My suspicion is that you'd have a really hard time doing that. For one, if so little of the light from the sun (notably the brightest thing in our solar system)

My suspicion is that you'd have a really hard time doing that. For one, if so little of the light from the sun (notably the brightest thing in our solar system) is being reflected, we'd be hard pressed to build something capable of spraying the whole search area and getting back enough particles to detect and count. But even more than that, the power requirements would be immense. We have retro reflectors on the moon, and even with knowing where the moon is and where they are on the moon, we get almost no photons back. From Wikipedia: > Out of a pulse of 3×1017 photons[25] aimed at the reflector, only about 1–5 are received back on Earth, even under good conditions. That's with a dedicated reflector positioned well on the moon's surface, about 0.002au away. You're talking about hitting a rocky lump in front of a bright background 400-800au away. The power requirements wouldn't be five orders of magnitude more, it would be perhaps hundreds of orders of magnitude more.