In a rare event, NASA’s Mars-orbiting MAVEN spacecraft was forced to perform a previously unplanned manoeuvre this week to avoid a head on collision with red planet’s lumpy, crater-filled moon Phobos.

The Mars Atmosphere and VolatileEvolutioN (MAVEN) spacecraft has been orbiting Mars for over two years, studying the red planet’s upper atmosphere, ionosphere and their interactions with the sun and solar wind.

The spacecraft carried out a rocket motor burn that boosted its velocity by 0.4 metres per second. Although a small correction, it was enough that MAVEN would miss the crater-filled moon by about 2.5 minutes.

This is the first collision avoidance manoeuvre that the MAVEN spacecraft has performed at Mars to steer clear of Phobos.

The orbits of both MAVEN and Phobos are known well-enough that this timing difference ensures that they will not collide. MAVEN has an orbit that crosses those of other spacecraft and the moon Phobos many times over the course of a year.

With one week’s advance notice, it looked like MAVEN and Phobos had a good chance of hitting each other on Monday, arriving at their orbit crossing point within about seven seconds of each other.