 Fifth planet (hypothetical)

The term "Fifth Planet" often refers to a hypothetical planet that could have existed in our solar system between Mars and Jupiter. This concept is primarily related to theories about the early solar system's formation and the dynamics of planetary bodies. In the mid-20th century, astrophysicists proposed that early in the solar system's history, there may have been a fifth terrestrial planet that was disrupted or ejected due to gravitational interactions with the other planets, particularly Jupiter.