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The collisionless nature of planetary magnetospheres means that electromagnetic forces are fundamental in controlling the flow of energy and momentum through these systems. We use Pioneer Venus Orbiter (PVO) observations to demonstrate that the magnetic pumping process can be active at Venus, in analogy to its recent discovery at Mars. The presented case study demonstrates the framework for how the process can work at Venus, and the results of a statistical analysis show that the ambient plasma conditions support the process being active. Magnetic pumping enables low frequency magnetosonic waves to heat ambient ionospheric electrons and provides a mechanism that couples the solar wind to the Venusian ionosphere. This is the first time the magnetic pumping process has been discussed at Venus. Plain Language Summary: Our Sun emits a stream of particles outward into our solar system, known as the solar wind. When these particles encounter planets and other bodies (such as comets), they either collide with the body (as happens with our Moon) or are deflected around the obstacle, similar to how water in a stream flows around a rock (this happens at most planets, including Earth, Venus and Mars). Understanding the physical forces that control this deflection enable us to understand how the Sun interacts with the planets in our solar system. We use in situ measurements made by the Pioneer Venus Orbiter spacecraft, which orbited the planet Venus, to investigate one specific process, known as "magnetic pumping." This process allows energy from the solar wind to flow into the Venusian atmosphere. We provide a case study demonstrating how this process can operate at Venus, and show that the average conditions in the near Venus space environment can support this process in a more general sense. Key Points: A case study demonstrates how the magnetic pumping process operates at VenusStatistical analysis of the plasma conditions at Venus support the notion that magnetic pumping can operate thereMagnetic pumping provides an avenue for the solar wind to couple to the Venusian ionosphere and heat ionospheric electrons [ABSTRACT FROM AUTHOR]

Steep electron density depletions in the Martian ionosphere are important, especially because they could be regions of significant plasma escape. Local electron density profiles of the Martian ionosphere obtained from the radar sounder onboard the Mars Express spacecraft often show large fluctuations. In some cases, these fluctuations are observed as deep depletions in the electron density. Investigation over the past 12 years of Mars Advanced Radar for Subsurface and Ionospheric Sounding data have revealed over 200 cases of density depletions where the lowest density is less than one fifth of the density in the surrounding regions. These density dips occur both on the dayside and the nightside, with an abundance between solar zenith angles of 50–70° and 100–120°. They occur at all altitudes in the ionosphere. Many of the depletions occur in the southern hemisphere where the crustal magnetic field is stronger and there are more regions where the crustal magnetic field is mostly vertical. In more than half of the cases, the depletion in the local electron density corresponds to a decrease in the electron flux measured with the Analyzer of Space Plasmas and Energetic Atoms electron spectrometer. Several different mechanisms could be responsible for the formation of the depletions, including regions of localized electric fields or magnetic fields creating areas of increased field pressure, escape of the plasma along magnetic field lines depleting density locally, and the density decrease around the photoelectron boundary followed by an increase in the plasma density due to plasma clouds. Plain Language Summary: Investigation of over one solar cycle of local electron density profiles from Mars Advanced Radar for Subsurface and Ionospheric Sounding onboard Mars Express revealed over 200 deep local electron density depletions. Individual and statistical study of these depletions show that they occur both on the dayside and nightside, and at all altitudes. According to Analyzer of Space Plasmas and Energetic Atoms electron spectrometer, some of the cases correspond to a decrease in electron flux. Others occur in regions where the electron flux increases or stays constant, suggesting different mechanisms should be responsible for the existence of density depletions. Many depletions occur over the regions where crustal magnetic fields are strong. Moreover, in many cases the radial component of the magnetic field is the dominant component, at least, in a portion of the depletions, which can have large sizes. Key Points: Local electron density depletions in the Martian ionosphere are individually and statistically studied with over one solar cycle of dataThe depletions correspond to a decrease in electron flux in some cases. In others, the electron flux increases or stays constantMajority of depletion cases are observed over strong crustal magnetic field regions, in many of which the crustal field is almost vertical [ABSTRACT FROM AUTHOR]

The typical subsolar stand‐off distance of Mars' bow shock is of the order of a solar wind ion convective gyroradius, making it highly non‐planar to incident ions. Using spacecraft observations and a test particle model, we illustrate the impact of the bow shock curvature on transient structures which form near the upstream edge of moving foreshocks caused by slow rotations in the interplanetary magnetic field (IMF). The structures exhibit noticeable decrease in the solar wind plasma density and the IMF strength within their core, are accompanied by a compressional shock layer, and are consistent with foreshock bubbles (FBs). Ion populations responsible for these structures include backstreaming ions that only appear within the moving foreshock and reflected ions with hybrid trajectories that straddle between the quasi‐perpendicular and quasi‐parallel bow shocks during slow IMF rotations. Both ion populations accumulate near the upstream edge of the moving foreshock which facilitates FB formation. Plain Language Summary: Planets in the solar system are continuously impacted by the solar wind, a plasma flow originating at the Sun and propagating through the interplanetary medium at high speeds. The solar wind also carries a magnetic field which at times contains twists or discontinuities. The discontinuities are associated with large scale electric currents that can have planar shapes. A planetary obstacle significantly modulate the solar wind plasma and the interaction of solar wind discontinuities with the modulated plasma upstream of the planet leads to formation of transient structures. Due to their relatively large size, these structures can significantly impact and destabilize plasma boundaries at lower altitudes closer to the surface. The results of this paper improve our understanding of solar wind interactions and formation of transient structures upstream of Mars. Key Points: Foreshock bubbles can form upstream of MarsSlow field rotations can cause foreshock bubbles while reflected ions from the quasi‐perpendicular bow shock contribute to their formationUnique ion kinetic scale processes exist around foreshock structures at Mars due to the different interaction size scale [ABSTRACT FROM AUTHOR]

The ion sensor of the Analyzer of Space Plasmas and Energetic Atoms (ASPERA‐3) experiment detects accelerated ions during pulses of radio emissions from the powerful topside sounder: the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) onboard Mars Express. Accelerated ions (O 2+, O+, and lighter ions) are observed in an energy range up to 800 eV when MARSIS transmits at a frequency close to the plasma frequency. Individual observations consist of almost monoenergetic ion beams aligned with the MARSIS antenna or lying in the plane perpendicular to the antenna. The observed ion beams are often accompanied by a small decrease in the electron flux observed by the electron sensor of Analyzer of Space Plasmas and Energetic Atoms 3. Observations indicate that the voltage applied to the antenna causes charging of the spacecraft to several hundreds of volts by the electrons of the ambient plasma. Positively charged ions are accelerated when the spacecraft discharges. Key Points: Accelerated ions are detected by IMA of ASPERA‐3 during sounding phase of MARSIS radarThe energy of accelerated ions is found to be in a range of 20 to 800 eVObservations coincide in time with periods when MARSIS transmits close to the plasma frequency [ABSTRACT FROM AUTHOR]

The goal of this paper is to understand the processes by which solar wind electrons are energized in the Martian magnetosphere and how this compares to processes at Venus and Earth. Each is unique in the source of its magnetic field topology and how this influences electron energization. To achieve this goal, 24 million spectra spanning 13 years have been examined using the electron spectrometer from the Mars Express spacecraft between about 12,000 km and about 250 km altitude, and from all latitudes and local times. The top 10 largest differential energy flux at energies above the differential energy flux peak have been found: seven spectra from the magnetosheath near noon, three from the dark tail (the largest two from the middle and ionospheric edge of the magnetosheath). Spectral comparisons show a decade range in the peak of the electron distributions; however, all distributions show a similar energy maximum dictated by solar wind/planet interaction. Similarly derived, the largest Venus spectrum occurred near the magnetosheath bow shock and had the same shape as the most intense Mars inner magnetosheath spectrum. The Mars and Venus dayside spectra compared to the Mars nightside spectrum that included an enhanced optical signal attributed to discrete "auroral" precipitation show a similar shape. These spectra are also compared to a selected auroral zone electron spectra from the Earth. The Mars and Venus results suggest that there is no more energy needed to generate electrons forming the nightside precipitation than is gained during the solar wind/planet interaction. Key Points: Top 10 orbit‐selected electron energy spectra from Mars are identified from MEx ASPERA‐3 ELS between 2004 and 2016The Mars and Venus dayside electron spectra are similar, and a discrete "auroral" spectrum from the nightside tail of Mars is also similarNo more energy than that supplied by the solar wind‐planet interaction is required to produce discrete auroral spectrum from the nightside tail of Mars [ABSTRACT FROM AUTHOR]

A compact diffraction-reaction chamber, using a 2-inch photodiode array detector, has been employed to investigate the chemical dynamics at the combustion front of a selected series of refractory metal carbides and di-borides from their constituent element reactants as well as binary products from B4C as a reactant. These systems are denoted as (i) M + C → MC; (ii) M + 2B → MB2; and (iii) 3 M + B4C → 2 MB2 + MC, where M = Ti, Zr, Nb, Hf or Ta. Time-resolved X-ray diffraction using intense synchrotron radiation at frame rates up to 10 frames s−1 (or 100 ms frame−1) was employed. The combustion reactions were found to complete within 200–400 ms. In contrast to the Ta + C → TaC combustion system studied earlier, in which a discernible intermediate sub-carbide phase was first formed, reacted further and disappeared to yield the final TaC product, no intermediate sub-carbide or sub-boride was detected in the current systems. Combustion for the Ti, Zr and Hf systems involved a liquid phase, in which the adiabatic temperatures Tad are well above the melting points of the respective reactant metals and have a typical combustion front velocity of 5–6 mm s−1. The Nb and Ta systems have lower Tad, involving no liquid phase. These are truly solid combustion systems and have a lower combustion front velocity of 1–2 mm s−1. The current study opens up a new avenue to chemical dynamics and macrokinetic investigations of high-temperature solid-state reactions. [ABSTRACT FROM AUTHOR]

An in situ cell has been constructed for temperature-dependent X-ray absorption experiments (EXAFS and XANES) of lead bromine (PbBr2) solutions in diethylene glycol in the temperature range from room temperature up to about 433 K. The solution is kept in a thermostated container made of carbon-reinforced teflon between two thin chemically inert quartz glass windows with a high transmission for hard X-rays. The construction of the cell ensures that these X-ray windows are thermalized so that any possible precipitation of solid products from the solution is inhibited. The cell consists mainly of two hermetically sealed teflon containers for the thermostating fluid (silicon oil) that were fitted together in such a way that a small and variable volume (∼2–4 cm³) for the liquid under investigation was achieved. A small thermocouple in a glass enclosure was placed in the solution to maintain temperature control and feedback to the thermostat. The cell design and its performance for temperature-dependent in situ investigations with X-rays are reported. Some preliminary results obtained for PbBr2 solutions in diethylene glycol are given. [ABSTRACT FROM AUTHOR]

The electron sensor of the Analyzer of Space Plasmas and Energetic Atoms experiment detects accelerated electrons during pulses of radio emissions from the powerful topside sounder: the Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS) on board the Mars Express spacecraft. Accelerated electrons are observed at energies up to 400 eV at the times when MARSIS transmits at a frequency between the local plasma frequency and its harmonics (up to 4 times the plasma frequency). When the electron density and magnetic field strength are low (∼103 cm −3, ∼ 10 nT), the accelerated electrons are almost monoenergetic electron beams. An increase in density and magnetic field (∼3·103 cm −3, ∼ 50 nT) leads to substantial broadening of the energy spectrum of the accelerated electrons. It is concluded that in the latter case, electrons are accelerated by the variable spacecraft potential resulting from the imbalance of the electron and ion currents to the MARSIS antenna during transmission. Key Points: Accelerated electrons are detected by the electron sensor of ASPERA‐3 during the sounding phase of the Mars Express sounder MARSISThe energy of the accelerated electrons is found to be in the range from 20 to 400 eVObservations coincide in time with periods when MARSIS transmits in frequencies between the local plasma frequency and its fourth harmonic [ABSTRACT FROM AUTHOR]