Active Experiments Beyond the Earth: Plasma Effects of Sounding Radar Operations in the Ionospheres of Venus, Mars, and the Jovian System

The operation of powerful satellite- and rocket-born sounding radars is often accompanied by a heating/acceleration of the local electrons and ions. Intense fluxes of sounder accelerated particles were detected in Earth's ionosphere when the frequency of the radar transmitter was close to one of the fundamental plasma resonances: harmonic of the electron-cyclotron frequency, plasma, or upper-hybrid frequencies. Recently it was found that running a sounder in the ionosphere of the non-magnetized Mars results in similar effects. Ion and electron sensors of the ASPERA-3 experiment (Analyzer of Space Plasma and Energetic neutral Atoms) onboard the Mars Express spacecraft discovered acceleration of the local ionospheric ions and electrons from thermal threshold energies to 100's of eV during the active sounding phase of the onboard sounder. ESA and NASA missions being studied or under development to Jupiter (JUICE- JUpiter ICy moon Explorer) in 2022, Europa Clipper in 2023 and to Venus (EnVision) in 2032 and ISRO Venus obiter in 2023 will also carry powerful sounding radars. The purpose of this study is to investigate what mechanisms can cause acceleration of the plasma particles during operations of the proposed sounding radars in the Jovian system and Venusian ionosphere. Using the results of the previous studies and characteristics of the proposed sounding radars onboard JUICE, Europa Clipper, EnVision, and ISRO Venus Obiter, we define the optimal conditions for observations of sounder accelerated particles, depending on the local conditions, such as plasma density, composition, and intensity of the magnetic field. The EnVision and ISRO Venus Obiter radar operations are expected to result in the most pronounced acceleration of ions and electrons, an effect that can be used to improve the local plasma diagnostics

Ionospheric ambipolar electric fields of Mars and Venus: Comparisons between theoretical predictions and direct observations of the electric potential drop.

We test the hypothesis that their dominant driver of a planetary ambipolar electric field is the ionospheric electron pressure gradient (∇P e). The ionospheres of Venus and Mars are mapped using Langmuir probe measurements from NASAs Pioneer Venus Orbiter (PVO) and Mars Atmosphere and Volatile Evolution (MAVEN) missions. We then determine the component of the ionospheric potential drop that can be explained by the electron pressure gradient drop along a simple draped field line. At Mars, this calculation is consistent with the mean potential drops measured statistically by MAVEN. However, at Venus, contrary to our current understanding, the thermal electron pressure gradient alone cannot explain Venus strong ambipolar field. These results strongly motivate a return to Venus with a comprehensive plasmas and fields package, similar to that on MAVEN, to investigate the physics of atmospheric escape at Earths closest analog

A case study of proton precipitation at Mars:Mars Express observations and hybrid simulations

Using the data from the Analyzer of Space Plasma and Energetic Atoms (ASPERA-3) experiment on board Mars Express and hybrid simulations, we have investigated the entry of protons into the Martian induced magnetosphere. We discuss one orbit on the dayside with observations of significant proton fluxes at altitudes down to 260 km on 27 February 2004. The protons observed below the induced magnetosphere boundary at an altitude of less than 700 km have energies of a few keV, travel downward, and precipitate onto the atmosphere. The measured energy flux and particle flux are 10^8–10^9 eV cm^−2 s^−1 and 10^5–10^6 H^+ cm^−2 s^−1, respectively. The proton precipitation occurs because the Martian magnetosheath is small with respect to the heated proton gyroradius in the subsolar region. The data suggest that the precipitation is not permanent but may occur when there are transient increases in the magnetosheath proton temperature. The higher-energy protons penetrate deeper because of their larger gyroradii. The proton entry into the induced magnetosphere is simulated using a hybrid code. A simulation using a fast solar wind as input can reproduce the high energies of the observed precipitating protons. The model shows that the precipitating protons originate from both the solar wind and the planetary exosphere. The precipitation extends over a few thousand kilometers along the orbit of the spacecraft. The proton precipitation does not necessarily correlate with the crustal magnetic anomalies

Cusp particle detection and ion injection source oscillations

The magnetic merging process has been suggested as a means for particle injection into the cusp regions of the earth's magnetosphere. If this process occurs, the injected plasma should reveal a characteristic signature. Electrostatic analyzers are used to detect this plasma. This thesis discusses the design of the electrostatic analyzers which are the central components of the High Altitude Plasma Instrument (HAPI) and Low Altitude Plasma Instrument (LAPI) flown on DE-A and DEHB (Dynamics Explorer satellites) respectively. Also discussed is the calibration of the electrostatic analyzers which I was involved in. This includes the co-authored calibration data acquisition program and my Calibration Data Reduction Routine. Typical satellite instrument output is in spectrogram energy-time format with the particle flux intensity indicated by gray shading. This presentation gives a "visual picture" of how the differential energy flux at each energy changes with time. A presentation of this type using the DE-A HAPI data shows the magnetic merging injection signature: multiple ion "V" structures as the satellite passes through the cusp region when the interplanetary magnetic field has a southward component. An alternative output format which I have helped create produces individual line spectra which allows these "V" structures to be examined in finer detail. If one looks at these "V" structure spectrograms, it is easily noticed that they appear to pulsate with time. I have conducted a harmonic analysis of the peak distribution function per spin from several satellite passes- to determine the periodicity of these pulsations, perhaps related to Kelvin-Helmholtz waves at the magnetopause

Predicting CO Cameron-band auroral emission at Venus using VEx Observations

peer reviewedVenus and Mars are similar in many aspects, such as a CO2 dominant atmosphere and an induced-like magnetosphere. Various types of auroral emissions have been observed at Mars by the Mars Express and MAVEN missions. Auroral emissions have also been made at Venus by Pioneer Venus Orbiter (PVO) and also ground-based telescopes. Meanwhile, Xu et al. [2022, GRL] empirically established a linear relation between auroral electron fluxes and the CO Cameron-band emissions using the combination of auroral observations and superthermal electron observations from MAVEN. By utilizing this empirical relation, we independently predict and analyze the possible CO Cameron-band emission brightness at Venus using the electron observations from the Venus Express mission. By comparing our predictions with the observations by PVO, we can infer whether the superthermal electrons are responsible for the auroral emissions and if so, characterize the source electrons and their possible dependence on upstream drivers. This study is particularly useful for future Venus mission design

A Survey of Strong Electric Potential Drops in the Ionosphere of Venus

Abstract Every planet or moon with an ionosphere is thought to generate a weak electrical potential which helps ions overcome gravity and escape to space. A pilot study at Venus by Collinson et al. (2016, https://doi.org/10.1002/2016GL068327) indicated a planetary potential an order of magnitude stronger than expected. Here we present a statistical study of the electrical potential drop in the ionosphere of Venus, which was found to be an average of 7.04 ± 2.19 V. However, these strong potentials measured by Venus Express are likely atypical and extreme outliers associated with a transient phenomenon in the Venusian ionosphere. We posit they are associated with transient and sporadic density cavities in the ionosphere and may be the result of sporadic electrostatic double layer formation in the dayside ionosphere

Effects of the 2007 Martian Global Dust Storm on Boundary Positions in the Induced Magnetosphere

Mars's magnetosphere is a sensitive system, varying due to external and internal factors, such as solar wind conditions and crustal magnetic fields. A signature of this influence can be seen in the position of two boundaries; the bow shock and the induced magnetospheric boundary (IMB). The bow shock moves closer to Mars during times of high solar activity, and both the bow shock and IMB bulge away from Mars over crustal magnetic fields in the southern hemisphere. This study investigates whether large-scale atmospheric events at Mars have any signature in these two magnetic boundaries, by investigating the 2007 storm. The 2007 global storm lasted for several months and increased atmospheric temperatures and densities of both water vapor and carbon dioxide in the atmosphere, leading to an increase in atmospheric escape. Using Mars Express, we identified boundary locations before, during, and after the event, and compared these to modeled boundary locations and areographical locations on Mars. We find that, while it is unclear whether the bow shock position is impacted by the storm, the IMB location does change significantly, despite the orbital bias introduced by Mars Express. The terminator distance for the IMB peaks at longitudes 0°–40° and 310°–360°, leaving a depression around 180° longitude, where the boundary usually extends to higher altitudes due to the crustal magnetic fields. We suggest this may be due to the confinement of ionospheric plasma over crustal fields preventing mixing with the dust, creating a dip in ionospheric pressure here

Solar Wind Induced Waves in the Skies of Mars: Ionospheric Compression, Energization, and Escape Resulting From the Impact of Ultralow Frequency Magnetosonic Waves Generated Upstream of the Martian Bow Shock

International audienceUsing data from the National Aeronautics and Space Administration Mars Atmosphere and Voltatile EvolutioN and the European Space Agency Mars Express spacecraft, we show that transient phenomena in the foreshock and solar wind can directly inject energy into the ionosphere of Mars. We demonstrate that the impact of compressive ultralow frequency waves in the solar wind on the induced magnetospheres drive compressional, linearly polarized, magnetosonic ultralow frequency waves in the ionosphere, and a localized electromagnetic "ringing" at the local proton gyrofrequency. The pulsations heat and energize ionospheric plasmas. A preliminary survey of events shows that no special upstream conditions are required in the interplanetary magnetic field or solar wind. Elevated ion densities and temperatures in the solar wind near to Mars are consistent with the presence of an additional population of Martian ions, leading to ion-ion instablities, associated wave-particle interactions, and heating of the solar wind. The phenomenon was found to be seasonal, occurring when Mars is near perihelion. Finally, we present simultaneous multipoint observations of the phenomenon, with the Mars Express observing the waves upstream, and Mars Atmosphere and Voltatile EvolutioN observing the response in the ionosphere. When these new observations are combined with decades of previous studies, they collectively provide strong evidence for a previously undemonstrated atmospheric loss process at unmagnetized planets: ionospheric escape driven by the direct impact of transient phenomena from the foreshock and solar wind

Discrete aurora and the nightside ionosphere of Mars: an EMM–MEX conjunction of FUV imaging, ionospheric radar sounding, and suprathermal electron measurements

Since 2021, a new surge in discrete aurora detections at Mars has been observed by the Emirates Mars Ultraviolet Spectrometer (EMUS) onboard the Emirates Mars Mission (EMM) Hope Orbiter as EMUS started to regularly obtain synoptic auroral images with a high sensitivity. Here we report on a fortuitous conjunction between EMM and Mars Express (MEX) using far ultraviolet (FUV) imaging of discrete aurora by EMM EMUS, in situ measurements of suprathermal electrons by the MEX Analyzer of Space Plasma and Energetic Atoms Electron Spectrometer (ELS), and topside radar sounding of the nightside ionosphere by the MEX Mars Advanced Radar for Subsurface and Ionosphere Sounding (MARSIS). In this event, EMM EMUS imaged a clear discrete aurora signature around moderately strong crustal magnetic fields on the nightside near the dusk terminator, 11 min before which MEX MARSIS measured a prominent local enhancement of the peak electron density in the nightside ionosphere and MEX ELS observed an in situ enhancement of suprathermal electrons at the corresponding location. A remarkable geographic agreement is found between the enhancements of the aurora, ionosphere, and suprathermal electrons, suggesting that the enhanced ionization and auroral emission are caused concurrently by precipitating suprathermal electrons. Subsequent images indicate that the discrete aurora slightly changed its shape in 15 min and mostly disappeared in a few hours. The MEX MARSIS measurements of the auroral ionosphere display overlapping ionospheric and surface echoes indicative of horizontal gradients of the peak electron density. Analysis of the overlapping echoes implies that the auroral ionosphere and electron precipitation could be highly structured with horizontal spatial scales on the order of several tens of km. MEX MARSIS also observed a non-auroral ionospheric enhancement with a wider spatial extent than the local auroral enhancement, suggesting alternative sources of the enhanced nightside ionosphere such as plasma transport. The comparison between the ionospheric structures measured by MEX MARSIS, suprathermal electron flux measured by MEX ELS, and discrete auroral emission imaged by EMM EMUS underscores the complexity of the auroral and non-auroral nightside ionospheres. This motivates further investigations of their sources, transport, and connections to the magnetotail dynamics of Mars.</p

The Electric Wind of Venus: A Global and Persistent Polar Wind -Like Ambipolar Electric Field Sufficient for the Direct Escape of Heavy Ionospheric Ions

Understanding what processes govern atmospheric escape and the loss of planetary water is of paramount importance for understanding how life in the universe can exist. One mechanism thought to be important at all planets is an ambipolar electric field that helps ions overcome gravity. We report the discovery and first quantitative extraterrestrial measurements of such a field at the planet Venus. Unexpectedly, despite comparable gravity, we show the field to be five times stronger than in Earths similar ionosphere. Contrary to our understanding, Venus would still lose heavy ions (including oxygen and all water-group species) to space, even if there were no stripping by the solar wind. We therefore find that it is possible for planets to lose heavy ions to space entirely through electric forces in their ionospheres and such an electric wind must be considered when studying the evolution and potential habitability of any planet in any star system