Siding Spring sounds like such a tranquil name for a massive comet. After traveling millions of years at the leisurely pace of about 33 miles per second, the comet will fly by Mars at around 2:25pm EDT or so, passing only 138,000 kilometers from the red planet. This is a little bit more than one-third the distance of the Earth from the Moon.
To impress upon you the importance of this occasion, an event like this has never taken place in the course of human history, and it's possible that we'll never see something like it again for a very long time. Luckily, NASA is more prepared than ever to make sure it captures some stunning views of the comet as it passes by with its three orbiters, including Mars newest arrival MAVEN. The timing couldn't be more perfect as Scientific American says that the flyby will help calibrate MAVEN's observations as it continues to search for the answer to Mars missing atmosphere.
Luckily, all of us terrestrial bound viewers will still be able to participate in the event via livestream. One, posted above, is being put together by the Virtual Telescope Project and another is a stream that will be starting at 2:15pm EDT that you can watch below. This won't exactly be as eye-popping and awesome as you'd expect from some high-budget Hollywood film, perhaps one with Bruce Willis or something, but it's something! Also, the real stunning views will be coming from NASA's various telescopes and orbiters in the coming hours and days.
NASA has also put together a collection of videos explaining why Siding Spring's close encounter with Mars is such a major celestial event for scientists and astronomers. JPL's Robert Shotwell, the Mars Program chief engineer, gives a pretty great walkthrough of the complicated choreography that NASA's instruments will have to do in order to avoid any potentially harmful space dust. Odyssey will be unable to capture the whole comet in one picture, so instead it will be sweeping the comet in order to construct a full composite image. Shotwell explains why this moment is so amazing:
This is a rare opportunity for us. Typically we send our orbiters to comets to do cometary science, but we're getting one for free where we've got three orbiters ready to go to image this comet as it gets close to Mars.