[justinpombrio]

My immediate thoughts after a couple minutes:

The message has length 65697, and it's extremely sparse (mostly zeroes) except for the beginning and end.

65697 is only 161 larger than 2^16, suggesting that it has size 2^16 with some extra bits tacked on. The beginning and end are less sparse, suggesting a "header" and "footer" as some Discorders said.

65697 also factors as 361359, so it could be an image of size 61*359, with 3-bit color. The color could be grayscale (0-7), or single-bit RGB (but why would the aliens have the same number of eye cones as us???)