Large‐Amplitude Oscillatory Motion of Mercury’s Cross‐Tail Current Sheet

We surveyed 4 years of MESSENGER magnetic field data and analyzed intervals with observations of large‐amplitude oscillatory motions of Mercury’s cross‐tail current sheet, or flapping waves, characterized by a decrease in magnetic field intensity and multiple reversals of BX, oscillating with a period on the order of ~4 – 25 seconds. We performed minimum variance analysis (MVA) on each flapping wave event to determine the current sheet normal. Statistical results showed that the flapping motion of the current sheet caused it to warp and tilt in the y‐z plane, which suggests that these flapping waves are kink‐type waves propagating in the cross‐tail direction of Mercury’s magnetotail. The occurrence of flapping waves shows a strong preference in Mercury’s duskside plasma sheet. We compared our results with the magnetic double‐gradient instability model and examined possible flapping wave excitation mechanism theories from internal (e.g., finite gyroradius effects of planetary sodium ions Na+ on magnetosonic waves) and external (e.g., solar wind variations and K‐H waves) sources.Key PointsLarge‐amplitude oscillations of Mercury’s cross‐tail current sheet (or flapping waves) with period of ~4 – 25 s were observedFlapping motion of Mercury’s cross‐tail current sheet warped and tilted the current sheet in the y‐z planeFlapping waves preferentially occur in Mercury’s duskside current sheetPeer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/156232/2/jgra55803.pdfhttp://deepblue.lib.umich.edu/bitstream/2027.42/156232/1/jgra55803_am.pd

Lunar Surface Electric Potential Changes Associated with Traversals through the Earth's Foreshock

We report an analysis of one year of Suprathermal Ion Detector Experiment (SIDE) Total Ion Detector (TID) resonance events observed between January 1972 and January 1973. The study includes only those events during which upstream solar wind conditions were readily available. The analysis shows that these events are associated with lunar traversals through the dawn flank of the terrestrial magnetospheric bow shock. We propose that the events result from an increase in lunar surface electric potential effected by secondary electron emission due to primary electrons in the Earth's foreshock region (although primary ions may play a role as well). This work establishes (1) the lunar surface potential changes as the Moon moves through the terrestrial bow shock, (2) the lunar surface achieves potentials in the upstream foreshock region that differ from those in the downstream magnetosheath region, (3) these differences can be explained by the presence of energetic electron beams in the upstream foreshock region and (4) if this explanation is correct, the location of the Moon with respect to the terrestrial bow shock influences lunar surface potential

Next generation magnetic field measurements from low-earth orbit satellites enable enhanced space weather operations

Large-scale current systems in the ionosphere and the magnetosphere are intimately controlled by the solar wind-magnetosphere interaction and the magnetosphere-ionosphere coupling. During space weather events, these currents reconfigure and intensify significantly in response to enhanced solar wind-magnetosphere interaction, facilitating explosive energy input from the magnetosphere into the ionosphere-thermosphere system and inducing electric current surges in electric power systems on the ground. Therefore, measurements of magnetic manifestations associated with the dynamic changes of the current systems are crucial for specifying the energy input into the ionosphere-thermosphere system, understanding energy dissipation mechanisms, and predicting the severity of their space weather impacts. We investigate the potential uses of high-quality magnetic field data for space weather operations and propose real-time data products from next generation constellation missions that enable improved space weather forecasting and mitigation. &nbsp;</p

Mosaic: A Satellite Constellation to Enable Groundbreaking Mars Climate System Science and Prepare for Human Exploration

The Martian climate system has been revealed to rival the complexity of Earth\u27s. Over the last 20 yr, a fragmented and incomplete picture has emerged of its structure and variability; we remain largely ignorant of many of the physical processes driving matter and energy flow between and within Mars\u27 diverse climate domains. Mars Orbiters for Surface, Atmosphere, and Ionosphere Connections (MOSAIC) is a constellation of ten platforms focused on understanding these climate connections, with orbits and instruments tailored to observe the Martian climate system from three complementary perspectives. First, low-circular near-polar Sun-synchronous orbits (a large mothership and three smallsats spaced in local time) enable vertical profiling of wind, aerosols, water, and temperature, as well as mapping of surface and subsurface ice. Second, elliptical orbits sampling all of Mars\u27 plasma regions enable multipoint measurements necessary to understand mass/energy transport and ion-driven escape, also enabling, with the polar orbiters, dense radio occultation coverage. Last, longitudinally spaced areostationary orbits enable synoptic views of the lower atmosphere necessary to understand global and mesoscale dynamics, global views of the hydrogen and oxygen exospheres, and upstream measurements of space weather conditions. MOSAIC will characterize climate system variability diurnally and seasonally, on meso-, regional, and global scales, targeting the shallow subsurface all the way out to the solar wind, making many first-of-their-kind measurements. Importantly, these measurements will also prepare for human exploration and habitation of Mars by providing water resource prospecting, operational forecasting of dust and radiation hazards, and ionospheric communication/positioning disruptions

Low frequency plasma waves at Mars

Mars Global Surveyor's magnetometer/electron reflectometer (MAG/ER) experiment has returned over eight years of observations of low frequency plasma waves produced in the interaction of the solar wind with the Martian ionosphere. Using the MAG/ER data, I identify the properties and physical origins of the waves in the magnetosheath, magnetic pileup region, and ionosphere. I find that the waves in the dayside magnetosheath are predominately mirror mode instabilities produced by plasma temperature anisotropies arising from the draping of the solar wind magnetic field around the ionosphere. The nightside magnetosheath shows evidence for resonant ion instabilities arising from the interaction of the solar wind plasma with the ionospheric plasma. These waves are therefore an indirect observation of ongoing atmospheric loss at Mars. During the large solar storm of October 2003, dramatic changes were observed in the plasma waves present; even the normally placid tail region showed signs of significant wave activity. Coherent oscillations are observed in the ionosphere and are presumably driven by solar wind fluctuations or are associated with field line resonances along crustal fields

The Martian Magnetosphere: Areas of Unsettled Terminology

The near-Mars space environment has a number of regions and boundaries that have numerous and confusing labels. The whole region is sometimes referred to as the induced Martian magnetosphere and sometimes as the solar wind interaction with Mars. The middle boundary where the shocked solar wind plasma gives way to predominately planetary-derived plasma has a variety of names. The region below that middle boundary and the top of the ionosphere also does not have a uniformly used name. There are several other regions and boundaries that also have naming confusion. The various terms that are currently used in the literature for these subjects are identified and discussed; regions and boundaries that have well-settled names are not discussed nor are the details of the physics involved

The Interplanetary Magnetic Field Observed by Juno Enroute to Jupiter

The Juno spacecraft was launched on 5 August 2011 and spent nearly 5 years traveling through the inner heliosphere on its way to Jupiter. The Magnetic Field Investigation was powered on shortly after launch and obtained vector measurements of the interplanetary magnetic field (IMF) at sample rates from 1 to 64 samples/second. The evolution of the magnetic field with radial distance from the Sun is compared to similar observations obtained by Voyager 1 and 2 and the Ulysses spacecraft, allowing a comparison of the radial evolution between prior solar cycles and the current depressed one. During the current solar cycle, the strength of the IMF has decreased throughout the inner heliosphere. A comparison of the variance of the normal component of the magnetic field shows that near Earth the variability of the IMF is similar during all three solar cycles but may be less at greater radial distances

The Lunar Potential Determination Using Apollo-Era Data and Modern Measurements and Models

Since the Apollo era the electric potential of the Moon has been a subject of interest and debate. Deployed by three Apollo missions, Apollo 12, Apollo 14 and Apollo 15, the Suprathermal Ion Detector Experiment (SIDE) determined the sunlit lunar surface potential to be about +10 Volts using the energy spectra of lunar ionospheric thermal ions accelerated toward the Moon. More recently, the Lunar Prospector (LP) Electron Reflectometer used electron distributions to infer negative lunar surface potentials, primarily in shadow. We will present initial results from a study to combine lunar surface potential measurements from both SIDE and the LP/Electron Reflectometer to calibrate an advanced model of lunar surface charging which includes effects from the plasma environment, photoemission, secondaries ejected by ion impact onto the lunar surface, and the lunar wake created downstream by the solar wind-lunar interaction

The Three-Dimensional Bow Shock of Mars as Observed by MAVEN

The Martian magnetosphere is a product of the interaction of Mars with the interplanetary magnetic field and the supersonic solar wind. The location of the bow shock has been previously modeled as conic sections using data from spacecraft such as Phobos 2, Mars Global Surveyor, and Mars Express. The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission spacecraft arrived in orbit about Mars in November 2014 resulting in thousands of crossings to date. We identify over 1,000 bow shock crossings. We model the bow shock as a three-dimensional surface accommodating asymmetry caused by crustal magnetic fields. By separating MAVEN's bow shock encounters based on solar condition, we also investigate the variability of the surface. We find that the shock surface varies in shape and location in response to changes in the solar radiation, the solar wind Mach number, dynamic pressure of the solar wind, and the relative local time location of the strong crustal magnetic fields (i.e., whether they are on the dayside or on the nightside)

Comet Siding Spring's influence on Mars' ionosphere at its closest approach

International audienceOn October 19th 2014, Mars experienced a close encounter with Comet C/2013 A1 (Siding Spring), at a distance of 141,000 km. The coma washed over Mars and the planet passed directly through the cometary debris stream, producing significant effects in Mars' upper atmosphere. We present here an overview of ionospheric measurements performed during the 10h that Mars was in the coma from the MARSIS radar on board Mars Express. We discuss the comet's influence on the ionosphere through different processes like dust attachment, water molecule recombination, and cometary magnetic field