MIT engineers and scientist colleagues have a new vision for the future of Mars exploration: a swarm of probes, each the size of a baseball, spreading out across the planet in every direction. Thousands of probes, powered by fuel cells, could cover a vast area now beyond the reach of today’s rovers, including exploring remote and rocky terrain that large rovers cannot navigate. “They would start to hop, bounce and roll and distribute themselves across the surface of the planet, exploring as they go, taking scientific data samples,” said Steven Dubowsky, the MIT professor of mechanical engineering who is leading the research team.