Comet to whizz past Mars
Scientists should get a close up view of a comet today when it makes a dramatic journey past Mars.
Satellites around Mars, and rovers on its surface, hope to capture the event on their cameras and instruments.
The icy object, known as Siding Spring, will miss the Red Planet by what is - in astronomical terms - a small distance, but it's actually 87,000 miles.
Fast-moving dust from the comet could damage the probes on Mars.