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The Ion Composition Analyzer (ICA) on the Rosetta spacecraft observed both the solar wind and the cometary ionosphere around comet 67P/Churyumov–Gerasimenko for nearly two years. However, observations of low energy cometary ions were affected by a highly negative spacecraft potential, and the ICA ion density estimates were often much lower than plasma densities found by other instruments. Since the low energy cometary ions are often the highest density population in the plasma environment, it is nonetheless desirable to understand their properties. To do so, we select ICA data with densities comparable to those of Rosetta’s Langmuir Probe (LAP)/Mutual Impedance Probe (MIP) throughout the mission. We then correct the cometary ion energy distribution of each energy-angle scan for spacecraft potential and fit a drifting Maxwell–Boltzmann distribution, which gives an estimate of the drift energy and temperature for 3521 scans. The resulting drift energy is generally between 11–18 eV and the temperature between 0.5–1 eV. The drift energy shows good agreement with published ion flow speeds from LAP/MIP during the same time period and is much higher than the cometary neutral speed. We see additional higher energy cometary ions in the spectra closest to perihelion that would be well described by a second Maxwellian-like distribution. The energy and temperature are negatively correlated with heliocentric distance, with a stronger dependence on heliocentric distance for temperature. It cannot be quantitatively determined whether this trend is primarily due to heliocentric distance or spacecraft distance to the comet, which increased with decreasing heliocentric distance.

In the Earth's magnetosphere wave-particle interaction is a major ion energization process, playing an important role for the atmospheric escape. A common type of ion heating is associated with low-frequency broadband electric wave fields. For such waves the energy is not concentrated to a certain narrow frequency range and exhibits no peaks or dips in a power spectrum. If there are enough fluctuations close to the ion gyrofrequency the electric field may still come in resonance with gyrating ions and heat them perpendicular to the background magnetic field. We perform a proof-of-concept study to investigate if this heating mechanism may contibute significantly to the energization of planetary ions also in the induced magnetosphere of Venus. We assume Alfvénic fluctuations and estimate the electric field spectral density based on magnetic field observations. We find typical estimated electric spectral densities of a few (Formula presented.) /Hz close to Venus. This corresponds to a heating rate of a few eV/s. We consider an available interaction time of (Formula presented.) 300 s and conclude that this mechanism could increase the energy of an oxygen ion by about a keV. Observed thermal energies are in the range 100–1,000 eV and thus, resonant wave heating may also be important at Venus.

Context: Rosetta followed comet 67P at heliocentric distances from 1.25 to 3.6 au. The solar wind was observed for much of this time, but was significantly deflected and to some extent slowed down by the interaction with the coma.

Aims: We use the different changes in the speed of H⁺ and He²⁺ when they interact with the coma to estimate the upstream speed of the solar wind. The different changes in the speed are due to the different mass per charge of the particles, while the electric force per charge due to the interaction is the same. A major assumption is that the speeds of H⁺ and He²⁺ were the same in the upstream region. This is investigated.

Methods: We derived a method for reconstructing the upstream solar wind from H⁺ and He²⁺ observations. The method is based on the assumption that the interaction of the comet with the solar wind can be described by an electric potential that is the same for both H⁺ and He²⁺. This is compared to estimates from the Tao model and to OMNI and Mars Express data that we propagated to the observation point.

Results: The reconstruction agrees well with the Tao model for most of the observations, in particular for the statistical distribution of the solar wind speed. The electrostatic potential relative to the upstream solar wind is derived and shows values from a few dozen volts at large heliocentric distances to about 1 kV during solar events and close to perihelion. The reconstructed values of the solar wind for periods of high electrostatic potential also agree well with propagated observations and model results.

Conclusions: The reconstructed upstream solar wind speed during the Rosetta mission agrees well with the Tao model. The Tao model captures some slowing down of high-speed streams as compared to observations at Earth or Mars. At low solar wind speeds, below 400 km s^-1, the agreement is better between our reconstruction and Mars observations than with the Tao model. The magnitude of the reconstructed electrostatic potential is a good measure of the slowing-down of the solar wind at the observation point.

We investigate the heavy ion density and velocity in the Venusian upper ionosphere near the North Pole, using the Ion Mass Analyzer, a part of the Analyzer of Space Plasmas and Energetic Atoms 4, together with the magnetic field instruments on Venus Express. The measurements were made during June-July 2014, covering the aerobraking campaign with lowered altitude measurements (similar to 130 km). The plasma scale heights are similar to 15 km below 150-km altitude and similar to 200 km at 150-400-km altitude. A clear trend of dusk-to-dawn heavy ion flow across the polar ionosphere was found, with speeds of similar to 2-10 km/s. In addition, the flow has a significant downward radial velocity component. The flow pattern does not depend on the interplanetary magnetic field directions nor the ionospheric magnetization states. Instead, we suggest a thermal pressure gradient between the equatorial and polar terminator regions, induced by the decrease in density between the regions, as the dominant mechanism driving the ion flow. Plain Language Summary We have calculated the ion density and velocities in the Venusian polar ionosphere using measurements from the Ion Mass Analyzer on board the Venus Express spacecraft. During June-July 2014 the periapsis was lowered to similar to 130 km, which allowed for measurements down to low altitudes of the ionosphere near the North Pole. The plasma scale heights are similar to 15 km below 150-km altitude and similar to 200 km at 150-400 km, which is similar to what was found near the equatorial region by the Pioneer Venus mission. In addition, there is a clear trend of dusk-to-dawn flow, along the terminator, for the heavy ions. This is surprising, as a general flow from day-to-night is expected for the Venusian ionosphere due to the long nights and significant heating of the dayside upper atmosphere. The interplanetary magnetic field direction does not appear to affect the ion flow pattern. Instead, we propose a thermal pressure gradient as the dominant accelerating mechanism, induced by the decrease in density from the equator toward the pole.

Whistler emissions close to the magnetopause on the magnetospheric side are investigated using the four Cluster spacecraft. The waves are found to be generated in thin (electron-scale) sheets moving with the plasma drift velocity. A feature in the electron data coincides with the waves; hot magnetospheric electrons disappear for a few satellite spins. This produces or enhances a temperature anisotropy, which is found to be responsible for the generation of the whistler mode waves. The high energy electrons are thought to be lost through the magnetopause and we suggest that the field lines, on which the waves are generated, are directly connected to a reconnection diffusion region at the magnetopause.