Ion acceleration in the Martian tail: Phobos observations

Abstract

The measurements carried out on the spacecraft Phobos‐2 have revealed that the plasma sheet of the Martian magnetosphere consists mainly of ions of planetary origin, accelerated up to ∼ 1 keV/q. Such an acceleration may result from the action of magnetic shear stresses of the draped field, the ion energy increasing toward the center of the tail where magnetic stresses are stronger. The energy gained by heavy ions does not depend on their mass and are proportional to the ion charge. The mechanism of the ion acceleration is related with the generation of a charge separation electric field, which extracts ions from “ray” structures in the Martian tail.

Oxygen ion escape from Venus in a global hybrid simulation: role of the ionospheric O<sup>+</sup> ions

“…3c and 4b). Similar planetary O + at the solar wind energies is seen in the Martian CTCS and is attributed to the J × B "slingshot" forces (Dubinin et al, 1993). Interestingly, in the simulation we see highly curved magnetic field lines and an intense re-energization of the solar wind H + in this region.…”

Oxygen ion precipitation in the Martian atmosphere and its relation with the crustal magnetic fields

“…A narrow low-energy O + precipitation belt is centered at midnight, where the plasma sheet is approximately located, which means when ions are swept by the solar wind to the nightside and drift into the central tail, some fraction of them will impact the atmosphere before they can be accelerated to high energy. In contrast, almost all the high-energy ions on the nightside escape (Figure 4c), since in the case without crustal field, the electric field resulting from the tension of the magnetic field points downstream [Dubinin et al, 1993], accelerating ions along −X direction.…”

“…[9] Previous modeling has demonstrated that the Hall term of the electric field is important when calculating ion acceleration in the Martian space where the finite gyroradii effects of ions are significant [Dubinin et al, 1993;Lichtenegger et al, 1995]. Since the main reason for pickup ions to reimpact the atmosphere is that they have large gyroradii, it is essential to consider the finite gyroradius effect of ions when simulating precipitation of O + ions.…”

“…What could be the influence of the crustal fields on the spatial distribution and energy spectrum of precipitating O + ? As previous studies were done in simplified electromagnetic environments neglecting the crustal magnetic fields, the effects of the crustal magnetic fields on the ion precipitation are still largely unknown; and little care was paid to the precipitation on the nightside, since the magnetic field configuration there when neglecting the crustal fields is favorable for accelerating ions downstream [Dubinin et al, 1993].…”

MAVEN SupraThermal and Thermal Ion Compostion (STATIC) Instrument

“…Bulk escape processes associated with Martian crustal fields (Brain et al 2006), trans-terminator flows (Fraenz et al 2010), shear flows at boundaries (Penz et al 2004), and the Martian magnetotail (Dubinin et al 1993;Fedorov et al 2006) may provide significant ion loss. Bulk escape may be the primary source of plasma into the Martian plasma sheet, whereas ambipolar fields may be the primary driver for polar wind outflows of protons into the tail lobes (Dubinin et al 2011) and from other regions magnetically 'open' to interplanetary space.…”