system
Given the following post, respond as if you're commenting on Reddit:
human
How does ISON's speed, currently estimated at > 0.1% the speed of light, compare to the fastest things in our Solar System?

Is ISON currently the fastest object (let's say bigger than a baseball) in our solar system? If not, what is?
gpt
Most things in the solar system go at 10s of km/s. Earth goes at about 0.01% of the speed of light, or about 30 km/s. Even Mercury is going at less than 60 km/s. So if ISON was going at 0.1% of the speed of light, it's going at 300 km/s, which is more than 5 times faster than the next fastest thing.

This speed basically comes from the Sun's gravity: the comet has "dropped" towards the Sun and picked up a lot of speed. The greatest speed you can get from falling downwards (assuming you start pretty stationary) is the same as the escape velocity from the Sun's surface - a bit over 600 km/s. So you'll not likely see anything natural in the solar system going at 600 km/s or faster.