2524: Comet Visitor

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Comet Visitor
It's a myth that the Great Wall of China is the only human-made structure visible from space--there are LOTS of structures for us to feel self-conscious about!
Title text: It's a myth that the Great Wall of China is the only human-made structure visible from space--there are LOTS of structures for us to feel self-conscious about!


Comet C/2014 UN271 is a large comet that was discovered in 2014 almost as far from the Sun as the orbit of Neptune, and it will reach its closest approach in 2031, near Saturn's orbit. It's an Oort Cloud comet, with a period of more than 4 million years. Since modern humans (homo sapiens) evolved about 300,000 years ago (although tool-making ancestors were around about 2.5 million years ago), the last time it was among the planets was indeed long before humans evolved.

When a long-period comet comes into the inner Solar System, it's often figuratively called a "visit". But Megan and Cueball treat this more literally (or perhaps more sarcastically). Just as one usually neatens up their home when they're expecting guests, to make a good impression, they realize they need to clean up the Earth and its vicinity in preparation for this "visitor". Cueball starts handing out assignments -- he'll clean up the Pacific Garbage Patch, and suggests that Megan take care of all the debris in orbit.

Cueball and Megan also make notes to sweep up the lunar footprints that NASA astronauts left on the Moon during the Apollo missions and put away the Mars rovers. It's also common for people expecting visitors to put various objects out of view with the intention of returning them to their normal place after the visit, usually because the objects are considered unsightly that under normal circumstances is outweighed by the convenience of being out in the open.

However, since the comet will not come anywhere close to Earth and Mars, all this hardly seems necessary; it would be like cleaning up your home because the President or some other dignitary will be visiting your town. In addition, while a dignitary would theoretically be able to see one's house, although comets have tails, they do not have eyes,[citation needed] so they would not be able to perceive any difference between Earth before and after tidying up (even if the nucleus had an eye, it would not be able to see because it is in a coma, no pun intended). Furthermore, sweeping footprints in the Moon, that Cueball sees as a way of tidying up, would be seen as destroying an invaluable archaeological sites by NASA and other people.

Alternatively, Megan and Cueball aren't "cleaning up" for a visitor as one might do if the visitor was a friend of theirs. They're hiding themselves and contraband as one might do if they were worried the police were visiting. Or more likely in this context that it could be an alien visit, and they would like to make it difficult to spot the human civilization from space. In that case they might need to shut down all light in every big city on Earth as well.

The title text debunks the claim that the Great Wall of China is the only human-made structure visible from outer space; in fact the Great Wall cannot easily be distinguished from space (as it is very long but not wide), but some other human constructions such as the Pyramids can (and cities are easily visible at night because they emit light).


[Megan sits at a desk in front of a computer, looking to the left off-panel and pointing at the screen]
Megan: Have you seen this big comet, C/2014 UN271?
Megan: It'll pass near Saturn's orbit in 10 years.
[In a frameless panel, Cueball stands behind Megan, who is now looking at the computer and typing]
Cueball: Wow, look at the orbital period.
Megan: Yeah, it hasn't been to this part of the solar system since humans evolved.
Megan: At least.
[Cueball starts running off-panel, holding his finger in the air. Megan looks towards him with both arms resting on the back of her chair]
Cueball: Well, we definitely need to tidy up. I'll start on the Pacific Garbage Patch, you tackle orbital debris.
Megan: What about the moon footprints?
Cueball: Sweep them up. Collect the Mars rovers, too!
Cueball: We can put them back once it's gone.

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Yup. nobody says that the Dinosaur Killer wasn't aliens saying "don't get cocky, lifeforms". Best to keep the head down. 06:53, 5 October 2021 (UTC)

AFAIK cosmonauts reported that the Great Wall of China actually isn't visible from space - it's too thin and blends in with the background. Though technically we can probably claim that everything visible on Google Satellite View qualifies as "visible from space"... 09:10, 5 October 2021 (UTC)

This somehow seems like the perfect setup for a "Your mom" joke. 20:49, 7 October 2021 (UTC)
If it were satellite view all along. It's aerial view for the higher zoom levels. BTW, anything on Earth is visible from space, provided there's equipment with sufficient resolution, selectivity and sensitivity vs. distance. From Saturn, well, it needs truly alien equipment to see anything of concern, no big worries. Sweep it under the rug and smile. Send some hello's over Arecibo... ah, crap. -- 10:29, 5 October 2021 (UTC)

Should we also mention that the Great Pacific Garbage Patch isn't visible AT ALL, even to humans who might be swimming in it? From Wiki: Despite the common public perception of the patch existing as giant islands of floating garbage, its low density (4 particles per cubic meter) prevents detection by satellite imagery, or even by casual boaters or divers in the area. This is because the patch is a widely dispersed area consisting primarily of suspended "fingernail-sized or smaller bits of plastic", often microscopic, particles in the upper water column known as microplastics. mezimm 13:46, 5 October 2021 (UTC)

Although perhaps obvious, I feel like this is Randall trying to provide motivation to clean up the Earth (eg. Global warming and what not) in general, but making it kinda fun instead of doomsday scenarios. Might be useful to mention in body of explanation. Stephenjuniverse (talk) 14:00, 5 October 2021 (UTC)

Possibly, but it could also be prompted by the plan to deploy lots of Starlink satellites that interfere with astronomy. And increasing concern over all the space junk in orbit. We're just messy on many levels, like a teenager who never cleans up his room. Barmar (talk) 14:28, 5 October 2021 (UTC)
That's a fair point. Stephenjuniverse (talk) 14:20, 6 October 2021 (UTC)

Regarding the visibility of the Great Wall, it is possible that the chain of geographical significant boundary features (upon which the wall was built, beacause it was a convenient definable and defendable ribbon of terrain to make a claim over) are notably visible. As might other (unrelated, unWalled) geographies/geologies, but you're not looking at those bits 'imagining' you can see the Wall and seeing man-made patterns where there should be none. (Also, if settlements and/or transport links roughly hug one side or the other of the vague and intrinsically non-visible route, for historical or recent reasons, they might add 'relief' enhancement to the scene by whatever geophysical 'smudged marks' they display to the orbital viewer. A bit like Belgium's borders are made very visible at night due to the legislatedly ubiquitous street-lighting, compared to its neighbours, or North Korea by the inverse effect - but especially against its southern neighbour.) 18:28, 5 October 2021 (UTC)