Geoscience Reference
In-Depth Information
Fig. 1. Heliosphere and heliospheric ENA. Regions and boundaries are in plain text,
and particles in italics. Dashed lines are ion trajectories, while solid lines those of neutral
atoms. Solid circles signify neutralization and open circles ionization. LIC ions charge
exchange with LIC atoms outside the HP can enter the heliosphere. Penetrating LIC neu-
trals become pickup ions (PUI) after ionization; and PUI accelerated at the termination
shock become anomalous cosmic rays (ACR).
LIC, mainly H, He, C, N, and O atoms, penetrate into the heliosphere with
lose, as they approach the Sun, due to ionization by solar photons, ions and
electrons. Depending on their ionization potentials, each atomic species has
its specific spatial distribution in the SW bubble. Most pronounced is the
gravitationally focused LIC He or the “He cone”, stretching from 0.3 AU
outward in the anti-apex direction.
4
Direct measurement of the distribu-
tion of interstellar He shows Sun's relative velocity of 26
.
3
±
0
.
4km/s in
0
.
2
◦
.
5
Interstellar atoms are the partners in charge exchange with energetic ions
of different origins and in different regions to produce ENA, as well as the
main source of PUI. Figure 1 shows ENA created in and near HS, and can
reach 1 AU for our detection, thus serving as signals from the heliospheric
boundaries.
Crudely speaking, ENA from the boundaries group into three: (1) those
from interstellar ions just outside the heliopause, especially those in the
hydrogen wall
6
in the apex region; (2) those from subsonic solar ions near
0
.
5
◦
and latitude
the direction of ecliptic longitude 74
.
7
±
−
5
.
2
±
