CIOCteam

A colleague just pointed out that Voyager 1 is moving so fast that it is unbound from the solar system, while Siding Spring is still bound. Thus, Voyager will win, even without the head start. [MK]

I can't easily run their orbits out later than the year 2020, but it looks like Voyager 1 would win. It's got a big head start (~100 AU) and is moving very fast (~17 km/s). Siding Spring is currently moving faster (~56 km/s), but as it moves away from the Sun it will be slowed down a lot by the Sun's gravity. [MK]

That's a great question...we're calculating it now. [MK]

To the first question: No, that's why this is so exciting! Siding Spring is coming about 1/10 the distance of the closest known comet passing by Earth since human's have been studying the sky. Here's a list of closest comets known to Earth: http://www.minorplanetcenter.net/iau/lists/ClosestComets.html [MK]

Yes but only if a ton more comets "hit" Mars. Even though the effects will be really interesting on the upper atmosphere, that's only because it's so thin up there. The amount of material actually delivered by this one comet is very small compared to the amount of material in the comparatively thick lower atmosphere. That said, you do occasionally see SF stories that deal with terraforming Mars by delivering comets to it. In the stories, however, they usually have the actual cometary nucleus hit the planet and deliver all its water content at once. Boom! [JE]