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Metallic ions deposited in planetary atmospheres via meteoroid ablation are an invaluable tool for understanding electric fields, atmospheric winds, and minor ion transport. At Mars, metallic ion distributions are poorly understood. We analyze MAVEN/NGIMS Fe+${\\mathrm{F}\\mathrm{e}}^{+}$distributions in the Martian ionosphere over the period of 2015–2020 at altitudes ∼120–200 km. The Fe+${\\mathrm{F}\\mathrm{e}}^{+}$vertical structure observed during individual low‐altitude MAVEN Deep Dip campaigns is highly variable likely due to variations in the ion magnetization altitude and corresponding ion transport conditions. Deep Dip campaigns on or near the martian nightside show evidence for in situ production of Fe+${\\mathrm{F}\\mathrm{e}}^{+}$ions via electron precipitation. On average, Fe+${\\mathrm{F}\\mathrm{e}}^{+}$ions are globally distributed in the martian ionosphere at altitudes >${ >} $ 120 km with only slight decreases on the martian nightside and in the southern hemisphere. We find a similar, albeit less intense, decrease in the Fe+${\\mathrm{F}\\mathrm{e}}^{+}$densities in the northern hemisphere near perihelion as has been reported for Mg+${\\mathrm{M}\\mathrm{g}}^{+}$ .

We use in situ plasma observations made by the Pioneer Venus Orbiter spacecraft to show for the first time that magnetosonic waves can couple the solar wind to the upper ionosphere and deposit energy there. The waves are generated upstream of Venus, are advected into the shock and propagate across the draped magnetic field, through the magnetosheath and into the dayside upper ionosphere. The magnetosonic waves damp in the upper ionosphere in a region where physical collisions are rare, and electromagnetic forces must control this damping. The waves damp when the ionospheric heavy ion density is a few thousand cm−3 and wave‐particle interactions with the dominant O+ ions are postulated as the damping mechanism. Estimates of ion heating rates show that 1%–5% of the O+ ion distribution function could be heated to escape energy in 10–40 s. Plain Language Summary Our Sun emits a stream of charged particles radially outward into our Solar system, known as the solar wind. When the solar wind encounters obstacles such as planets and comets, a variety of forces may act to divert the flow around the obstacle, much like when flowing water in a stream encounters a rock and is diverted around it. This study uses measurements made by a spacecraft that orbited Venus, known as Pioneer Venus Orbiter, to investigate some of the side effects that can arise when the solar wind flow is diverted around Venus. We show for the first time how a particular pathway allows energy to be deposited from the flowing solar wind into the Venusian atmosphere, and that this energy can be deposited quickly enough to significantly impact the particles in the atmosphere. The characteristics observed in this study at Venus are similar to those at Mars where this process has also been observed, suggesting that the solar wind can interact with the two planets in similar ways in this respect. Key Points Magnetosonic waves propagate from upstream into the dayside upper ionosphere of Venus Magnetosonic waves are damped by wave‐particle interactions with heavy ionospheric ions Subsequent ion heating rates could heat 1%–5% of the ion distribution function to escape energy in 10–40 s

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 Venus Statistical analysis of the plasma conditions at Venus support the notion that magnetic pumping can operate there Magnetic pumping provides an avenue for the solar wind to couple to the Venusian ionosphere and heat ionospheric electrons

By comparison of the methane mixing ratio and the carbon isotope ratio (δ13CCH4) in Arctic air with regional background, the incremental input of CH4 in an air parcel and the source δ13CCH4 signature can be determined. Using this technique the bulk Arctic CH4 source signature of air arriving at Spitsbergen in late summer 2008 and 2009 was found to be −68‰, indicative of the dominance of a biogenic CH4 source. This is close to the source signature of CH4 emissions from boreal wetlands. In spring, when wetland was frozen, the CH4 source signature was more enriched in 13C at −53 ± 6‰ with air mass back trajectories indicating a large influence from gas field emissions in the Ob River region. Emissions of CH4 to the water column from the seabed on the Spitsbergen continental slope are occurring but none has yet been detected reaching the atmosphere. The measurements illustrate the significance of wetland emissions. Potentially, these may respond quickly and powerfully to meteorological variations and to sustained climate warming. Key Points Isotopic measurements have been used to identify major sources of Arctic methane In late summer biogenic methane sources dominate the bulk Arctic source mix Seabed emissions near Spitsbergen have not been detected reaching the atmosphere

Mars' dayside ionosphere is maintained primarily by ionization from solar ultraviolet photons and subsequent chemical reactions, with small contributions from other mechanisms such as impact ionization and charge exchange. In December 2023, the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission observed the impact of an interplanetary coronal mass ejection (ICME) on Mars' ionosphere, including strongly enhanced fluxes of suprathermal electrons. We show that this enhancement in suprathermal electron fluxes increased ion production from electron impact, so that dayside electron impact ionization rates exceeded photoionization rates during the ICME. This change in ion production mechanisms led to unusually high densities of the minor ions C+${\\mathrm{C}}^{+}$and O++${\\mathrm{O}}^{++}$ . Space weather events are known to increase ion escape rates, so changes in ion composition during space weather events have important implications for atmospheric evolution. We show that scaling nominal loss rates to account for space weather may underestimate carbon loss from Mars' atmosphere. Plain Language Summary Dayside planetary ionospheres are primarily produced through interactions between atmospheric neutral gases and sunlight. Impact by energetic particles, especially electrons, typically only contributes a small amount of plasma. We observed unusually high densities of the minor ions C+${\\mathrm{C}}^{+}$and O++${\\mathrm{O}}^{++}$in Mars' ionosphere during a space weather event in December 2023, when a large bubble of magnetized plasma launched from the Sun impacted the planet. This plasma bubble compressed the Mars magnetosheath, pushing suprathermal electrons to lower altitudes, where they impacted the atmosphere and significantly increased plasma production through impact ionization. Changes in the production mechanisms of the ionosphere during space weather events lead to changes in its density and composition. This is important because space weather events are known to increase the amount of atmospheric gas escaping from a planet, which can have important implications for how the atmosphere evolves over millions of years. Key Points Unexpected increases in C+ and rarely detected O++ densities were observed during the December 2023 space weather event at Mars These ions were produced by electron impact ionization from the intense electron fluxes associated with the space weather event Electron impact ionization exceeded photoionization during the event, which temporarily altered the composition of ions escaping Mars

Dust is common close to the martian surface, but no known process can lift appreciable concentrations of particles to altitudes above ~150 kilometers. We present observations of dust at altitudes ranging from 150 to above 1000 kilometers by the Langmuir Probe and Wave instrument on the Mars Atmosphere and Volatile Evolution spacecraft. Based on its distribution, we interpret this dust to be interplanetary in origin. A comparison with laboratory measurements indicates that the dust grain size ranges from 1 to 12 micrometers, assuming a typical grain velocity of ~18 kilometers per second. These direct observations of dust entering the martian atmosphere improve our understanding of the sources, sinks, and transport of interplanetary dust throughout the inner solar system and the associated impacts on Mars’s atmosphere.

Magnetic reconnection in collisional plasmas has been widely studied in solar and laboratory plasma disciplines, but in situ measurements in space plasmas have rarely been utilized to explore this reconnection regime. Here we study collisional effects on magnetic reconnection in the Martian ionosphere by analyzing in situ data obtained by the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft. A case study and statistical results demonstrate that current sheets are commonly observed in both collisionless and collisional regions in the Martian ionosphere. Meanwhile, reconnection ion jets become hardly detectable in collisional current sheets, suggesting suppression of reconnection outflows by ion‐neutral friction effects. MAVEN observations allow us to access multiple regimes of magnetic reconnection, thereby providing valuable opportunities for cross‐disciplinary studies of collisional reconnection.

Rapid global warming marked the boundary between the Palaeocene and Eocene periods 55.6 million years ago, but how the temperature rise was initiated remains elusive. A catastrophic release of greenhouse gases from the Kilda basin could have served as a trigger.

We propose the hypothesis that natural selection, acting on the specificity or preference for CO2 over O2 of the enzyme rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase), has controlled the CO2:O2 ratio of the atmosphere since the evolution of photosynthesis and has also sustained the Earth's greenhouse-set surface temperature. Rubisco works in partnership with the nitrogen-fixing enzyme nitrogenase to control atmospheric pressure. Together, these two enzymes control global surface temperature and indirectly the pH and oxygenation of the ocean. Thus, the co-evolution of these two enzymes may have produced clement conditions on the Earth's surface, allowing life to be sustained.

Atmospheric CO at Egham in SE England has shown a marked and progressive decline since 1997, following adoption of strict controls on emissions. The Egham site is uniquely positioned to allow both assessment and comparison of ‘clean Atlantic background’ air and CO-enriched air downwind from the London conurbation. The decline is strongest (approximately 50 ppb per year) in the 1997–2003 period but continues post 2003. A ‘local CO increment’ can be identified as the residual after subtraction of contemporary background Atlantic CO mixing ratios from measured values at Egham. This increment, which is primarily from regional sources (during anticyclonic or northerly winds) or from the European continent (with easterly air mass origins), has significant seasonality, but overall has declined steadily since 1997. On many days of the year CO measured at Egham is now not far above Atlantic background levels measured at Mace Head (Ireland). The results are consistent with MOPITT satellite observations and ‘bottom-up’ inventory results. Comparison with urban and regional background CO mixing ratios in Hong Kong demonstrates the importance of regional, as opposed to local reduction of CO emission. The Egham record implies that controls on emissions subsequent to legislation have been extremely successful in the UK.