Budget and Roles of Heavy Ions in the Solar System M. Yamauchi, I. Sandahl, H. Nilsson, R. Lundin, and L. Eliasson Swedish Institute of Space Physics (IRF) Kiruna, Sweden

Abstract Oxygen and other major heavy species such as C, N, S, and Na circulate through the entire solar system: e.g., lithosphere, ocean, atmosphere, exosphere, and heliosphere. The amount of O + escaping from Earth/Mars is substantial (as large as 1~10 kg/s). Hence, studying the space-level circulation of oxygen/heavy ions has an obvious cross-disciplinary importance on subjects such as: * Evolution of Earth, planets, satellites * Modeling ancient Earth (astrobiology) / Environmental issue * Chemistry of reservoir (CO 2, SiO 2, SO) at planetary surface and atmosphere * Basic plasma physics (e.g. energization process, instabilities) * Planetary magnetospheric physics (e.g. circulation) * Solar-terrestrial and Jupiter-satellite interaction But not well understood at all. Therefore, it is important to measure thermal and non-thermal heavy ions with mass-resolution in both the Earth's and planetary magnetospheres, also in planetology missions.

Phobos-2 result: unexpected high loss rate ~ 1 kg/s Figure 1

Mars Express result: quick energization of O + Figure 2: MEX Confirmed quick ion escape, but the energization mechanism is still not at all clear. None of present/ planned Mars mission has sufficient plasma physics instrumentation.

O + escape (Cluster example) Figure 3: Major mass carrier of the escape is CNO ions for the Earth (most cases O + except for storm time when N + contributes). Considering Martian result, the same things are expected to happen at the other planets/satellites. Need confirmation !

Budget above the Earth's ionosphere ion escapeH+H+ O+O+ < 10 eV (2~3 Re)2~51~3 > 10 eV (3~4 Re)2~81.5~20 ion precipitationionelectron > 10 eV (DMSP)0.2~0.99~60 in /s mass budgetH+H+ O+O+ meteors out0.05~0.20.5~5- in< 0.02?0.5 in kg/s (cf. Figure 5)

Oxygen escape is large and important ! Terrestrial and Martian studies (Figures 1-3) revealed that non- thermal escape of heavy ions is substantial (100~500 ton/day). The oxygen circulation may no longer be ignored in the time scale of planetary evolution. Furthermore, the escape strongly depends on the magnetospheric activity (Figure 4). The largest source is near the cusp where the solar wind is injected (Figure 4), showing that the planetary magnetic field plays an important role. The study of the heavy ion circulation and budget must include: * Its driving mechanism, i.e., energization mechanism ? * Its variability at different planets ? * Roles of solar UV, solar wind (or planetary convection), planetary (or satellite) magnetic field, and its atmosphere ? * Circulation route or return route (Table, Figure 5) ? * Active roles of heavy ions to the space plasma (Figure 6) ? * Coupling to its reservoir (atmosphere and surface) ?

Ion heating (Freja statistics) Figure 4: Distribution and Kp-dependence of ion heating (and escape) (Broad-Band Electrostatic Low Frequency wave) (Lower Hybrid or Electro-Magnetic Ion Cyclotron wave)

O+ injection Figure 5: O + actually returns to the Earth in many forms. Furthermore, some unknown process is taking place between Freja and FAST altitudes.

Roles of escaped ions? Earth ? Mars ? Venus ? Io & other Satellites? Figure 6: Heavy ions play active roles in plasma, such as mass-loading, wave instability, and atmospheric chemistry.

Request for the future missions Technology for mass-resolving energy spectroscopy is available for both three-axis stabilized spacecraft (<3 kg) and spinning spacecraft (< 2 kg) although extra mass is required to resolve CNO. Therefore, heavy ion measurements can easily be included in any solar system missions including planetology missions for: * Comparative planetary science including satellites * Exo/astrobiology missions to study the habitable conditions * Missions to study small-bodies * And of course terrestrial missions To understand the dynamics, however, we simultaneously need to monitor the solar wind condition (or planetary wind condition for satellites of giant planets). Therefore, we must have in-situ measurements at a minimum of two points.

Conclusions 1. Dynamics and circulation of heavy ions in space have wide and cross-disciplinary importance, but are poorly understood. 2. Measuring heavy ions can easily be done in any solar system missions. 3. We need at least two-point in-situ measurements, one monitoring incoming plasma flow and the other for the actual heavy ion measurements. 4. In missions to the other planets (even planetology missions), we need sub-spacecraft that monitor the upstream conditions.

More than two types of O+ escape ~ 1 kg/s loss means complete loss in 200 M year without refill

Ion heating/escape (Freja example) [eV] [eV] O + H + Density e - Freja orbit 1798 ( ) — Transverse Acc. outflow — — Bulk plasma outflow —

O+ injection (Freja statistics) Distribution of heavy ion injection events at keV range. One can recognize nightside preference.