1633: Possible Undiscovered Planets

2016-01-23T04:33:11Z

Dakkus:

{{comic
| number = 1633
| date = January 22, 2016
| title = Possible Undiscovered Planets
| image = possible_undiscovered_planets.png
| titletext = Superman lies near the bird/plane boundary over a range of distances, which explains the confusion.
}}

==Explanation==
This comic is about {{w|Planet Nine}}, a possible Neptune-sized planet far beyond Pluto, whose influence is suggested to explain the unusual orbits of a group of outer solar system objects. Randall's chart categorizes objects based on their size and distance from himself (probably from center to center, which explains the position of the Earth, one Earth radius plus one Randall radius). Stating the obvious, this diagram shows that for an object to be an unknown planet it has to be far and small enough that we did not see it yet, but big enough to be a planet. Astronomer Mike Brown recently published a paper showing indirect evidence that such a planet may exist, due to perturbations in the orbits of several dwarf planets.

The chart uses a generous {{w|definition of planet}} (from the Greek word for "wanderer"), and allows any distinct solid object as a possible planet, whereas the {{w|IAU definition of planet}} requires a solar orbit, gravitational rounding, and "clearing the neighborhood", a controversial calculation of relative size that excludes Kuiper Belt Objects such as Pluto. Planet Nine would be large enough to meet the IAU definition, however.

That said, the actual planets are prominently marked on the chart: they are the solid black dots. Besides Earth and Planet Nine, the bottom row of 3 is (from left to right) Mercury, Venus, and Mars; it seems that Randall is using the average distance over the planets' orbits, so swap Mercury and Venus if he is using the current distance (but then they should be a bit farther to the left). (Yes, Mercury is closer than Venus on average, although Venus is closer right now.) The top row of 4 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 grey 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. 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 (so I guess this means that we would see Sun during the day even if it weren't shining?). In general, "planets ruled out because we would see them during the day" refers to objects big enough to be stars, but all stars other than Sun are too far away to fit on the chart.

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 that the planet would be inside him).

"Planets ruled out by the WISE survey" refers to the {{w|Wide-field Infrared Survey Explorer}}, a spaaaaaace telescope designed to look for warm objects such as {{w|brown dwarf}}s, 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" because it's too cold (if it exists).

The title text explains why some people {{w|It's a Bird...It's a Plane...It's Superman|confuse Superman for a bird or a plane}}, since he often flies at the limit between the two categories in the diagram.

The comic seems to imply a flat (or mostly birdless) 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.

==Transcript==
Possible Undiscovered Planets 
in our Solar System 
By Size and Distance (from me) 

[Graph with logarithmic axes] 
[Y axis: Diameter, scale 1 mm to 1 AU] 
[X axis: Distance from me, scale 1 cm to 10000 AU]

[red rectangle] Possible undiscovered planets 
[black dot] Known planets

{{comic discussion}}
[[Category:Charts]]
[[Category:Space]]
[[Category:Comics with color]]

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1633: Possible Undiscovered Planets