'The line is getting fuzzier': Asteroids and comets may be more similar than we think

As anyone who has ever tried to clean a home knows, ridding yourself of dust is a Sisyphean effort. No surface stays free of it for long. It turns out that space is somewhat similar. Space is filled with interplanetary dust, which the Earth constantly collects as it plods around the sun--in orbit, in the atmosphere, and if it's large enough, on the ground as micrometeorites.