Then, DA, you know that -

"There is an asteroid that "might" hit earth in 2039. Consider all of the reasons that we just don't know for sure."

- you're talking about predictability again - and that's a very different thing from determinacy. The fact that an event cannot be predicted - for example, next week's weather - is a non-issue. Chaotic systems, even though unpredictable, are still subject to cause and effect.

Having said that, it's academic if we agree that this is not a determinate universe.

"Time is what prevents everything from happening at once" - John Wheeler