Documentary series. Mercury, unique amongst the planets, is shrinking. And that's only the beginning of how strange the solar system's smallest planet is. In October 2018 a new mission to Mercury was launched - BepiColombo. It's a spacecraft consisting of two separate orbiters. Together, these hope to achieve the most complete exploration of Mercury to date.Since its launch, the spacecraft has been hurtling through space towards the inner solar system on an arduous seven-year journey that includes nine fly-bys of other planets. Its destination is dangerous: Mercury has some of the most extreme conditions in the Solar System.The Sky at Night investigates how Bepi was built, how it will get to Mercury and what it hopes to discover. Three big questions are at stake. How did Mercury form? Why is it shrinking? And how has it survived the full blast of the sun?