The exploit in the boot ROM of iOS devices was first announced by iPhone Dev-Team member pod2g. It was soon confirmed by other hackers, who said that because the exploit targets such a low-level part of the operating system, Apple won't be able to stop jailbreakers without making significant hardware changes.
The nature of the impactor is presently unknown. It might have been an asteroid or a comet. In either case, a dark and cindery debris field is expected to develop around the impact point; that's what has happened in the aftermath of previous Jupiter impacts. Professional and amateur astronomers are encouraged to monitor Jupiter in the hours ahead, and stay tuned for updates.