Muttnik
Yesterday's I Did Not Know That Yesterday! tidbit concerned Sputnik 1, the Soviet satellite launched in 1957.
But what fate befell the iconic satellite? After 1,400 trips around the Earth, Sputnik burned up when it reentered the atmosphere in January of 1958 (just as it was supposed to).
The very next Sputnick launched contained the first terrestrial space traveller, Laika, a dog. Ok, wait. The first one burned up in earth's atmosphere after three months and the second one contained a dog...that's right, the Soviets killed that poor dog! When I heard the story of Laika as a kid, whoever I heard it from omitted that part. Although Laika didn't burn up in the atmosphere, she was also not euthanized after 10 days of flight as Soviet scientists had planned. A Sputnik scientist recently revealed that Laika died after only a few hours in orbit from stress and overheating.
Two other (unrelated) things I didn't know about Sputnik: that it was tiny (smaller than a basketball) and that Herb Caen coined the word "beatnik" based on Sputnik.