The US and China are spending billions of headline-grabbing dollars in a tacit race to put humans on Mars. Japan prefers lower-key missions in the opposite direction, sending mechanical explorers toward Venus and Mercury for a fraction of the price. A $290-million probe orbiting Venus is collecting information about the scorching atmosphere that may foretell Earth’s future. A collaborative mission with Europe will measure Mercury’s magnetic field and electromagnetic waves. Here is a look at Japan’s space missions: