Alien Mission
Alien Mission
[Two 'classic' Flying Saucer spacecraft are hovering in the sky with speech-lines indicating communication from someone within each saucer. The rightmost is tilted a bit, like it is being attentive to the left.] Left Saucer: Sir, can we talk? Left Saucer: We've been observing earth for almost a century.
[Same setting but both saucers are level.] Left Saucer: Hovering and zooming from place to place, trying to avoid being spotted by humans. Right Saucer: Yeah.
[In a Frameless panel only the left saucer is shown. The right saucer's voice emerges from an edge-of-panel starburst.] Left Saucer: By now we've flown over every inch of the surface many times. Right Saucer (off-panel): Yes? And?
[Same setting as in the first panel, with the right one tilted towards the left saucer.] Left Saucer: Face it: If Bigfoot is real, he's not anywhere on this planet. Right Saucer: But humans have captured some intriguing videos! Left Saucer: *sigh* Right Saucer: How else do you explain the...

This comic followed directly after 2572: Alien Observers , both comics featuring alien flying saucers observe Earth. It is not specifically stated that these two form a series, but this comic could be seen as a direct follow up to the previous one, indicating that the aliens are the same in the two comics. Just 6 comics later 2579: Tractor Beam also used similar spacecraft.
The comic portrays a conversation between aliens inside two flying saucers (or alternately, two aliens whose form is that of flying saucers) in which they discuss their long-secret observation of Earth. It seems that the leader of the mission is in the right saucer, as the alien in left saucer begins by saying "Sir, can we talk". The left alien then continues to state that they have been secretly observing Earth for almost a century (perhaps from the early 1930's or late 1920's, and the title text suggests they already were there in 1937). During these almost 100 years, they have repeatedly flown over every (square) inch of Earth's surface, while trying to avoid being spotted by humans. (This is related to the previous comic, which is about improving cell-phone cameras making it increasingly difficult for flying saucer occupants to avoid being photographed.)
This leads up to the punchline, which reveals that the leader in the right saucer has been hunting for Bigfoot . The left alien tells him that if a Bigfoot exist anywhere in the universe, it is not on planet Earth. Apparently even advanced aliens have been unable to spot Bigfoot.  The alien leader continues his delusion by citing intriguing human videos of something that looks like Bigfoot. When the other alien sighs, implying that this conversation has occurred many times before, the leader continues his arguments with the typical conspiracy line, "How else do you explain the..."
The first panel alludes to the fact that UFO sightings became commonplace only in the 1940s .
The humor derives from the fact that UFO enthusiasts and cryptozoology enthusiasts have a similar mindset: They both believe in phenomena that the scientific establishment believes baseless. Both systems are fully lacking in clear evidence but have an abundance of eyewitness accounts and vague/blurry photographic evidence. And both belief systems have existed for many years, but rapidly advancing technology, accumulating data, and ubiquity of high quality cameras have still failed to capture any clear and detailed evidence. ( Randall seems to find this point particularly significant, and although his previous comic explained the bad flying saucer photos, he already made the comic 1235: Settled long ago, where he calls it settled that Bigfoot, UFOs, and similar phenomena don't exist since everyone has a camera handy at all times.) While these concepts are parallel, they're logically independent, as one deals with species that are presumably native to Earth and the other deals with advanced alien species visiting the Earth. The notion of alien visitors being interested in cryptozoology is incongruous: to them, all Earth animals would presumably seem equally alien.
In previous strips, Randall has suggested playing conspiracy theories off against one another (see 966: Jet Fuel ). This comic has a similar theme: suggesting that UFOs are here to search for Bigfoot (and the Yeti) sounds ridiculous on its face. But any explanation of why it's ridiculous would apply equally well to the notion of Bigfoot and UFO's individually.
Some of the aliens clearly have a similar belief, at least in Bigfoot, which is why they came to Earth. This implies that they had some prior knowledge or suspicion of its existence, and only then possibly narrowed it down to this one planet because of the videos humans have made.
Whatever the arguments about Bigfoot, the title text reveals a separate discussion regarding the Yeti , a similar large hominid purported to reside in the Himalayas , and the tentative permission to conduct one last search for it. As the Yeti and Bigfoot are very similarly described, they could also be seen as the same, so the only difference is that finding a Bigfoot in the Himalayas would make it a Yeti. In the discussion about this last search, they caution about staying high above the Pacific and watch where they are going. This is because, as it turns out, they were the cause of the Amelia Earhart incident. Amelia Earhart disappeared  while flying over the Pacific Ocean in 1937 and neither her nor her plane have ever been found. The title text implies that she disappeared because of an encounter with a flying saucer. She has previously been the main character in 950: Mystery Solved and has since been a recurring theme on xkcd.
That their clearly superior observation technology and methods have been apparently unable to resolve these issues at first seems like it shouldn't bode well for our own cryptozoologists. But since lack of results does nothing to deter them, and since it is always impossible to prove a negative, they would likely not change their beliefs even if they heard of the alien results: "Bigfoot of course hides when the aliens look! And how else do you explain the..."
[Two 'classic' Flying Saucer spacecraft are hovering in the sky with speech-lines indicating communication from someone within each saucer. The rightmost is tilted a bit, like it is being attentive to the left.] Left Saucer: Sir, can we talk? Left Saucer: We've been observing earth for almost a century.
[Same setting but both saucers are level.] Left Saucer: Hovering and zooming from place to place, trying to avoid being spotted by humans. Right Saucer: Yeah.
[In a Frameless panel only the left saucer is shown. The right saucer's voice emerges from an edge-of-panel starburst.] Left Saucer: By now we've flown over every inch of the surface many times. Right Saucer (off-panel): Yes? And?
[Same setting as in the first panel, with the right one tilted towards the left saucer.] Left Saucer: Face it: If Bigfoot is real, he's not anywhere on this planet. Right Saucer: But humans have captured some intriguing videos! Left Saucer: *sigh* Right Saucer: How else do you explain the...
