detected "Planet Nine" (even if it exists) because it is too small and thus too cold to be detected. There is a chance that it can be seen in some more temperature sensitive measurements. But these have not been checked for such a planet yet, (see the news story).
The comic seems to imply a flat (or mostly bird-less) Earth, as birds are not shown to exist further than about 1000 km away from the "me", while Earth's diameter is in the ballpark of 10000 km.
The region of "satellites" should be extended down an order of magnitude or so to account for 10 cm cubesats.
The title text explains why some people confuse Superman for a bird or a plane, since Superman often flies at the limit between the two categories in the diagram. This is though not really true as can be seen in the bottom of the table below and in this image
Table of items in the chart
- This table lists the limits of all regions and dots in the image.
- Some of the more stretched out regions has also been split into two or three smaller parts.
- The planet dots has the limits from the edges of the circle the dots makes used for maximum and minimum limits.
- The table is sort-able, but at the moment the distances are with units, and these change, so it is not sort-able in a very meaningful way. (Maybe someone could improve on that?)
- The data has been read out using the image inserted below the table.
- Note that superman is also drawn in
|Regions and objects||Min. distance||Max. distance||Min. diameter||Max. diameter||Explanation|
|Planets ruled out because I would be inside them||1 cm||109 km||1 cm||109 km||Planets that would either have Randall inside, or if smaller than Randall would be inside Randall. Earth comes close since Randall is on its surface (most of the time). The line dividing this region from the Planets we see at night has the dot representing Earth on it at around 12,000 km = Earths diameter. It hits the Y-axis at 1 cm and then goes to the top at almost 10 AU|
|Planets ruled out because they wouldn’t fit through my door||1 m||60 m||1 m||60 m||As these "planets" are more than 1 m in diameter it is likely they would not fit through his door. It is assumed that if a planet were within 60 m from Randall that they would be within his house, but because they can't fit through his door, they wouldn't be in his house. The real planets would of course also not fit through any door.|
|Birds that got into my house||20 cm||60 m||20 cm||1 m||Small birds that get into Randall's house. They are not planets… He has a fairly big house as they can be 60 m away from Randall (when he is inside) and still be inside his house.|
|Region with bugs and skin||1 cm||25 km||0.15 mm||20 cm||The giant bugs region is not inside this one, thus takes a cut out of the top right of this region. The bottom of the chart is at 0.15 mm. Only at the very bottom for very small items does the region stretch out beyond 10 km…|
|Bugs (Not planets)||10 m||1 km||1 mm||1 cm||This is only the approximate region where the words Bugs (not planets) are written. As the skin part probably is at the origin, the whole region is probably related to bugs. See above for the size of this item.|
|Skin flora||1 cm||1 cm||0.15 mm||0.15 mm||There is an arrow pointing to the corner of the diagram. The values are thus the same for min. and max. as it is a point value. Of course it may also mean that they are outside the chart, but this is not clear.|
|Giant bugs||100 m||10 km||3 cm||20 cm||Giant bugs are for Randall from about 5 cm. It seems like he tries to keep them at least 100 m away.|
|Planets which are actually birds||60 m||45 km||20 cm||8 m||Birds bigger than the birds that can get into Randall’s house, and up to the biggest possible birds (and even bigger). These are so big that they actually look so much like planets that you have to be told that they are actually just birds.|
|Airplanes (Fool’s planets’)||200 m||60 km||8 m||100 m||Planes in the sky can often be mistaken for a planet, especially at night and at a distance. This may be a comment on fool's Gold, i.e. the metal Pyrite, that looks so much like gold that it is easy for people finding Pyrite to believe they have found gold. The same goes for airplanes and planets according to Randall|
|Region with with junk, asteroids and Oort||10 km||5.7 ly||0.15 mm||500 km||Space junk can get as close as 10 km from Randall and be of a sub millimeter size. And then the objects in the asteroid belt and Oort cloud that are not to be considered dwarf planets can be up to 500 km and can reach out to the next star as the edge of the graph is almost at 6 light-years (ly)|
|Space junk||10 km||105 km||0.15 mm||10 m||This is only the approximate region around where the words Space junk are written in this large region. From the left to halfway to the next label for comets and asteroids and the max diameter taken at this point|
|Comets and asteroids||105 km||100 AU||0.15 mm||225 km||This is only the approximate region around where the words comets and asteroids is written in this large region. It goes from halfway to the previous label for Space junk and halfway to the next label for Oort cloud. The max diameter is taken at this last point. A small part of this section just reaches into the Dwarf planet territory, making sense as Ceres is a dwarf planet in the asteroid belt.|
|Oort cloud||100 AU||5.7 ly||0.15 mm||500 km||This is only the approximate region around where the words Oort cloud are written in this large region. From halfway to the previous label for comets and asteroids and to the end of the chart at the right near the nearest stars at almost 6 light-years (ly)|
|Satellites||100 km||105 km||1 m||10 m||This is only the approximate region where the word Satellites is written. The words cross the border between the Space junk etc. region below and the Stuff we can see through telescopes region above. In principle it could thus go down into the space junk region and reach the 10 cm diameter of a cube sat, and up to the size of the International space station.|
|Stuff we can see through telescopes||60 km||800 AU||1 m||430,000 km||The max and min. values are not very representative as the region follows a shifted diagonal. Close items can be seen with telescope even if they are small, and large object might not be visible if they are far enough away. Hence this section has been split in three, see below. At the top left of the region there are two dots representing Uranus and Neptune, the planets not visible to the naked eye.|
|Stuff we can see through telescopes (over satellites)||60 km||105 km||1 m||1 km||This section has been split in three, see the entire region above. This is objects in the satellite range|
|Stuff we can see through telescopes (over asteroids)||106 km||10 AU||30 m||20,000 km||This section has been split in three, see the entire region above. This is objects in the asteroids range|
|Stuff we can see through telescopes (Past asteroids)||10 AU||800 AU||100 km||430,000 km||This section has been split in three, see the entire region above. This is objects in the outer planet range. Here are also the two dots representing Uranus and Neptune, the planets not visible to the naked eye. The reason the upper cut of it at (almost) the same level through all this region it that if the "planets" got any bigger, then they would turn into a brown dwarf that could be seen during the day, or if they got bigger they could even turn into a small star (or big star see below), and thus would be visible by day|
|Region with both planets above house and visible at night||60 m||43 AU||3.5 m||300,000 km||The max and min. values are not very representative as the region follows a shifted diagonal. Close items can be seen with the naked eye at night even if they are small, and large object might not be visible if they are far enough away. Hence this section has been split in two sections as there are two labels, see below. At the top left of the region there are five dots representing the five planets visible to the naked eye. Also the moon is shown with a gray dot (i.e. not a planet), this is more in the middle of the region, and finally the Earth is on the border to the region to the left, with planets that Randall would be inside if they did exist.|
|Planets ruled out because I would have noticed them above my house||1 km||105 km||100 m||10 km||This is only the approximate region around where the words of this part of the region are written in this large region. Just to show how much smaller the limits are in the small scale of the region. However, this entire region is about things that are visible at night, including the five planets and the moon. Those can be seen as labels for the dots, not another label for the region. Also Saturn is above Randall’s house when he sees it! Of course so is another bright object only 1 km above his house. But anyway planet or not he would be able to rule it out as a new planet, as if there were any that close and this big they would have been spotted long ago.|
|Planets we can see at night||108 km||10 AU||10,000 km||300,000 km||This is only the edges of the region of the five dots representing the five planets visible to the naked eye. They do belong to the region of planets Randall can spot from above his house, and as such this may be a label for the planets not for the region. But the limits here are interesting to compare with the entire region or with that of the part with smaller dimensions as shown above. The reason the upper cut of it at the same level through all this region it that if the "planets" got any bigger, then they would turn into a brown dwarf that could be seen during the day, or if they got bigger they could even turn into a small star (or big star see below), and thus would be visible by day|
|Dwarf planets||13 AU||5.7 ly||170 km||16,000 km||Dwarf planets can in principle be anywhere in the solar system. But this region only covers undiscovered dwarf planets, and thus they should be at least a given distance away, before it is realistic they would not already have been discovered. Also they need to be a certain size to be able to round themselves under their own gravity. And if they are too big, it is not realistic that they are only dwarf planets. The region reaches out to the next star as the edge of the graph is almost at 6 light-years (ly)|
|Planet Nine?||100 AU||5.7 ly||3,600 km||300,000 km||This is the region the whole comic is about. Here be planets yet undiscovered. They have to have a certain size to be a planet if they are this far away, and also have to be this far away before it is realistic they would not already have been discovered. If they were any bigger, it would be like with the other planet regions to the left, that they would turn into a brown dwarf, (or at least Saturn sized planet) and although maybe not visible with telescopes just above this size, they would have been spotted by the WISE survey (see below). The region reaches out to the next star as the edge of the graph is almost at 6 light-years (ly)|
|Planets ruled out by the WISE survey||450 AU||5.7 ly||70,000 km||106 km||This region refers to the Wide-field Infrared Survey Explorer (WISE), a space telescope designed to look for warm objects such as brown dwarfs, which generate heat at their centers. It was capable of detecting Saturn-sized or larger planets in the outer reaches of our solar system, but did not find any. WISE would not have detected "Planet Nine" (even if it exists) because it is too small and thus too cold to be detected. It the objects got any bigger than the upper limit they would turn into small stars, which would be visible during the night probably even with the naked eye. This is the last section below this. The region reaches out to the next star as the edge of the graph is almost at 6 light-years (ly)|
|Planets ruled out because we would see them during the day||360,000 km||5.7 ly||360,000 km||109 km||This region covers object that are either brown dwarfs close enough to us that we could see them (even by day) or if even bigger real stars, that would be closer to us than almost any other star system. The upper limit is at the top of the chart which almost reaches 10 AU. When the sun turns into a red giant after its main sequence when it has exausted its hydrogen it will swell up to a size of 2 AU and not only swallow Earth but also Mars. But there are also start swelling to more than 10 AU. The max. distance actually reaches the nearest star system of Alpha Centauri. And the biggest of those stars would be inside this last region, as it is 1.2 times bigger than the sun, and thus have a diameter of approximately 1.7 106 km, and they are "only" about 4,37 light-years (ly) away and the graph goes to 5.7 ly. But these stars are definitely not visible during the day. If the graph had stopped at 10,000 AU, at the last tick, this may have been true, but now it is an error, as starts in this entire region will not be visible during day time. But they would at night, if not by eye then by telescope. So no planets in this region, and also no undiscovered objects of that size!|
|Dot 1 Earth||10,000 km||32,000 km||10,000 km||23,000 km||This dot represents Earth. The Earth has a diameter of 12,000 km and Randall is on top of it, thus distance is zero. Thus the dot makes no sense. The max and min given here is at the limit of the circle the dot makes.|
|Gray Dot (Moon)||1.3x106 km||3x106 km||5,000 km||12,000 km||This dot represents the Moon. It is gray and moon is written in brackets to indicate that it is not a planet. Randall seems to have misplaced the dot completely. The Moon has a diameter of 3,400 km and the min limit is 5,000 km. It is even worse with the distance which is a factor 10 too large, at least at the max. The moon is on average 380,000 km from earth, and at the max distance is 406,700 km, to which Randall can add 6000 km when on the other side of the Earth to get him about 413,000 km from the Moon (but then he cannot see it). However, the minimum distance given is more than one million km, and thus more than a factor two of, and the max distance is almost a factor 10 off. The max and min given here is at the limit of the circle the dot makes.|
|Dot 2 (Mercury?)||0.8 AU||1.2 AU||15,000 km||30,000 km||This dot either represents Mercury or Venus, as they are the one closest to 1 AU from Earth. Mercury comes closest to this limit as it never gets far from the sun and thus also never strays far from being 1 AU from the Earth. The range of distances from Earth is from 0.5 to 1.5 AU. The max and min given here is at the limit of the circle the dot makes. And for the distance this is within the limits for Mercuries orbit. However, the diameter is 5,000 km and this does not fit well, so from that principle it fits better with Venus. But Venus can be much longer from the Earth when on the other side of the sun...|
|Dot 3 (Venus?)||1.2 AU||2.3 AU||12,000 km||25,000 km||This dot either represents Mercury or Venus, as they are the one closest to Earth. Venus can get close to the Earth when they are on the same side of the sun. The range of distances from Earth is from 0.25 to 1.7 AU. The max and min given here is at the limit of the circle the dot makes. The distance for this dot fits equally bad with both planets. The diameter is smaller than before, but it is still way too big for Mercury’s 5,000 km and it is not too small but just at the limit of the 12,000 km of Venus. This does thus fit well with Venus on both parameters. Then Mercury will be off as the Dot 2 with diameter, but fit better with distance.|
|Dot 4 Mars||2.5 AU||4.7 AU||12,000 km||23,000 km||This dot represents Mars. Mars has a diameter of 6,700 km and, so here it is set to at least double its diameter. The max and min given here is at the limit of the circle the dot makes. The range of distances from Earth is from 0.4 to 2.7 AU. The min distance at least is lower than 2.7 AU thus making this the dot that fits best with Mars.|
|Dot 5 Jupiter||2.6 AU||6.7 AU||100,000 km||240,000 km||This dot represents Jupiter. Jupiter has a diameter of 140,000 km so it falls within the range. The distances from the sun is about 5 AU and thus from the Earth it ranges from about 4 to 6 AU. This dot thus fit nicely on both parameters with the largest planet. The max and min given here is at the limit of the circle the dot makes.|
|Dot 6 Saturn||6.7 AU||13 AU||53,000 km||126,000 km||This dot represents Saturn. Saturn has a diameter of 120,000 km so it falls within the range. The distances from the sun is about 9-10 AU and thus from the Earth it ranges from about 8 to 11 AU. This dot thus fit nicely on both parameters with the 2nd largest planet. The max and min given here is at the limit of the circle the dot makes.|
|Dot 7 Uranus||21 AU||43 AU||38,000 km||83,000 km||This dot represents Uranus. Uranus has a diameter of 50,000 km so it falls within the range. The distances from the sun is about 18-20 AU and thus from the Earth it ranges from about 17 to 21 AU. This dot thus just reaches down to this distance, but it is within the limits on both parameters. The max and min given here is at the limit of the circle the dot makes.|
|Dot 8 Neptune||45 AU||100 AU||37,000 km||83,000 km||This dot represents Neptune. Neptune has a diameter of 49,000 km so it falls within the range. The distances from the sun is about 30 AU and thus from the Earth it ranges from about 29 to 31 AU. This dot is thus too far out on this parameter. The max and min given here is at the limit of the circle the dot makes.|
|Dot 9 Planet Nine?||700 AU||1550 AU||21,000 km||50,000 km||This is the dot representing the possible undiscovered planet that is the reason for this entire comic. As it is only speculations made on well documented features of dwarf plants orbits, nothing much is known. But the guess is that is has a diameter between 26,000 to 52,000 km (fine with the dots min and max) and although it could get into 200 AU this may take thousands of year, and it is expected that it will be further out than 700 AU most of the time going all the way out to 1200 AU, so this dot fits perfectly with the newest estimates.|
|Superman (title text)||1 m||1 km||0.5 m||2 m||Arms length away, and cannot be seen much more than 1 km away. He is about 2 m high and 0.5 m over the shoulder. This does not fit very well with the title text, as he is not even near the plane limit, but still at a distance it can be hard to tell if the flying object is a plane far away (on Earth scale) or a man closer or a small bird really close...|
Image used to create data for the table
- This image was used for obtaining the data in the table.
- The image was created in a power-point slide show and moving lines along and reading out the position gave the values, with the help of Excel...
- The lines going all through the image goes through existing ticks on the axes
- Lines not going all the way out to the axes are not over existing ticks
- Values for the lines have been added both for those without ticks but also for ticks without values in the comic
- Lines have been color coded, so red for metric, green for AU and purple for units that is not used in the comic.
- Superman has been drawn in as best as possible in blue.
- [Caption above the chart]
- Possible Undiscovered Planets
- in our Solar System
- By size and distance (from me)
- [A chart of possible undiscovered planets with a log-log plot, with the objects diameter on the y-axis and the distance from “me” (Randall) on the X-axis. Both axes are labeled and have several ticks most of which also have labels. A region to the right, with possible new planets including Planet 9 with a “?”, is shaded light red, and a small rectangle at the top left with the same color tells what this color means. The region, of undiscovered dwarf planets, is shaded pink, also to indicate that here may be more of these, but the lighter color indicate that these will not be new “planets”. The eight known planets are marked with a black dot, and also this is explained with a dot under the colored rectangle. The Moon is indicated with a similar dot, but in gray, and the name is in brackets. The chart itself is divided into several labeled regions, the smallest with the label outside and an arrow pointing in. In one case a label breaks a border, and in two regions there are more labels, although these clearly belong to different regions within these regions, with different sizes and/or distances.]
- [Y-axis, with a label written to the left, from bottom and up, with an arrow pointing up, and 15 ticks with a label each:]
- 1 mm
- 1 cm
- 10 cm
- 1 m
- 10 m
- 100 m
- 1 km
- 10 km
- 100 km
- 1,000 km
- 10,000 km
- 100,000 km
- 106 km
- 107 km
- 1 AU
- [X-axis, with a label written below, with an arrow pointing right, and 17 ticks but only 11 labels as the ticks at 100 km, between 1000 and 106 km, 107 km as well as 10 and 1000 AU is not labeled:]
- Distance from me
- 10 cm
- 1 m
- 10 m
- 100 m
- 1 km
- 10 km
- 1000 km
- 106 km
- 1 AU
- 100 AU
- 10,000 AU
- [At the top left of the chart is the light-red rectangle and the black dot labeled:]
- Possible undiscovered planets
- Known planets
- [Going down and anti-clockwise from these two labels, the rest of the chart is transcribed:]
- Planets ruled out because I would be inside them
- Planets ruled out because I would have noticed them above my house
- Planets ruled out because they wouldn’t fit through my door
- Birds that got into my house
- Skin flora
- (Not planets)
- Giant bugs
- Planets which are actually birds
- (Fool’s planets’)
- Space junk
- Comets and asteroids
- Oort cloud
- Stuff we can see through telescopes
- Planets we can see at night
- Dwarf planets
- Planet Nine?
- Planets ruled out by the WISE survey
- Planets ruled out because we would see them during the day
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