The Wakes and Magnetotails of Venus and Mars R. Lundin and S. Barabash Swedish Institute of Space Physics, box 812, S-981 28, Kiruna, Sweden The ”hairiness” of a magnetotail The plasma environment near Mars and Venus Atmospheric escape from Mars and Venus Evolutionary aspects of Venus and Mars

COMETS after the greek Aster kometes = ”hairy stars”

Hale-Bop magnetotail at different stages of ”hairyness” ”Hairiness”, the characteristics of a magnetotail Hale-Bop magnetotail at different stages of ”hairyness”

Current Filaments in plasma tail of Comet Hale-Bop Cometopause High speed escape Closeup view of filamentation Current filament (flux rope) scale size ≈ electron gyroradii Dust tail Bow shock Flux ropes

The Hairiness reflecting the characteristic filamentation of plasma in the wake of a volatile rich body interacting with the solar wind narrow beams KH-waves ? Producing structured outflow Disconnection ..... and long tails

Phobos-2 traversal of the inner martian magnetotail(1)

Phobos-2 traversal of the inner martian magnetotail(2)

Martian magnetospheric cavity ... filled with plasma of ionospheric origin Molecular ions

Elliptic orbit magnetotail crossings

3 consecutive circular orbits (PP marked out) 1. Central tail O+ dominated 2. Increased O+ flux in flank boundary layer

Ionization+Acceleration at the Martian Bow Shock

Bow-shock ionization layer (critical velocity ionization?)

Ionization+Acceleration at the Martian Bow Shock Dissipation region

Energy-Mass (E/q - m/q) spectrogram plot illustrating the ion acceleration to equal energy independent of mass (right), and to equal velocities for all masses (left).

Mass-loaded ion pickup in the boundary layer Same velocity Same energy

Mars plasma outflow and the magnetotail Solar Wind Bow Shock MLB ”Planetopause” Tail/beamed outflow Ion pickup

Mass-Loading in the boundary layer of Mars and Venus

Mars Phobos-2 Venus PVO

Volatile content: Earth, Venus, and Mars Atmospheric pressure: 90 Bar (mainly CO2) Venus surface: 4.5·1014 m2 Venus atmospheric mass: 4.1·1020 kg CO2 inventory on Venus is about 4.5 times higher than that on the Earth, Volatile inventory on the Earth is 4.3 times higher than that on Venus! Mars Atmospheric pressure: 0.007 Bar (mainly CO2) Mars surface: 1.5·1014 m2 Mars atmospheric mass: 1.0·1016 kg Atmospheric loss, oxygen/hydrogen: ≈1 kg/s => Atmospheric lifetime: ≈200 million years (2·108 years)

CONCLUSIONS (1) The wakes and magnetotails of Venus and Mars are (like comets) expected to be very structured and ”hairy” The Martian magnetotail constitute a central tail with a ”lobe” and plasma sheet, enclosed in a region of heavy mass-loading of the solar wind, bordering the magnetosheath by a mass-loading boundary. The magnetotails of Venus and Mars are mainly controlled by the solar wind, except for potential perturbations from magnetic ducts at Mars and the effects of Phobos and Deimos. The flaring-angle of the tail boundary differs between Mars (≈3.5 RM at 10 RM) and Venus (≈2 RV and 10 RV). Bow shock flaring – virtually identical, i.e. ≈6.5 RM and ≈6.5 RV respectively. The Bow shock at Mars is associated with an ”ionization layer”. Implications for the tail? Venus?

CONCLUSIONS (2) The magnetotails of Mars and Venus are characterized by large ionospheric ion outflows. Two types of outflows are observed (Mars): – Upward acceleration in the topside ionosphere + mass loaded acceleration => energies ≈ ESW – Pickup processes in the magnetosheath => velocities ≈vSW The tail outflow due to direct solar wind scavenging at the topside ionosphere on Mars and Venus is substantial on a cosmogonic time scale. BUT More data is required to elucidate the magnetotail properties of Mars and Venus. A particularly urgent case is Venus, considering the (surprisingly) scant data available up to now.