Bow Shocks at Comets

Comets provide a wonderful laboratory to study the interaction of a fast flowing plasma, the solar wind, with neutral gas from the comet. On ionization, the more massive newly‐born cometary ions are assimilated into the solar wind flow, eventually causing its deceleration via this ‘mass loading’. One of the effects of this is the cometary bow shock. The exploration of comet Halley by an armada of spacecraft in 1986, as well as the in‐situ exploration of comets Giacobini‐Zinner (1985), Grigg‐Skjellerup (1992) and Borrelly (2001), has revealed important results on the behavior of these weak shocks and showed that mass loading plays a key role. In 2014, the Rosetta mission will provide the first observations of the formation of the cometary bow shock as a comet, Churyumov‐Gerasimenko, nears the Sun. Rosetta will also provide the first measurements of the collision‐dominated near‐nucleus region. Here, we briefly review what we know about cometary bow shocks, and we examine the prospects for Rosetta.