Miniaturization will inevitably mean limitation—less power, fewer instruments, and reduced ability to store and broadcast data. But dust-mote-size spacecraft could do things that no current space probe can do: coast without a parachute onto the plains of Mars or float for weeks in the soupy atmosphere of Titan. They could be mass-produced and launched by the thousands to form vast space-based networks of sensors. And if the probes could be made thin and lightweight enough, alternative forms of propulsion could eventually send them to distant worlds, without the need for rocket fuel.
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