Estimating a mass for a potentially hazardous asteroid (PHA) is perhaps the single most important thing to understand about it, after its trajectory. Actually doing so isn't easy though, as the mass for objects in the tens to hundreds of kilometers in size are too small to have their mass calculated by traditional radio-frequency tracking techniques. A new paper from Justin Atchison of the Johns Hopkins University Applied Physics Laboratory and his co-authors proposes a method that could find th...