There wasnt enough time to track it, especially with a Bird Of Prey on their tail. The rocket would have made it to the star, several light minutes away, in SECONDS, so it must have accelerated far faster than phasers or photon torpedoes lauched at sublight
Alt answer: Because the script required it. The Enterprise has FTL sensors, derp.
They could. It's just that it would potentially take too long. Worf said it would take between eight and fifteen seconds.
While I'm not one to over-analyse movie scrips, but anyone with even basic scientific knowledge should know that a chemically propelled probe or rocket would take more than a few seconds to reach a star from the surface of a class-M planet. Even at low warp, it would take a few minutes, and the probe doesn't seem to have FTL speed. Now I'm not trying to throw off on the movie, not at all. But as Arsenio used to say, it's something to make you say "Hmmmmmm". Admiral William Thomas Riker 19:18, August 4, 2011 (UTC)
WORF: "Sir, according to my calculations, a solar probe launched from either the Klingon ship or the planet's surface will take eleven seconds to reach the star. However, since we do not know the exact point of origin, it will take us between eight and fifteen seconds to lock our weapons onto it."