Now in PDS4
















    Measurement Objectives

    The main role of SWIA on MAVEN is to measure the flux of solar wind ions (primarily protons) into the Martian system, enabling parameterization of atmospheric escape channels as a function of solar wind input and extrapolation back in time. SWIA provides complementary measurements to those from the mass-resolving STATIC instrument, which will focus on planetary ions derived from the Martian upper atmosphere. SWIA measures the density, temperature, and velocity of solar wind ions, both in the undisturbed upstream interplanetary medium, and as they encounter the Martian atmosphere. The wide energy range of the instrument allows measurements of velocities ranging from a few tens of km/s up to 2,000 km/s. Using these data, we can derive the dynamic pressure of the solar wind, the rate at which neutral atmospheric atoms are ionized by the solar wind, and the acceleration of these newly born ions in the magnetic and electric fields around Mars.

    SWIA's measurements contribute to the goal of understanding the current state of the upper atmosphere, as part of a full suite of plasma instrumentation including STATIC, SWEA, LPW, SEP, and MAG. SWIA will make measurements of the ion dynamic pressure that together with the interplanetary magnetic field controls the overall structure of the Martian magnetosphere and can drive enhanced escape. SWIA will also make measurements relevant to individual non-thermal ion escape channels, including but not limited to ion pickup and subsequent sputtering, magnetic reconnection, auroral processes, wave-particle interactions, shear-driven boundary layer processes, and plasma sheet acceleration.

    SWIA measures the 3-d velocity distributions of ions. Since telemetry constraints prevent sending data at the intrinsic resolution for the entire field of view, SWIA provides two basic 3-d products. The "Fine 3d" product provides coverage of an energy/angle range targeted around the peak of the distribution, with 4.5x3.75 degree resolution and 9.4% energy resolution. This product is designed to measure the upstream solar wind. Meanwhile, the "Coarse 3d" product provides full coverage of all energies and angles, with 22.5x22.5 degree resolution and as good as 18.8% energy resolution. This product is designed to measure the slowed and heated ion distribution in the magnetosheath. In addition, SWIA calculates energy spectra and density, velocity, pressure/temperature, and heat flux moments of the distribution on board, allowing very high cadence coverage of the basic properties of the distribution.