3311: Planet Database
| Planet Database |
 Title text: Atmospheric transmission spectroscopy has revealed that the sunsets from the observatory are really pretty. |
Explanation[edit]
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This is one of 65 incomplete explanations: |
Cueball and Megan are browsing through a list of potentially habitable planets. Planetary habitability depends on many factors, including having a temperature range in which water is a liquid, having a solid surface, and having an atmosphere.
The first exoplanet Megan looks at, despite being in the habitable zone, turns out to have an unfavorable surface temperature. While the habitable zone, in theory, should account for an ideal surface temperature (thus its alternate name of 'Goldilocks zone', in reference to the fable's "not too hot, not too cold, just right"), it is far from a guarantee. One counterexample within our own star system is Venus: Venus is within the Sun's habitable zone, but its runaway greenhouse effect (among other factors) has left it a terrible place with a surface temperature hot enough to melt lead.
The second exoplanet appears to be a water planet, which is promising for habitability. Unfortunately, its mass relative to its size prohibits a solid surface. Cueball identifies this as a "mini-Neptune" - a planet which shares traits with gas giants like Neptune, but smaller in size. Mini-Neptunes were previously mentioned in 3103: Exoplanet System.
Megan describes the third exoplanet to catch her eye as "habitable if it has a greenhouse effect". The greenhouse effect, which induces temperature increases, is caused by buildup of greenhouse gases within the atmosphere trapping heat within it. However, Megan then observes that spectroscopy of the mentioned exoplanet indicates that it has no atmosphere whatsoever, thus prohibiting a greenhouse effect. It is therefore likely to be an icy world where it is difficult for life to survive. (Also, Earth life requires oxygen to breathe, thus necessitating an atmosphere.[citation needed])
Eventually, Megan finds a planet with all the correct habitable factors. Alas, she is looking at our Earth, which orbits our Sun (which is also called Sol). This is similar to 1231: Habitable Zone, where an astronomer fails to realize that he is looking at (a reflection of) Earth before he gets excited about its habitability.
The difficulty in finding an exoplanet similar to Earth is related to the Rare Earth hypothesis. See also this micro-story which suggests that other intelligent life in the universe will be too far away for communication with Earth.
The title text suggests that astronomers are using the observatory to look at pretty sunsets instead of doing scientific work on planets, but have tried to disguise the fact by dressing it up in scientific language. It's not clear if this is being done with the observatory's instruments or just with people's eyes, which also act spectroscopically, since we can see different colors. Light at sunset (or sunrise) travels through more of the atmosphere before reaching the ground, so more of its blue color gets scattered and we see more red and orange colors — making it colorful, and pretty.
Exoplanets are a recurring theme in xkcd, and the habitability or environment of other planets was also mentioned in 1298: Exoplanet Neighborhood, 1456: On the Moon, 1517: Spectroscopy, 1253: Exoplanet Names, 1555: Exoplanet Names 2, 1752: Interplanetary Experience, 1991: Research Areas by Size and Countedness, 2202: Earth-Like Exoplanet, 2762: Diffraction Spikes, 3255: Planetary Science and 3103: Exoplanet System.
Transcript[edit]
- [Megan is sitting at her desk looking at a laptop. Cueball stands behind her.]
- Megan: I'm browsing the list of potentially habitable planets.
- Megan: This one is promising!
- Megan: Wait, no, the surface is thousands of degrees.
- [Similar panel.]
- Megan: This one could be a water planet!
- Megan: ... But it's not dense enough to be solid.
- Cueball: Yeah, that's a mini-Neptune.
- [Megan points at the laptop screen.]
- Megan: This one could be habitable if it has a greenhouse effect!
- Megan: Sadly, spectroscopy shows no atmosphere.
- Cueball: Aww.
- Megan: Here's one in the habitable zone, 1 Earth mass, with an atmosphere!
- Cueball: Ooh, what star does it orbit?
- Megan: ...Sol.
- Cueball: Dammit.
Discussion
i THINK they would have known if they were looking at earth or not... probably? 73.132.167.116 20:38, 14 October 2026 (UTC)
- I think this has happend before somehow 107.1.219.44 20:41, 14 October 2026 (UTC)
- They aren't 'looking at Earth', so much as trawling through the database of all known planets. Selecting those that are known to have the right qualities or deselecting those that are known to not have the right qualities, to cut the whole database down to a short-list of useful ones for the study's purpose.
- Among the "known planets" is Earth, of course. The name, and the precise star around which any given planet orbits, isn't a useful selection criteria, so it's only when looking for more detail (in this case, the name of the planet's star... they haven't even looked at the name/ID of the planet yet) that they realise - in the absence of there somehow being a Counter-Earth in the database - the actual nature of the planet record. 78.151.45.31 21:23, 14 October 2026 (UTC)
- oh, and the title of the thingy was f1rst p0st by the way 73.132.167.116 22:00, 14 October 2026 (UTC)
- just clerifying 73.132.167.116 22:00, 14 October 2026 (UTC)
aww i cant firstpost it! - someonefrompluto 2605:59C0:450B:3400:5894:750F:5D48:6C85 21:03, 14 October 2026 (UTC) (i dont get why it doesnt auto sign.)
- sorry, I got to it first. and again, sorry. its just TOO TEMPTING to do first post and I'm trying to resist and failing. 73.132.167.116 21:59, 14 October 2026 (UTC)
"It's not clear if this is being done with the observatory's instruments or just with people's eyes, which act spectroscopically since we can see different colors." - consider whether this belongs: Human eyes typically see three broad-ish overlapping color channels and one very broad channel that overlaps the other three. Spectrographic equipment sees many more. 2603:8081:9700:1224:0:0:0:3 06:19, 15 October 2026 (UTC)
I would just like to note that theoretically they could be talking about Venus, which would be perfectly feasible for a different type of organisms, but not habitable for us earth based organisms, due to the toxicity of its atmosphere to us. Sorry if this is less intellectual, I am only 15 :( 204.193.7.28 12:18, 15 October 2026 (UTC)thepathlesstraveledby
- An excellent point. Venus is in the habitable zone, has an atmosphere, and is one earth mass (within 20%, which is good accuracy for exoplanet work). 2601:282:2180:81C0:24D1:6CAF:4E63:8CE0 20:48, 19 October 2026 (UTC)
It seems Randall really wants to make Mini-Neptune a thing (term also used in 3103). Maur11cio (talk) 13:26, 15 October 2026 (UTC)
Isn't the red/orange/yellow at sunset not because the blue is more scattered going the longer distance through the atmosphere, but because the red/orange/yellow is more scattered? 163.116.145.66 14:25, 15 October 2026 (UTC)
- The red colours of sunsets are a combination of two factors - the greater scattering of blue light through passage through a greater amount of atmosphere (which is why the setting sun looks yellow or red), and the reflection of the remaining light by the underside of clouds. 87.75.44.11 07:00, 16 October 2026 (UTC)
Relevant: Rare Earth hypothesis Rps (talk) 12:17, 16 October 2026 (UTC)
Could this be related to the 2nd gen telsa roadster, which uses spacex rockets? Velocifyer (talk) 16:21, 16 October 2026 (UTC)
The point is that we should stop looking for other habitable planets and concentrate the resources and efforts on improving Earth, which is the only habitable planet we are certain about. 103.62.49.154 (talk) 05:35, 17 October 2026 (UTC) (please sign your comments with ~~~~)
- That may be a point, but I don't think it's Randall's point, as it directly contradicts the implied message of 1232: Realistic Criteria (unless you don't read that as a bluntly sarcastic response, for some reason), and his general support of all things spaceward-looking/-going. There certainly isn't enough subtext in this comic to highlight any particular need (which Randall also supports, but differently and not to the total exclusion of space things) to not ruin this planet. You may have to be bringing something similar to White Hat's laser-focused viewpoint, from that other comic, into your own reading. 78.151.45.31 10:17, 17 October 2026 (UTC)
Browsing this database seems reminiscent of house hunting, and finding your own current residence as the only likely match can be either disappointing or shocking—wait, I didn't realize our current residence would be listed! 71.178.24.234 22:09, 18 October 2026 (UTC)
- Helluva moment to discover that your landlord/parents/spouse want to sell up and move on, certainly... 78.151.45.31 23:11, 18 October 2026 (UTC)
I agree with Ryland Grace; While the Goldilock's Zone is useful for finding planets that WE could live on, there is no reason to rule out all planets outside of it in our search for extraterrestrial life. --DollarStoreBa'alConverse 13:46, 20 October 2026 (UTC)
- Indeed, that is true. Though as we don't know what 'kind of porridge' any xenogoldilocks might instead prefer, or what of the many porridges out there actually have some goldilockses that could enjoy them, we're probably better off playing the odds and focussing one eye on "well, we know of one environment that has life, so if we can find similar environments out there then these might also have life".
- At the same time, of course, keep the other eye glancing around for any other interesting phenomena that might be life-like footprints in unexpected places. It might be the first clue that not only can there be something able to make use of a particularly off-Earth environment, but that this is a case where it has one. It'll be at least as exciting, though potentially far more improbable, to find that sort of thing. But then it might help us understand more about the fuller paramaters of the 'metagoldilocks' zones that encompass so many more paragoldilocks options. 92.23.2.123 21:29, 20 October 2026 (UTC)
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