Solar Exploration

The Moon is Earth's only natural satellite and the fifth-largest moon in the solar system, unusually large relative to its parent planet compared to most other moon-planet pairs. The leading theory for its origin is the giant-impact hypothesis: roughly 4.5 billion years ago, a Mars-sized body collided with the young Earth, and debris from that collision coalesced into the Moon.

The Moon is tidally locked to Earth, meaning the same face — the 'near side' — always points toward us, while the 'far side' remained completely unseen by human eyes until Soviet spacecraft photographed it in 1959. Its gravitational pull is also responsible for Earth's ocean tides and has gradually slowed Earth's rotation over billions of years, lengthening our day.

With no meaningful atmosphere to trap heat or block radiation, the Moon experiences brutal temperature swings between scorching lunar day and freezing lunar night. Its surface is dominated by two terrains: bright, heavily cratered highlands, and darker, smoother 'maria' — ancient basaltic lava plains that early astronomers mistook for seas. Permanently shadowed craters near the lunar poles are cold enough to trap water ice, a resource future missions hope to use for fuel and life support.