The exact same question was asked by astronomers during the 1800s after studying Mercury’s orbital motion around the Sun. French mathematician Urbain Le Verrier noticed that Mercury’s perihelion – the point of closest approach to the Sun – advanced a small amount on each orbit the tiny planet completed. Le Verrier thought that the precession could be explained by the existence of a small planet between Mercury and the Sun and it was here that the idea of a planet, dubbed “Vulcan”, was introduced.
Despite the attempts of astronomers around the world to try and find the elusive planet, nothing was ever uncovered other than the observations of sunspots or even stars which were mistaken for the intra-mercurial planet.
It was not until the early 1900s when great scientist Albert Einstein successfully proposed the theory of relativity to explain the odd progression of Mercury’s orbit that the majority of astronomers abandoned the search for Vulcan. However some remain convinced that objects exist where the planet was once sought bringing forward the idea of vulcanoid asteroids. To date, none have been found as of yet with searches ruling out asteroids larger than 60km. Even ESA/NASA’s SOHO (Solar and Heliospheric Observatory) and NASA’s STEREO (Solar TErrestrial RElations Observatory) spacecraft have been unsuccessful in detecting a planet or other object inside the orbit of Mercury.
Answered by science journalist Gemma Lavender