Exospheric Ly-α observations of UVIS/HDAC at CASSINI on its Earth swing-by and TWINS are combined to derive the exospheric H-density profile of the ecliptic dayside between 3–15 R_E. At 10 R_E n_H=35 cm⁻³ is found in the vicinity of the subsolar point for quiet space weather conditions. Also a faster radial fall of the dayside H density above 8 R_E (r⁻³) compared to lower distances of 3–7 R_E (r^−2.37) is found and possibly indicates enhanced loss of H atoms near the magnetopause and beyond.

We investigate what fraction of the hot hydrogen atoms recently found from Lyman-alpha measurements in the Earth's upper exosphere could have their origin as energetic neutral atoms via charge exchange from protons of the shocked solar wind ahead of the magnetopause. Our calculations show that this contribution, although definitely present at larger exospheric heights, cannot explain the observations at lower altitudes.

The Voyager plasma observations show that the physics of the heliosheath is rather complex and that temperature derived from observation particularly differs from expectations. To explain this fact, the temperature in the heliosheath should be based on κ distributions instead of Maxwellians because the former allows for much higher temperature. Here we show an easy way to calculate the κ temperatures.