The habitability of the surface of any planet is determined by a complex evolution of its interior, surface, and atmosphere. The electromagnetic and particle radiation of stars drive thermal, ...chemical, and physical alteration of planetary atmospheres, including escape. Many known extrasolar planets experience vastly different stellar environments than those in our solar system: It is crucial to understand the broad range of processes that lead to atmospheric escape and evolution under a wide range of conditions if we are to assess the habitability of worlds around other stars. One problem encountered between the planetary and the astrophysics communities is a lack of common language for describing escape processes. Each community has customary approximations that may be questioned by the other, such as the hypothesis of H‐dominated thermosphere for astrophysicists or the Sun‐like nature of the stars for planetary scientists. Since exoplanets are becoming one of the main targets for the detection of life, a common set of definitions and hypotheses are required. We review the different escape mechanisms proposed for the evolution of planetary and exoplanetary atmospheres. We propose a common definition for the different escape mechanisms, and we show the important parameters to take into account when evaluating the escape at a planet in time. We show that the paradigm of the magnetic field as an atmospheric shield should be changed and that recent work on the history of Xenon in Earth's atmosphere gives an elegant explanation to its enrichment in heavier isotopes: the so‐called Xenon paradox.
Plain Language Summary
In addition to having the right surface temperature, a planet needs an atmosphere to keep surface liquid water stable. Although many planets have been found that may lie in the right temperature range, the existence of an atmosphere is not guaranteed. In particular, for planets that are kept warm by being close to dim stars, there are a number of ways that the star may remove a planetary atmosphere. These atmospheric escape processes depend on the behavior of the star as well as the nature of the planet, including the presence of a planetary magnetic field. Under certain conditions, a magnetic field can protect a planet's atmosphere from the loss due to the direct impact of the stellar wind, but it may actually enhance total atmospheric loss by connecting to the highly variable magnetic field of the stellar wind. These enhancements happen especially for planets close to dim stars. We review the complete range of atmospheric loss processes driven by interaction between a planet and a star to aid in the identification of planets that are both the correct temperature for liquid water and that have a chance of maintaining an atmosphere over long periods of time.
Key Points
The different escape processes at planets and exoplanets are reviewed along with their mathematical formulation
The major parameters for each escape processes are described; some escape processes negligible in the solar system may be major source at exoplanets, or for the early solar system
A magnetic field should not be a priori considered as a protection for the atmosphere
High-fidelity single-shot readout of spin qubits requires distinguishing states much faster than the T
time of the spin state. One approach to improving readout fidelity and bandwidth (BW) is ...cryogenic amplification, where the signal from the qubit is amplified before noise sources are introduced and room-temperature amplifiers can operate at lower gain and higher BW. We compare the performance of two cryogenic amplification circuits: a current-biased heterojunction bipolar transistor circuit (CB-HBT), and an AC-coupled HBT circuit (AC-HBT). Both circuits are mounted on the mixing-chamber stage of a dilution refrigerator and are connected to silicon metal oxide semiconductor (Si-MOS) quantum dot devices on a printed circuit board (PCB). The power dissipated by the CB-HBT ranges from 0.1 to 1 μW whereas the power of the AC-HBT ranges from 1 to 20 μW. Referred to the input, the noise spectral density is low for both circuits, in the 15 to 30 fA/Formula: see text range. The charge sensitivity for the CB-HBT and AC-HBT is 330 μe/Formula: see text and 400 μe/Formula: see text, respectively. For the single-shot readout performed, less than 10 μs is required for both circuits to achieve bit error rates below 10
, which is a putative threshold for quantum error correction.
We present observations by the Mars Atmosphere and Volatile EvolutioN (MAVEN) mission of a substantial plume‐like distribution of escaping ions from the Martian atmosphere, organized by the upstream ...solar wind convection electric field. From a case study of MAVEN particle‐and‐field data during one spacecraft orbit, we identified three escaping planetary ion populations: plume fluxes mainly along the upstream electric field over the north pole region of the Mars‐Sun‐Electric field (MSE) coordinate system, antisunward ion fluxes in the tail region, and much weaker upstream pickup ion fluxes. A statistical study of O+ fluxes using 3 month MAVEN data shows that the plume is a constant structure with strong fluxes widely distributed in the MSE northern hemisphere, which constitutes an important planetary ion escape channel. The escape rate through the plume is estimated to be ~30% of the tailward escape and ~23% of the total escape for > 25 eV O+ ions.
Key Points
Three escaping planetary ion populations near Mars are identified in MAVEN observations
MAVEN observed a substantial plume with strong escaping ion fluxes over the MSE north pole region
The plume contributes ~23% to the total >25 eV O+ escape of ~2 × 1024 s−1
The Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft has been continuously observing the variability of solar soft X‐rays and EUV irradiance, monitoring the upstream solar wind and ...interplanetary magnetic field conditions and measuring the fluxes of solar energetic ions and electrons since its arrival to Mars. In this paper, we provide a comprehensive overview of the space weather events observed during the first ∼1.9 years of the science mission, which includes the description of the solar and heliospheric sources of the space weather activity. To illustrate the variety of upstream conditions observed, we characterize a subset of the event periods by describing the Sun‐to‐Mars details using observations from the MAVEN solar Extreme Ultraviolet Monitor, solar energetic particle (SEP) instrument, Solar Wind Ion Analyzer, and Magnetometer together with solar observations using near‐Earth assets and numerical solar wind simulation results from the Wang‐Sheeley‐Arge‐Enlil model for some global context of the event periods. The subset of events includes an extensive period of intense SEP electron particle fluxes triggered by a series of solar flares and coronal mass ejection (CME) activity in December 2014, the impact by a succession of interplanetary CMEs and their associated SEPs in March 2015, and the passage of a strong corotating interaction region (CIR) and arrival of the CIR shock‐accelerated energetic particles in June 2015. However, in the context of the weaker heliospheric conditions observed throughout solar cycle 24, these events were moderate in comparison to the stronger storms observed previously at Mars.
Key Points
We present a comprehensive overview of the first 1.9 years of MAVEN space weather conditions measured upstream at Mars
We characterize a subset of Mars‐impacting events due to an extensive period of SEP electrons, a succession of ICMEs, and a strong CIR
We discuss the space weather implications of the weaker solar cycle 24 heliospheric conditions on the events observed by MAVEN
•Nursery pigs infected with PEDV can recover digestive function within 7 days.•Sialomucin to sulfomucins ratio change over time in nursery pig jejunum.•Abundance of claudin 2 and 4 are reduced in ...nursery pig jejunum during PEDV infection.
The pig intestinal epithelium can be compromised by pathogens leading to reduced integrity and function. Porcine epidemic diarrhea virus (PEDV), recently detected in North America, exemplifies intestinal epithelial insult. Although several studies have investigated the molecular aspects and host immune response to PEDV, there are little data on the impact of PEDV on pig intestinal physiology. The objective of this study was to investigate the longitudinal impact of PEDV on nursery pig intestinal function and integrity. Fifty recently-weaned, 5-week-old barrows and gilts (BW=9.92±0.49kg) were sorted based on body weight (BW) and sex into two treatments: 1) Control or 2) PEDV inoculated. At 2, 5, 7, and 14days post inoculation (dpi), 4 pigs per treatment were euthanized and jejunum sections collected. PEDV antigen was detected in inoculated pigs by immunohistochemistry in 50% (2/4) at dpi 2, 100% (4/4) at dpi 5, and none at later time points. PEDV-infected pigs had reduced (P<0.05) villus height and decreased transepithelial resistance compared with controls. Total acidic mucins, particularly sialomucin, were reduced in PEDV pigs at dpi 2 and then increased compared with controls at dpi 7 and 14. In addition, PEDV pigs had increased stem cell proliferation (P<0.05) and a numerical increase in DNA fragmentation compared with controls through dpi 7 which coincided with an observed return of digestive function to that of controls. Collectively, these data reveal that PEDV infection results in time-dependent changes not only in intestinal morphology but also barrier integrity and function.
On 10 September 2017, the Mars Atmosphere and Volatile EvolutioN mission observed a particularly strong X‐class flare. This paper will focus on observations made by Neutral Gas and Ion Mass ...Spectrometer (NGIMS) and the flare response detected by extreme ultraviolet monitor. We focus the data to the region of the upper atmosphere from 160 to 300 km and to 10 orbits before and after the flare. The flare peaked near 16:12 UTC with the closest periapsis pass from 17:30 to 17:54 UTC (Lee et al., , https://doi.org/10.1029/2018GL079162). NGIMS measured a significant enhancement in the neutral densities above 195 km for the flare. This enhancement stands out for the major species measured by NGIMS (Ar, CO2, CO, O, and N2). The correlation of the flare and the enhancement in density and temperature in the upper atmosphere indicates that solar flare heating is most likely the main driver and has important implications for the effects of space weather events on terrestrial atmospheres.
Plain Language Summary
10 September 2017 saw an extraordinary solar flare event that affected both Mars and Earth, providing an unique observational opportunity. It has been observed in the past that solar flares can cause tremendous rapid heating of the upper atmosphere of the Earth, but the extent of this heating on the neutral atmosphere is yet to be well observed at Mars. Early MAVEN observations caught smaller flare effects and observed rapid heating to a lightly lesser extent. The 10 September 2017 flare is not only significantly more intense than previous observations, but the timing of neutral observations was optimal to observe just how much and how quickly the upper atmosphere responded to the flare. This can lead to refinement of atmospheric escape and atmospheric evolution.
Key Points
Solar X‐class flares rapidly heat the neutral upper atmosphere on time scales similar to the duration of the flare
Scale height enhancements due to the EUV from the flare are higher for O, CO, and N2 than for CO2 and Ar
Responsiveness of the neutral atmosphere to EUV solar flares has implications for atmosphere escape and the early Sun
The Mars Atmosphere and Volatile Evolution mission (MAVEN) is a NASA spacecraft that has been orbiting Mars since 2014. The Mars Atmosphere and Volatile Evolution mission team has established a ...current set of best practices to strengthen Diversity, Equity, Inclusion, and Accessibility (DEIA) initiatives; there are numerous axes of diversity, and this paper does not focus on one specific aspect of diversity but rather focuses on mission-specific approaches to inclusion. We present the past and present approaches as well as future initiatives and areas of improvement to continuing our efforts towards maximizing inclusion and engagement on the Mars Atmosphere and Volatile Evolution mission team and its working environment. The approaches presented in this paper are applicable to the space physics and planetary science communities, as well as any large-scale science or mission teams.
Extreme space weather events can episodically release solar energetic particles (SEPs) that precipitate into planetary atmospheres, leading to aurora and increased ionization. While the induced ...magnetosphere of Mars does not substantially obstruct SEP protons, the effect on SEP electrons is not known. We use a test particle model modified for relativistic electrons to model transport of 10–200 keV electrons from outside the bow shock and deep in the magnetotail of Mars. We find a substantial influence of curvature and gradient drifts on precipitation, leading to depletions in the bow shock and transport onto closed field lines. The model estimates ∼3% of incident flux precipitates into the Mars atmosphere for a typical SEP event under nominal solar wind conditions, exceeding the estimate from the guiding center path approximation without drift terms. Precipitation is globally patchy. The model estimates 55% of electrons precipitating into cusps along open field lines and 45% precipitating on closed field lines, suggesting drift and nonadiabatic transport mechanisms have a significant influence on precipitation. We also predict that the fraction of precipitating differential flux increases as a function of energy. We discuss how these predictions would be affected by disturbed conditions that tend to accompany the arrival of SEPs and by differing SEP electron spectra hardness and anisotropy. We finally discuss how the simulation predictions compare to observations of diffuse aurora.
Key Points
For a “typical” event, only 3% of incident energetic (10–200 keV) electron flux will precipitate
Energetic electron depletions occur within the bow shock
Precipitation is patchy, occurring along open field lines into cusps and closed field lines via drift and nonadiabatic transport mechanisms
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