The Galileo spacecraft provided this unusual view of Earth’s nearby neighbor as it sped past Earth in December 1990. The gravitational pull of Earth was used to increase the speed of the spacecraft, relative to the Sun, so that it could carry out its primary mission to study Jupiter and its moons beginning in 1995. A partially deployed radio antenna has restricted the rate at which data can be transmitted from the spacecraft to Earth, but onboard tape recorders allowed Galileo to store much information as it sped past both Earth and the Moon. This image gives us a view of the Moon that is unattainable from Earth. The right side corresponds to the hemisphere that always points toward Earth, with its large areas covered by dark basaltic lavas. The left side shows the hemisphere that is never visible from Earth, including confirmation of an enormous ancient impact basin visible as a subtle gray area near the lower left limb. The dark feature at the center of the lunar disk is the Orientale impact basin, the interior of which is flooded with dark basalt.
Galileo image (Press Release P-37329).