> I wonder how long it would be before we could reasonably send a probe to explore a potential rogue.
New Horizons took around a decade to reach Pluto, which is about 50 AU from the sun.
The nearest distance Planet 9 could be is approximately 200 AU. Right now, waiting seems to best bet before sending anything, so that we can hopefully find ways to send probes faster and meanwhile try to better identify its location.