408 research outputs found
Test Particle Analysis of High Altitude Ion Transport and Escape on Mars.
Because Mars has a weak magnetic field in comparison with Earth, the solar wind can directly interact with the neutral planetary environment and drive atmospheric erosion. Located in the overlap region of the atmosphere and the solar wind, the neutral constituents of the atmosphere are ionized and instantaneously affected by the fast-moving solar wind and interplanetary magnetic field. These newly-created ions are 'picked up' by the solar wind, and accelerated away from Mars by the solar wind's motional electric field. The main objective of this work is to extensively probe the high altitude ion transport and escape on Mars using a test particle model that tracks the motion and acceleration of pick-up ions through near-Mars space using virtual detectors.
The first focus of this study addresses how the escape of O+ is influenced relative to the production mechanisms: photoionization, charge exchange and electron impact, finding that the total production and loss rates differ up to two orders of magnitude. This dissertation also investigates the influence of the hot oxygen corona and the solar cycle on the individual ion trajectories. This study found that the inclusion of the corona roughly doubles the total escape for solar minimum conditions and directly contributing to high energy sources above 1 keV and increases the O+ flux and total escape by an order of magnitude from solar minimum to maximum. Two other related focal points for this dissertation included examining which species dominates pick-up ion loss from Mars and quantifying how the ionospheric source influences subsequent pick-up ion acceleration. While the results indicate that O+ dominate the loss, the ionospheric species O2+ and CO2+ were most likely to escape.
The simulations have robustly described the physics controlling high altitude ion escape by isolating the influence of ion production, the solar cycle, the ionospheric contributions, the dominant species and the background fields. The results presented are significant for the eventual interpretation of ion observations at Mars in order to quantify how much of the atmosphere is escaping, which is a critical aspect of understanding how water has evolved on Mars.PHDAtmos, Oceanic & Space SciencesUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/97939/1/smcurry_1.pd
Atmospheric Escape Processes and Planetary Atmospheric Evolution
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
Exoplanet Diversity in the Era of Space-based Direct Imaging Missions
This whitepaper discusses the diversity of exoplanets that could be detected
by future observations, so that comparative exoplanetology can be performed in
the upcoming era of large space-based flagship missions. The primary focus will
be on characterizing Earth-like worlds around Sun-like stars. However, we will
also be able to characterize companion planets in the system simultaneously.
This will not only provide a contextual picture with regards to our Solar
system, but also presents a unique opportunity to observe size dependent
planetary atmospheres at different orbital distances. We propose a preliminary
scheme based on chemical behavior of gases and condensates in a planet's
atmosphere that classifies them with respect to planetary radius and incident
stellar flux.Comment: A white paper submitted to the National Academy of Sciences Exoplanet
Science Strateg
The case for studying other planetary magnetospheres and atmospheres in Heliophysics
Heliophysics is the field that "studies the nature of the Sun, and how it
influences the very nature of space - and, in turn, the atmospheres of
planetary bodies and the technology that exists there." However, NASA's
Heliophysics Division tends to limit study of planetary magnetospheres and
atmospheres to only those of Earth. This leaves exploration and understanding
of space plasma physics at other worlds to the purview of the Planetary Science
and Astrophysics Divisions. This is detrimental to the study of space plasma
physics in general since, although some cross-divisional funding opportunities
do exist, vital elements of space plasma physics can be best addressed by
extending the expertise of Heliophysics scientists to other stellar and
planetary magnetospheres. However, the diverse worlds within the solar system
provide crucial environmental conditions that are not replicated at Earth but
can provide deep insight into fundamental space plasma physics processes.
Studying planetary systems with Heliophysics objectives, comprehensive
instrumentation, and new grant opportunities for analysis and modeling would
enable a novel understanding of fundamental and universal processes of space
plasma physics. As such, the Heliophysics community should be prepared to
consider, prioritize, and fund dedicated Heliophysics efforts to planetary
targets to specifically study space physics and aeronomy objectives
Mosaic: A Satellite Constellation to Enable Groundbreaking Mars Climate System Science and Prepare for Human Exploration
The Martian climate system has been revealed to rival the complexity of Earth\u27s. Over the last 20 yr, a fragmented and incomplete picture has emerged of its structure and variability; we remain largely ignorant of many of the physical processes driving matter and energy flow between and within Mars\u27 diverse climate domains. Mars Orbiters for Surface, Atmosphere, and Ionosphere Connections (MOSAIC) is a constellation of ten platforms focused on understanding these climate connections, with orbits and instruments tailored to observe the Martian climate system from three complementary perspectives. First, low-circular near-polar Sun-synchronous orbits (a large mothership and three smallsats spaced in local time) enable vertical profiling of wind, aerosols, water, and temperature, as well as mapping of surface and subsurface ice. Second, elliptical orbits sampling all of Mars\u27 plasma regions enable multipoint measurements necessary to understand mass/energy transport and ion-driven escape, also enabling, with the polar orbiters, dense radio occultation coverage. Last, longitudinally spaced areostationary orbits enable synoptic views of the lower atmosphere necessary to understand global and mesoscale dynamics, global views of the hydrogen and oxygen exospheres, and upstream measurements of space weather conditions. MOSAIC will characterize climate system variability diurnally and seasonally, on meso-, regional, and global scales, targeting the shallow subsurface all the way out to the solar wind, making many first-of-their-kind measurements. Importantly, these measurements will also prepare for human exploration and habitation of Mars by providing water resource prospecting, operational forecasting of dust and radiation hazards, and ionospheric communication/positioning disruptions
The Prevalence of Sexually Transmitted Infections in Papua New Guinea: A Systematic Review and Meta-Analysis
Patellofemoral osteoarthritis (PF OA) is more prevalent than previously thought and contributes to patient's suffering from knee OA. Synthesis of prevalence data can provide estimates of the burden of PF OA
Study of Z boson production in pPb collisions at √sNN=5.02 TeV
The production of Z bosons in pPb collisions at root S-NN = 5.02 TeV is studied by the CMS experiment via the electron and muon decay channels. The inclusive cross section is compared to pp collision predictions, and found to scale with the number of elementary nucleon-nucleon collisions. The differential cross sections as a function of the Z boson rapidity and transverse momentum are measured. Though they are found to be consistent within uncertainty with theoretical predictions both with and without nuclear effects, the forward-backward asymmetry suggests the presence of nuclear effects at large rapidities. These results provide new data for constraining nuclear parton distribution functions
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