Unfortunately, many of us don't have to imagine the first scenario - and fortunately, the second scenario is unlikely for the vast majority of us. But for the few lucky people who fly in space, the chance of a bit of debris with disaster written on it is frighteningly real. We've been looking at impact and debris for the past several weeks - how a body the size of Mars slammed into the new Earth billions of years ago to form our moon and how a spacecraft is now busy at work sweeping up microscopic debris in interplanetary space. These little guys are the size of a speck of dust to the size of a softball, but are just as troublesome. In fact, they're more of an immediate threat to humans who venture out of our protective atmosphere than the microscopic particles and the catastrophic monsters.
Impact is a way of life in the solar system.
Accretion, the snowball-like bringing together of small bits of matter into a large body, is how the sun and planets formed in the first place. Impacts gave us dark features on the moon, created when darker, newer material welled up from the moon's interior at impact sites. These impacts haven't stopped. We haven't had a cataclysmic impact for quite some time, but we do continue to have impacts from tiny bodies. Just because a piece of rock from space is small doesn't mean it's not dangerous.