Before the space age, our neighboring "sister planet" Venus was a mysterious clouded world that science-fiction writers envisioned as covered by swamps and dinosaurs. Dozens of space probes were then sent to Venus and completely changed that vision to that of a world as hot as a furnace and blanketed by acid-laced clouds.
Mercury, the closest planet to the Sun, is difficult to send space probes to, being only visited once and partially mapped in the 20th century. It was not seen as being as interesting as Venus, but in the 21st century further missions are being performed to the planet. This document provides a history of efforts to explore the two inner planets, Venus and Mercury. A list of illustration credits is provided at the end of this document.
