Which planet other than Earth was the first to be studied by a satellite launched from Earth?

The first planet other than Earth to be studied by a satellite launched from Earth was Mars. The satellite was Mariner 4, which was launched by NASA on November 28, 1964. Here are the steps:

1. The Mariner 4 spacecraft was launched from Cape Canaveral Air Force Station by an Atlas-Agena D rocket.
2. The spacecraft traveled through space for about 7.5 months before reaching Mars.
3. On July 14, 1965, Mariner 4 performed a flyby of Mars, becoming the first spacecraft to take close-up photos of another planet.
4. The spacecraft took 21 photos in total, which were transmitted back to Earth over the following days.
5. These photos provided the first "close-up" data of Mars, revealing a barren, moon-like surface.
6. The success of Mariner 4 led to further Mars exploration missions, including more advanced orbiters, landers, and rovers.