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Venus lacks a significant intrinsic magnetic field, and thus, its atmosphere and ionosphere interact directly with the solar wind flow and magnetic field from the Sun. Interplanetary magnetic fields (IMF) can penetrate into the ionosphere when the upstream solar wind dynamic pressure is stronger than the ionospheric plasma pressure. Magnetic topology can be inferred at Venus if it is defined as the magnetic connectivity to the collisional atmosphere/ionosphere, rather than connectivity to the planet’s surface. Magnetic topology can be inferred from the pitch angle and energy distribution of superthermal (> ~1 eV) electrons. More specifically, the presence of loss cones in electron pitch angle distributions infers connectivity to the nightside collisional atmosphere and the presence of ionospheric photoelectrons (identified from electron energy distributions) indicates connectivity to the dayside collisional ionosphere. We design automated procedures to determine magnetic topology with electron and magnetic field measurements by the Venus Express spacecraft over its entire mission (2006-2014). This allows us to provide the first statistical mapping of magnetic topology at Venus. We also examine how the upstream drivers affect the low-altitude magnetic topology, revealing different magnetized states of the Venus ionosphere. We find that open and closed (a surprising topology not expected at Venus) fields cluster around the terminator and draped fields dominate other regions. Our results also reveal that there is more dayside magnetic connectivity in the -E (solar wind motional electric field) hemisphere than the +E hemisphere, and during solar maximum. During solar minimum, however, there is more nightside magnetic connectivity. Last but not the least, to understand the true nature of these magnetic topologies and broadly speaking the planet-solar wind interaction, we need to think about possible ways to measure the deeply penetrated magnetic fields at Venus and Mars.

Interplanetary (IP) shocks can be driven in the solar wind by fast coronal mass ejections and by the interaction of fast solar wind with slow streams of plasma. These shocks can be preceded by extended wave and suprathermal ion foreshocks. We use STEREO data to study wave modes upstream and downstream of IP shocks. Understanding these waves is important because they contribute to shock acceleration processes and modify the solar wind as the shocks propagate in the heliosphere. We find that upstream regions can be permeated by whistler waves (f ~ 1 Hz) and/or ultra low frequency (ULF) right-handed waves (f~10-2–10-1 Hz). While whistlers appear to be generated at the shock, the origin of ULF waves is most probably associated with local kinetic ion instabilities. In contrast with planetary bow shocks, most IP shocks have a small Mach number (

Magnetic pulsations are observed at Mars in the magnetotail and on the surface by the Maven and InSight magnetometers. The surface observations exhibit a frequency-dependent polarization in which the amplitude of the vertical component weakens with increasing frequency. This frequency dependence is not seen in the source regions studied by MAVEN. The source of the frequency dependence must be in the subsurface of Mars. The attenuation is consistent with an aquifer that is 3 km thick, containing water of the conductivity of terrestrial seawater.

Superthermal electron precipitation is one of the main sources supporting the Mars nightside ionosphere. It is expected that solar wind electron fluxes are to increase significantly during interplanetary coronal mass ejections (ICME) and therefore an enhanced nightside ionospheric density. This study is to quantify the variation of the precipitating and deposited electron fluxes during five of the most extreme ICMEs encountered by Mars Global Surveyor (MGS). We find energy fluxes correlate better with the upstream dynamic pressure proxy than number fluxes and electron fluxes increase more at high energies, which means electrons tend to have a lower peak production altitude during storm times. The precipitating and net/deposited fluxes are increased up to an order of magnitude from low to high dynamic pressures. The estimated total electron content (TEC) is a few times of 1014 m-2 for quiet times and on the order of 1015 m-2 for storm times, with an enhancement up to an order of magnitude locally near strong crustal fields. Crustal magnetic fields have an effect on the deposited fluxes with more prominent magnetic reflection over strong magnetic fields during quiet periods, which is significantly reduced during storm times. Lastly, we estimate a global energy input from downward fluxes of 1.3×108 W and 5.5×108 W and the globally deposited energy from net fluxes of 2.3×107 W and 1.6×108 W for quiet and storm time periods, a factor of 4 and 7 enhancement globally, respectively, but up to an order of magnitude locally near strong crustal fields.

We advocate for a mission concept study for a space telescope dedicated to solar system science in Earth orbit. Such a study was recommended by the Committee on Astrobiology and Planetary Science (CAPS) report "Getting Ready for the Next Planetary Science Decadal Survey." The Mid-Decadal Review also recommended NASA to assess the role and value of space telescopes for planetary science. The need for high-resolution, UV-Visible capabilities is especially acute for planetary science with the impending end of the Hubble Space Telescope (HST); however, NASA has not funded a planetary telescope concept study, and the need to assess its value remains. Here, we present potential design options that should be explored to inform the decadal survey., Whitepaper submitted to Planetary Science and Astrobiology Decadal Survey

In this Letter, we make use of sophisticated 3D numerical simulations to assess the extent of atmospheric ion and photochemical losses from Mars over time. We demonstrate that the atmospheric ion escape rates were significantly higher (by more than two orders of magnitude) in the past at $\sim 4$ Ga compared to the present-day value owing to the stronger solar wind and higher ultraviolet fluxes from the young Sun. We found that the photochemical loss of atomic hot oxygen dominates over the total ion loss at the current epoch whilst the atmospheric ion loss is likely much more important at ancient times. We briefly discuss the ensuing implications of high atmospheric ion escape rates in the context of ancient Mars, and exoplanets with similar atmospheric compositions around young solar-type stars and M-dwarfs., 6 pages, 4 figures, 1 table, accepted for publication in ApJ Letters

We study roles of the thermosphere and exosphere on the Martian ionospheric structure and ion escape rates in the process of the solar wind-Mars interaction. We employ a four-species multifluid MHD (MF-MHD) model to simulate the Martian ionosphere and magnetosphere. The $cold$ thermosphere background is taken from the Mars Global Ionosphere Thermosphere Model (M-GITM) and the $hot$ oxygen exosphere is adopted from the Mars exosphere Monte Carlo model - Adaptive Mesh Particle Simulator (AMPS). A total of four cases with the combination of 1D (globally averaged) and 3D thermospheres and exospheres are studied. The ion escape rates calculated by adopting 1D and 3D atmospheres are similar; however, the latter are required to adequately reproduce MAVEN ionospheric observations. In addition, our simulations show that the 3D hot oxygen corona plays an important role in preventing planetary molecular ions (O$_2^+$ and CO$_2^+$) escaping from Mars, mainly resulting from the mass loading of the high-altitude exospheric O$^+$ ions. The $cold$ thermospheric oxygen atom, however, is demonstrated to be the primary neutral source for O$^+$ ion escape during the relatively weak solar cycle 24., Comment: 21 pages, 10 figures, 4 tables, accepted for publication in Journal of Geophysical Research-Space Physics

International audience; The Mars Atmosphere and Volatile Evolution mission has obtained comprehensive particle and magnetic field measurements. The Solar Wind Electron Analyzer provides electron energy-pitch angle distributions along the spacecraft trajectory that can be used to infer magnetic topology. This study presents pitch angle-resolved electron energy shape parameters that can distinguish photoelectrons from solar wind electrons, which we use to deduce the Martian magnetic topology and connectivity to the dayside ionosphere. Magnetic topology in the Mars environment is mapped in three dimensions for the first time. At low altitudes (