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Despite Venus having insignificant intrinsic magnetic fields, the magnetic connectivity between the solar wind and the Venus ionosphere, or magnetic topology, is not as simple as expected and is also important for characterizing the Venus space environment. This study provides a technique combining superthermal electron energy and pitch angle distributions to infer up to 6 subtypes of magnetic topology at Venus. This enables us to determine magnetic topology with automated procedures using the Venus Express (VEx) observations from May 2006 to November 2014. We find that the draped topology (both ends of a field line not connected to the collisional ionosphere) is the dominant topology in the near-Venus space environment, >70%, except at low altitudes close to the ionosphere. The open (a field line connected to both the solar wind and the collisional ionosphere) and closed (a field line connected only to the collisional ionosphere) topologies make up 20%-30% on average of the magnetotail and up to 50% at low altitudes. This study provides the first characterization of the statistical distributions of different magnetic topologies at Venus.

Renjun Lv,1– 5 Shanjing Nie,1– 4 Zhenhua Liu,6 Yunliang Guo,1– 4 Yue Zhang,7 Song Xu,1– 4 Xunyao Hou,1– 4 Jian Chen,1– 4 Yingjuan Ma,8 Zhongyu Fan,1– 5 Xueping Liu1– 4 1Department of Geriatrics, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan 250021, Shandong, People’s Republic of China; 2Department of Geriatric Neurology, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan 250021, Shandong, People’s Republic of China; 3Anti-Aging Monitoring Laboratory, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan 250021, Shandong, People’s Republic of China; 4Department of Anti-Aging, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan 250021, Shandong, People’s Republic of China; 5Shandong Provincial Hospital, Shandong First Medical University & Shandong Academy of Medical Sciences, Jinan 250021, Shandong, People’s Republic of China; 6Center of Sleep Medicine, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan 250021, Shandong, People’s Republic of China; 7Department of Geriatric Neurology, Shandong Provincial Hospital Affiliated to Shandong University, Jinan 250021, Shandong, People’s Republic of China; 8Department of Otolaryngology Head and Neck Surgery, Shandong Provincial Hospital Affiliated to Shandong First Medical University, Jinan, Shandong, 250021, People’s Republic of ChinaCorrespondence: Xueping Liu Tel +86-53168777165Email Liuxueping1962@163.comAim: Obstructive sleep apnea syndrome (OSAS) is a prevalent chronic disease characterized by sleep fragmentation and intermittent hypoxemia. Several studies suggested that electrophysiological changes and neurocognitive abnormalities occurred in OSAS patients. In this study, we compared automati

Intrinsic magnetic fields have long been thought to shield planets from atmospheric erosion via stellar winds; however, the influence of the plasma environment on atmospheric escape is complex. Here we study the influence of a weak intrinsic dipolar planetary magnetic field on the plasma environment and subsequent ion escape from a Mars sized planet in a global three-dimensional hybrid simulation. We find that increasing the strength of a planet's magnetic field enhances ion escape until the magnetic dipole's standoff distance reaches the induced magnetosphere boundary. After this point increasing the planetary magnetic field begins to inhibit ion escape. This reflects a balance between shielding of the southern hemisphere from ``misaligned" ion pickup forces and trapping of escaping ions by an equatorial plasmasphere. Thus, the planetary magnetic field associated with the peak ion escape rate is critically dependent on the stellar wind pressure. Where possible we have fit power laws for the variation of fundamental parameters (escape rate, escape power, polar cap opening angle and effective interaction area) with magnetic field, and assessed upper and lower limits for the relationships., Comment: Accepted to MNRAS. 17 pages, 10 figures

We report the first global, time-dependent simulation of the Mars upper atmospheric responses to a realistic solar flare event, an X8.2 eruption on 10 September 2017. The Mars Global Ionosphere-Thermosphere Model runs with realistically specified flare irradiance, giving results in reasonably good agreement with the Mars Atmosphere and Volatile EvolutioN spacecraft measurements. It is found that the ionized and neutral regimes of the upper atmosphere are significantly disturbed by the flare but react differently. The ionospheric electron density enhancement is concentrated below ~110-km altitude due to enhanced solar X-rays, closely following the time evolution of the flare. The neutral atmospheric perturbation increases with altitude and is important above ~150-km altitude, in association with atmospheric upwelling driven by solar extreme ultraviolet heating. It takes ~2.5 hr past the flare peak to reach the maximum disturbance and then additional ~10 hr to generally settle down to preflare levels.

Intrinsic magnetic fields have long been thought to shield planets from atmospheric erosion via stellar winds; however, the influence of the plasma environment on atmospheric escape is complex. Here we study the influence of a weak intrinsic dipolar planetary magnetic field on the plasma environment and subsequent ion escape from a Mars sized planet in a global three-dimensional hybrid simulation. We find that increasing the strength of a planet's magnetic field enhances ion escape until the magnetic dipole's standoff distance reaches the induced magnetosphere boundary. After this point increasing the planetary magnetic field begins to inhibit ion escape. This reflects a balance between shielding of the southern hemisphere from ``misaligned" ion pickup forces and trapping of escaping ions by an equatorial plasmasphere. Thus, the planetary magnetic field associated with the peak ion escape rate is critically dependent on the stellar wind pressure. Where possible we have fit power laws for the variation of fundamental parameters (escape rate, escape power, polar cap opening angle and effective interaction area) with magnetic field, and assessed upper and lower limits for the relationships., Comment: Accepted to MNRAS. 17 pages, 10 figures

Mars Atmosphere and Volatile EvolutioN (MAVEN) mission observations show clear evidence of the occurrence of the magnetic reconnection process in the Martian plasma tail. In this study, we use sophisticated numerical models to help us understand the effects of magnetic reconnection in the plasma tail. The numerical models used in this study are (a) a multispecies global Hall-magnetohydrodynamic (HMHD) model and (b) a global HMHD model two-way coupled to an embedded fully kinetic particle-in-cell code. Comparison with MAVEN observations clearly shows that the general interaction pattern is well reproduced by the global HMHD model. The coupled model takes advantage of both the efficiency of the MHD model and the ability to incorporate kinetic processes of the particle-in-cell model, making it feasible to conduct kinetic simulations for Mars under realistic solar wind conditions for the first time. Results from the coupled model show that the Martian magnetotail is highly dynamic due to magnetic reconnection, and the resulting Mars-ward plasma flow velocities are significantly higher for the lighter ion fluid, which are quantitatively consistent with MAVEN observations. The HMHD with Embedded Particle-in-Cell model predicts that the ion loss rates are more variable but with similar mean values as compared with HMHD model results., QC 20180719

In this Letter, we make use of sophisticated 3D numerical simulations to assess the extent of atmospheric ion and photochemical losses from Mars over time. We demonstrate that the atmospheric ion escape rates were significantly higher (by more than two orders of magnitude) in the past at $\sim 4$ Ga compared to the present-day value owing to the stronger solar wind and higher ultraviolet fluxes from the young Sun. We found that the photochemical loss of atomic hot oxygen dominates over the total ion loss at the current epoch whilst the atmospheric ion loss is likely much more important at ancient times. We briefly discuss the ensuing implications of high atmospheric ion escape rates in the context of ancient Mars, and exoplanets with similar atmospheric compositions around young solar-type stars and M-dwarfs., Comment: 6 pages, 4 figures, 1 table, accepted for publication in ApJ Letters

We study roles of the thermosphere and exosphere on the Martian ionospheric structure and ion escape rates in the process of the solar wind-Mars interaction. We employ a four-species multifluid MHD (MF-MHD) model to simulate the Martian ionosphere and magnetosphere. The $cold$ thermosphere background is taken from the Mars Global Ionosphere Thermosphere Model (M-GITM) and the $hot$ oxygen exosphere is adopted from the Mars exosphere Monte Carlo model - Adaptive Mesh Particle Simulator (AMPS). A total of four cases with the combination of 1D (globally averaged) and 3D thermospheres and exospheres are studied. The ion escape rates calculated by adopting 1D and 3D atmospheres are similar; however, the latter are required to adequately reproduce MAVEN ionospheric observations. In addition, our simulations show that the 3D hot oxygen corona plays an important role in preventing planetary molecular ions (O$_2^+$ and CO$_2^+$) escaping from Mars, mainly resulting from the mass loading of the high-altitude exospheric O$^+$ ions. The $cold$ thermospheric oxygen atom, however, is demonstrated to be the primary neutral source for O$^+$ ion escape during the relatively weak solar cycle 24., Comment: 21 pages, 10 figures, 4 tables, accepted for publication in Journal of Geophysical Research-Space Physics

In this Letter, we make use of sophisticated 3D numerical simulations to assess the extent of atmospheric ion and photochemical losses from Mars over time. We demonstrate that the atmospheric ion escape rates were significantly higher (by more than two orders of magnitude) in the past at $\sim 4$ Ga compared to the present-day value owing to the stronger solar wind and higher ultraviolet fluxes from the young Sun. We found that the photochemical loss of atomic hot oxygen dominates over the total ion loss at the current epoch whilst the atmospheric ion loss is likely much more important at ancient times. We briefly discuss the ensuing implications of high atmospheric ion escape rates in the context of ancient Mars, and exoplanets with similar atmospheric compositions around young solar-type stars and M-dwarfs., Comment: 6 pages, 4 figures, 1 table, accepted for publication in ApJ Letters

We study roles of the thermosphere and exosphere on the Martian ionospheric structure and ion escape rates in the process of the solar wind-Mars interaction. We employ a four-species multifluid MHD (MF-MHD) model to simulate the Martian ionosphere and magnetosphere. The $cold$ thermosphere background is taken from the Mars Global Ionosphere Thermosphere Model (M-GITM) and the $hot$ oxygen exosphere is adopted from the Mars exosphere Monte Carlo model - Adaptive Mesh Particle Simulator (AMPS). A total of four cases with the combination of 1D (globally averaged) and 3D thermospheres and exospheres are studied. The ion escape rates calculated by adopting 1D and 3D atmospheres are similar; however, the latter are required to adequately reproduce MAVEN ionospheric observations. In addition, our simulations show that the 3D hot oxygen corona plays an important role in preventing planetary molecular ions (O$_2^+$ and CO$_2^+$) escaping from Mars, mainly resulting from the mass loading of the high-altitude exospheric O$^+$ ions. The $cold$ thermospheric oxygen atom, however, is demonstrated to be the primary neutral source for O$^+$ ion escape during the relatively weak solar cycle 24., Comment: 21 pages, 10 figures, 4 tables, accepted for publication in Journal of Geophysical Research-Space Physics

The presence of an atmosphere over sufficiently long timescales is widely perceived as one of the most prominent criteria associated with planetary surface habitability. We address the crucial question as to whether the seven Earth-sized planets transiting the recently discovered ultracool dwarf star TRAPPIST-1 are capable of retaining their atmospheres. To this effect, we carry out numerical simulations to characterize the stellar wind of TRAPPIST-1 and the atmospheric ion escape rates for all the seven planets. We also estimate the escape rates analytically and demonstrate that they are in good agreement with the numerical results. We conclude that the outer planets of the TRAPPIST-1 system are capable of retaining their atmospheres over billion-year timescales. The consequences arising from our results are also explored in the context of abiogenesis, biodiversity, and searches for future exoplanets. In light of the many unknowns and assumptions involved, we recommend that these conclusions must be interpreted with due caution., Comment: 19 pages, 4 figures, 3 tables

We address the important question of whether the newly discovered exoplanet, Proxima Centauri b (PCb), is capable of retaining an atmosphere over long periods of time. This is done by adapting a sophisticated multi-species MHD model originally developed for Venus and Mars, and computing the ion escape losses from PCb. The results suggest that the ion escape rates are about two orders of magnitude higher than the terrestrial planets of our Solar system if PCb is unmagnetized. In contrast, if the planet does have an intrinsic dipole magnetic field, the rates are lowered for certain values of the stellar wind dynamic pressure, but they are still higher than the observed values for our Solar system's terrestrial planets. These results must be interpreted with due caution, since most of the relevant parameters for PCb remain partly or wholly unknown., Comment: 7 pages, 2 figures, accepted for publication in ApJL

The presence of an atmosphere over sufficiently long timescales is widely perceived as one of the most prominent criteria associated with planetary surface habitability. We address the crucial question as to whether the seven Earth-sized planets transiting the recently discovered ultracool dwarf star TRAPPIST-1 are capable of retaining their atmospheres. To this effect, we carry out numerical simulations to characterize the stellar wind of TRAPPIST-1 and the atmospheric ion escape rates for all the seven planets. We also estimate the escape rates analytically and demonstrate that they are in good agreement with the numerical results. We conclude that the outer planets of the TRAPPIST-1 system are capable of retaining their atmospheres over billion-year timescales. The consequences arising from our results are also explored in the context of abiogenesis, biodiversity, and searches for future exoplanets. In light of the many unknowns and assumptions involved, we recommend that these conclusions must be interpreted with due caution., Comment: 19 pages, 4 figures, 3 tables

We address the important question of whether the newly discovered exoplanet, Proxima Centauri b (PCb), is capable of retaining an atmosphere over long periods of time. This is done by adapting a sophisticated multi-species MHD model originally developed for Venus and Mars, and computing the ion escape losses from PCb. The results suggest that the ion escape rates are about two orders of magnitude higher than the terrestrial planets of our Solar system if PCb is unmagnetized. In contrast, if the planet does have an intrinsic dipole magnetic field, the rates are lowered for certain values of the stellar wind dynamic pressure, but they are still higher than the observed values for our Solar system's terrestrial planets. These results must be interpreted with due caution, since most of the relevant parameters for PCb remain partly or wholly unknown., Comment: 7 pages, 2 figures, accepted for publication in ApJL