[Darteaus94025]

“ This space rock is probably at least a mile wide (1.8 km) and maybe 2 1/2 times that big4.1 km)”

Not to quibble, but the term big can be misleading. Big means size, and for a sphere that means volume. Using the formula for volume, a 1.8 km wide object has a volume of 24.4 km. A 4 km while object, has a volume of 268 km. Clearly, the size, “bigness”, is vastly larger when the diameter is a little more than double.

[Telepathic Intruder]

v = ⁴/₃ π r³

You used the asteroid's diameter when you should have used the radius.

Sorry but I get a morbid thrill correcting other people's work.