Passing asteroid MOONS the HUMAN RACE Space-watchers peering at the fly-by asteroid 2004 BL86 will have missed a detail that NASA caught: the flying mountain has its own moon. Future discoveries excluded, BL86 is expected to be the Earth's nearest-and-largest encounter for quite some years, until it approached its moon hadn't been seen. As Space.com states, the …
It is possible that all the media people are copying from each other, and the first one shifted the decimal point. The writeups I've read, has the moon being between 20 and 25% of the diameter of the asteroid. In the JPL "movie", this seems unlikely unless the orbit is large. But the parent body is not that massive, so the orbit can't be large, otherwise it would escape.
The original size estimate I seen at Spaceweather, was 680m, and the sizes from JPL are a bit less than half that. If the distance from the surface of the asteroid to the moon is 180m, and this moon is much more reflective than the asteroid is, that would explain why the inital size estimate was off by about a factor of 2.
And the media is just being "professional" in repeating what everyone else in the media are reporting.
But, this isn't my area of expertice, and I could be wrong as well.
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