What MPO and Mio observations could teach us about Mercury's deep Magnetotail

Previous studies have reported magnetotail twisting in several planetary magnetospheres in the solar system.

Such twisted tails may be the result of magnetic reconnection between the Interplanetary Magnetic Field (IMF) and the planetary intrinsic magnetic field.

In particular, MESSENGER observations of Mercury's tail twist reveal a rather small twist of up to 3 degrees, despite the Hermean magnetosphere being continuously driven by reconnection.
However, given that the influence of the planetary magnetic field weakens as the downtail distance increases, an increasing tail twist could be expected, depending on the IMF direction. 
In this study, we model Mercury's magnetotail response to 4 major Parker-Spiral-aligned Interplanetary Magnetic Field (IMF) directions and address what MPO and Mio might observe in their orbital phase with the hybrid model AIKEF.
Our hybrid model results indicate that Mercury's magnetotail topology exhibits a similar small twist at MPO and MESSENGER altitudes, gradually increasing to significant tail twists at the altitudes of Mio and beyond.
The Hermean magnetotail is reacting to IMF By and Bz directions just as it is known from Earth observations but with higher ferocity.
In addition, we find that observations along specific Mio orbits could be used to provide a proxy for the upstream IMF polarity even if both orbiters stay within the magnetopause boundaries.
Finally, we investigate how the current Mio observation planning affects these results.

Our results indicate that the determination of, e.g., the uncertainty of the tail twist angle is about a factor of 2 worse compared to a determination of the full data set, suggesting that alternative observing strategies for Mio during nightside passages could significantly improve the mission science return.