Earth's Exosphere Research Articles

Calculation of the influence of the entropy of stars on the Earth's exosphere and the theory of entropic gravity

In the first part of this study, the entropic contribution of star objects, observable during the night between November 13 and 14, 2021, in the sky above Belgrade (Lat. 44o 49' 04'' N, Long. 20o 27' 25'' E, mean Elev. 117 m), Serbia, to the thermodynamic equilibrium of the Earth's exosphere, was determined. In the second part of the study, the force of gravitational attraction between the considered star objects and the Earth was calculated, by applying entropic gravity theory. The obtained results shed new light on the importance of star objects for sustaining the Earth's thermodynamic system.

Soft X‐Ray Imaging of Earth's Dayside Magnetosheath and Cusps Using Hybrid Simulations

AbstractInteractions between solar wind ions and neutral hydrogen atoms in Earth's exosphere can lead to the emission of soft X‐rays. Upcoming missions such as SMILE and LEXI aim to use soft X‐ray imaging to study the global structure of the magnetosphere. Although the magnetosheath and dayside magnetopause can often be driven by kinetic physics, it has typically been omitted from fluid simulations used to predict X‐ray emissions. We study the possible results of soft X‐ray imaging using hybrid simulations under quasi‐radial interplanetary magnetic fields, where ion‐ion instabilities drive ultra‐low frequency foreshock waves, leading to turbulence in the magnetosheath, affecting the dynamics of the cusp and magnetopause. We simulate soft X‐ray emission to determine what may be seen by missions such as LEXI, and evaluate the possibility of identifying kinetic structures. While kinetic structures are visible in high‐cadence imaging, current instruments may not have the time resolution to discern kinetic signals.

Devolatilization of Subducting Slabs, Part II: Volatile Fluxes and Storage

AbstractSubduction is a crucial part of the long‐term water and carbon cycling between Earth's exosphere and interior. However, there is broad disagreement over how much water and carbon is liberated from subducting slabs to the mantle wedge and transported to island‐arc volcanoes. In the Tian et al. (2019) Part I, we parameterize the metamorphic reactions involving H2O and CO2 for representative subducting lithologies. On this basis, a two‐dimensional reactive transport model is constructed in this Part II. We assess the various controlling factors of CO2 and H2O release from subducting slabs. Model results show that up‐slab fluid flow directions produce a flux peak of CO2 and H2O at subarc depths. Moreover, infiltration of H2O‐rich fluids sourced from hydrated slab mantle enhances decarbonation or carbonation at lithological interfaces, increases slab surface fluxes, and redistributes CO2 from basalt and gabbro layers to the overlying sedimentary layer. As a result, removal of the cap sediments (by diapirism or off‐scraping) leads to elevated slab surface CO2 and H2O fluxes. The modeled subduction efficiency (the percentage of initially subducted volatiles retained until ∼200 km deep) of H2O and CO2 is increased by open‐system effects due to fractionation within the interior of lithological layers.

Earth as an exoplanet mission concept for a lunar orbiting cubesat

There is a growing interest in Lunar exploration fed by the perception that the Moon can be made accessible to low-cost missions in the next decade. The on-going projects to set a communications relay in Lunar orbit and a deep space Gateway, as well as the spreading of commercial-of-the shelf (COTS) technology for small space platforms such as the cubesats contribute to this perception. Small, cubesat size satellites orbiting the Moon offer ample opportunities to study the Moon and enjoy an advantage point to monitor the Solar System and the large scale interaction between the Earth and the solar wind. In this article, we describe the technical characteristics of a 12U cubesat to be set in polar Lunar orbit for this purpose and the science behind it. The mission is named EarthASAP (Earth AS An exoPlanet) and was submitted to the Lunar Cubesats for Exploration (LUCE) call in 2016. EarthASAP was designed to monitor hydrated rock reservoirs in the Lunar poles and to study the interaction between the large Earth's exosphere and the solar wind in preparation for future exoplanetary missions.

On the feasibility of studying the exospheres of Earth-like exoplanets by Lyman-α monitoring

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.

Discovery of Suprathermal Ionospheric Origin Fe+ in and Near Earth's Magnetosphere

AbstractSuprathermal (87–212 keV/e) singly charged iron, Fe+, has been discovered in and near Earth's ~9–30 RE equatorial magnetosphere using ~21 years of Geotail STICS (suprathermal ion composition spectrometer) data. Its detection is enhanced during higher geomagnetic and solar activity levels. Fe+, rare compared to dominant suprathermal solar wind and ionospheric origin heavy ions, might derive from one or all three candidate lower‐energy sources: (a) ionospheric outflow of Fe+ escaped from ion layers near ~100 km altitude, (b) charge exchange of nominal solar wind iron, Fe+≥7, in Earth's exosphere, or (c) inner source pickup Fe+ carried by the solar wind, likely formed by solar wind Fe interaction with near‐Sun interplanetary dust particles. Earth's semipermanent ionospheric Fe+ layers derive from tons of interplanetary dust particles entering Earth's atmosphere daily, and Fe+ scattered from these layers is observed up to ~1000 km altitude, likely escaping in strong ionospheric outflows. Using ~26% of STICS's magnetosphere‐dominated data when possible Fe+2 ions are not masked by other ions, we demonstrate that solar wind Fe charge exchange secondaries are not an obvious Fe+ source. Contemporaneous Earth flyby and cruise data from charge‐energy‐mass spectrometer on the Cassini spacecraft, a functionally identical instrument, show that inner source pickup Fe+ is likely not important at suprathermal energies. Consequently, we suggest that ionospheric Fe+ constitutes at least a significant portion of Earth's suprathermal Fe+, comparable to the situation at Saturn where suprathermal Fe+ is also likely of ionospheric origin.

Scientists Map Temperature and Density in Earth's Exosphere

Data from multiple orbiters give a clearer picture of how density and temperature interact and what that could mean for future satellite missions.

Rethinking the Ancient Sulfur Cycle

The sulfur biogeochemical cycle integrates the metabolic activity of multiple microbial pathways (e.g., sulfate reduction, disproportionation, and sulfide oxidation) along with abiotic reactions and geological processes that cycle sulfur through various reservoirs. The sulfur cycle impacts the global carbon cycle and climate primarily through the remineralization of organic carbon. Over geological timescales, cycling of sulfur is closely tied to the redox state of Earth's exosphere through the burial of oxidized (sulfate) and reduced (sulfide) sulfur species in marine sediments. Biological sulfur cycling is associated with isotopic fractionations that can be used to trace the fluxes through various metabolic pathways. The resulting isotopic data provide insights into sulfur cycling in both modern and ancient environments via isotopic signatures in sedimentary sulfate and sulfide phases. Here, we review the deep-time δ34S record of marine sulfates and sulfides in light of recent advances in understanding how isotopic signatures are generated by microbial activity, how these signatures are encoded in marine sediments, and how they may be altered following deposition. The resulting picture shows a sulfur cycle intimately coupled to ambient carbon cycling, where sulfur isotopic records preserved in sedimentary rocks are critically dependent on sedimentological and geochemical conditions (e.g., iron availability) during deposition.

Terrestrial exospheric hydrogen density distributions under solar minimum and solar maximum conditions observed by the TWINS stereo mission

Abstract. Circumterrestrial Lyman-α column brightness observations above 3 Earth radii (Re) have been used to derive separate 3-D neutral hydrogen density models of the Earth's exosphere for solar minimum (2008, 2010) and near-solar-maximum (2012) conditions. The data used were measured by Lyman-α detectors (LAD1/2) onboard each of the TWINS satellites from very different orbital positions with respect to the exosphere. Exospheric H atoms resonantly scatter the near-line-center solar Lyman-α flux at 121.6 nm. Assuming optically thin conditions above 3Re along a line of sight (LOS), the scattered LOS-column intensity is proportional to the LOS H-column density. We found significant differences in the density distribution of the terrestrial exosphere under different solar conditions. Under solar maximum conditions we found higher H densities and a larger spatial extension compared to solar minimum. After a continuous, 2-month decrease in (27 day averaged) solar activity, significantly lower densities were found. Differences in shape and orientation of the exosphere under different solar conditions exist. Above 3 Re, independent of solar activity, increased H densities appear on the Earth's nightside shifted towards dawn. With increasing distance (as measured at 8Re) this feature is shifted westward/duskward by between −4 and −5° with respect to midnight. Thus, at larger geocentric distance the exosphere seems to be aligned with the aberrated Earth–solar-wind line, defined by the solar wind velocity and the orbital velocity of the Earth. The results presented in this paper are valid for geocentric distances between 3 and 8Re.

Measuring the faint glow of the Earth's thin exosphere

There is no “edge of space,” no sharp demarcation where the Earth's atmosphere ends and outer space begins. Instead, there is the fuzzy, progressively thinning exosphere, a region filled mostly by neutral hydrogen atoms that stretches from an altitude of 500 kilometers to hundreds of thousands of kilometers above the Earth's surface. So far, the outer detectable limit of the exosphere is around 15.5 Earth radii—roughly half the distance between the Earth and the Moon.

Modeling the satellite particle population in the planetary exospheres: Application to Earth, Titan and Mars

The planetary exospheres are poorly known in their outer parts, since the low neutral densities are difficult to measure in situ. The exospheric models are thus often the main source of information at such high altitudes. We revisit here the importance of a specific exospheric population, i.e. the satellite particles, which is usually neglected in the models. These particles are indeed produced through rare collisions in the exospheres, and may either be negligible or dominate the exospheres of all planets with dense atmospheres in our Solar System, depending on the balance between their sources and losses. Richter et al. (Richter, E., Fahr, H.J., Nass, H.U. [1979]. Planet. Space Sci. 27, 1163–1173) were the first to propose, beyond the Chamberlain’s (Chamberlain, J.W. [1963]. Planet. Space Sci. 11, 901–901) rough approximation, a rigorous approach for these particles by using the Boltzmann equation in the Earth exosphere below 3000km altitude. They pointed out their negligible presence at low altitudes without doing this calculation at higher altitudes. We further investigate this approach at Earth and apply it another planetary exospheres – Mars and Titan – thanks to improvements in the computing power and the collected planetary data. We determine the contribution of the satellite particles densities of light elements (H2 at Titan, H at Earth and Mars), and show in particular that the H satellite particles may contribute very significantly to the martian exospheric densities at high altitudes. The H2 satellite particles are also nonnegligible at Titan whereas the H satellite population represents only a small fraction of the total density at Earth. Considering collisionless exospheric profiles – such as the Chamberlain (Chamberlain, J.W. [1963]. Planet. Space Sci. 11, 901–901) approach including the ballistic and escaping populations only – could thus lead to significant underestimations of the total densities at high altitudes in some conditions.

Non‐thermal processes in coronae and beyond

AbstractThis contribution summarizes the splinter session “Non‐thermal processes in coronae and beyond” held at the Cool Stars 17 workshop in Barcelona in 2012. It covers new developments in high energy non‐thermal effects in the Earth's exosphere, solar and stellar flares, the diffuse emission in star forming regions and reviews the state and the challenges of the underlying atomic databases. (© 2013 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

AXIOM: Advanced X‐ray imaging of the magnetosheath

AbstractAXIOM (Advanced X‐ray Imaging Of the Magnetosphere) is a concept mission which aims to explain how the Earth's magnetosphere responds to the changing impact of the solar wind using a unique method never attempted before; performing wide‐field soft X‐ray imaging and spectroscopy of the magnetosheath, magnetopause and bow shock at high spatial and temporal resolution. Global imaging of these regions is possible because of the solar wind charge exchange (SWCX) process which produces elevated soft X‐ray emission from the interaction of high charge‐state solar wind ions with primarily neutral hydrogen in the Earth's exosphere and near‐interplanetary space (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Exospheric solar wind charge exchange as seen by XMM‐Newton

AbstractWe review a selection of recent papers describing solar wind charge exchange emission occurring in the Earth's exosphere as seen by the X‐ray observatory XMM‐Newton. We discuss the detection of this emission, the occurrence with respect to the solar cycle and solar activity, and various spectral signatures observed. We also describe a model developed to predict the X‐ray signal from exospheric charge exchange as would be detected by XMM‐Newton, given the upstream solar wind conditions obtained from in situ solar wind monitors (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Suzaku observations of charge exchange emission from solar system objects

AbstractRecent results of charge exchange emission from solar system objects observed with the Japanese Suzaku satellite are reviewed. Suzaku is of great importance to investigate diffuse X‐ray emission like the charge exchange from planetary exospheres and comets. The Suzaku studies of Earth's exosphere, Martian exosphere, Jupiter's aurorae, and comets are overviewed (© 2012 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

A high charge state coronal mass ejection seen through solar wind charge exchange emission as detected by XMM-Newton

We present the analysis of an observation by XMM-Newton that exhibits strongly variable, low-energy diffuse X-ray line emission. We reason that this emission is due to localised solar wind charge exchange (SWCX), originating from a passing cloud of plasma associated with a Coronal Mass Ejection (CME) interacting with neutrals in the Earth's exosphere. This case of SWCX exhibits a much richer emission line spectrum in comparison with previous examples of geocoronal SWCX or in interplanetary space. We show that emission from OVIII is very prominent in the SWCX spectrum. The observed flux from oxygen ions of 18.9 keV cm-2 s-1 sr-1 is consistent with SWCX resulting from a passing CME. Highly ionised silicon is also observed in the spectrum, and the presence of highly charged iron is an additional spectral indicator that we are observing emission from a CME. We argue that this is the same event detected by the solar wind monitors ACE and Wind which measured an intense increase in the solar wind flux due to a CME that had been released from the Sun two days previous to the XMM-Newton observation.

The H/C ratios of Earth's near-surface and deep reservoirs, and consequences for deep Earth volatile cycles

The H/C mass ratio of the Earth's exosphere, which consists of the fluid envelopes plus the crust, is 1.95 ± 0.15. In contrast, the H/C ratios of undegassed oceanic basalts are significantly lower, ranging from 1.2 down to 0.05. Reconstruction of source H/C ratios by accounting for H/C fractionation during partial melting and addition of carbon-enriched low-degree partial melts suggests that the source regions of MORB have H/C ratios in the range of 0.75 ± 0.25 and those of OIB have ratios in the interval 0.5 ± 0.3. Combining these estimates with plausible limits on the relative proportions of the OIB and MORB sources indicates that the total H inventory of the mantle is equivalent to between 0.2 and 1.6 times the H in the exosphere, assuming that there are no significant hidden reservoirs unsampled by oceanic basalts. Combining the H contents and H/C ratios of the mantle and the exosphere suggests that the H/C ratio of the bulk silicate Earth, (H/C) BSE, is 0.99 ± 0.42, significantly greater than the H/C ratio of chondrites, which have H/C ratios no greater than 0.55. The superchondritic (H/C) BSE ratio likely results from preferential sequestration of C in the core, though it may also partly reflect a cometary origin for some portion of the BSE volatile inventory. The high (H/C) BSE ratio, combined with a D/H ratio similar to chondrites, argues strongly that the BSE volatile inventory is not chiefly derived from a late veneer. The large difference in H/C ratio between the exosphere and the mantle could reflect early Earth processes such as preferential retention of C in a crystallizing magma ocean in reduced phases such as diamond, or selective loss of a massive CO 2-rich atmosphere. Alternatively, it may have arisen by enhanced subduction of carbon relative to hydrogen. If the latter is the case, carbon in the mantle is likely dominantly recycled.

Storm phase dependence of ion outflow: Statistical signatures obtained by IMAGE/LENA

[1] The low-energy neutral atom (LENA) imager on board the Imager for Magnetopause-to-Aurora Global Exploration (IMAGE) spacecraft can observe energetic neutral atoms (ENA) of 10 eV to a few keV generated by upflowing ions through charge exchange with the Earth's exosphere. Using IMAGE/LENA data, we statistically analyzed behaviors of the ion outflow in the main and recovery phases of the magnetic storms from June 2000 to December 2001. Results show that during the main phase, most of ENA emissions from the Earth's direction are accompanied by the solar wind dynamic pressure (Pdy) enhancements. For the recovery phase, there are no such tendencies. Instead, the ENA flux shows large values at the beginning of the recovery phase, and then decreases with the storm recovery. These results suggest that the dominant mechanism responsible for the ion outflow during the magnetic storms can be totally different between the two phases.

Ion-cyclotron wave generation by planetary ion pickup

Ion-cyclotron waves play important roles in planetary magnetospheres and are diagnostic of the processes operating in the magnetosphere and of the composition of the plasma producing the waves. At Jupiter, Io's exosphere interacts with the corotating magnetospheric plasma. At Saturn, the neutral torus around the E ring interacts with the corotating plasma. At the unmagnetized planets, Mars and Venus, the interaction is between the solar-wind flow and the planetary exosphere. A possible analog of these processes exists in the vicinity of the Earth's polar cusp where the shocked solar-wind plasma penetrates the Earth's exosphere.

XMM‐NewtonObservation of Solar Wind Charge Exchange Emission

We present an XMM-Newton spectrum of diffuse X-ray emission from within the solar system. The spectrum is dominated by O VII and O VIII lines at 0.57 keV and 0.65 keV, O VIII (and possibly Fe XVII) lines at approximately 0.8 keV, Ne IX lines at approximately 0.92 keV, and Mg XI lines at approximately 1.35 keV. This spectrum is consistent with what is expected from charge exchange emission between the highly ionized solar wind and either interstellar neutrals in the heliosphere or material from Earth's exosphere. The emission is clearly seen as a low-energy ( E less than 1.5 keV) spectral enhancement in one of a series of observations of the Hubble Deep Field North. The X-ray enhancement is concurrent with an enhancement in the solar wind measured by the ACE satellite. The solar wind enhancement reaches a flux level an order of magnitude more intense than typical fluxes at 1 AU, and has ion ratios with significantly enhanced higher ionization states. Whereas observations of the solar wind plasma made at a single point reflect only local conditions which may only be representative of solar wind properties with spatial scales ranging from less than half of an Earth radii (approximately 10 s) to 100 Earth radii, X-ray observations of solar wind charge exchange are remote sensing measurements which may provide observations which are significantly more global in character. Besides being of interest in its own right for studies of the solar system, this emission can have significant consequences for observations of more cosmological objects. It can provide emission lines at zero redshift which are of particular interest (e.g., O VII and O VIII) in studies of diffuse thermal emission, and which can therefore act as contamination in objects which cover the entire detector field of view. We propose the use of solar wind monitoring data, such as from the ACE and Wind spacecraft, as a diagnostic to screen for such possibilities.