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This article aims to understand the pitch angle distributions (PADs) of the charged particles in the Earth’s inner magnetosphere using test-particle simulations. The emphasis is on characterizing the variation in pitch angle of the charged particles trapped along the Earth’s magnetic field lines. These charged particles undergo gyration, bounce, and azimuthal drift motions in the Earth’s inner magnetosphere. They are trapped until their pitch angle falls into the loss-cone to get lost into the upper atmosphere. We have developed a three-dimensional test-particle simulation model in which the relativistic equation of motion is solved numerically to track these trapped particle’s trajectories. We have examined the pitch angle distributions of the electron, proton, and oxygen for the cases where adiabatic invariants are conserved and non-conserved. For this purpose, we have considered the particle’s trajectory in the latitudinal range of [ - 40 ° , 40 ° ] for one complete drift around the Earth. We found that when adiabatic invariants are conserved, the particles possess butterfly-type pitch angle distributions. Whereas, when adiabatic invariants are not conserved, the particle’s pitch angle distribution bunches toward the 90°-peaked distribution. The situation of non-conservation of adiabatic invariants demonstrated in the present simulation is arising due to larger gyro-radius (few Earth radii) over which the ambient magnetic field is not constant. We have noticed that in the static dipolar magnetic field, all three, 1st, 2nd, and partly 3rd adiabatic invariants are non-conserved when gyro-radius is larger. The information on the change in the pitch angle distribution pattern from butterfly-type to 90°-peak distribution will be useful to understand the pitch angle distributions observed by the recent spacecraft in the Earth’s radiation belts.

According to measurements of the electric component of the electromagnetic field in the frequency range from 2 kHz to 10 MHz by the Japanese ERG satellite, generation regions of kilometric continuum radiation and new hectometric continuum radiation have been determined. It is demonstrated that the kilometric continuum is mainly observed on the dayside of the magnetosphere, its source is located near the geomagnetic equatorial plane, and the size of the source does not exceed ±(0.1–0.3)RE across this plane, where RE is the Earth radius. Hectometric radiation mainly observed in the nightside magnetosphere has two sources. One of them is located near the plasmasphere and its distance from the geomagnetic equator can reach 3RE. The second source is observed near the Earth at distances from 1.1RE to 2RE.

The effective earth radius can transform the curved ray path into a straight line, and the modified refractive index can transform the spherical ground into a plane. Using them can simplify the propagation modeling of electromagnetic waves in the atmosphere, so they are widely used in the calculation of long-range propagation of electromagnetic wave, and adopted by the ITU Recommendations and the IEEE Standards. In this paper, upon employing simple geometric methods, we provide general formulas for the effective earth radius and the modified refractive index, pointing out that they both originate from the use of conformal transformations. In turn, we prove that for both quantities the formulas contained in the ITU Recommendations and the IEEE Standards are special cases of the general formulas given in this paper. Our results provide a solid mathematical background to the concepts of effective earth radius and modified refractive index, and pave the way for their use beyond the propagation of electromagnetic waves in the earth atmosphere, e.g. to the propagation of other types of waves in generic media.

Made available in DSpace on 2020-12-12T02:42:41Z (GMT). No. of bitstreams: 0 Previous issue date: 2020-05-01 During their lifetime, the Near-Earth Asteroids (NEAs) suffer numerous close encounters (CE) with Earth, Mars and Venus. It has been demonstrated that gravitational interactions during close planetary encounters can alter an asteroid’s spin state, and hence, along with collisions, play a role in the rotational evolution of NEAs. The variation of the rotational angular momentum during the encounters can increase or decrease the rotation rate depending on the initial condition. In addition to the rotation rate, close encounters cause variation in the movement of precession and nutation of the asteroid. Using a numerical model that takes into account the spin-orbit coupling of a body with ellipsoidal shape, the subject of this study is to analyze the rotational motion (rotation, precession and nutation) of asteroids during CE with the Earth for different initial conditions. We computed the variation of the obliquity and the variation of spin period after the CE. We found significant change in obliquity and spin period only in cases with strong encounter, that is in cases that the impact parameter of the encounter (1.2 ≤ d ≤ 7 (Earth radii) and the relative velocity (v) are small. Our results also show that the variation of rotational motion due to the close encounter is capable of tumbling the axis of rotation and gravitational rupture may occur in a few cases. São Paulo State University (UNESP) Guaratinguetá Grupo de Dinâmica Orbital & Planetologia INPE – National Institute for Space Research São Paulo State University (UNESP) Guaratinguetá Grupo de Dinâmica Orbital & Planetologia

The scaling of the energy of ion beams (beamlets) WN ∼ NA in the N resonant regions of the current sheet in data from the SC-1 and SC-4 CLUSTER satellites has been analyzed. The case on February 5, 2003, for energy dispersive small-scale substructures, which are signatures of 1–20 keV beamlets in the auroral magnetosphere at geocentric distances (4.5–5.3)RE, where RE is the radius of the Earth, has been studied. This case is anomalous, since the energies of beamlets in the resonant regions (seven regions N = 1−7 with resonances R = 1−7 are identified and the region with R = 7 is located in the highest latitude auroral region) do not obey a single scaling law. The exponents A are 0.04 and 0.40 for the regions with resonances R = 1−4 and are 0.83 and 1.14 for the regions with R = 5−7 according to the SC-1 and SC-4 data, respectively. The exponents obtained from the CLUSTER satellite data differ from the theoretically predicted value A = 1.33 [L.M. Zeleny et al., JETP Lett. 85, 187 (2007)]. The beamlet energy scales for the regions with R = 5−7 can be explained by taking into account the electric field Ez perpendicular to the plane of the current sheet. The observed exponents A in the regions N = 1−4 can occur because the spatial decrease in the normal component Bz of the magnetic field, which controls the increment of the energy of ion beams in the current sheet, in these resonant regions is smaller than that in the regions N = 5−7.

The most striking contrasts that are found on the continents in paleogeographic reconstructions of the end of the Mesozoic era are the occurrence on the place of the disappeared humid subtropics of the largest Gobi Desert in Eurasia with air temperatures falling below 50° from the freezing point and annual precipitation totals at the level of 100 mm. Science does not know the processes that can lead to a cooling of the atmosphere at 70° and other equally radical changes in nature with a stable position of the blocks of the earth’s crust in space. Changes in the environment of this magnitude can only be the result of land moving northward for a distance equal to about half the radius of the Earth. Titanosaurs, described by the remains in the Gobi deposits, had a body volume, which at modern gravity corresponds to a mass of 10 to 30 ton. However, animals with such a mass and such growth could not exist now. To create the necessary pressure in the vessels and provide energy to the body, Mongolian sauropods would need a heart of 2 - 3 m in diameter. Known types of muscle tissue are unable to maintain an elongated neck and head with a mass of more than a ton. The femur bones of four-legged dinosaurs had strength sufficient to move on land only animals weighing no more than 5 - 7 tons. The bones of giant bipedal dinosaurs at a constant gravitational field would have to be subjected to specific loads, several times greater than the bones of modern elephants, which is excluded. The natural conclusion about the action of a lesser gravity in the Mesozoic provides a solution to the mystery of the truly global spread in that era of bipedal mode of movement as the most energy efficient.

On the basis of the Petschek reconnection model and the characteristics of reconnection, hundreds of reconnection exhausts were reported in the solar wind. Many multi-spacecraft observations also indicated that interplanetary magnetic reconnection is a quasi–steady-state plasma process and the reconnection X-line can extend hundreds of Earth radii. In this study, we report an interplanetary flapping reconnection exhaust observed by Wind on April 1, 2003 at one AU. The magnetic reconnection event has two adjacent accelerated flows. We compared the plasma and magnetic characteristics of the two accelerated flows and found that the second accelerated flow was due to the back-and-forth movement of the reconnection exhaust. Our observations reveal that not all interplanetary reconnections operate in a quasi–steady-state manner; some reconnection current sheets can move rapidly back and forth.

In this work, we aimed to see how changes in the Earth's gravitational field in the context of general relativity modify the radius and age values of the universe in the previously developed distance-determining model. By applying the relationships of light propagating in accelerating systems and gravity to the Earth moving with the Milky Way galaxy in the expanding universe and to the light propagating in the surface gravity of our planet moving in this way, the radius and age of the universe can be determined. For a redshift extent of 3.1415 in the cosmos, we can determine a so-called “short evolving distance” from the Einstein equation. Knowledge of the entire plane angle (2.\(\pi\)) and the deviating angle of a light beam (\(\alpha\)) passing through the Earth’s surface gravity it is possible to determine extreme distances by utilizing the rules of trigonometry. This “long evolving distance,” which is approximately in the range of the radius of the universe, can be transformed into the “evolving time” divided by the speed of light. Based upon this dating method, the universe may have been formed at an average value of 13.7536 billion years. In addition to the cosmos radius and age, different but small changes can be observed in these, taking into account the changes in the Earth's surface gravity associated with its shape and position. These values fall between 13.6879 and 13.8498 billion years, almost completely covering the range given by the analysis of the measurement results of the WMAP and Planck satellites.

International audience; Icecube neutrino detector a cubic kilometer in South Pole, traces energetic TeVs-PeVs neutrino signals by their cascades or better by their tracks inside its icy volume. Cascades, explosivespherical showers in icy, are mostly for electron or tau or neutral current, tracks are made by muons. High energy tau tracks might show a birth place cascade and a second decay tau shower,allowing a peculiar directional track. In general hundreds TeVs-PeVs Cascades show very poor directionality. Therefore they are nearly blind to disentangle the source event. Therefore wesuggest to neglect such cascades in future Gen-2 Icecube. Indeed the most interesting signals are the tens TeVs up to PeVs muon upgoing tracks, either born inside, HESE, or outside Icecube: thetrought going muon tracks. These ones are more abundant at ultra high energy (UHE) regimes because their interactions is outside the Icecube, mainly in the wider volume of dense rock aroundand below the Icecube volume. Such several kilometers tracks offer the most energetic and precise neutrino astronomy. Moreover highest tens TeV or PeVs neutrinos become opaque to theEarth radius. Therefore they are arriving mainly as up-going nearly horizontal tracks, because they are crossing only short Earth cords. In consequence we suggest an upgrade Muon Icecubedetector by a widest kilometers spaced concentric spiral array rings (around old Icecube), each arm nearly a kilometer far from the other, leading to the largest and widest array net (for anygiven string number). Such wider (km) empty array volumes, like a sponge, may better amplify, almost quadratically, the observed mass volume, in comparision to a more dense but homogeneousvolumetric cubic one (at 240 or 330 meters distance among strings) as the Icecube Gen-2 project. In our first approximation one may obtain an increased cubic volume reaching about 50 times the kilometer Icecube array, by a shell like spiral volume or a honeycomb cell net, leading not to a few rare (hundred TeV energy) event a year but to many tens or even a hundred of such neutrino tracks each year, running toward a more statistical rich astronomy.

Terrestrial ecliptic dayside observations of the exospheric Lyman-α column intensity between 3–15 Earth radii (Re) by UVIS/HDAC at CASSINI have been analysed to derive the neutral exospheric H-density profile at the Earth's ecliptic dayside in this radial range. The data were measured during CASSINIS's swing by manoeuvre at the Earth on 18 August 1999 and are published by (Werner et al., 2004). In this study the dayside HDAC Lyman-α observations published by (Werner et al., 2004) are compared to calculated Lyman-α intensities based on the 3D H-density model derived from TWINS Lyman-α observations between 2008–2010 (Zoennchen et al., 2015). It was found, that both Lyman-α profiles show a very similar radial dependence in particular between 3–8 Re. Between 3.0–5.5 Re impact distance Lyman-α observations of both TWINS and UVIS/HDAC are existing at the ecliptic dayside. In this overlapping region the cross-calibration of the HDAC profile against the calculated TWINS profile was done, assuming, that the exosphere there was similar for both due to comparable space weather conditions. As result of the cross-calibration the conversion factor between counts/s and Rayleigh fc = 3.285 [counts/s/R] is determined for these HDAC observations. Using this factor the radial H-density profile for the Earths ecliptic dayside was derived from the UVIS/HDAC observations, which constrained the neutral H-density there at 10 Re to a value of 35 cm−3. Furthermore, a faster radial H-density decrease was found at distances above 8 Re (≈ r−3) compared to the lower distances 3–7 Re (≈ r−2.37). This increased loss of neutral H above 8 Re might indicate a higher rate of H ionization in the vicinity of the magnetopause at 9–11 Re (near sub solar point) and beyond, because of increasing charge exchange interactions of exospheric H atoms with solar wind ions outside the magnetosphere.

The surface refractivity, the refractivity gradient and effective earth radius factor (k-factor) are useful ingredients for predicting the local radio wave propagation conditions in the troposphere. In this study the surface refractivity, refractivity gradient and k-factor were estimated and analyzed from the measurements of air temperature, relative humidity and atmospheric pressure in Auchi area of Edo State, Nigeria which is located within Latitude 7.07°N and Longitude 6.27°E using a set of three self designed cost effective portable weather monitoring systems for a period of two years (2016 and 2017) in order to derive the radio propagation conditions. The weather monitoring devices were positioned at three different height levels of 50, 100 and 150 m at the administrative block of Edo University Iyamho, Auchi area of Edo State, Nigeria of about 200 m height for the measurements of the atmospheric weather variables respectively. The results show that the surface refractivity and the k-factor values were generally higher during rainy seasons compared to that of the dry seasons; while the refractivity gradient values were higher in the dry seasons compared to the rainy seasons and that surface refractivity was inversely proportional to the height; while the refractivity gradient and the k-factor have no defined pattern of proportionality variance with the height for the period under consideration. The average values of the surface refractivity, refractivity gradient and the k-factor for the period under consideration are 355.83 N-units, −55.85 N-units/km and 1.50 respectively. Consequently, it is deductively concluded that the local radio propagation condition for the Auchi area of Edo State, Nigeria is predominantly super-refractive.

Using viscoelastic mass spring model simulations to track heat distribution inside a tidally perturbed body, we measure the asymmetry of heating in the crust of a spin synchronous Moon in eccentric orbit about the Earth. With the Moon within a few Earth radii of the Earth, we find that tidal heating per unit area in a lunar crustal shell is asymmetric due to the octupole order moment in the Earth's tidal field and is 10 to 20\% higher on its near side than on its far side. Tidal heating reduces the crustal basal heat flux and the rate of magma ocean crystallization. Assuming that the local crustal growth rate depends on the local basal heat flux and the distribution of tidal heating in latitude and longitude, a heat conductivity model illustrates that a moderately asymmetric and growing lunar crust could maintain its asymmetry. Near/far side asymmetric tidal heating could serve as a trigger for uneven lunar crustal growth., Comment: Accepted Icarus

The present study examines the response of the terrestrial magnetosphere to the long-term steady declining trends observed in solar magnetic fields and solar wind micro-turbulence levels since mid-1990's that has been continuing beyond the mini-solar maximum of cycle 24. A detailed analysis of the response of the terrestrial magnetosphere has been carried out by studying the extent and shape of the Earth's magnetopause and bow shock over the past four solar cycles. We estimate sub-solar stand-off distance of the magnetopause and bow shock, and the shape of the magnetopause using numerical as well as empirical models. The computed magnetopause and bow shock stand-off distances have been found to be increasing steadily since around mid-1990's, consistent with the steady declining trend seen in solar magnetic fields and solar wind micro-turbulence levels. Similarly, we find an expansion in the shape of the magnetopause since 1996. The implications of the increasing trend seen in the magnetopause and bow shock stand-off distances are discussed and a forecast of the shape of the magnetopause in 2020, the minimum of cycle 24, has been made. Importantly, we also find two instances between 1968 and 1991 when the magnetopause stand-off distance dropped to values close to 6.6 earth radii, the geostationary orbit, for duration ranging from 9$-$11 hours and one event in 2005, post 1995 when the decline in photospheric fields began. Though there have been no such events since 2005, it represents a clear and present danger to our satellite systems., Accepted for publication in JGR-Space Physics. arXiv admin note: text overlap with arXiv:1709.01407

A compilation was made of N = 89 planets or moons for which the mass and radius are known, between the limits of 0.01 and 10 times the mass of Earth. Although starting from a larger and higher-quality (because it excludes m sin i figures) sample than that of Weiss and Marcy (Astrophys J Lett 783:L6–L12, 2014), the chart of log density versus radius confirms the WM14 results: Density increases up to about 1.5 Earth radii and decreases for larger radii, probably as the planet retains hydrogen and helium on formation.

Recent space geodetic and gravimetric studies have given indications that the Earth's radius is increasing at 0.1–0.4 mm yr−1 at present. Seismic studies have also shown that earthquakes alone could be causing the radius to increase at 0.011–0.06 mm yr−1. Deep mantle plumes provide a geophysical context within which such radial expansion, if confirmed, could possibly be explained. Both theory and observation suggest that these rising plumes more readily penetrate the 670 km barrier than do subducting slabs moving in the opposite direction towards the core-mantle boundary. If so, there would be a net flow of mass from the deep lower mantle into the upper mantle. Due to the lower pressures in the upper mantle, the excess mass of plume materials reaching there would transform to minerals with lower densities than they had at the mantle base. An increase in the mantle volume and the Earth's radius would therefore be implied. Using previously published data for the African superplume, it is estimated that this mechanism could cause the Earth's radius to increase at rates of 0.02–0.3 mm yr−1, similar to the rates possibly indicated in the present studies. This mechanism could also explain the very large range in current estimates of mantle plume heat and volume fluxes. A possible energy source for this plume-driven mode of expansion is discussed. Keywords: Deep mantle plumes, Expanding earth, Heat budget, Seismic tomography, African superplume

Different magnetopause models with a diverse level of complexity are in use. One thing that they have in common is that they are mainly based on near-earth observations; i.e. they use measurements at distances of about ±10 Earth radii along the GSM x axis. Only very few observations of magnetopause crossings at larger distances are used for model fitting. In this study we compare position and normal direction predictions of the Shue et al. (1997) magnetopause model with actual observations of magnetopause crossings identified using the ARTEMIS spacecraft at lunar distance, about 60 Earth radii. We find differences in the location prediction between model and actual observation but good agreement in predictions about the magnetopause normal direction.

Previous studies suggest that dipolarization fronts (DFs) are 1 to 3RE (RE is the earth radius) wide in the dawn-dusk direction. Recent kinetic simulations have found that DFs may break up into small-scale structures after they are produced by reconnection. Motivated by this simulation, we revisited the scale size of DFs in the dawn-dusk direction by using Cluster observations during the years when the inter-distance among Cluster spacecraft was between 1000 and 2000 km. We selected the DFs that were detected by more than one spacecraft and estimated the radii of these DFs by a simple geometrical analysis, which is based on comparison of DF normals observed by different spacecraft. We found a few DFs that were only a few ion inertial lengths in the dawn-dusk direction. These results point out the importance of multi-scale coupling during the evolution of DFs.

In this work, we present the analysis of 35,464 M-dwarf stars located within 100 parsecs in the Transiting Exoplanet Survey Satellite (TESS) Full Frame Images (FFIs) of the observed southern ecliptic hemisphere sectors 1 – 5. We present a new pipeline called NEMESIS which was developed to extract photometry, remove instrumental effects and perform transit searches of single sector data in TESS FFIs. As many M-dwarfs are faint and are not observed with a 2 minute cadence by TESS, FFI transit surveys can give an empirical validation of how many planets are missed by using the 30 minute cadence data. In this work, we detected 183 threshold crossing events and present 29 planet candidates for Sectors 1 – 5, 24 of which are new detections. Our sample contains orbital periods ranging from 1.25 – 6.84 days and planetary radii from 1.26 – 5.31 R⊕. We intend to extract light curves of other nearby M-dwarfs in TESS FFIs observed in Sectors 6 – 26 and will provide all of our data products for our planet candidates., Submitted to The Astronomical Journal, {"references":["arxiv:1710.00193","http://dx.doi.org/10.3847/1538-3881/ab3984"]}

Results from the NASA Van Allen Probes mission indicate extensive observations of mirror/drift‐mirror (M/D‐M hereafter) unstable plasma regions in the night‐side inner magnetosphere. Said plasmas lie on the threshold between the kinetic and frozen‐in plasma regimes and have favorable conditions for the formation of M/D‐M modes and subsequent ultralow frequency (ULF) wave signatures in the surrounding plasma. We present the results of a climatological analysis of plasma‐γ (anisotropy measure) and total plasma‐β (ratio of particle to magnetic field pressure) in regard to the satisfaction of instability conditions on said M/D‐M modes under bi‐Maxwellian distribution assumption, and ascertain the most likely region for such plasmas to occur. Our results indicate a strong preference for the premidnight sector of the night‐side magnetosphere, with events ranging in time scales from half a minute (roughly 200 km in scale size) to several hours (multiple Earth radii). The statistical distribution of these plasma regions explicitly identifies the source region of “storm time Pc5 ULF waves” and suggests an alternative mechanism for their generation in the night‐side inner magnetosphere., Key Points Mirror mode unstable plasmas occur in the dusk‐to‐midnight inner magnetosphereMirror‐unstable plasmas are likely due to magnetotail injectionsMirror mode propagation can lead to ultra‐low frequency (ULF) mode generation

As the thickness of the terrestrial atmosphere is much less than the radius of the Earth, the sphericity of the atmosphere is often neglected and the atmospheric radiative transfer is described in the framework of one-dimensional models, assuming that the properties of the atmosphere (such as density, temperature, pressure and concentration of atmospheric gases/particulate matter) change along the vertical direction only, while the solar radiation at the top of the atmosphere is described as a plane-parallel source of radiation. The horizontal inhomogeneity of the atmosphere and underlying surface cannot be ignored in a number of atmospheric optics and remote sensing problems, including radiative transfer/atmospheric remote sensing in the presence of broken cloud fields.

Prevailing models for the formation of the Moon invoke a giant impact between a planetary embryo and the proto-Earth \citep{Canup_2004, Cuk_Stewart_2012}. Despite similarities in the isotopic and chemical abundances of refractory elements compared to Earth's mantle, the Moon is depleted in volatiles \citep{Wolf_Anders_1980}. Current models favour devolatilisation via incomplete condensation of the proto-Moon in an Earth-Moon debris-disk \citep{Charnoz_Michaut_2015,Canup_2015,Lock_2018}. However the physics of this protolunar disk is poorly understood and thermal escape of gas is inhibited by the Earth's strong gravitational field \citep{Nakajima_Stevenson_2014}. Here we investigate a simple process, wherein the Earth's tidal pull promotes intense hydrodynamic escape from the liquid surface of a molten proto-Moon assembling at 3-6 Earth radii. Such tidally-driven atmospheric escape persisting for less than 1 Kyr at temperatures $\sim 1600-1700$ K reproduces the measured lunar depletion in K and Na., Comment: Accepted for publication in ICARUS

The first attempt to determine the size of the Solar System was by Ptolemy, who assumed that the Solar System was filled by the epicycles of the planets and there is no empty space in the Universe. From the sizes of the planetary epicycles need to fit the observed planetary orbits, he was able to estimate the size of the Solar System (Sect. 15.1, Vol. 1). In his book Planetary Hypothesis, Ptolemy listed the maximum distance of Saturn from Earth as 19,865 Earth radii, and this was used as the maximum extent of the Solar System. In the heliocentric model, Copernicus was able to determine the relative sizes of the planetary orbits (Sect. 16.2, Vol. 1). Because the physical sizes of the planetary orbits are scaled to the distance between the Earth and the Sun, this distance represents the key parameter for determining the size of the Solar System.

In Ptolemaic cosmology, the Universe has a finite size defined by the celestial sphere upon which the fixed stars lie. Within this celestial sphere are the five planets and the Sun revolving around the Earth. Assuming that the interior volume of the celestial sphere is filled by orbits and epicycles of the planets, Ptolemy derived a size of the Universe that is 20,000 times the radius of the Earth (Chap. 15, volume 1). After the development of the heliocentric theory, the hypothesis of the daily rotation of the celestial sphere was replaced by the hypothesis of the rotation of the Earth. This removes the need for the stars to lie at the same distance and rotate together, which in turn opens the possibility that the stars may have different distances from Earth and that the Universe could be infinite in size (Chap. 18, Vol. 1). While Copernicus replaced the Earth with the Sun as the center of the Universe, this cannot be true in an infinite Universe. An infinite Universe has no center, and therefore whether the Universe is finite or infinite has implications for our place in the Universe.

GEO-X (GEOspace X-ray imager) is a 50 kg-class small satellite to image the global Earth’s magnetosphere in X-rays via solar wind charge exchange emission. A 12U CubeSat will be injected into an elliptical orbit with an apogee distance of ∼40 Earth radii. In order to observe the diffuse soft X-ray emission in 0.3-2 keV and to verify X-ray imaging of the dayside structures of the magnetosphere such as cusps, magnetosheaths and magnetopauses which are identified statistically by in-situ satellite observations, an original light-weight X-ray imaging spectrometer (∼10 kg, ∼10 W, ∼10×10×30 cm) will be carried. The payload is composed of a ultra light-weight MEMS Wolter type-I telescope (∼4×4 deg2 FOV

The Earth orientation sensor (ERS) device installed on board the spacecraft (SC) is discussed. In this device related to the local vertical reference, the so-called circular scanning principle is implemented. The circular scanning principle implies the angular field being scanned in a circumferential direction, with the angular radius coinciding with the angular radius of the Earth, and the signal of the receiving device being detected by two phase-sensitive detectors, which generate signals that determine the deviation of the instrument's optical reference axis from the vertical in two mutually perpendicular planes. Provided a mathematical description of the kinematic model of the Earth orientation sensor (EOS). Performed the validation of the analytical description of the device by using the Matlab system and with a model-based approach. As a result, defined that for reliable recognition of four points of the Earth-Space border intersection, it is desirable that the time between transitions approaches to 125ms. Thus, to receive a substantial measurement base on Z axis the angle at the apex of the scanning cone should be reduced. Modeling has shown that the optimal angle at the apex of the scanning cone for an orbital altitude range of 200-2000 km is 55 degrees.

Apollo lunar samples reveal that the Moon generated its own global magnetosphere, lasting from ~4.25 to ~2.5 billion years (Ga) ago. At peak lunar magnetic intensity (4 Ga ago), the Moon was volcanically active, likely generating a very tenuous atmosphere, and, it is believed, was at a geocentric distance of ~18 Earth radii (RE). Solar storms strip a planet’s atmosphere over time, and only a strong magnetosphere would be able to provide maximum protection. We present simplified magnetic dipole field modeling confined within a paraboloidal-shaped magnetopause to show how the expected Earth-Moon coupled magnetospheres provide a substantial buffer from the expected intense solar wind, reducing Earth’s atmospheric loss to space.

In July 2017, the MMS constellation was in the magnetotail with an apogee of 25 Earth radiiand an average inter-satellite distance of 10 km (i.e. at electron scales). On 23 July around16:19 UT, MMS was located at the edge of the current sheet which was in a quasi-staticstate. Then, MMS suddenly entered in the central plasma sheet and detected the local onsetof a small substorm as indicated by the AE index (~400 nT). Fast earthward plasma flowswere measured for about 1 hour starting with a period of quasi-steady flow and followed bya saw-tooth like series of fast flows associated with dipolarization fronts. This plasmatransport sequence finished with a flow reversal still occurring close to the magneticequator. In the present study, we investigate the energy conversion processes at ion andelectron scales for these different phases with particular attention on the processes in thevicinity of the dipolarization fronts.

Launch window design for the Magnetospheric Multiscale (MMS) mission ensured that no excessive eclipses would be encountered during the prime mission. However, no orbit solutions exist that satisfy the eclipse constraints indefinitely: most extended mission years contain 1–3 eclipses long enough to potentially damage either the spacecraft or its scientific instruments. Two steps were taken to improve the situation. Firstly, raising apogee radius from 25 to 29.34 Earth radii altered the Sun-Earth-MMS phasing, so efficiently achieving reductions in the long eclipse durations. These maneuvers were performed in February 2019, in preparation for the first pair of long eclipses during the subsequent August. Secondly, a set of operational steps were taken around the time of the eclipses to help maintain spacecraft and instrument temperatures while preventing power load shedding. These steps included raising key onboard temperatures through adjusting the spacecraft attitude to tilt the instrument deck towards the Sun, and engaging select heaters prior to going into eclipses. In addition, all scientific instruments were turned off, as well as high-power, non-critical spacecraft systems, to conserve energy. These steps each came with trade-offs which will be discussed in the paper. Finally, the results that were obtained when the spacecraft experienced the first set of extremely long eclipses will be discussed, as will lessons learned for future long eclipses.

Dark matter could be composed of compact dark objects (CDOs). These objects may interact very weakly with normal matter and could move freely {\it inside} the Earth. A CDO moving in the inner core of the Earth will have an orbital period near 55 min and produce a time dependent signal in a gravimeter. Data from superconducting gravimeters rule out such objects moving inside the Earth unless their mass $m_D$ and or orbital radius $a$ are very small so that $m_D\, a < 1.2\times 10^{-13}M_\oplus R_\oplus$. Here $M_\oplus$ and $R_\oplus$ are the mass and radius of the Earth., 8 pages, 7 figures

The Particle Detector (PD) experiment aboard the geostationary satellite GEO-KOMPSAT-2A (GK2A) measures populations of electrons and positive ions in the Earth’s geostationary orbit at a geographic longitude of $128.2^{\circ }\mbox{E}$, inclination of $0^{\circ }$ and a mean orbital radius of 6.6 Earth radii ($R_{E}$). The PD experiment consists of three sensors with different viewing angles relative to the spacecraft. Each sensor consists of two telescopes that are mechanically configured back-to-back with a field-of-view of $20^{\circ }\times 20^{\circ }$ and measures electrons and ions, using silicon detectors equipped with foils and magnets for the separation of ions and electrons. The energy ranges of the sensor for electrons and ions are 100–3800 keV and 148–22500 keV, respectively. A particular emphasis on electron measurement is given by allocating 48 energy bins in the measured energy range, whereas 22 energy bins are allocated for ion measurements. This unprecedented energy resolution of $\Delta E/E$ in the range 5–25% for the electron and ion flux measurements is acquired every three seconds with cyclic polling of each sensor every second to provide an effective temporal resolution of one second. Together with the magnetometer aboard the spacecraft, the PD experiment will provide quantitative observations that will enable improved understanding of the adiabatic and nonadiabatic dynamics of the Earth’s magnetosphere for space weather studies at geostationary orbits from the vantage point of a far-east longitude.

As an important source for large geomagnetic storms, an "ICME-in-sheath" is a completely shocked interplanetary coronal mass ejection (ICME) stuck in the sheath between a shock and host ejecta. Typical characteristics are identified from coordinated multi-sets of observations: (1) it is usually short in duration and lasts a few hours at 1 AU; (2) its solar wind parameters, in particular the magnetic field, seem to keep enhanced for a large range of distances; and (3) common ICME signatures are often lost. The host ejecta could be a single ICME or a complex ejecta, being fast enough to drive a shock. These results clarify previous misinterpretations of this phenomenon as a normal part of a sheath region. The "ICME-in-sheath" phenomenon, together with a preconditioning effect, produced an extreme set of the magnetic field, speed and density near 1 AU in the 2012 July 23 case, all around their upper limits at the same time. This is probably the most extreme solar wind driving at 1 AU and enables us to estimate the plausible upper limit for geomagnetic storm activity. With an appropriate modification in the southward field, we suggest that a geomagnetic storm with a minimum $D_{\rm st}$ of about $-2000$ nT could occur in principle. The magnetopause would be compressed to about 3.3 Earth radii from the Earth's center, well inside the geosynchronous orbit., Comment: Accepted for publication in The Astrophysical Journal Letters

We examine how water is produced globally over the lunar surface as it orbits in/out of the magnetotail. Due to the interaction of the solar wind (SW) with Earth's magnetic field, upstream the magnetic field is compressed down to ~10 Earth radii. However, the diverted stream of SW around Earth's magnetic field results in an extended depleted region of SW protons (positively charged hydrogen) out to 1000's of Earth radii, referred to as the magnetotail. The Moon orbits at a distance of ~40 Earth radii; therefore, upstream it is within the SW, but downstream it is partially shielded while in the magnetotail during full Moon. SW protons penetrate lunar soil particles and some H atoms can chemical react with oxygen to form water-like molecules such as OH/H2O. Most of the H atoms bounce around within grains until finding another hydrogen atom, chemically combine, and then escape the grain as H2 into the thin atmosphere. We developed a model to calculate the global distribution of OH produced in the lunar surface and H2 released to the atmosphere as the Moon orbits in/out of Earth's magnetotail. The model results are in good agreement with available observations., Comment: Under review with JGR

Asteroid impacts pose a major threat to all life on Earth. Deflecting an asteroid on an impact trajectory is critical to mitigating this threat. A kinetic impactor remains the most feasible asteroid deflection method. However, due to launch capability constraints, an impactor with a limited mass can only minimally change the velocity of an asteroid. To improve the deflection efficiency of the kinetic impactor strategy, this paper proposes the Assembled Kinetic Impactor (AKI), which combines the spacecraft with the launch vehicle upper stage. After the launch vehicle upper stage sends the spacecraft into an Earth-escaping trajectory, the spacecraft-rocket separation is not performed, and the spacecraft controls the AKI to impact the asteroid. By retaining the mass of the launch vehicle upper stage, the mass of the impactor is increased, thereby enhancing the deflection efficiency. According to the technical data of the Long March 5 (CZ-5) launch vehicle, missions to deflect Bennu are designed to demonstrate the power of the AKI concept. Simulation results of the AKI compared with the Classical Kinetic Impactor (CKI, with spacecraft-rocket separation) show that the addition of the mass of the upper stage increases the deflection distance by >3 times. To achieve a given deflection distance, the addition of the upper stage mass reduces the number of launches to 1/3 that of the number of CKI launches. The AKI concept makes it possible to deflect large Bennu-like asteroids with a nuclear-free technique with a 10-year launch lead time. Additionally, with a single CZ-5, the deflection distance of a 140-m-diameter asteroid with a 10-year launch lead time increases from less than 1 to more than 1 Earth radius, representing an improvement in the reliability and efficiency of asteroid deflection missions.

An interplanetary (IP) shock wave was recorded crossing the Magnetospheric Multiscale (MMS) constellation on 2018 January 8. Plasma measurements upstream of the shock indicate efficient proton acceleration in the IP shock ramp: 2-7 keV protons are observed upstream for about three minutes (~8000 km) ahead of the IP shock ramp, outrunning the upstream waves. The differential energy flux (DEF) of 2-7 keV protons decays slowly with distance from the ramp towards the upstream region (dropping by about half within 8 Earth radii from the ramp) and is lessened by a factor of about four in the downstream compared to the ramp (within a distance comparable to the gyroradius of ~keV protons). Comparison with test-particle simulations has confirmed that the mechanism accelerating the solar wind protons and injecting them upstream is classical shock drift acceleration. This example of observed proton acceleration by a low-Mach, quasi-perpendicular shock may be applicable to astrophysical contexts, such as supernova remnants or the acceleration of cosmic rays., Comment: 19 pages, 5 figures. To be published in the Astrophysical Journal Letters

Recent exoplanet statistics indicate that photo-evaporation has a great impact on the mass and bulk composition of close-in low-mass planets. While there are many studies addressing photo-evaporation of hydrogen-rich or water-rich atmospheres, no detailed investigation regarding rocky vapor atmospheres (or mineral atmospheres) has been conducted. Here, we develop a new 1-D hydrodynamic model of the UV-irradiated mineral atmosphere composed of Na, Mg, O, Si, their ions and electrons, includin molecular diffusion, thermal conduction, photo-/thermo-chemistry, X--ray and UV heating, and radiative line cooling (i.e., the effects of the optical thickness and non-LTE). The focus of this paper is on describing our methodology but presents some new findings. Our hydrodynamic simulations demonstrate that almost all of the incident X-ray and UV energy from the host-star is converted into and lost by the radiative emission of the coolant gas species such as Na, Mg, Mg$^+$, Si$^{2+}$, Na$^{3+}$ and Si$^{3+}$. For an Earth-size planet orbiting 0.02~AU around a young solar-type star, we find that the X-ray and UV heating efficiency is as small as $1 \times 10^{-3}$, which corresponds to 0.3~$\Mearth$/Gyr of the mass loss rate simply integrated over all the directions. Because of such efficient cooling, the photo-evaporation of the mineral atmosphere on hot rocky exoplanets with masses of $1\Mearth$ is not massive enough to exert a great influence on the planetary mass and bulk composition. This suggests that close-in high-density exoplanets with sizes larger than the Earth radius survive in the high-UV environments., Comment: 23 pages, accepted for publication in the Monthly Notices of the Royal Astronomical Society

Exoplanet discoveries have reached into the realm of terrestrial planets that are becoming the subject of atmospheric studies. One such discovery is LHS 3844b, a 1.3 Earth radius planet in a 0.46 day orbit around an M4.5-5 dwarf star. Follow-up observations indicate that the planet is largely devoid of substantial atmosphere. This lack of significant atmosphere places astrophysical and geophysical constraints on LHS 3844b, primarily the degree of volatile outgassing and the rate of atmosphere erosion. We estimate the age of the host star as $7.8\pm1.6$ Gyrs and find evidence of an active past comparable to Proxima Centauri. We use geodynamical models of volcanic outgassing and atmospheric erosion to show that the apparent lack of atmosphere is consistent with a volatile-poor mantle for LHS 3844b. We show the core is unlikely to host enough C to produce a sufficiently volatile-poor mantle, unless the bulk planet is volatile-poor relative to Earth. While we cannot rule out a giant impact stripping LHS 3844b's atmosphere, we show this mechanism would require significant mantle stripping, potentially leaving LHS 3844b as an Fe-rich "super-Mercury". Atmospheric erosion by smaller impacts is possible, but only if the planet has already begun degassing and is bombarded by $10^3$ impactors of radius 500-1000 km traveling at escape velocity. We discuss formation and migration scenarios that could account for a volatile poor origin, including the potential for an unobserved massive companion planet. A relatively volatile-poor composition of LHS 3844b suggests that the planet formed interior to the system snow-line., Comment: 23 pages, 14 figures, accepted for publication in the Planetary Science Journal

Solar neutrinos upscattering inside the Earth can source unstable particles that can decay inside terrestrial detectors. Contrary to naive expectations we show that when the decay length is much shorter than the radius of the \emph{Earth} (rather than the detector), the event rate is independent of the decay length. In this paper we study a transition dipole operator (neutrino dipole portal) and show that Borexino's existing data probes previously untouched parameter space in the 0.5--20 MeV regime, complementing recent cosmological and supernova bounds. We briefly comment on similarities and differences with luminous dark matter and comment on future prospects for analogous signals stemming from atmospheric neutrinos., Comment: Code made public, bug fixed, sensitivities updated, qualitative results unchanged

The angle at which an observer in the centre of the moon would see the apparent radius of the earth in the sky is called the parallax of the moon.

Observations of the Earth's exosphere have unveiled an extended envelope of hydrogen reaching further than 10 Earth radii composed of atoms orbiting around the Earth. This large envelope increases significantly the opacity of the Earth to Lyman-alpha (Lya) photons coming from the Sun, to the point of making feasible the detection of the Earth's transit signature from 1.35 pc if pointing with an 8~meter primary mirror space telescope through a clean line of sight (NH < 1e17 cm-2), as we show. In this work, we evaluate the potential detectability of Earth analogues orbiting around nearby M-type stars by monitoring the variability of the Lya flux. We show that, in spite of the interstellar, heliospheric and astrospheric absorption, the transit signature in M5 V type stars would be detectable with a dedicated Lya flux monitor implemented in a 4-8 m class space telescope. Such monitoring programs would enable measuring the robustness of planetary atmospheres under heavy space weather conditions like those produced by M-type stars. A 2-m class telescope, such as the World Space Observatory, would suffice to detect an Earth-like planet orbiting around Proxima Centauri, if there was such a planet or nearby M5 type stars., submitted to Experimental Astronomy, 7 figures

Magnetosheath high‐speed jets—localized dynamic pressure enhancements typically of ∼1 Earth radius in size—impact the dayside magnetopause several times per hour. Here we present the first in situ measurements suggesting that such an impact triggered magnetopause reconnection. We use observations from the five Time History of Events and Macroscale Interactions during Substorms spacecraft in a string‐of‐pearls configuration on 7 August 2007. The spacecraft recorded magnetopause in‐and‐out motion during an impact of a magnetosheath jet (VN∼−300 km/s along the magnetopause normal direction). There was no evidence for reconnection for the preimpact crossing, yet three probes observed reconnection after the impact. We infer that the jet impact compressed the originally thick (60–70 di), high magnetic shear (140–160° magnetopause until it was thin enough for reconnection to occur. Magnetosheath high‐speed jets could therefore act as a driver for bursty dayside reconnection.

The vertical refractivity gradient (VRG) is critical to weather radar beam propagation. The most common method of calculating beam paths uses the 4/3 Earth radius model, which corresponds to standard refraction conditions. In the present work, to better document propagation conditions for radar electromagnetic waves, which is essential for hydrology and numerical weather forecast models to more fully benefit from observations taken from the new-generation weather radar network in China, VRG spatial and temporal variations in the first kilometers above the surface are explored using 6-yr sounding observations. Under the effects of both regional climatic and topographic conditions, VRG values for most of the radars are generally smaller than those of the standard conditions for much of the year. There are similar or slightly larger values at only a few radar sites. Smaller VRG values are more frequent and widespread, especially during rainy seasons when weather radar observations are important. In such conditions, beam heights estimated using standard atmospheric refraction are overestimated relative to actual heights for most of the radars. Underestimates are much less common and of much shorter duration. However, height deviations are acceptable for being well within the uncertainty of radar echo height owing to the ~1° beamwidth. In coastal areas and the middle and lower reaches of the Yangtze River, radar observations should be applied with much more caution because of the greater risk of beam blockage and clutter contamination.

The hydrogen exosphere constitutes the uppermost atmospheric layer of the Earth, and its shape may reflect the last stage of the atmospheric escape process. The distribution of hydrogen in the outer exosphere remains unobserved because outer geocoronal emissions are difficult to observe from within the exosphere. In this study, we used the Lyman Alpha Imaging Camera (LAICA) onboard the Proximate Object Close Flyby with Optical Navigation (PROCYON) spacecraft, located outside the exosphere, to obtain the first image of the entire geocorona that extends to more than 38 Earth radii. The observed emission intensity distribution can be reproduced using our analytical model that has three parameters: exobase temperature, exobase density, and solar radiation pressure, which implies that hot hydrogen production in the magnetized plasmasphere is not the dominant process shaping the outer hydrogen exosphere. However, the role of the magnetic effect in determining the total escape flux cannot be ruled out

The Earth's geomagnetic poles represent the axis of a dipole field of best fit to the Earth's true magnetic field. Canada currently hosts the Geomagnetic North Pole on Ellesmere Island, near 80 N 75 W. In the vicinity of the geomagnetic pole, the magnetic field lines of the Earth extend many Earth radii into space and interact with the solar wind, leading to particle precipitation and horizontal ionospheric plasma drifts. Particle precipitation produces the visible Aurora Borealis in the area shown as green in Figure 1, which we denote the auroral oval. North of the auroral oval is the region of the polar cap, where the solar wind drives horizontal plasma drifts, shown by the red contours in Figure 1. Previous over-thehorizon radar (OTHR) experiments have looked at operation in both the auroral oval and the polar cap.

We investigate a new class of habitable planets composed of water-rich interiors with massive oceans underlying H2-rich atmospheres, referred to here as Hycean worlds. With densities between those of rocky super-Earths and more extended mini-Neptunes, Hycean planets can be optimal candidates in the search for exoplanetary habitability and may be abundant in the exoplanet population. We investigate the bulk properties (masses, radii, and temperatures), potential for habitability, and observable biosignatures of Hycean planets. We show that Hycean planets can be significantly larger compared to previous considerations for habitable planets, with radii as large as 2.6 Earth radii (2.3 Earth radii) for a mass of 10 Earth masses (5 Earth masses). We construct the Hycean habitable zone (HZ), considering stellar hosts from late M to sun-like stars, and find it to be significantly wider than the terrestrial-like HZ. While the inner boundary of the Hycean HZ corresponds to equilibrium temperatures as high as ~500 K for late M dwarfs, the outer boundary is unrestricted to arbitrarily large orbital separations. Our investigations include tidally locked `Dark Hycean' worlds that permit habitable conditions only on their permanent nightsides and `Cold Hycean' worlds that see negligible irradiation. Finally, we investigate the observability of possible biosignatures in Hycean atmospheres. We find that a number of trace terrestrial biomarkers which may be expected to be present in Hycean atmospheres would be readily detectable using modest observing time with the James Webb Space Telescope (JWST). We identify a sizable sample of nearby potential Hycean planets that can be ideal targets for such observations in search of exoplanetary biosignatures., Comment: Published in The Astrophysical Journal

No circumbinary planets have been discovered smaller than 3 Earth radii, yet planets of this small size comprise over 75% of the discoveries around single stars. The observations do not prove the non-existence of small circumbinary planets, but rather they are much harder to find than around single stars, because their transit timing variations are much larger than the transit durations. We present STANLEY: an automated algorithm to find small circumbinary planets. It employs custom methods to detrend eclipsing binary light curves and stack shallow transits of variable duration and interval using N-body integrations. Applied to the Kepler circumbinaries, we recover all known planets, including the three planets of Kepler-47, and constrain the absence of additional planets of similar or smaller size. We also show that we could have detected < 3 Earth radii planets in half of the known systems. Our work will ultimately be applied to a broad sample of eclipsing binaries to (hopefully) produce new discoveries, and derive a circumbinary size distribution which can be compared to that for single stars., Under review at ApJ after responding to first referee report. 32 pages. 17 figures (some pretty)

Kepler planets (including super-Earths and sub-Neptunes, from 1 to 4 Earth radii) are likely formed before the gaseous proto-planetary disks have dissipated, as are the Jovian planets. If the metal content in these disks resembles that in the host stars, one might expect Kepler planets to occur more frequently, and to be more massive, around metal-rich stars. Contrary to these expectations, we find that the radii of Kepler planets (a proxy for mass) are independent of host metallicity. Previous claims that larger planets prefer more metal-rich stars can be adequately explained by the combined facts that more massive stars tend to host bigger planets, and that more massive stars are also more metal rich in the Kepler sample. We interpret this independence as that the mass of a Kepler planet is not determined by the availability of solids, but is instead regulated by an as yet unknown process. Moreover, we find that the occurrence rates of Kepler planets rise only weakly with stellar metallicity, a trend that is further flattened when the influence of close stellar binaries is accounted for. We explain this weak dependence, in contrast to the strong dependence exhibited by Jovian planets, using a phenomenological model, wherein the masses of proto-planetary disks have a much larger spread than the spread in stellar metallicity, and wherein the formation of Jovian planets requires disks that contain some $5$ times more solid than that needed to form Kepler planets. This model predicts that stars more metal-poor than half-solar should rarely host any Kepler planets., Accepted to AJ, major expansion on sample bias and completeness correction. Conclusions unchanged

The disintegrating planet candidate K2-22 b shows periodic and stochastic transits best explained by an escaping debris cloud. However, the mechanism that creates the debris cloud is unknown. The grain size of the debris as well as its sublimation rate can be helpful in understanding the environment that disintegrates the planet. Here, we present simultaneous photometry with the g band at 0.48 microns and KS band at 2.1 microns using the Large Binocular Telescope. During an event with very low dust activity, we put a new upper limit on the size of the planet of 0.71 earth radii or 4500 km. We also detected a medium-depth transit which can be used to constrain the dust particle sizes. We find that the median particle size must be larger than about 0.5 to 1.0 microns, depending on the composition of the debris. This leads to a high mass loss rate of about 3e8 kg/s that is consistent with hydrodynamic escape models. If they are produced by some alternate mechanism such as explosive volcanism, it would require extraordinary geological activity. Combining our upper limits on the planet size with the high mass loss rate, we find a lifetime of the planet of less than 370 Myr. This drops to just 21 Myr when adopting the 0.02 earth masses predicted from hydrodynamical models., AJ, accepted, 13 pages

Plasma energization in Earth's magnetotail is supported by acceleration processes in (and around) magnetic reconnection regions. Hot plasma flows and strong electromagnetic waves, generated by magnetic energy release during reconnection, transport energy necessary for current system intensification and particle acceleration in the inner magnetosphere. Earth's magnetotail configuration includes two main reconnection regions (X lines): the near-Earth X line, which has been well studied by several multispacecraft missions, and the distant X line, which has been much less investigated. In this paper, we utilize the unique data set gathered by two ARTEMIS spacecraft in 2010 at radial distances between lunar orbit and ∼200 RE (Earth radii). We identify an X line at around ∼80 RE and collect statistics on hot plasma flows observed around and beyond this distance. Ion spectra within these flows are well fitted by a power law with the exponential tail starting above an energy ϵ0∼ 2–5 keV. Assuming that these spectra are originated at the distant X line, we examine the characteristics of the acceleration at the distant tail reconnection region.