Uncovering the mystery of the bow shock

An international team of astrophysicists has revealed more about interactions between Mars and the solar wind – charged particles released from the Sun.

As these particles speed across interplanetary space, their movements are affected by objects in their path. Bow shock is a well-known example of this, where particles slow down before diverting around an obstacle, however, researchers wanted to understand both how and why this location varies during the Martian year.

Martian atmosphere

After analysing five Martian years’ worth of measurements, scientists discovered that there may be some correlation between bow shock distance and annual changes in the amount of dust in the Martian atmosphere. Dr Benjamin Hall, from Lancaster University and lead author, said: “Dust storms have been previously shown to interact with the upper atmosphere and ionosphere of Mars, so there may be an indirect coupling between the dust storms and bow shock location.“

The researchers found that on average, the bow shock is closer to Mars near aphelion – the planet’s furthest point from the Sun – and further away from Mars near perihelion – its closest point to the Sun. The bow shock’s average distance from Mars, when measured from above the day-night boundary reaches a minimum of 8,102km around aphelion. A maximum distance of 8,984km occurs around perihelion – an overall variation of approximately 11% during each Martian orbit.

Dr Hall said: “Future investigations of links between atmospheric dust loading and the Martian upper atmosphere are needed, involving joint investigations by ESA’s Mars Express and Trace Gas Orbiter, and NASA’s MAVEN mission. Early data from MAVEN seem to confirm the trends that we discovered.”

The paper was published in Journal of Geophysical Research: Space Physics.