The Search for Magnetotail Twisting at Mercury: Comparing MESSENGER Observations With the Terrestrial Case

Previous studies reported that the terrestrial and Martian magnetotails can become twisted due to the solar wind‐planetary interaction; however, the associated physical processes proper of intrinsic and induced magnetospheres are still under debate. In particular, there is evidence that the Interplanetary Magnetic Field (IMF) dawn‐dusk component (By) plays a major role in both environments, affecting the sense of twist. Here, we analyze all MErcury, Surface, Space ENvironment, GEochemistry and Ranging Magnetometer observations to investigate the IMF By influence on Mercury's magnetotail. We find that Mercury's tail twist is very small (≲3°), for a median downtail distance of ∼2 Mercury radii. We also identify a correlation between the IMF By and the local By component around the magnetotail current sheet. These results suggest the small (or lack of) twist may be explained by the dipolar field strength in the near‐magnetotail. We examine this hypothesis by putting these observations into context with studies on the terrestrial magnetotail.