"Hot Jupiter" is the monicker give to the gas giants planets that have been found in close orbits with their parent stars. Of generally Jupiter-like mass, these planets are strongly heated by the stellar radiation. They also reside within the influence of the star's magnetosphere and their survival against evaporation due to heating and erosion due to interaction with the stellar wind is a key question,
HD189722 is one of the few stars with planets whose surface magnetic field has been mapped using the zeeman-Doppler imaging. The Sun's magnetic field is the source of the driving of the solar wind, and we can use established methods of modelling the solar wind and apply them to the surface magnetic field map of HD189722 to make a supercomputer model of the wind and its interaction with the planet. The first figure shows the density distribution of the plasma in the system. The star is in the centre and the axes are labelled in stellar radii. The planet has a notable plasma "tail" that arises because of the dragging of magnetic field lines by orbital , and the white arrow marks where reconnection of magnetic fields is taking place that will snip the end of the plasma tail off.
The second figure shows the magnetic field distribution around the planet and the magnetospheric boundary. The boundary, indicated by the red line, marks the balance between the magnetic pressure of the planet and the dynamic and magnetic pressure of the stellar wind. This shows how close the wind penetrates to the planet. The simulation demonstrates that magnetic reconnection events are important for understanding the plasma distribution and mass loss from the system.