The rotation period of Uranus was estimated to be 17.24 +/- 0.01 h in 1986 from radio auroral measurements during the brief Voyager 2 flyby. This value is the basis for the Uranian SIII longitude system still in use. However, the poor period uncertainty limited its validity to a few years, after which the orientation of the magnetic axis was lost. Alternate, conflicting, rotation periods have also been proposed since then. Here we use the long-term tracking of Uranus' magnetic poles between 2011 and 2022 from Hubble Space Telescope images of its ultraviolet aurorae to achieve an updated, independent, extremely precise rotation period of 17.247864 +/- 0.000010 h, only consistent with the Voyager 2 estimate. Its 28-s-longer value and improved accuracy yields a new longitude model now valid over decades, up to the arrival of any future Uranus mission, which will allow the reanalysis of the whole set of Uranus observations. In addition, it has strong direct implications for formation scenarios, interior models, dynamo theories and studies of the magnetosphere. This approach stands as a new method to determine the rotation rate of any object hosting a magnetosphere and a rotationally modulated aurorae, in our Solar System and beyond.

We examine the newly discovered phenomena of sinuous aurora on the nightside of Mars, using images of 130.4 and 135.6 nm oxygen emission measured by the Emirates Mars Mission EMUS ultraviolet spectrograph, and upstream measurements from the MAVEN and Mars Express spacecraft. They are detected in similar to 3% of observations, totaling 73 clear detections. These emissions are narrow, elongated (1,000-6,000 km), cross Mars' UV terminator, and are oriented generally toward the anti-solar point, clustering into north, south, east, and west-oriented groups. Diverse morphologies are observed, though some spatial features, such as broad curves, may in some cases be due to temporal aliasing of aurora motion as each image is built up over 15-20 min. Sinuous aurora form away from Mars' strongest crustal magnetic fields and can be interrupted by moderate crustal fields. Sinuous aurora occurrence increases strongly with solar wind pressure, though brightness shows only a weak positive dependence on pressure. Interplanetary magnetic field (IMF) clock angle affects their occurrence and orientation: sinuous aurora show a broad range of orientations centered on the solar wind convection electric field (Econv) direction and forming in the +Econv hemisphere, although with moderate clockwise and counterclockwise average "twists" for westward and eastward IMF, respectively. From these features we infer a link between sinuous aurora and electron energization in Mars' magnetotail current sheet, where field geometry on the +Econv side of the sheet is more organized and symmetric. Determination of specific triggering conditions for sinuous aurora requires further investigation. Sinuous aurora are narrow, extended patterns of UV emission caused by long, thin channels of energized electrons striking Mars' nightside upper atmosphere. We study images of these aurora taken by the Emirates Mars Mission EMUS instrument. 73 cases of sinuous auroras were found (similar to 3% occurrence rate) with lengths ranging from 1,000 to 6,000 km. These auroras usually cross Mars' day-night boundary and extend in the direction opposite to the Sun. They tend to cluster into groups oriented toward the north, south, east, and west directions with a diverse array of shapes. Sinuous aurora generally form away from Mars' strongest crustal magnetic fields. They occur more frequently for higher solar wind pressure. Their orientations are affected by the interplanetary magnetic field (IMF), displaying a broad range of orientations centered on the direction of the electric field in the solar wind, and forming in the hemisphere to which this electric field points, although with moderate counterclockwise and clockwise average "twists" for eastward and westward IMF, respectively. From these features we infer a link between sinuous aurora and a sheet of current in Mars magnetic tail, wherein the aurora-causing electrons may be energized before falling into the upper atmosphere to produce aurora. These narrow emission features form away from strong crustal fields, oriented anti-sunward, cross the terminator, are detected in 3% observations Occurrence increases with solar wind pressure, certain interplanetary magnetic field orientations, and in the positive motional electric field hemisphere Sinuous aurora may be related to magnetotail asymmetry and electron energization processes occurring in the tail current sheet

The global nature of the interaction of the heliosphere and the Local Interstellar Medium (LISM) is among one of the most outstanding space physics problems of today. Ultimately, our magnetic bubble is upheld by the expanding solar wind born in the solar corona that is now accessible by Parker Solar Probe. At the other extreme boundary, a completely new regime of physical interactions is at work that shape the unseen global structure of the entire heliosphere. Voyager 1 and 2 are soon nearing their end of operations inside of 170 AU and their payloads dedicated to planetary science have uncovered a region of space that defies our understanding. At the same time, IBEX and Cassini have obtained complementary “inside-out” ENA images of the heliospheric boundary region that cannot be fully explained. An Interstellar Probe through the heliospheric boundary, in to the LISM would be the first dedicated mission to venture into this largely unexplored frontier of space. With a dedicated suite of in-situ and remote-sensing instrumentation, such a probe would not only open the door for a new regime of space physics acting at the boundary and in other astrospheres, but would also obtain the very first images from the outside of the global structure of the heliosphere that, in context with the in-situ measurements would enable a quantum leap in understanding the global nature of our own habitable astrosphere. Beyond the Heliopause, the Interstellar Probe would offer the first sampling of the properties of the Local Interstellar Cloud and interstellar dust that are completely new scientific territories. Relatively modest contributions across divisions would offer historic science returns, including a flyby of one or two Kuiper Belt Objects, first insights in to the structure of the circum-solar dust disk, and the first measurements of the Extra-galactic Background Light beyond the obscuring Zodiacal cloud. In summary, an Interstellar Probe would represent humanity’s first step in to the galaxy and become the farthest space exploration ever undertaken. The idea of an Interstellar Probe and a Solar Probe shares a common beginning as two of the “Special Probes” that the Simpson Committee carried forward in their Interim Report to the Space Studies Board in 1960. Since then, an Interstellar Probe has scientifically been highly rated in the Solar and Space Physics Decadal Surveys, but the lack of propulsion technologies and launch vehicles have presented a stumbling block for its realization. However, this bottleneck is now being removed with the development of the Space Launch System (SLS) Block 2 with first launch projected to end of the 2020’s. A study funded by NASA is now progressing towards its third year of developing realistic mission architectures for an Interstellar Probe using technology ready for launch beginning 2030. An SLS Block 2, with an Atlas Centaur 3rdstage, a Star 48 4th stage could propel a spacecraft up to about 8.5 AU/year, which would be more than twice the fastest escaping spacecraft (Voyager 1 at 3.6 AU/year). The scenario would use a direct inject to Jupiter followed by a Jupiter Gravity assist powered by the 4th stage. The mission trade space is bound by requirements to be able to operate out to 1000 AU, 600 W of power beginning of mission, and survive up to 50 years. Here, we discuss the outstanding science questions that could be addressed by a mission to the LISM, notional science payload and report on realistic mission architectures, design concepts and trades, enabling technologies, and programmatic challenges.

Energetic Neutral Atom (ENA) cameras on orbiting spacecraft at Earth and Saturn have helped greatly to diagnose these complex magnetospheres. Within this decade, the European Space Agency’s Jupiter Icy Moons Explorer (JUICE) mission will arrive at Jupiter and make ENA imaging a major thrust in helping to understand its complex magnetosphere. The present polar-orbiting Juno mission carries no ENA camera, but the energetic particle JEDI instrument is serendipitously sensitive to ENA’s with energies > 50 keV, provided there are no charged particles in the environment to mask their presence. Juno offers great service to the interpretation of both past and future ENA imaging with its orbit allowing unique viewing perspectives. Here we report on several components of ENA emissions that can probe the dynamical state of the regions involved, including the space environment of the orbit of Io, that of Europa, and Jupiter itself. A special focus here will be new observations of ENA emissions from Jupiter’s polar regions, the proper interpretation of which may end up being unique to the Juno mission, even after the JUICE mission.

A mission that traverses through our solar system, past the boundaries of our heliosphere, and out of our habitable astrosphere to the very local interstellar medium (VLISM) provides a unique opportunity for various in-situ and remote observations during this long journey. The Interstellar Probe mission concept explores a near term, pragmatic basis for designing such a mission, prioritizing critical science measurements while identifying and working with the engineering constraints that come with a long duration mission operating far away from Earth. One of the many challenges of such a mission is selecting instrumentation that will collectively meet science requirements over a long baseline. In order to accomplish this, a variety of instruments will be need to be included in the payload, while keeping in mind size, mass, and power constraints for the mission. These may include particle and field sensors, imaging spectrometers, spectrographs, mass spectrometers, and dust analyzers.Magnetometers (MAG), placed on a boom away from the spacecraft, will be one of the most critical instruments in the payload. With the exception of composition analysis and particle detection, magnetometers are capable of answering many questions related to the nature of the heliosphere, VLISM, and interactions between the two. While both vector helium magnetometers and fluxgate magnetometers have heritage, due to the lengthy duration of this mission fluxgates may provide a more reliable instrument.Another set of critical instruments will be a particle suite that covers a wide range of energies. Particle sensors will play a key role in learning more about our heliosphere and VLISM, providing insight into everything but the neutral hydrogen wall. The suite would most likely include four sensors. First, a plasma system (PLS) would detect thermal ions and electrons up through light pick-up ions (PUI) with energies in the 10s-10000s eV. Detecting energetic ions, electrons, inner source PUIs, and PUI in the ISM would require an energetic particle system and dedicated pick-up ion instrument (EPS and PUI) for particles with energies 10s-1000s keV. A cosmic ray system (CRS) would account for the highest energy particles, observing anomalous cosmic rays (ACRs) and galactic cosmic rays (GCRs) with energies most likely ranging from 1-1000 MeV. Each of these systems would need as close to full coverage of the sky as possible, most likely achieved through angular coverage provided by a spinning spacecraft.The final particle and field sensor that might be included on such a mission is a plasma wave instrument (PWI). This would support measurements made by the magnetometers and particle suite, enabling a better understanding of the size and shape of the heliosphere, particle acceleration in shock regions and the heliosheath, the structure and nature of the heliopause, and properties of the VLISM and GCR spectra outside the heliopause. While the measurements would most likely be made with four components spaced 90° from each other, all perpendicular to ram direction, determining the length and type of antenna used for this instrument is a trade between plasma wave science, guidance navigation and control capabilities, and mission operations.Another critical sensor suite would involve energetic neutral atom (ENA) imagers, where the suite might include one or more imagers designed to image at different energy levels (the low energy ENA-L at 10-2000 eV, medium energy ENA-M at 0.5-15 keV, and high energy ENA-H at 1-100 keV). ENA imagers would result in a better understanding of the force balance and ENA ribbon, as well as solar/heliosphere/VLISM interaction and influence on each other. In particular, an ENA-H that has the capability to point back at our heliosphere once we are well into the VLISM would allow scientists to gain insight into what our astrosphere looks like from the outside. While the two lower energy ENA imagers would only require noseward hemisphere angular coverage, in order to perform the study of the heliosphere from the outside the ENA-H would need full sky coverage with a sun exclusion zone.A neutral mass spectrometer (NMS) would provide key compositional insight during the mission by measuring neutral gas and dust in the VLISM, as well as the neutral hydrogen wall and neutral ISM gas and dust inside the heliosphere. Direct measurements of elemental and isotopic gas compositions of the VLISM would place an important constraint on models of stellar nucleosynthesis which holds implications for the formation of matter in the galaxy. This would enable a much better understanding of the properties and potential history of the ISM as a whole. The instrument would be placed facing the ram direction. Co-boresighted to perform complementary measurements to the NMS would be an Interstellar Dust Analyzer (IDA), which would further establish properties of the VLISM and how it affects our heliosphere. It would also provide important insight into the formation of planetary systems through the examination of interplanetary dust.There are additional choices that could augment these core instruments, including a Lyman-alpha spectrograph (LYA) to provide vital information about interplanetary and VLISM hydrogen phasespace density, imaging spectrometers in the ultraviolet/visible/infrared (UVS/VIR) to study planet formation in the solar system by examining the debris disk and potential nearby Kuiper Belt objects and dwarf planets, and a visIR spectral mapper (IRM) to observe the diffuse red-shifted light emitted by the universe beyond the dominant Zodiacal cloud foreground that obfuscates such studies when performed within our heliosphere.Taking the science objectives into account along with size, mass, and power constraints, two example payloads were developed for the Interstellar Probe concept study: one baseline payload which focuses on heliophysics objectives and an augmentation payload which accommodates a visNIR imager and the visIR mapper for performing a dwarf planet flyby and studying the extragalactic background light in addition to core heliophysics instrumentation. This presentation provides an overview of these example payloads, their accommodation on the spacecraft, and reliability issues associated with requiring up to 50 years of functionality.

The goal of NASA’s Europa Clipper mission is to assess the habitability of Jupiter’s moon Europa. After entering Jupiter orbit in 2030, the flight system will collect science data while flying past Europa 49 times at typical closest approach distances of 25–100 km. The mission’s objectives are to investigate Europa’s interior (ice shell and ocean), composition, and geology; the mission will also search for and characterize any current activity including possible plumes. The science objectives will be accomplished with a payload consisting of remote sensing and in-situ instruments. Remote sensing investigations cover the ultraviolet, visible, near infrared, and thermal infrared wavelength ranges of the electromagnetic spectrum, as well as an ice-penetrating radar. In-situ investigations measure the magnetic field, dust grains, neutral gas, and plasma surrounding Europa. Gravity science will be achieved using the telecommunication system, and a radiation monitoring engineering subsystem will provide complementary science data. The flight system is designed to enable all science instruments to operate and gather data simultaneously. Mission planning and operations are guided by scientific requirements and observation strategies, while appropriate updates to the plan will be made tactically as the instruments and Europa are characterized and discoveries emerge. Following collection and validation, all science data will be archived in NASA’s Planetary Data System. Communication, data sharing, and publication policies promote visibility, collaboration, and mutual interdependence across the full Europa Clipper science team, to best achieve the interdisciplinary science necessary to understand Europa.

Abstract Mercury's small magnetosphere is embedded in the dynamic and intense solar wind environment characteristic of the inner heliosphere. Both the magnitude and orientation of the interplanetary magnetic field (IMF) significantly influence the solar wind‐magnetospheric interaction at Mercury, driving phenomena such as magnetic reconnection. The MErcury Surface, Space Environment, Geochemistry and Ranging (MESSENGER) spacecraft provided in‐situ magnetic field measurements of the solar wind, the magnetosheath, and the magnetosphere along each orbit. However, it is a challenge to directly assess the IMF's impact on Mercury's plasma environment due to the temporal separation between observations within the solar wind and the magnetosphere, especially in the absence of an upstream monitor. Here, we present a feedforward neural network (FNN) trained on a subset of magnetosheath observations to estimate the strength and orientation of the IMF upstream of the bow shock. Utilizing magnetosheath magnetic field, cylindrical spatial coordinates, and heliocentric distance measurements, the FNN predicts upstream IMF conditions with an r2 score of 0.70 and mean averaged error of 5.3 nT, thereby greatly decreasing the temporal separation between IMF estimates and magnetospheric measurements throughout the MESSENGER mission. This approach yields IMF estimates for all magnetosheath data measured by MESSENGER, providing a useful tool for future investigations of the IMF impact on Mercury's magnetosphere. This method will be integrable with the dual‐spacecraft BepiColombo magnetosheath measurements, providing useful estimates of upstream IMF conditions particularly during the extended periods in which neither spacecraft sample the solar wind. Our results demonstrate the utility of machine learning techniques on advancing space science research.

During its evolution, the Sun and its protective magnetic bubble – the heliosphere - has completed nearly twenty revolutions around the Galactic Core. During this “Solar Journey” it has plowed through widely different interstellar environments that have all shaped the system we live in today. The orders-of-magnitude differences in interstellar properties have had dramatic consequences for the penetration of interstellar material and have affected elemental and isotopic abundances, atmospheric evolution and perhaps even conditions for habitability. As far as we know, only some 60, 000 years ago, the Sun entered what we call the Local Interstellar Cloud (LIC), and in less than 1,900 years the Sun will be entering a very different interstellar environment that will continue to shape its evolution and fate.The Interstellar Probe is a pragmatic mission with a possible launch already in the next decade that would explore the heliospheric boundary and how it interacts with the Very Local Interstellar Medium (VLISM) to understand the current state along this Solar Journey and, ultimately understand where our home came from, and where we are going. During its 50-year nominal design life, it would go far beyond where the Voyager missions have gone, out to about 400 astronomical units (au) and likely survive out to 1000 au. Therefore, the Interstellar Probe mission would represent humanity’s first explicit step in to the galaxy and become NASA's boldest step in space exploration.When the Voyager missions traversed the heliospheric boundary with their very limited payload it became clear that we are faced with a whole new regime of space physics that is not only decisive for our own heliosphere, but also for understanding the physics of other astrospheres as well. Today we still do not understand the force that is upholding the magnetic shell (the heliosheath) around our heliosphere, or the mechanisms that shield the solar system from galactic cosmic rays, and many other mysteries. Once beyond where the furthest Voyager spacecraft will cease operations (likely at ~170 au), Interstellar Probe would step in to the unknown, traverse the hydrogen wall and the complex magnetic topology at the very edge of the Sun’s sphere of influence, and then directly sample for the first time the interstellar material that has made all of us. There, measurements of the unperturbed gas, plasma, and fields would allow accurate determination of the current state of the LIC and how it affects the global heliosphere. Measurements of unshielded interstellar dust and galactic cosmic rays would provide unprecedented information on stellar and galactic evolution. The physical processes that occur as the solar wind and magnetic field interact with VLISM would also provide the only directly measurable prototypes for understanding the astrospheres surrounding other stars that control the atmospheres and habitability of their exoplanets. All this newly acquired knowledge would then enable an understanding of the current state of the heliosphere and the VLISM, and how they interact, which ultimately can be used to extrapolate the understanding of our system back to the past and into the future.At the same time, the outward trajectory is a natural opportunity for exploring one of the ~4,000 Kuiper Belt Objects or ~130 dwarf planets similar to and beyond Pluto and determine the large-scale structure of the circum-solar dust disk to provide the ground truth for planetary system formation in general. Once beyond the obscuring dust, the infrared sky would open a window to early galaxy formation.An Interstellar Probe has been discussed and studied since 1960, but the stumbling block has always been propulsion. Now this hurdle has been overcome by the availability of new and larger launch vehicles. An international team of scientists and experts are now in the final year of a NASA-funded study led by The Johns Hopkins University Applied Physics Laboratory (APL) to develop pragmatic example mission concepts for Interstellar Probe with a nominal design lifetime of 50 years. Together with the Space Launch System (SLS) Program Office at NASA’s Marshall Space Flight Center, the team has analyzed dozens of launch configurations and demonstrated that asymptotic speeds in excess of 7.5 au per year can be achieved using existing or near-term propulsion stages with a powered or passive Jupiter Gravity Assist (JGA). These speeds are more than twice that of the fastest escaping man-made spacecraft to date, which is Voyager 1 currently at 3.59 au/year. Launching near the nose direction of the heliosphere, Interstellar Probe would therefore reach the Termination Shock (TS) in less than 12 years and cross the Heliopause into the VLISM after about 16 years from launch.In this presentation we provide an overview and update of the study, the science mission concept, the compelling discoveries that await, and the associated example science payload, measurements and operations ensuring a historic data return that would push the boundaries of space exploration by going where no one has gone before.

We present a case study of plasma and magnetic field observations in the Martian magnetotail using data from the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission during an orbit when the spacecraft was in the optical shadow, past the dusk terminator and downstream of the strongest crustal magnetic fields. In this region, we observed multiple magnetic field rotations (a signature of currents) closely associated with energized (up to 100 eV) electron populations. Several transitions between closed and draped magnetic topologies also occur in this region, which are likely to be caused by magnetic reconnection between the interplanetary magnetic field (IMF) and crustal magnetic fields. We also observe two regions of energized, counter-streaming electrons, which are rare in the magnetotail, but twice as likely to occur downstream of strong crustal magnetic fields when they are near the evening terminator. Together, the multiple magnetic field rotations, topological changes, and counter streaming electrons suggest the presence of an electric potential structure similar to those observed above the auroral arc regions at Earth.

On 26-27 December 2022, Mars experienced an extremely low-density solar wind stream, which was encountered first by Earth because of the radial alignment of the two planets (i.e., Mars opposition). During this event, two important properties of the ionospheric and magnetospheric states changed significantly in response to the low solar wind ram pressure, as inferred from the superthermal electron observations from the Mars Atmospheric and Volatile EvolutioN (MAVEN) mission. The interface between the ionosphere and magnetosphere expanded to thousands of kilometers, outside of the nominal bow shock locations, coinciding with the expansion of the cold planetary ions. Meanwhile, the ambipolar electrostatic potential arising from the ionospheric electron pressure gradient increased from the nominal similar to -0.7 to similar to -2 V (relative to the lower ionosphere). This enhanced ambipolar potential likely facilitated the observed ionosphere expansion. This study characterizes Mars's magnetospheric and ionospheric response to the disappearing solar wind event in December 2022 During the event, open and closed field lines extend beyond the nominal bow shock location, just as the planetary cold ions The ionospheric ambipolar potential drop is enhanced from the nominal similar to -0.7 to similar to -2 V, likely facilitating the ionosphere expansion

Ultraviolet Imaging Spectrograph (UVIS) observations show the Enceladus auroral footprint on Saturn on 2017 September 14, near the end of the Cassini mission. A series of Saturn north polar auroral images were obtained by slowly slewing the Cassini spacecraft at right angles to the UVIS long slit. The images were limb-fit to improve the spacecraft geometry. Enhanced extreme-ultraviolet 88–118 nm channel emissions due to electron impact on atomic and molecular hydrogen were seen in the expected location for the Enceladus auroral footprint on five successive images spanning almost 4 hr. Enhanced emissions were also seen in simultaneously obtained far-ultraviolet 111–165 nm images in at least two of these images, with the spectral signature expected for auroral emissions. While most Cassini UVIS auroral images do not show the Enceladus auroral footprint, these 2017 images support the earlier detection of an Enceladus-linked spot on Saturn in 2008 Cassini UVIS data.

Jupiter's icy moon, Europa, harbors a subsurface liquid water ocean; the prospect of this ocean being habitable motivates further exploration of the moon with the upcoming NASA Europa Clipper mission. Key among the mission goals is a comprehensive assessment of the moon's composition, which is essential for assessing Europa's habitability. Through powerful remote sensing and in situ investigations, the Europa Clipper mission will explore the composition of Europa's surface and subsurface, its tenuous atmosphere, and the local space environment surrounding the moon. Clues on the interior composition of Europa will be gathered through these assessments, especially in regions that may expose subsurface materials, including compelling geologic landforms or locations indicative of recent or current activity such as potential plumes. The planned reconnaissance of the icy world will constrain models that simulate the ongoing external and internal processes that act to alter its composition. This paper presents the composition-themed goals for the Europa Clipper mission, the synergistic, composition-focused investigations that will be conducted, and how the anticipated scientific return will advance our understanding of the origin, evolution, and current state of Europa.

While the near-term Interstellar Probe mission will revolutionize our understanding of the astrosphere in which we live, it will provide only a snapshot of the history of the heliosphere.Trans-Neptunian objects (TNOs), with numerous options conveniently located along whichever Interstellar Probe trajectory would ultimately be chosen, provide an opportunity to examine the history of the heliosphere measurable in the colors, spectra, and geologies of their surfaces.Interstellar Probe with a planetary augmentation would enable a scientifically rich close flyby of a TNO along with "remote" observations.The spacecraft can function as an in situ observatory to study TNOs up to 2 -3 au away, an order of magnitude closer than they are to the Earth.

We outline specific steps that NASA and the space science community can take to advance collaboration and coordination between the communities represented by the four NASA Science Mission Directorate Divisions. It is important to note that the only way that this effort can succeed is if NASA initiates and supports it through directed resources.

Heliophysics is the field that "studies the nature of the Sun, and how it influences the very nature of space - and, in turn, the atmospheres of planetary bodies and the technology that exists there." However, NASA's Heliophysics Division tends to limit study of planetary magnetospheres and atmospheres to only those of Earth. This leaves exploration and understanding of space plasma physics at other worlds to the purview of the Planetary Science and Astrophysics Divisions. This is detrimental to the study of space plasma physics in general since, although some cross-divisional funding opportunities do exist, vital elements of space plasma physics can be best addressed by extending the expertise of Heliophysics scientists to other stellar and planetary magnetospheres. However, the diverse worlds within the solar system provide crucial environmental conditions that are not replicated at Earth but can provide deep insight into fundamental space plasma physics processes. Studying planetary systems with Heliophysics objectives, comprehensive instrumentation, and new grant opportunities for analysis and modeling would enable a novel understanding of fundamental and universal processes of space plasma physics. As such, the Heliophysics community should be prepared to consider, prioritize, and fund dedicated Heliophysics efforts to planetary targets to specifically study space physics and aeronomy objectives.

Characterizing Europa’s subsurface ocean is essential for assessing Europa’s habitability. The suite of instruments on the Europa Clipper spacecraft will, among others, magnetically sound Europa’s interior by measuring the ocean’s induced magnetic field. This magnetic field is generated in response to the Jovian time-varying magnetic environment in which Europa is immersed. However, the dynamic magnetized plasma flow of the Jovian magnetosphere creates electrical currents that give rise to magnetic perturbations near Europa. These perturbations complicate the interpretation of the induction signal, and hence the characterization and inferences on potential habitability. Thus, characterization of the ocean by magnetic sounding requires an accurate characterization of the plasma as it flows across Europa. We present the Plasma Instrument for Magnetic Sounding (PIMS), the instrument for the Europa Clipper mission that will measure the plasma contribution to the magnetic field perturbations sensed by the Europa Clipper Magnetometer. PIMS is composed of four Faraday Cup plasma spectrometers that use voltage-biased gridded apertures to dissect the space plasmas that they encounter. The instrument uses sensitive preamplifiers and processing electronics to measure the current that results when charged particles strike the instrument’s metal collector plates, thus enabling a measure of the plasma characteristics near Europa to produce a more accurate magnetic sounding of Europa’s subsurface ocean. PIMS consists of two sensors: one placed near the top of the Europa Clipper spacecraft and one near the bottom. Each sensor contains two Faraday Cups with a 90° full-width field-of-view. The sensors were specifically designed to withstand the Europa environment, measure both ions and electrons, and have two separate voltage ranges intended to analyze the magnetospheric and ionospheric environments, respectively. In this paper, we describe the scientific motivation for this experiment, the design considerations for the PIMS instrument, the details of the ground calibration, and other details pertinent to understanding the scientific data retrieved by PIMS.

Benefiting from a large orbit and high sensitivity, the Emirates Mars mission EMUS instrument has provided the first opportunity to regularly image Mars’ discrete FUV aurora synoptically. EMUS has collected nearly 1000 synoptic observations of the Mars nightside have revealed at least three distinct types of discrete Aurora: 1) crustal field aurora, appearing in regions of mostly radial crustal magnetic fields, 2) patchy discrete aurora, observed away from strong crustal fields, and 3) sinuous discrete aurora, extending from the terminator typically thousands of kilometers onto the nightside, away from crustal fields.Sinuous Discrete Aurora (SDA) is observed in approximately 5% of observations and is characterized by 2 primary attributes: morphology and the local time of its intersection with the terminator. Morphologies include serpentine, approximately linear, and short/lumpy. Dusk-side SDA does not occur preferentially for any particular interplanetary magnetic field (IMF) orientation, while Dawn and Midnight SDA appear to show a preference for northeastward IMF directions measured in situ by the MAVEN spacecraft. Dusk SDA observed about twice as often as Dawn or Midnight SDA. SDA reflect conditions whereby particular magnetic topologies connect the nightside atmosphere to a source of abundant electrons, whether dayside photoelectrons or sufficiently energetic magnetotail/sheath electrons. In particular, midnight sinuous discrete aurora appear to be a projection of the tail current sheet, a persistent but highly variable feature of Mars’ double-lobed magnetotail resulting from the draping of the IMF around the conducting obstacle of Mars’ dayside ionosphere. This interpretation is supported by magnetohydrodynamic (MHD) simulations, showing that the orientation of the tail current sheet approximately matches the orientation of midnight SDA.EMM EMUS promises to be an invaluable tool in helping to understand the drivers of Martian Aurora.

We present an overview of the radiation environment monitoring program planned for the Europa Clipper mission. The harsh radiation environment of Jupiter will be measured by a dedicated Radiation Monitor (RadMon) subsystem, yielding mission accumulative Total Ionizing Dose (TID) and instantaneous electron flux measurements with a 1-Hz cadence. The radiation monitoring subsystem is comprised of a stand alone sensor assembly along with distributed TID assemblies at various locations on the spacecraft. The sensor assembly itself is made of a TID sensor stack using the Metal-Oxide Semiconducting Field-Effect Transistor (MOSFET) and a Charge Rate Monitor (CRM) that uses a stack of bulk charge collection plates. The TID measurements will provide the critical information about the overall radiation levels relevant to the degradation of electronics over time, and the electron flux data can serve as a proxy for the Internal ElectroStatic Discharge (IESD) environment by measuring the >∼1 MeV electron environment. In addition, the radiation monitoring subsystem data will be augmented by serendipitous radiation data from science instruments onboard. This will be enabled by careful modeling and analysis of opportunistic background data from potentially the following instruments: Europa Imaging System (EIS), Europa-Ultraviolet Spectrograph (Europa-UVS), Mapping Imaging Spectrometer for Europa (MISE), MAss Spectrometer for Planetary EXploration (MASPEX), Plasma Instrument for Magnetic Sounding (PIMS), and SUrface Dust Analyzer (SUDA). Based on the current analysis, these instruments will be most sensitive to >1 MeV electrons. As such, the high-energy electron data obtained by the radiation monitoring subsystem will be qualitatively and quantitatively enhanced by the high-energy electron data acquired by the instruments. The holistic radiation monitoring program for the mission will be an extensive collaboration among many teams across the flight and payload systems. Although the radiation monitoring subsystem itself is an engineering resource for the mission, the collective data from the mission can also be used to improve the scientific understanding of the Jovian magnetosphere and the high-energy electron environment near Europa, where the motion of charged particles is perturbed by the local electromagnetic environment. The data could also help in the understanding of the radiation modification of Europa surface compounds, which could subsequently help guide lab experiments to aid in understanding the origin and evolution of surface materials and in constraining the interpretation of observational data. To this end, the radiation monitoring subsystem is a useful resource for helping address the Europa Clipper mission’s primary goal of assessing the habitability of Europa.

Simultaneous infrared observations of H3+ ${\mathrm{H}}_{3}<<^>>{+}$ and H2 emissions from Jupiter's northern aurora using the Near Infrared Spectrograph at Keck Observatory were used to measure the ionospheric and thermospheric wind velocities. H3+ ${\mathrm{H}}_{3}<<^>>{+}$ ions supercorotate near the dawn auroral oval and subcorotate across the dusk sector and in the dawn polar region relative to the planetary rotation rate, broadly in agreement with past observations and models. An anticyclonic vortex is discovered in H2 flows, closely matching the mean magnetospheric subcorotation when the observed magnetospheric flows are averaged azimuthally. In comparing ion and neutral winds, we measure the line-of-sight effective ion drift in the neutral reference frame for the first time, revealing two blue-shifted sunward flows of similar to 2 km/s. Observed H3+ ${\mathrm{H}}_{3}<<^>>{+}$ and H2 emissions overlap with predictions of the Pedersen conductivity layer, suggesting two different regions of the ionosphere: (a) a deep layer, where neutral forces dominate the thermosphere and symmetric breakdown-in-corotation currents can close, and (b) a higher layer, where the observed effective ion drift allows dawn-to-dusk Pedersen currents within the upper atmosphere, in turn closing asymmetric currents within the magnetosphere. This ionospheric structure aligns well with recent Juno observations of Jupiter's aurora. The detected thermospheric vortex implies the driving of neutral flows by the momentum from the magnetosphere within the thermosphere and deeper in the atmosphere to potentially 20 mbar. Jovian neutral thermosphere might bridge the gap between current observations and modelings and perhaps be significant to the dynamics of aurora on Earth and other outer planets. We observed both charged and neutral molecules in Jupiter's northern aurora from the Keck Observatory. The velocity of the charged particles shows that they are controlled by magnetic field lines that stretch into the surrounding space environment, as expected at the top of the atmosphere. However, neutrals at the top of the atmosphere also appear to be indirectly controlled by the magnetic field, driven by impacts with the ions into a large vortex that sits within Jupiter's auroral region. Because the charged and neutral molecules move differently from one another, this can drive high-altitude currents. Charged particles flow through the neutrals in two jets, moving toward the Sun on both sides of Jupiter's aurora, driving asymmetric currents more like the system of currents that form Earth's aurora. It suggests that Jupiter has different currents closing at different altitudes in the auroral region. This layering of currents matches recent observations made by the Juno mission and may help explain some of the apparent conflicts between different Juno data sets. Our discovery also highlights the importance of interactions between charged and neutral particles on other planets, including Earth, making Jupiter an important comparator for future studies of these interactions. An aurorally aligned subcorotational thermospheric vortex is detected in Jupiter's upper atmosphereTwo sunward ionospheric jets flowing through the thermosphere are revealed on both dawn and duskJupiter potentially has a multilayer ionosphere driven separately by asymmetric currents and breakdown-in-corotation Pedersen currents

The Galileo mission to Jupiter revealed that Europa is an ocean world. The Galileo magnetometer experiment in particular provided strong evidence for a salty subsurface ocean beneath the ice shell, likely in contact with the rocky core. Within the ice shell and ocean, a number of tectonic and geodynamic processes may operate today or have operated at some point in the past, including solid ice convection, diapirism, subsumption, and interstitial lake formation. The science objectives of the Europa Clipper mission include the characterization of Europa’s interior; confirmation of the presence of a subsurface ocean; identification of constraints on the depth to this ocean, and on its salinity and thickness; and determination of processes of material exchange between the surface, ice shell, and ocean. Three broad categories of investigation are planned to interrogate different aspects of the subsurface structure and properties of the ice shell and ocean: magnetic induction, subsurface radar sounding, and tidal deformation. These investigations are supplemented by several auxiliary measurements. Alone, each of these investigations will reveal unique information. Together, the synergy between these investigations will expose the secrets of the Europan interior in unprecedented detail, an essential step in evaluating the habitability of this ocean world.