Total Escape Rate Research Articles

A One‐Dimensional Model of Atmospheric Sputtering at Io Driven by S++ and O+

AbstractIo, the closest of Jupiter's four Galilean moons, suffers from intense ion bombardment from Jupiter's magnetosphere. The constant atmospheric erosion by energetic ion precipitation, referred to atmospheric sputtering, serves as an important mechanism of Io's atmospheric escape. This study is devoted to a state‐of‐the‐art study of atmospheric sputtering at Io, with the aid of constantly accumulated understandings of Io's space environment and atmospheric photochemistry, as well as the updated laboratory measurements. A Monte Carlo model is constructed to track the energy degradation of incident S++ and O+ and atmospheric recoils from which the sputtering yields of different atmospheric species are determined. Our calculations suggest a total escape rate of 3 × 1029 atom s−1 on Io, and SO2 is the dominant sputtered species. Further investigations reveal that S++ is the most efficient species for atmospheric sputtering on Io, and sputtering yields increase substantially with increasing incident ion mass, energy, and incidence angle. The model sensitivity to different influence factors is also discussed, including scattering angle distribution, atmospheric column density, proton precipitation, inelastic process, and surface sputtering, of which the former two dominate.

Effects of an Intrinsic Magnetic Field on Ion Escape From Ancient Mars Based on MAESTRO Multifluid MHD Simulations

AbstractIon escape has played a key role in atmospheric loss on ancient Mars due to intense solar activity. Under the existence of a strong global intrinsic magnetic field, as expected on ancient Mars, differential flows between different ion species can be important for ion escape. To assess effects of differential flows, we here developed a new global multifluid magnetohydrodynamics model with a cubed sphere grid named Multifluid Atmospheric Escape Simulations Toward Real elucidatiOn (MAESTRO). A test simulation under present‐day Mars conditions showed solar wind‐Mars interactions, for example, plasma boundaries, ionospheric profiles, and tailward outflows, consistent with observations and simulation studies. We then conducted multifluid and multispecies simulations with six different dipole field strengths under ancient Mars conditions. The multifluid cases show asymmetric outflow distributions with respect to the solar wind convection electric field, as pointed out by previous studies on present‐day Mars. Compared with multispecies cases, the multifluid representation increases the escape rates of O2+ and CO2+ by more than two orders of magnitude in the strong dipole field cases where the cusp outflow is dominant. The O+ escape rate is slightly lower in the multifluid cases with no or weak dipole field due to suppression of ion pickup in the −E hemisphere, while it is reduced by one order of magnitude in the strongest dipole field case. The existence of a dipole field can reduce the total escape rate by a factor of six. The impact on atmospheric evolution is diminished but still significant.

High-performance of Mg2+ additive for addressing NH3 escape in inorganic ammonia carbon capture

The urgency to reduce the energy consumption of organic amine carbon capture, while the inorganic ammonia carbon capture (IACC) and co-production of ammonium fertilizer eliminates the desorption energy consumption. Inhabiting NH3 escape at the end of IACC process requires a large amount of water consumption, and there is a lack of corresponding process parameters and technical routes. In this paper, Mg2+, one of major components in desulfurization wastewater, was used as an NH3 inhibitor. It’s found that the addition of MgCl2 can increase the total NH3 absorption rate by 13.02 % and reduce the total NH3 escape rate by 87.02 %. Furthermore, the effects of six process parameters in the forward and reverse NH3 mass transfer experiments could be distinctly quantified by the normalization method to determine the differentiation between priority and others. It’s concluded that NH3 can enter the first solvent shell of Mg2+ to replace some H2O based on the first-principles calculations, which is the main cause for the decrease of NH3 diffusion coefficient. Finally, simulation with Aspen Plus was applied to construct the complete process route, and the Arrhenius formula for the Mg(OH)2 nucleation was used to refine the reaction kinetic parameters of the simulation. The heat and water balance of IACC could achieve within this system, and the excellent NH3 inhibition effect of added Mg2+ was verified, which could effectively keep from the NH3 escape within 3 ppm.

Enhanced Ion Escape Rate During IMF Rotation Under Weak Intrinsic Magnetic Field Conditions on a Mars‐Like Planet

AbstractThe rotation of the interplanetary magnetic field (IMF) provides details of the escape mechanism that varies with the interaction between the intrinsic magnetic field and the IMF. A multispecies magnetohydrodynamic simulation is conducted on a Mars‐like planet under the conditions of a weak intrinsic magnetic field and the IMF rotating by 180° over 12 hr, which is comparable to the coronal mass ejection (CME) time scale. The total ion escape rate increases from ∼5 × 1023 s−1 to ∼3 × 1025 s−1 during the IMF rotation from due north (parallel to the assumed intrinsic magnetic field) to due south (antiparallel to the assumed intrinsic magnetic field). The escape rate increases significantly with the IMF rotating from due north to clock angles of 45°–75°, followed by a gentle increase until the IMF rotates to due south. The trigger for the large increase is multiple reconnections in the magnetospheric flank region, and the subsequent increase is due to the expansion of the reconnection area into the equatorial region. The IMF mass loading in the ionosphere is also responsible for the gentle increase with IMF clock angles above 90° in addition to the flank reconnection. The IMF rotation is a general feature for a CME. Exoplanets orbiting in the vicinity of M‐dwarfs might be frequently affected by IMF rotation, as they could be exposed to severe stellar winds such as in CME environments, and the current study could be helpful for future planned observations of the exoplanetary environment.

The dependence of Martian ion escape on solar EUV irradiance as observed by MAVEN

We analyze the planetary ion, solar wind, interplanetary magnetic field (IMF), and solar extreme ultraviolet (EUV) irradiance data from the NASA Mars Atmosphere and Volatile EvolutioN (MAVEN) mission to quantify the variation in ion escape with solar EUV irradiance. With relatively strict constraints on the upstream solar wind and IMF conditions, we divide the planetary ion data into 4 subsets with different solar EUV conditions to estimate ion escape rates. The results show that the total ion escape rate may increase nonlinearly with solar EUV irradiance and eventually approach an asymptotic limit as EUV increases. Further analysis on different ion species, escape channels, and energy ranges show that the dependence on solar EUV varies between these different ion populations. We also find that the spatial distributions of ion density and velocity vary between high and low solar EUV conditions, which is likely caused by the variations of electromagnetic field distributions. These results suggest that as solar EUV controls the ion production and affects the ion distributions near Mars, it will in turn influence the electromagnetic field distributions and thus affect the acceleration of escaping ions. This feedback mechanism may limit the total ion escape rate as solar EUV increases under constrained solar wind and IMF conditions.

Ion acceleration in Mars’ twisted magnetotail

ABSTRACT Mars lacks a global magnetic field and instead has a unique, ‘hybrid’ magnetosphere composed of crustal magnetic fields, which are stronger in the Southern hemisphere than the Northern hemisphere. These crustal fields are believed to drive a twist in the magnetotail at Mars. This is important because heavy ions escape from this induced magnetotail, which is a major source of atmospheric erosion. We present analysis of heavy ions produced in Mars’ upper atmosphere that are transported downtail along the twisted current sheet and observed by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission. We identified O+, O$_2\, ^+$, and CO$_2\, ^+$ being accelerated to different energies at a range of distances downtail and found that heavy ions in the 10–50 eV energy population have the highest flux. We present tail slices of ion fluxes for different interplanetary magnetic field (IMF) configurations based on the BY component of the IMF and find that the different configurations affect the degree of tail twist and the transport of heavy ions in the induced magnetotail lobes. We find that the total escape rate for O+, O$_2\, ^+$, and CO$_2\, ^+$ is 5.5e24 s-1, with 50% escaping between 2–200 eV.

Multispecies MHD Study of Ion Escape at Ancient Mars: Effects of an Intrinsic Magnetic Field and Solar XUV Radiation

AbstractIon escape is one of the key processes responsible for drastic climate change on ancient Mars. Ion escape is affected by the solar X‐ray and EUV (X‐ray and extreme ultraviolet (XUV)) flux, the solar wind, and the presence of a planetary intrinsic magnetic field, all of which was much different at ancient Mars. We investigated how the presence and strength of a dipole field affects the ion escape under 50 or 10 times higher solar XUV flux and strong solar wind with multispecies magnetohydrodynamics model. The results showed two opposite effects on the escape rates, which is associated with the pressure ratio of the dipolar magnetic pressure at the equatorial surface to the solar wind dynamic pressure. The escape rates increase by up to a factor of 6 for O2+ and CO2+ but change little for O+ if the pressure ratio is below 0.1. On the other hand, the escape rates decrease by more than one order of magnitude for the three ions if the pressure ratio is above 0.1. The threshold can be described by the pressure balance between the solar wind flow and the dipole field at high latitudes, where the ionospheric outflow emerges in the unmagnetized cases. The effects on the escape rates are stronger under lower solar XUV cases. The total escape rate reaches 1027 s−1 in the unmagnetized case, which may lead to a large contribution to atmospheric loss at ancient Mars, but it can be reduced by an order of magnitude in the presence of a dipole field.

P-winds: An open-source Python code to model planetary outflows and upper atmospheres

Atmospheric escape is considered to be one of the main channels for evolution in sub-Jovian planets, particularly in their early lives. While there are several hypotheses proposed to explain escape in exoplanets, testing them with atmospheric observations remains a challenge. In this context, high-resolution transmission spectroscopy of transiting exoplanets for the metastable helium triplet (He 23S) at 1083 nm has emerged as a reliable technique for observing and measuring escape. To aid in the prediction and interpretation of metastable He transmission spectroscopy observations, we developed the code p-winds. This is an open-source, fully documented, scalable Python implementation of the one-dimensional, purely H+He Parker wind model for upper atmospheres coupled with ionization balance, ray-tracing, and radiative transfer routines. We demonstrate an atmospheric retrieval by fitting p-winds models to the observed metastable He transmission spectrum of the warm Neptune HAT-P-11 b and take the variation in the in-transit absorption caused by transit geometry into account. For this planet, our best fit yields a total atmospheric escape rate of approximately 2.5 × 1010 g s−1 and an outflow temperature of 7200 K. The range of retrieved mass loss rates increases significantly when we let the H atom fraction be a free parameter, but its posterior distribution remains unconstrained by He observations alone. The stellar host limb darkening does not have a significant impact on the retrieved escape rate or outflow temperature for HAT-P-11 b. Based on the non-detection of escaping He for GJ 436 b, we are able to rule out total escape rates higher than 3.4 × 1010 g s−1 at 99.7% (3σ) confidence.

On the structure of the Enceladus plume

ABSTRACT The detection of a water-rich plume erupting from ‘tiger stripes’ near the Enceladus south polar region is an important discovery of geologically active satellites within the Solar system. In this work, we apply an analytical approach to model the plume structure, using as a diagnostic the CO2 distribution extracted from the Cassini Ion and Neutral Mass Spectrometer measurements made during the E14, E17, and E18 flybys. Special focus is placed on the modelling of the spike-like structures by including only sources with substantial contributions to the plume densities. Such a procedure reduces greatly the model complexity and helps to better constrain the source parameters. Both the model source rate and Mach number are found to vary considerably among different sources during the same flyby and also among different flybys for the same source, revealing a complicated spatio-temporal variability in the plume structure. Our analysis suggests a total escape rate of (1.0–7.1) × 1026 s−1 for CO2 and (2.4–6.6) × 1028 s−1 for H2O, in broad agreement with previous estimates. Of particular interest is our identification of a tentative correlation between the Mach number and thermal brightness, of which the latter is a tracer of the geological activity of the emission source. Such a relation should be able to provide more insights into the nature of geyser emission along the ‘tiger stripes’.

The high-energy environment and atmospheric escape of the mini-Neptune K2-18 b

K2-18 b is a transiting mini-Neptune that orbits a nearby (38 pc), cool M3 dwarf and is located inside its region of temperate irradiation. We report on the search for hydrogen escape from the atmosphere K2-18 b using Lyman-α transit spectroscopy with the Space Telescope Imaging Spectrograph instrument installed on the Hubble Space Telescope. We analyzed the time-series of fluxes of the stellar Lyman-α emission of K2-18 in both its blue- and redshifted wings. We found that the average blueshifted emission of K2-18 decreases by 67% ± 18% during the transit of the planet compared to the pre-transit emission, tentatively indicating the presence of H atoms escaping vigorously and being blown away by radiation pressure. This interpretation is not definitive because it relies on one partial transit. Based on the reconstructed Lyman-α emission of K2-18, we estimate an EUV irradiation in the range 101 − 102 erg s−1 cm−2 and a total escape rate on the order of 108 g s−1. The inferred escape rate suggests that the planet will lose only a small fraction (< 1%) of its mass and retain its volatile-rich atmosphere during its lifetime. More observations are needed to rule out stellar variability effects, confirm the in-transit absorption, and better assess the atmospheric escape and high-energy environment of K2-18 b.

Species-dependent ion escape on Titan

Cassini observations over the past ten years have revealed that Titan possesses a chemically complex ionosphere. In this study, we investigate the relative contributions of different ion species to the total ion escape on Titan, by dividing all ion species probed by the Cassini Ion Neutral Mass Spectrometer (INMS) into six groups according to their mass-to-charge ratios (M/Z). For the three lightest ion groups, with characteristic M/Z of 22, 41, and 52 daltons , the observed scale heights tend to be lower than the scale heights predicted by assuming diffusive equilibrium; for the three heavier groups, observed and predicted scale heights are in general agreement, implying that most ion escape from Titan is by relatively light species, with M/Z < 60 daltons. A diffusion model is constructed to describe the density distribution of each ion group in regions where the effect of ionospheric chemistry could be neglected. The data model comparison predicts an optimal total ion escape rate of 3.1×1024 s–1, of which more than 99% is contributed by relatively light ions with M/Z < 32 daltons.

A Test Particle Monte Carlo Investigation of the CH4 Torus around Saturn

Abstract The issue of CH4 escape on Titan is still under debate, and a range of escape rates from 1024 to 1027 s−1 has been reported in previous studies. One effective way of solving the CH4 escape dilemma is to investigate the morphology of the CH4 torus around Saturn, which varies with both the total CH4 escape rate on Titan and the CH4 energy distribution near its exobase. Such a torus is modeled via a test particle Monte Carlo approach in this study for a variety of CH4 escaping scenarios characterized by different energy distributions near the exobase. The model calculations indicate that the extension of the CH4 torus depends critically on the population of the high-energy tail of the CH4 energy distribution. The model also predicts several distinctive cavities in CH4 density related to mean motion resonances between Titan and the torus particles.

Effect of Viscosity on Nonlinear Tempering for Anomalous Diffusion of Viscous Particle: A Subdiffusive Case

In this study, we introduced another parameter on nonlinear particle interaction into sub- diffusive transport involving nonlinear effects such as adhesion, volume filling, etc. We also introduce an additional variable which is the effect of viscosity on the nonlinear escape rate of particle which affects the resulting integral escape rate. This paper focuses only on the in- vestigation of the effect of the added variable on the total escape rate. Lastly, we can see the importance of this study when dealing viscous macroparticles.

Global Mars‐solar wind coupling and ion escape

AbstractLoss of the early Martian atmosphere is often thought to have occurred due to an effective transfer of the solar wind energy through the Martian induced magnetic barrier to the ionosphere. We have quantified the coupling efficiency by comparing the power of the heavy ion outflow with the available power supplied by the upstream solar wind. Constraining upstream solar wind density nsw, velocity vsw, and EUV intensity IEUV/photoionizing flux FXUV in varying intervals reveals a decrease in coupling efficiency, k, with solar wind dynamic pressure as and with FXUV as . Despite the decrease in coupling efficiency, higher FXUV enhances the cold ion outflow, increasing the total ion escape rate as Q(FXUV) = 1010(0.82 ± 0.05)FXUV. The discrepancy between coupling and escape suggests that ion escape from Mars is primarily production limited in the modern era, though decreased coupling may lead to an energy‐limited solar wind interaction under early Sun conditions.

Non-thermal production and escape of OH from the upper atmosphere of Mars

We present a theoretical analysis of formation and kinetics of hot OH molecules in the upper atmosphere of Mars produced in reactions of thermal molecular hydrogen and energetic oxygen atoms. Two major sources of energetic O considered are the photochemical production, via dissociative recombination of O2+ ions, and energizing collisions with fast atoms produced by the precipitating Solar Wind (SW) ions, mostly H+ and He2+, and energetic neutral atoms (ENAs) originating in the charge-exchange collisions between the SW ions and atmospheric gases. Energizing collisions of O with atmospheric secondary hot atoms, induced by precipitating SW ions and ENAs, are also included in our consideration. The non-thermal reaction O + H2(v, j) → H + OH(v′, j′) is described using recent quantum-mechanical state-to-state cross sections, which allow us to predict non-equilibrium distributions of excited rotational and vibrational states (v′, j′) of OH and expected emission spectra. A fraction of produced translationally hot OH is sufficiently energetic to overcome Mars’ gravitational potential and escape into space, contributing to the hot corona. We estimate its total escape flux from the dayside of Mars for low solar activity conditions at about 1.1 × 1023 s−1, or about 0.1% of the total escape rate of atomic O and H. The described non-thermal OH production mechanism is general and expected to contribute to the evolution of atmospheres of the planets, satellites, and exoplanets with similar atmospheric compositions.

Multifluid MHD study of the solar wind interaction with Mars' upper atmosphere during the 2015 March 8th ICME event

AbstractWe study the solar wind interaction with the Martian upper atmosphere during the 8 March 2015 interplanetary coronal mass ejection (ICME) by using a global multifluid MHD model. Comparison of the simulation results with observations from Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft shows good agreement. The total ion escape rate is increased by an order of magnitude, from 2.05 × 1024 s−1 (pre‐ICME phase) to 2.25 × 1025 s−1 (ICME sheath phase), during this time period. Two major ion escape channels are illustrated: accelerated pickup ion loss through the dayside plume and ionospheric ion loss through the nightside plasma wake region. Interestingly, the tailward ion loss is significantly increased at the ejecta phase. Both bow shock and magnetic pileup boundary (BS and MPB) locations are decreased from (1.2RM, 1.57RM) at the pre‐ICME phase to (1.16RM, 1.47RM), respectively, during the sheath phase along the dayside Mars‐Sun line. Furthermore, both simulation and observational results indicate that there is no significant variation in the Martian ionosphere (at altitudes ≲ 200 km, i.e., the photochemical region) during this event.

Mars atmospheric losses induced by the solar wind: Comparison of observations with models

With new results from Mars-Express on plasma environment of Mars and two new Mars satellites the study Martian atmospheric losses receives new attention. Paper summarizes experimental results concentrating on configuration of Martian magnetosphere and the measurements of planetary ion escape induced by the solar wind. Several plasma populations constituting solar wind induced mass loss have been identified and studied: pick-up ions in shocked solar wind flow and induced (accretion) tail, ions accelerated in the tail current sheet, and outflow of ionospheric ions. Measured ion flux values and calculations of the total escape rate including solar cycle variations are summarized. Several types of simulation of the solar wind with Mars are considered and results of representative models are given and compared with experimental results. These computer models allowed one to much better understand solar wind–Mars interaction. However, there is significant difference between total loss rates obtained from simulation and ones from measurements on the spacecraft. Both measurements and simulation provide significant flux values that are considered as an important factor of mass loss during cosmogonic time of the planet. The origin of each solar wind induced loss component and its contribution to total amount are discussed and compared with relevant computer models. Future progress in experiments and simulation is briefly discussed.

Cold ion escape from the Martian ionosphere

We here report on new measurements of the escape flux of oxygen ions from Mars by combining the observations of the ASPERA-3 and MARSIS experiments on board the European Mars Express spacecraft. We show that in previous estimates of the total heavy ion escape flow the contribution of the cold ionospheric outflow with energies below 10eV has been underestimated. Both case studies and the derived flow pattern indicate that the cold plasma observed by MARSIS and the superthermal plasma observed by ASPERA-3 move with the same bulk speed in most regions of the Martian tail. We determine maps of the tailside heavy ion flux distribution derived from mean ion velocity distributions sampled over 7 years. If we assume that the superthermal bulk speed derived from these long time averages of the ion distribution function represent the total plasma bulk speed we derive the total tailside plasma flux. Assuming cylindrical symmetry we determine the mean total escape rate for the years 2007–2014 at 2.8±0.4×1025atoms/s which is in good agreement with model estimates. A possible mechanism to generate this flux can be the ionospheric pressure gradient between dayside and nightside.

Conservation of total escape from hydrodynamic planetary atmospheres

Atmosphere escape is one key process controlling the evolution of planets. However, estimating the escape rate in any detail is difficult because there are many physical processes contributing to the total escape rate. Here we show that as a result of energy conservation the total escape rate from hydrodynamic planetary atmospheres where the outflow remains subsonic is nearly constant under the same stellar XUV photon flux when increasing the escape efficiency from the exobase level, consistent with the energy-limited escape approximation. Thus the estimate of atmospheric escape in a planetʼs evolution history can be greatly simplified.

Phobos 2/ASPERA data revisited: Planetary ion escape rate from Mars near the 1989 solar maximum

AbstractInsights about the near‐Mars space environment from Mars Express observations have motivated a revisit of the Phobos 2/ASPERA ion data from 1989. We have expanded the analysis to now include all usable heavy ion (O+, O, CO) measurements from the circular orbits of Phobos 2. Phobos 2/ASPERA ion fluxes in the Martian tail are compared with previous results obtained by the instruments on Phobos 2. Further validation of the measurement results is obtained by comparing IMP‐8 and Phobos 2/ASPERA solar wind ion fluxes, taking into account the time lag between Earth and Mars. Heavy ion flux measurements from 18 circular equatorial orbits around Mars are bin‐averaged to a grid, using the MSE (electric field) frame of reference. The binned data are subsequently integrated to determine the total escape rate of planetary ions. From this we derive a total planetary heavy ion escape rate of (2–3) × 1025 s−1 from Mars for the 1989 solar maximum.