What celestial body did the Artemis II astronauts enter the 'sphere of influence' of on April 6, 2026?

On April 6, 2026, the Artemis II astronauts entered the sphere of influence of the Moon. This critical milestone signifies the point in their journey where the gravitational pull of the Moon became the dominant force acting on their Orion spacecraft, overriding Earth's gravitational influence. It marked a significant step in their lunar flyby mission, setting the stage for their close approach to the lunar surface.

A celestial body's "sphere of influence," or SOI, is an invisible region in space where its gravity is stronger than that of any other, larger nearby celestial body. For a spacecraft traveling from Earth to the Moon, it first operates primarily under Earth's gravity. Upon entering the Moon's sphere of influence, the Moon's gravity becomes the primary factor dictating the spacecraft's trajectory. This concept is crucial for mission planners to accurately plot spacecraft paths and execute maneuvers.

The Artemis II mission, which launched on April 1, 2026, is a crewed test flight designed to send four astronauts around the Moon and back to Earth. It is the first time humans have journeyed to the Moon since the Apollo 17 mission in 1972. This mission serves as a vital precursor to future Artemis missions that aim to establish a sustainable human presence on the lunar surface, ultimately paving the way for human exploration of Mars. The crew will perform various tests on the Orion spacecraft's systems in deep space, ensuring its readiness for longer-duration missions.