The average comet travels at 40km per second.
It could travel 200AU in roughly 23.7 years or 1500AU in 177.75 years.
While not thousands of years, it's still a long time.
Yes, but the taxpayer funded grants that sustain his livelihood are expiring this month.
Good points, both of you. However taking Mausa’s math as correct, if the last time this “Planet Nine” was 200 AU’s from the Sun, it knocked (via its gravity of course) a comet or asteroid on our way to us, such a killer could indeed be only weeks away. This is because the scientist in the article believes it is at that distance (200 AU’s) where Planet Nine may knock a Kiaper Belt object towards us.
The real math would involve determining when Planet Nine was last at perogee with respect to the Sun. Then, from those dates, determining when we are in the most danger of being hit by a rogue body sent by that planet by adding 23.7 years to the last date Planet Nine was at 200 AU’s from the Sun (and thus in the Kaiper Belt region).
I assume that’s what the “some” described in the article did when predicting our doom “as soon as this month”. Who knows though.
Assuming it was knocked into an exact bee-line toward the Earth you are correct. More likely though, these gravitational disturbance events knock the comets into DIFFERENT orbits that send them into the inner solar system where they wreak all kinds of havoc with the orbital mechanics before things settle down. It's the multiple passes from each changing orbit that put the planets in peril. Impact with a planetary body could occur on the first orbit, or it could be on the tenth or fiftieth time around, taking many hundreds, thousands, or tens of thousands of years depending on how much it gets perturbed by Jupiter and any of the other smaller planets on its new path each time around - mere blips in solar system history but far from "next month" in human time.