Yeah, it's the low albedo that kills you. Something that large made of ice would probably be quite bright. Quick OOM calc: This thing has an area proportional

Yeah, it's the low albedo that kills you. Something that large made of ice would probably be quite bright. Quick OOM calc: This thing has an area proportional to the moon of (200m/1700km)^2. The moon has an albedo of ~0.12. An object with albedo 1 would thus have a brightness of ~1e-7 of the Moon's. The full Moon has a magnitude of -12.7, so such an object would have a magnitude of -12.7-2.5log10(1e-7), or about 4.8. That's clearly visible to the naked eye at a dark site, but not very impressive.