51 Pegasi b: The first exoplanet
This one is a bit different. It shows postcards with the line “Greetings from your first exoplanet.” There’s some debate surrounding which exoplanet truly counts as first, but “51 Pegasi b,” discovered in 1995, is truly special. About half the mass of Jupiter and orbiting so close to its star that it orbits it in just 4.2 Earth days, it was the first planet to be confirmed to orbit a sun-like star.
Since then, we’ve been discovering exoplanets are an accelerating pace. NASA’s exoplanet archive currently lists 1,941 confirmed ones.