I shall define the magnetic field and the equivalence between a body's mass and its electric charge. On this basis, the mass of the Earth's core shall be theoretically calculated, and shall result in a value that corresponds to established findings. The Earth is like a magneto, of which its rotor behaves like an alternator. The inner and outer cores rotate in opposite directions to each other, with the inner core behaving like an inductor and the outer core being induced. Then I shall obtain the electric charge, the force of electric fields and the electric potential at the Earth's surface. Throughout, I shall be applying some theoretical propositions to the concept of Earth's electrical energy. I shall calculate the frequency of alternating electric currents generated by the Earth.
NASA’s OSIRIS-REx mission observed millimeter- to centimeter-scale pebbles being ejected from the surface of asteroid (101955) Bennu, indicating that Bennu is an active asteroid. About 30% of these particles escape from Bennu, and the minimum orbital intersection distance (MOID) between Bennu and Earth suggest the possibility of a ‘Bennuid’ particle flux at Earth. We characterize the evolution of Bennu’s particle stream and potential for meteor flux by simulating weekly particle ejections between the years 1780 - 2135 continuing their dynamical evolution until 2200. Ejections are modelled as a discrete release of 95 particles every week. The meteoroid stream is found to circularize in 80 +/- 40 years. Individual particles and streams remain associable to Bennu for the entire 420 years simulated. Particle flux at Earth is predicted to begin in 2101, as the Bennu-Earth MOID reaches minimum values. The year of highest particle flux, 2182, experiences 161 Earth intersections and accounts for ~1/4 of our predicted meteors. Our methods can be expanded to study the history and structure of the general meteoroid population and to estimate flux from specific near-Earth asteroids.
Windblown sand produces distinctive bedforms at scales ranging from normal sand ripples to large reversing sand dunes. We explore how aeolian bedforms evolve at both extremes of this range. An investigation of the transition from sand ripples (<1 cm height) to granule-coated megaripples (25 cm height) is underway at Great Sand Dunes National Park and Preserve (GSDNPP) in central Colorado. Sand-to-megaripple transitions at GSDNPP were documented in May and Sept of 2019 using stereophotogrammetry that produced digital terrain models that resolved granule (1-2 mm) particles as well as some sand grains; these data show the spatial distribution of particles across sand ripples whose crests merge directly into crests of megaripples. To date we have not observed that sand ripples are a necessary prerequisite for the initiation and growth of megaripples; the spatial density of granule particles appears to influence the evolution of megaripples. Reversing sand dunes are being monitored using differential navigation satellite system data at GSDNPP (up to 10 m height) and at Bruneau Dunes State Park (BDSP) in central Idaho (individual dunes >100 m height). Surveys of the crests of reversing dunes at GSDNPP reveal a northeastward migration of individual dunes along the southern margin of the main dune mass, consistent with dominant local winds, yet the symmetric reversing dune profile is maintained during the translation. Surveys of the crests of large reversing dunes at BDSP reveal variable adjustments of the crests that may be affected by wind flow altered by the bulk of the dunes themselves, sheltering the southern end of the dunes from one of the seasonal bimodal winds. Results to date indicate that the deformable shape of aeolian bedforms affect wind flow at all spatial scales, influencing the evolution of the features over diverse time scales.
PTFO 8-8695 (CVSO 30) is a star in the 7-10 million year old Orion-OB1a cluster that shows brightness dips that resemble planetary transits. Although strong evidence against the planet hypothesis for this system has been presented, the possibility remains debated in the literature. To obtain further clues, we inspected data from the NASA TESS and the ESA Gaia missions. The Gaia data suggest that PTFO 8-8695 is a binary: the photometric data show it to be over-luminous with respect to members of its kinematic group, and the astrometric data are inconsistent with a single star. The TESS light curve shows two different photometric periods. The variability is dominated by a sinusoidal signal with a period of 11.98 hr, probably caused by stellar rotation. Also present is a 10.76 hr signal consisting of a not-quite sinusoid interrupted by hour-long dips, the type of signal previously interpreted as planetary transits. The phase of the dips is nearly 180° away from the phase of the originally reported dips. This makes the dips difficult to explain as planetary transits. Instead, we believe that PTFO 8-8695 is a pair of young and rapidly rotating M dwarfs, one of which shows the same “transient-dip” behavior that has been seen in at least 5 other cases. The origin of these transient dips is still unknown but likely involves circumstellar material. Combined with recent counter-arguments against the planetary nature of CI Tau b and V830 Tau b, the rejection of the planetary hypothesis for PTFO 8-8695b suggests that the number of known hot Jupiters younger than 100 Myr is approximately zero.
The Mars Science Laboratory (MSL) Curiosity rover has explored over 400 meters of vertical stratigraphy within Gale crater to date. These fluvio-deltaic, lacustrine, and aeolian strata have been well-documented by Curiosity’s in-situ and remote science instruments, including the Mast Camera (Mastcam) pair of multispectral imagers. Mastcam visible to near-infrared (VNIR) spectra can broadly distinguish between iron phases and oxidation states, and in combination with chemical data from other instruments, Mastcam spectra can help constrain mineralogy, depositional origin, and diagenesis. However, no traverse-scale analysis of Mastcam multispectral data has yet been performed. We compiled a database of Mastcam spectra from >600 multispectral observations and 1 quantified spectral variations across Curiosity’s traverse through Vera Rubin ridge (sols 0-2302). From principal component analysis and an examination of spectral parameters, we identified 9 rock spectral classes and 5 soil spectral classes. Rock classes are dominated by spectral differences attributed to hematite and other oxides (due to variations in grain size, composition, and abundance) and are mostly confined to specific stratigraphic members. Soil classes fall along a mixing line between soil spectra dominated by fine-grained Fe-oxides and those dominated by olivine-bearing sands. By comparing trends in soil vs. rock spectra, we find that locally derived sediments are not significantly contributing to the spectra of soils. Rather, varying contributions of dark, mafic sands from the active Bagnold Dune field is the primary spectral characteristic of soils. These spectral classes and their trends with stratigraphy provide a basis for comparison in Curiosity’s ongoing exploration of Gale crater.
Topographic flexure in response to vertical loads reveals key lithospheric properties, including elastic thickness and the heat flow from the interior. Flexural stresses may also control volcano morphology. One previous study predicted that steep-sided domes on Venus usually form where the elastic thickness is ~15-40 km. We surveyed flexural signatures around steep-sided domes and confirmed this hypothesis. We determined elastic thickness from topographic profiles with a curve-fitting algorithm and a plate bending model in Cartesian and axisymmetric geometry. We used a yield stress envelope to convert elastic thickness and plate curvature into mechanical thickness and surface heat flow. The average elastic thickness for domes not near coronae is ~30 km, corresponding to a heat flow of ~60 mW/m2. Coronae on Venus are typically associated with elastic thicknesses of <10-15 km. Domes near coronae yielded elastic thicknesses in this range, and higher heat flows than domes not near coronae.
Stable paleomagnetic information in meteoritic metal is carried by the cloudy zone ~1-10 micron wide regions containing islands of ferromagnetic tetrataenite embedded in a paramagnetic antitaenite matrix. Due to their small size and high coercivity (~2.2 T), the tetrataenite islands carry very stable magnetic remanence. However, these characteristics also make it difficult to image their magnetic state with the necessary spatial resolution and applied magnetic field. Here we describe the first application of X-ray holography to image the magnetic structure of the cloudy zone of the Tazewell IIICD meteorite with spatial resolution down to ~40 nm and in applied magnetic fields up to 1.1 T, sufficient to extract high-field hysteresis data from individual islands. Images were acquired as a function of magnetic fields applied both parallel and perpendicular to the surface of a ~100 nm thick slice of the cloudy zone. Broad distributions of coercivity are observed, including values that likely exceed the maximum applied field. Horizontal offsets in the hysteresis loops indicate an interaction field distribution with half width of ~100 mT between the islands in their room-temperature single-domain state, providing a good match to first-order reversal curve diagrams. The role of interactions during the acquisition of transformation chemical remnant magnetization as the meteorite parent body is cooled, and the implications for extracting quantitative estimates of the paleofield, are discussed
Our understanding of the nature of crustal formation in the Eoarchean is severely curbed by the scarcity and poor preservation of the oldest rocks, and variable and imperfect preservation of protolith magmatic signatures. These limitations hamper our ability to place quantitative constraints on thermomechanical models for early crustal genesis and hence on the operative geodynamical regimes at that time. Controls on the liquid line of descent responsible for Eoarchean crust petrogenesis could help us understand more, but these remain vague. Growth of Archean crust may have occurred dominantly via processes akin to modern oceanic crustal genesis, coupled to a vertical geodynamic regime. Equally, convergent boundary processes, including subduction, are argued to be important in the development of the crust before about 3.8 Ga. The recently discovered ca. 3.75 Ga Ukaliq supracrustal enclave (northern Québec) is mainly composed of serpentinized ultramafic rocks and amphibolitized mafic schists. Inferred protoliths to the Ukaliq serpentinites include dunites, pyroxenites, and hornblendites with compositions similar to that of arc crust cumulates, whereas the mafic rocks were probably basalts to basaltic andesites. The Ukaliq cumulates record two liquid lines of descent: (i) a tholeiitic suite, partially hydrated, resulting from the fractionation of a basaltic liquid; and (ii) a boninitic suite documenting the evolution of an initially primitive basaltic to andesitic melt at ~0.5 GPa and containing >6 wt% H2O. Together with the presence of negative μ142Nd anomalies, this information points to a deep fluid input via recycling of Hadean crust in the Eoarchean via modern-style subduction.
Abstract The key to evaluating the formation history and evolution of the Moon lies in understanding the current state of its interior. We used a multidisciplinary approach to explore the current day lunar structure and composition with the aim of identifying signatures of formation and early evolution. We constructed a large number of 1D lunar interior models to explore a wide range of potential structures and identified those models that match the present day mass, moment of inertia, and bulk silicate composition of the Moon. In an advance on previous studies, we explicitly calculate the physical and elastic properties of the varying mineral assemblages in the lunar interior using multicomponent equations of state. We considered models with either a compositionally homogeneous mantle or a stratified mantle that preserved remnants of magma ocean crystallization, and tested thermal profiles that span the range of proposed selenotherms. For the models that reproduced the observed mass and moment of inertia, we found a narrow range of possible metallic (iron) core radii (269-387 km) consistent with previous determinations. We explored the possibility of an ilmenite bearing layer both below the crust and at the core-mantle boundary as a potential tracer of magma ocean solidification and overturn. We observed a trade-off between the mass of the upper and lower ilmenite-bearing layers and structures that have undergone mantle overturn are both consistent with present observations. Plain Language Summary In order to understand how the Moon formed, along with the following history including the processes that change and shape it, the current state of the lunar interior offers a lot of valuable information or clues. We used several different computer simulation tools from different disciplines to calculate the Moon’s interior structure. We then compared our calculations with observations of the Moon’s mass and moment of inertia (a measure of how its weight is distributed through the interior) and the average composition and chemistry of the Moon. We considered a Moon that is well mixed and one that has preserved layers from its early history and tried different temperature structures. We find that the Moon has to have a small dense iron core and that it may have a hot soft layer just above the core that can dampen moonquakes.
While liquid environments with high salt content are of broad interest to the Earth and Planetary Science communities, instruments face challenges in detecting organics in hypersaline samples due to the effects of salts. Therefore, technology to desalt samples before analysis by these instruments would be enabling for liquid sampling on missions to Mars or ocean worlds. Electrodialysis (ED) removes salt from aqueous solutions by applying an electric potential across a series of ion-selective membranes, and is demonstrated to retain a significant percentage of dissolved organic molecules (DOM) in marine samples. However, current electrodialysis systems used for DOM recovery are too large for deployment on missions or for use in terrestrial fieldwork. Here we present the design and evaluation of the Minature Robotic Electrodialysis (MR ED) system, which is approximately 1/20th the size of heritage instruments and processes as little as 50 mL of sample at a time. We present tests of the instrument efficiency and DOM recovery using lab-created solutions as well as natural samples taken from an estuary of the Skidaway River (Savannah, GA) and from South Bay Saltworks (San Diego, CA). Our results show that the MR ED system removed 97-99% of the salts in most samples, with an average DOC recovery range from 53 to 77%, achieving similar capability to tabletop instruments. This work both demonstrates MR ED as a possible field instrument and increases the technology readiness level of miniaturized electrodialysis systems for future missions.
Gamma-Ray Glows (GRGs) are high energy radiation originating from thunderclouds, in the MeV energy regime, with typical duration of seconds to minutes, and sources extended over several to tens of square kilometers. GRGs have been observed from detectors placed on ground, inside aircraft and on balloons. In this paper, we present a general purpose Monte-Carlo model of GRG production and propagation. This model is first compared to a model from Zhou et al. (2016) relying on another Monte-Carlo framework, and small differences are observed. We then have built an extensive simulation library, made available to the community. This library is used to reproduce five previous gamma-ray glow observations, from five airborne campaigns: balloons from Eack et al. (1996b), Eack et al. (2000); and aircrafts from ADELE (Kelley et al., 2015), ILDAS (Kochkin et al., 2017) and ALOFT (Østgaard et al., 2019). Our simulation results confirm that fluxes of cosmic-ray secondary particles present in the background at a given altitude can be enhanced by several percent (MOS process), and up to several orders of magnitude (RREA process) due to the effect of thunderstorms’ electric fields, and explain the five observations. While some GRG can be explained purely by the MOS process, E-fields significantly larger than E_th (the RREA threshold) are required to explain the strongest GRGs observed. Some of the observations also came with in-situ electric field measurements, that were always lower than E_th , but may not have been obtained from regions where the glows are produced. This study supports the claim that kilometer-scale E-fields magnitudes of at least the level of E_th must be present inside some thunderstorms.
Ganymede is the only Solar System moon that generates a permanent magnetic field. Dynamics inside Ganymede’s magnetosphere is likely driven by energy-transfer interactions on its upstream magnetopause. Previously in Kaweeyanun et al. (2020), we created a steady-state analytical model of Ganymede’s magnetopause and predicted global-scale magnetic reconnection to occur frequently throughout the surface. Using the same model, this paper provides the first assessment of Kelvin-Helmholtz (K-H) instability growth on the magnetopause in isolation from reconnection effects. The linear K-H instability growth rate is calculated at Ganymede’s equatorial magnetopause flank points under the magnetohydrodynamic with finite Larmor radius effect (MHD-FLR) theory, which accounts for inter-flank growth rate asymmetry due to large gyroradii of Jovian plasma ions. The calculation gives growth rates between γ ≈ 0.01-48 /s with notable enhancement at the equatorial flank point closer to Jupiter. Then, the ideal MHD K-H instability onset condition is evaluated across the entire Ganymedean magnetopause. We find the conditions along both magnetopause flanks to be K-H favorable at all latitudes with growth rates similar to those at respective equatorial flank points. Using Mercury’s magnetopause case as a comparison, we determined that nonlinear K-H vortices are viable at Ganymede based on the calculated growth rates, but the vortex growth will likely be suppressed once global reconnection is taken into account.
In the Jovian magnetosphere, an electric current system within the ‘current sheet’ generates a magnetic field, which is comparable to or dominating the Jovian intrinsic field in the nightside magnetosphere. However, update of an existing model of the magnetospheric field using newly acquired data by Galileo and Juno have never been conducted since it was first formulated in 1997. Here we used the data by Voyager 1/2, Galileo and Juno to revise the current sheet model as well as the magnetospheric field model based on each spacecraft data. We derived models that reproduced each data well, and revealed long-term variations of both current sheet and magnetospheric field over several decades. The updated models were found useful to detect dynamic events in the magnetosphere such as magnetopause deformation and plasmoid generation. They can also be used as external fields necessary for probing into the Galilean icy moons by electromagnetic induction methods.
As there are strong crustal magnetic fields in some Martian concentrated regions. it has long been a goal of Martian science to understand how crustal magnetic field affects surrounding space environment. In the paper, using the data measured by MAVEN, the ratio of electron/CO2 density ( Ne/NCO2) in region with different levels of Martian ionospheric magnetic fields are studied. It seems that ratio of dayside Ne/NCO2 in region with stronger ionospheric magnetic field is larger while the altitude is more than 260 km. On the other hand, the effect of crustal magnetic field intensity on the nightside ratio of Ne/NCO2 is weak. Since the topological structure of magnetic field is very vulnerable to the solar wind, the correlation between Ne/NCO2 and solar wind parameters are analyzed. We find that there is obvious negative correlation between dayside ratio of Ne/NCO2 and solar wind dynamic pressure in the region with strong ionospheric magnetic field, which may imply that the ionospheric plasmas are significantly escaped in response to enhanced solar wind dynamic pressure pulses in the dayside region. However, the effect of solar wind on nightside ratio of Ne/NCO2 is very little. These results can be useful for understanding the dynamic process in the Martian ionosphere.
The MASER (Measuring, Analysing and Simulating Radio Emissions) project provides a comprehensive infrastructure dedicated to low frequency radio emissions (typically < 50 to 100 MHz). The four main radio sources observed in this frequency are the Earth, the Sun, Jupiter and Saturn. They are observed either from ground (down to 10 MHz) or from space (down to a few kHz). Ground observatories are more sensitive than space observatories and capture high resolution data streams (up to a few TB per day for modern instruments). Conversely, space-borne instruments can observe below the ionospheric cut-off (10 MHz) and can be placed closer to the studied object. Several tools have been developed in the last decade for sharing space physcis data. Data visualization tools developed by the CDPP (http://cdpp.eu, Centre de Données de la Physique des Plasmas, in Toulouse, France) and the University of Iowa (Autoplot, http://autoplot.org) are available to display and analyse space physics time series and spectrograms. A planetary radio emission simulation software is developed in LESIA (ExPRES: Exoplanetary and Planetary Radio Emission Simulator). The VESPA (Virtual European Solar and Planetary Access) provides a search interface that allows to discover data of interest for scientific users, and is based on IVOA standards (astronomical International Virtual Observatory Alliance). The University of Iowa also develops Das2server that allows to distribute data with adjustable temporal resolution. MASER is making use of all these tools and standards to distribute datasets from space and ground radio instruments available from the Observatoire de Paris, the Station de Radioastronomie de Nançay and the CDPP deep archive. These datasets include Cassini/RPWS, STEREO/Waves, WIND/Waves, Ulysses/URAP, ISEE3/SBH, Voyager/PRA, Nançay Decameter Array (Routine, NewRoutine, JunoN), RadioJove archive, swedish Viking mission, Interball/POLRAD… MASER also includes a Python software library for reading raw data. This work is supported by CDPP, CNES, PADC and Europlanet-2020-RI. The Europlanet 2020 Research Infrastructure project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 654208.
Crater morphology and surface age of asteroid (162173) Ryugu are characterized using the high-resolution images obtained by the Hayabusa2 spacecraft. Our observations reveal that the abundant boulders on and under the surface of the rubble-pile asteroid affect crater morphology. Most of the craters on Ryugu exhibit well-defined circular depressions, unlike those observed on asteroid Itokawa. The craters are typically outlined by boulders remaining on the rim. Large craters (diameter >100 m) host abundant and sometimes unproportionally large boulders on their floors. Small craters (<20 m) are characterized by smooth circular floors distinguishable from the boulder-rich exterior. Such small craters tend to have dark centers of unclear origin. The correlation between crater size and boulder number density suggests that some processes sort the size of boulders in the shallow (<30 m) subsurface. Furthermore, the crater size-frequency distributions (CSFDs) of different regions on Ryugu record multiple geologic events, revealing the diverse geologic history on this 1-km asteroid. Our crater counting analyses indicate that the equatorial ridge is the oldest structure of Ryugu and was formed 23-29 Myr ago. Then, Ryugu was partially resurfaced, possibly by the impact that formed the Urashima crater 5-12 Myr ago. Subsequently, a large-scale resurfacing event formed the western bulge and the fossae 2-9 Myr ago. Following this process, the spin of Ryugu slowed down plausibly due to the YORP effect. The transition of isochrons in a CSFD suggests that Ryugu was decoupled from the main belt and transferred to a near-Earth orbit 0.2-7 Myr ago.
Remote sensing observations are our primary method of studying planetary surfaces, and in the inner solar system, in situ exploration quickly provided ground truth to these remote sensing observations. Our view of the surface appearance of worlds like the Moon, Mars, and even Venus has grown in tandem with our understanding of the large-scale structure from remote sensing. However, our knowledge of the icy worlds of the outer solar system is based solely on decades of remote sensing observations without any in situ surface data to help understand how geological processes are manifest on these worlds. The surfaces of icy worlds like Europa are likely to be truly alien in appearance, dominated by processes such as impact gardening, sputtering, sintering, and other types of physical and chemical weathering that act together in ways we have never yet observed in situ. Remote sensing has revealed that Europa’s surface consists of an icy layer, exposed to the vacuum of space at cryogenic temperatures. The airless rocky Moon may be the best landed analog for Europa’s surface, but the Moon is an old, battered world covered with impact craters, which have gardened the surface to a highly-mixed regolith depth of 5-15 meters overlying kilometers of broken-up megaregolith. Europa’s young surface, approximately tens of millions of years old, likely has a gardening depth on the scale of centimeters up to a meter (Costello et al., AGU Fall Meeting, 2019). The rocky Moon is also compositionally different from icy Europa, and the thermal and radiolytic processes that shape the texture of the uppermost surface of an icy body have no rocky analog. As study of icy worlds has continued on the basis of remote sensing data only, multiple competing models exist for the formation of various surface features. Follow-up flyby and orbital missions may not be able to resolve these situations even with higher-resolution remote sensing data and digital elevation models. Images taken by an in situ surface lander on an icy world such as Europa, coupled with ground truth compositional and other measurements, will be essential to our understanding of how geologic processes work on these worlds. A mission such as a Europa Lander is the necessary next step, and will revolutionize our ability to interpret remote sensing data from myriad other bodies in the outer solar system.
The shallowest intracrustal layer (extending to 8 ± 2 km depth) beneath the Mars InSight Lander site exhibits low seismic wave velocity, which are likely related to a combination of high porosity and other lithological factors. The SsPp phase, an SV-to P-wave reflection on the receiver side, is naturally suited for constraining the seismic structure of this top crustal layer since its prominent signal makes it observable with a single station without the need for stacking. We have analyzed eight broadband and low-frequency seismic events recorded on Mars and made the first coherent detection of the SsPp phase on the red planet. The timing and amplitude of SsPp confirm the existence of the ~8 km interface in the crust and the large wave speed (or impedance) contrast across it. With our new constraints from the SsPp phase, we determined that the P-wave speed in the top crustal layer is between 2.5 km/s and 3.3 km/s, which is a more precise and robust estimate than the previous range of 2.0-3.5 km/s obtained by receiver function analysis. The porosity in Layer 1 is estimated to be as much as 21-31% (assuming an aspect ratio of 0.1 for the pore space), but could be lower if some pores are filled by low-density cements or other secondary 1 mineral phases. These porosities and P-wave speeds are compatible with our current understanding of the upper crustal stratigraphy beneath the InSight Lander site.