To Fig.3: The flow of stellar wind protons and the exospheric hydrogen cloud seen from above the direction of the negative z-axis (perpendicular to the orbital plane). Each point corresponds to neutral hydrogen (red), or a proton (blue) meta particle in the slice -107 ≤ z ≤ 107m (107m = 0.13 RJup). The scale on the axes are 109m (0.14 RJup). The circle without particles corresponds to the inner boundary of the simulation, and the large area without protons corresponds to the assumed obstacle to the stellar wind, on which the protons are reflected (Eckenbäck et al. 2008).
One can see that the hydrogen cloud reaches (with significant density) outside the obstacle boundary (magnetospause) and can produce ENAs by charge exchange with stellar wind protons.
Magnetic moment estimations:
Since ENA production depends on the planetary obsacle to the stellar wind, ENA observations can yield information on a magnetosphere if an extrasolar planet. The size of the magnetosphere of an extrasolar planet cannot be measured directly, but it has implications on many processes. It determines the intensity of planetary radio emission (Desch and Kaiser 1984; Zarka et al. 1997; Farrell et al. 1999; Grießmeier et al. 2007) as well as the protection of the planetary atmosphere against atmospheric loss by the solar wind and by CMEs (Grießmeier et al. 2004; Khodachenko et al. 2008). By varying the obstacle standoff distance by Eckenbäck et al. (2008) and shown in Table 1 the model and observations generate the best fit when the obstacle distance (magnetosphere) is decreased down to about 4 RJup.