The Mini Induced Magnetospheres at Mars Dubinin, E.; Fraenz, M.; Pätzold, M. ...
Geophysical research letters,
16 February 2023, Letnik:
50, Številka:
3
Journal Article
Recenzirano
Odprti dostop
We report on observations made by the Mars Atmosphere and Volatile EvolutioN spacecraft at Mars, in the region of the ion plume. We observe that in some cases, when the number density of oxygen ions ...is comparable to the density of the solar wind protons interaction between both plasmas leads to formation in the magnetosheath of mini induced magnetospheres possessing all typical features of induced magnetospheres typically observed at Mars or Venus: a pileup of the magnetic field at the head of the ion cloud, magnetospheric cavity, partially void of solar wind protons, draping of the interplanetary magnetic field around the mini obstacle, formation of a magnetic tail with a current sheet, in which protons are accelerated by the magnetic field tensions. These new observations may shed a light on the mechanism of formation of induced magnetospheres.
Plain Language Summary
There is a class of the induced planetary magnetospheres when the absence of intrinsic magnetic field allows a direct interaction of solar wind with planetary atmospheres/ionospheres. We have shown the existence of mini‐induced magnetospheres at Mars. When the density of the extracted from the ionosphere oxygen ions becomes comparable with the proton density in solar wind mini‐induced magnetospheres with all typical features of the planetary induced magnetospheres arise.
Key Points
Oxygen ions extracted from the Martian ionosphere interact with shocked solar wind in the magnetosheath
When the ion densities of both plasmas become comparable the mini induced magnetospheres are built
These Magnetospheres possess all typical features of the classical induced magnetospheres
Analysis of Mars Atmosphere and Volatile Evolution (MAVEN)/Supra‐Thermal And Thermal Ion Composition observations in the Martian upper atmosphere, bounded at higher altitudes by the shocked solar ...wind, shows that the draping of interplanetary magnetic field penetrates down to low altitudes (∼200−250 km) and governs dynamics of the ionosphere. The upper ionospheric plasma is driven into motion flowing around Mars similar to the shocked solar wind in the adjacent magnetosheath. Such a fluid‐like motion is accompanied by ion acceleration caused by the bending of the magnetic field, leading to ion extraction and finally to ion pickup. Extraction of ions and their acceleration produces a recoil effect of the bulk ionosphere in the opposite direction. This provides a strong asymmetry in ion dynamics in two different hemispheres, accompanied by wrapping of the magnetic field lines around Mars and respective reconnection.
Plain Language Summary
Although the Martian magnetosphere is hybrid and contains components of the induced and intrinsic magnetosphere, is possible to display these components by using the specific coordinate systems. Here we study the properties of the induced magnetosphere using the data obtained by MAVEN spacecraft. The interplanetary magnetic field penetrates deep into the Martian ionosphere draping around Mars and drive to the motion dense ionospheric plasma. Draping features and the induced plasma motions occur different in two hemispheres determined by the direction of the motional electric field in the solar wind. Ion acceleration and extraction is accompanied by a recoil effect that leads to a shift and asymmetry of the ionosphere.
Key Points
Draping of the interplanetary magnetic field around Mars penetrates deep to the ionosphere enveloping the planet and driving the ionosphere to the bulk motion
Draping and motion of the ionospheric plasma is characterized by asymmetry by the direction of the motional electric field in solar wind
Ion acceleration and extraction from the ionosphere is accompanied by a shift of the bulk ionosphere in the opposite direction
We report on observations made by the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft, in the shocked solar wind‐ionosphere interface of Mars. We observe a strong asymmetry in plasma flow ...governed by the direction of the motional electric field. In the hemisphere, in which the motional electric field ∼−V × B is pointed outward the planet the solar wind flow is decelerated by the j × B force related to the magnetic field compression in the barrier. In contrast, in the opposite hemisphere, the solar wind flow is accelerated. The gain in velocity is about 100–200 km/s. The dynamics of ionospheric ions are also very different on both sides. Such an asymmetry implies very different patterns of the electric current closure and the electromagnetic forces in both hemispheres.
Plain Language Summary
Solar wind interacts directly with the ionosphere of Mars. The flow pattern in the interface region of such an interaction turns out to be different for different orientations of the interplanetary magnetic field. This asymmetry is governed by the direction of the motional electric field −1/c(V × B) aroused due to the solar wind flow across the magnetic field. Structure of the interface occurs very different. In the hemisphere, in which the motional electric field is pointed outward of Mars, the shocked solar wind flow is decelerated. In the hemisphere, in which the motional electric field is pointed toward the planet, the plasma flow is accelerated.
Key Points
Plasma flow in the solar wind‐ionosphere interface at Mars depends on sign of the cross‐flow component of the interplanetary magnetic field
The motional electric field in the solar wind controls such a flow in the interface
The shocked solar wind is accelerated in the interface of the hemisphere in which the motional electric field pointed toward the planet
Based on the Mars Atmosphere and Volatile EvolutioN (MAVEN) observations, we have analyzed the role of the crustal magnetic field on ion loss driven by the direct interaction of the solar wind with ...the Mars ionosphere. Crustal magnetic fields significantly attenuate the ion ionospheric motions and raise the flux of returning ions. On the other hand, since the ion densities in the ionosphere with strong crustal field are significantly higher than in the ionosphere with a weak crustal magnetic field, the net escape fluxes from the ionosphere with the crustal sources remain vital. The crustal magnetic field also leads to the expansion of the ionosphere and increase of the area exposed to solar wind. As a result, fluxes from higher altitudes essentially contribute to the flow pattern in Martian tail producing an excess of ion loss rate (∼15%) through the southern part of the tail. Thus, effects of inhibition and enhancement of the escape rate by the crustal magnetic field at Mars operate in competition producing a minor influence on the total ion loss.
Key Points
Crustal magnetic field at Mars has a twofold effect on atmospheric erosion
At lower altitudes the crustal fields form a protective shield around the ionized atmosphere
Due to expansion of ionosphere to higher altitudes, a larger cross‐section area is exposed to the solar wind that increases ion losses
Cometary nuclei consist mostly of dust and water ice. Previous observations have found nuclei to be low-density and highly porous bodies, but have only moderately constrained the range of allowed ...densities because of the measurement uncertainties. Here we report the precise mass, bulk density, porosity and internal structure of the nucleus of comet 67P/Churyumov-Gerasimenko on the basis of its gravity field. The mass and gravity field are derived from measured spacecraft velocity perturbations at fly-by distances between 10 and 100 kilometres. The gravitational point mass is GM = 666.2 ± 0.2 cubic metres per second squared, giving a mass M = (9,982 ± 3) × 10(9) kilograms. Together with the current estimate of the volume of the nucleus, the average bulk density of the nucleus is 533 ± 6 kilograms per cubic metre. The nucleus appears to be a low-density, highly porous (72-74 per cent) dusty body, similar to that of comet 9P/Tempel 1. The most likely composition mix has approximately four times more dust than ice by mass and two times more dust than ice by volume. We conclude that the interior of the nucleus is homogeneous and constant in density on a global scale without large voids. The high porosity seems to be an inherent property of the nucleus material.
We present multi‐instrument observations of the effects of solar wind on ion escape fluxes on Mars based on the Mars Atmosphere and Volatile EvolutioN (MAVEN) data from 1 November 2014 to 15 May ...2016. Losses of oxygen ions through different channels (plasma sheet, magnetic lobes, boundary layer, and ion plume) as a function of the solar wind and the interplanetary magnetic field variations were studied. We have utilized the modified Mars Solar Electric (MSE) coordinate system for separation of the different escape routes. Fluxes of the low‐energy (≤30 eV) and high‐energy (≥30 eV) ions reveal different trends with changes in the solar wind dynamic pressure, the solar wind flux, and the motional electric field. Major oxygen fluxes occur through the tail of the induced magnetosphere. The solar wind motional electric field produces an asymmetry in the ion fluxes and leads to different relations between ion fluxes supplying the tail from the different hemispheres and the solar wind dynamic pressure (or flux) and the motional electric field. The main driver for escape of the high‐energy oxygen ions is the solar wind flux (or dynamic pressure). On the other hand, the low‐energy ion component shows the opposite trend: ion flux decreases with increasing solar wind flux. As a result, the averaged total oxygen ion fluxes reveal a low variability with the solar wind strength. The large standard deviations from the averages values of the escape fluxes indicate the existence of mechanisms which can enhance or suppress the efficiency of the ion escape. It is shown that the Martian magnetosphere possesses the properties of a combined magnetosphere which contains different classes of field lines. The existence of the closed magnetic field lines in the near‐Mars tail might be responsible for suppression of the ion escape fluxes.
Plain Language Summary
In the past Mars was wet and the problem of its present dehydration is open. It is thought that the solar wind could blow off the volatiles at Mars. In the past solar wind was much stronger and we should know how escape of planetary ions forced by solar wind depends on the solar wind parameters. Using the data from the Mars Atmosphere and Volatile EvolutioN spacecraft, we study relations between ion fluxes of oxygen ions and solar wind and the interplanetary magnetic field characteristics.
Key Points
To separate different escape channel, we have modified the MSE coordinate system
Fluxes of the low‐energy and high‐energy oxygen ions reveal different trends with changes in solar wind
The main driver for escape of the high‐energy oxygen ions is the solar wind flux (or dynamic pressure)
The Venus Express radio science experiment VeRa provided more than 900 neutral atmospheric profiles between the years 2006 and 2014. About 800 of these could be used for an analysis of the radio ...signal absorption at X-Band (wavelength: 3.6 cm), which is mainly caused by sulfuric acid vapor within the Venus atmosphere. The absorptivity profiles were converted into sulfuric acid vapor profiles. The combined measurements from the entire Venus Express mission reveal a distinct latitudinal H2SO4(g) variation. A latitudinal gradient can be observed at the topside of the H2SO4(g) layer, which is located approx. 4 km higher at equatorial latitudes compared to polar latitudes. Regions of enhanced sulfuric acid vapor abundance were found at equatorial and polar latitudes. The highest H2SO4(g) values at equatorial latitudes show mean maximal values of more than 12 ppm at around 47 km altitude. At polar latitudes mean maximal values were found at around 43 km altitude and ranged from 9 to 12 ppm. Both latitudinal regions of increased sulfuric acid vapor abundance are clearly separated by a low abundance region located at mid-latitudes with values of 5 to 7 ppm.
A simplified two-dimensional transport model was developed to study the formation processes of sulfuric acid vapor accumulation at equatorial and polar latitudes. It turned out that the H2SO4(g) accumulation observed at high latitudes can be explained by precipitation of H2SO4(l) droplets that evaporate into gaseous sulfuric acid upon entering lower (warmer) altitudes. The influence of wind transport on this formation process was minor. In contrast, the H2SO4(g) accumulation observed at equatorial latitudes could be reproduced in the model by oppositely directed mass transport (upward winds and sedimentation) as well as by simplified evaporation and condensation processes. The low H2SO4(g) abundance observed at mid-latitudes was reproduced by downward winds in the model calculations.
The VeRa observations were additionally used to estimate the abundance of SO2 above the cloud bottom. A latitudinal dependence was found with highest values of 90 ± 60 ppm at equatorial latitudes, compared to 150 ± 50 ppm and 160 ± 50 ppm at southern and northern polar latitudes, respectively.
Both the equatorial and polar regions displayed show large variability of the H2SO4(g) and SO2 abundances from observation to observation. A weak tidal influence is also visible in the sulfuric acid vapor abundance in the equatorial region. The northern polar H2SO4(g) abundance, as well as the southern and northern SO2 abundances, exhibit distinct long-term variations.
•Venus Express radio absorption measurements were used to study the H2SO4 vapor and SO2 abundances in Venus' atmosphere.•Distinct latitudinal and long-term variations of the trace gases were observed.•A 2D mass transport model was developed in order to study the wind dynamics in the Venus lower and middle atmosphere.
ABSTRACT
Several close spacecraft flybys of Phobos have been performed over the past 40 yr in order to determine the gravity field of this tiny Martian moon. In this work, the second-degree ...coefficients of the gravity field of Phobos were derived from the radio tracking data of two combined Mars Express flybys (2010 and 2013), by applying a least squares regularized inverse technique, that introduces as an a priori the gravity field retrieved from a shape model based on constant density hypothesis. A gravitational mass estimate of $(7.0765\pm 0.0075)\times 10^5 \, \mathrm{m^3\, s}^{-2}$ and second-degree gravity coefficients C20 = −0.1378 ± 0.0348 and C22 = 0.0166 ± 0.0153(3σ) were derived. The estimated C20 value, in contrast to the value of C20 computed from the shape model under the constant density assumption, supports an inhomogeneous distribution inside Phobos at a confidence interval of 95 per cent (1.96σ). This result indicates a denser mass in the equatorial region or lighter mass in polar areas.
Bursty Ion Escape Fluxes at Mars Dubinin, E.; Fraenz, M.; Pätzold, M. ...
Journal of geophysical research. Space physics,
April 2021, 2021-04-00, 20210401, Letnik:
126, Številka:
4
Journal Article
Recenzirano
Odprti dostop
Based on the Mars Atmosphere and Volatile Evolution measurements we have observed cases when the fluxes of oxygen ions escaping the Martian ionosphere exceed their median values by more than a factor ...of 100. In the Martian tail very high fluxes of the more energetic (E > 30 eV) oxygen ions fill the plasma sheet which then becomes much broader than under conditions with median values of ion fluxes. We have analyzed the occurrence of such events in the upper ionosphere near the terminator plane, which is the main source region of ions in the plasma tail. The maximum values of fluxes of oxygen ions with E > 30 eV were observed mostly in the hemisphere where the motional electric field imposed by the solar wind is directed outward from the planet. Although high values of the solar wind dynamic pressure and (or) the motional electric field are favorable for the observation of the extreme values of ion fluxes with E > 30 eV, there must also be other factors which initiate these events. In particular, we found a close relation of the maximum ion fluxes with the values of the simultaneously measured fluxes of solar wind penetrating into the upper ionosphere. Direct interaction of both plasmas might be a critical factor for the strong growth of the oxygen ion escape. Very high fluxes of the low‐energy oxygen ions (E < 30 eV) are often related with ion “clouds” with anomalously large number density observed in the upper ionosphere.
Key Points
Fluxes of oxygen ions escaping the Martian ionosphere with values exceeding their median values by more than a factor of 100 are observed
Burst fluxes of the high‐energy oxygen ions are often related with high values of the simultaneously measured fluxes of the solar wind
High fluxes of the low‐energy oxygen ions are often related with over dense ion clouds observed in the top‐side ionosphere of Mars
Aeronomy of the Venus Upper Atmosphere Gérard, J.-C.; Bougher, S. W.; López-Valverde, M. A. ...
Space science reviews,
11/2017, Letnik:
212, Številka:
3-4
Journal Article, Web Resource
Recenzirano
Odprti dostop
We present aeronomical observations collected using remote sensing instruments on board Venus Express, complemented with ground-based observations and numerical modeling. They are mostly based on ...VIRTIS and SPICAV measurements of airglow obtained in the nadir mode and at the limb above 90 km. They complement our understanding of the behavior of Venus’ upper atmosphere that was largely based on Pioneer Venus observations mostly performed over thirty years earlier. Following a summary of recent spectral data from the EUV to the infrared, we examine how these observations have improved our knowledge of the composition, thermal structure, dynamics and transport of the Venus upper atmosphere. We then synthesize progress in three-dimensional modeling of the upper atmosphere which is largely based on global mapping and observations of time variations of the nitric oxide and O
2
nightglow emissions. Processes controlling the escape flux of atoms to space are described. Results based on the VeRA radio propagation experiment are summarized and compared to ionospheric measurements collected during earlier space missions. Finally, we point out some unsolved and open questions generated by these recent datasets and model comparisons.
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