Mars is ready for its close-up. On June 21, Earth and Mars will be about 42 million miles (67.3 million kilometers) apart, the closest the two planets have been since 1988 when they came within 37 million miles (59 million kilometers) of each other. As Earth races toward the red planet at 22,000 mph, Mars appears as a brilliant orange disk, brighter than any other object in its region of the sky — except on nights when the moon is nearby.