system
Given the following post, respond as if you're commenting on Reddit:
human
The bennu asteroid has a 1 in 2,700 chance of striking Earth on September 25, 2135. How are odds of an asteroid impact calculated? How are they adjusted over time? What don't we know that makes them measured by chance?

I keep seeing articles about the bennu asteroid having a 1 in 2,700 chance of striking Earth on September 25, 2135. I'm curious about what factors into how these chances are progressively changed over time.
gpt
With complete knowledge of the asteroid's position and velocity (and those of other bodies that interact with it gravitationally), we would be able to give a definite answer - that is, our estimate of the collision probability would be either 0 or 1.

Because there are uncertainties in our knowledge of the asteroid's initial conditions, its calculated trajectory is also uncertain. Some possible trajectories take it to a collision with Earth, and some don't. We therefore express that uncertainty as a probability between 0 and 1.

As more measurements come in, we can re-calculate the trajectory and our estimate of the collision probability.