An investigation of solar wind effects on the evolution of the Martian atmosphere

This investigation concentrated on the question of how atmosphere escape, related to both photochemistry and the Mars solar wind interaction, may have affected the evolution of Mars' atmosphere over time. The principal investigator and postdoctoral researcher adopted the premise that contemporary escape processes have dominated the losses to space over the past 3.5 billion years, but that the associated loss rates have been modified by solar evolution. A model was constructed for the contemporary escape scenario based on knowledge gained from both Venus in-situ measurements from Pioneer Venus Orbiter and Mars measurements from Phobos-2. Venus provided a valuable second example of a weakly magnetized planet having a similar solar wind interaction where we have more knowledge from observations. The model included photochemical losses from recombining ionospheric molecular ions, scavenging Martian upper atmosphere ('pickup') ions by the solar wind, and sputtering of the atmosphere by reentering pickup ions. The existence of the latter mechanism was realized during the course of the supported investigation, and is now thought by Jakosky and Pepin to explain some of the Martian noble gas isotope ratios

Solar Wind Effects on Atmospheres of the Weakly Magnetized Bodies: Mars, Titan and the Moon

The atmospheres of planetary bodies without significant intrinsic magnetic fields exhibit unique features because they interact with the external plasma flows in their space environment. The plasma interactions also have the potential of altering the evolutionary paths of these atmospheres since the processes (such as ion pickup and sputtering) that lead to loss of constituents have effects unlike those of other escape mechanisms. This ongoing investigation has been concentrating on the characterization of the plasma interactions and the associated plasma physical escape processes at Mars and Titan. The results are relevant to both mission planning and interpretation of data from past and future Mars and Lunar missions, and to tour and mission operations planning for the Cassini Orbiter. The also contribute to our general understanding, from a comparative planetology standpoint, of the role that planetary magnetic field play in determining the state and fate of a planetary atmosphere

Co-Investigator Participation in the Mars-94 Mission Studies of the Mars-Solar Wind Interaction: Topside Sounder and Magnetometer

The purpose of this investigation has been to provide United States co-investigator support toward the preparation of the Topside Ionospheric Sounder and Magnetometer experiments on the Russian Mars-96 (previously Mars-94) mission. The main role has been to assist in the preparation of software tools for the optimum design of the investigation and the evaluation of mission operational plans and orbits

Propagation of the 2012 March Coronal Mass Ejections from the Sun to Heliopause

In 2012 March the Sun exhibited extraordinary activities. In particular, the active region NOAA AR 11429 emitted a series of large coronal mass ejections (CMEs) which were imaged by STEREO as it rotated with the Sun from the east to west. These sustained eruptions are expected to generate a global shell of disturbed material sweeping through the heliosphere. A cluster of shocks and interplanetary CMEs (ICMEs) were observed near the Earth, and are propagated outward from 1 AU using an MHD model. The transient streams interact with each other, which erases memory of the source and results in a large merged interaction region (MIR) with a preceding shock. The MHD model predicts that the shock and MIR would reach 120 AU around 2013 April 22, which agrees well with the period of radio emissions and the time of a transient disturbance in galactic cosmic rays detected by Voyager 1. These results are important for understanding the "fate" of CMEs in the outer heliosphere and provide confidence that the heliopause is located around 120 AU from the Sun.Comment: 13 pages, 5 figures, accepted for publication in ApJ Letter

Sun-to-Earth Characteristics of Two Coronal Mass Ejections Interacting near 1 AU: Formation of a Complex Ejecta and Generation of a Two-Step Geomagnetic Storm

On 2012 September 30 - October 1 the Earth underwent a two-step geomagnetic storm. We examine the Sun-to-Earth characteristics of the coronal mass ejections (CMEs) responsible for the geomagnetic storm with combined heliospheric imaging and in situ observations. The first CME, which occurred on 2012 September 25, is a slow event and shows an acceleration followed by a nearly invariant speed in the whole Sun-Earth space. The second event, launched from the Sun on 2012 September 27, exhibits a quick acceleration, then a rapid deceleration and finally a nearly constant speed, a typical Sun-to-Earth propagation profile for fast CMEs \citep{liu13}. These two CMEs interacted near 1 AU as predicted by the heliospheric imaging observations and formed a complex ejecta observed at Wind, with a shock inside that enhanced the pre-existing southward magnetic field. Reconstruction of the complex ejecta with the in situ data indicates an overall left-handed flux rope-like configuration, with an embedded concave-outward shock front, a maximum magnetic field strength deviating from the flux rope axis and convex-outward field lines ahead of the shock. While the reconstruction results are consistent with the picture of CME-CME interactions, a magnetic cloud-like structure without clear signs of CME interactions \citep{lugaz14} is anticipated when the merging process is finished.Comment: 15 pages, 5 figures. Accepted for publication in ApJ Letter

On Sun-to-Earth Propagation of Coronal Mass Ejections: 2. Slow Events and Comparison with Others

As a follow-up study on Sun-to-Earth propagation of fast coronal mass ejections (CMEs), we examine the Sun-to-Earth characteristics of slow CMEs combining heliospheric imaging and in situ observations. Three events of particular interest, the 2010 June 16, 2011 March 25 and 2012 September 25 CMEs, are selected for this study. We compare slow CMEs with fast and intermediate-speed events, and obtain key results complementing the attempt of \citet{liu13} to create a general picture of CME Sun-to-Earth propagation: (1) the Sun-to-Earth propagation of a typical slow CME can be approximately described by two phases, a gradual acceleration out to about 20-30 solar radii, followed by a nearly invariant speed around the average solar wind level, (2) comparison between different types of CMEs indicates that faster CMEs tend to accelerate and decelerate more rapidly and have shorter cessation distances for the acceleration and deceleration, (3) both intermediate-speed and slow CMEs would have a speed comparable to the average solar wind level before reaching 1 AU, (4) slow CMEs have a high potential to interact with other solar wind structures in the Sun-Earth space due to their slow motion, providing critical ingredients to enhance space weather, and (5) the slow CMEs studied here lack strong magnetic fields at the Earth but tend to preserve a flux-rope structure with axis generally perpendicular to the radial direction from the Sun. We also suggest a "best" strategy for the application of a triangulation concept in determining CME Sun-to-Earth kinematics, which helps to clarify confusions about CME geometry assumptions in the triangulation and to improve CME analysis and observations.Comment: 37 pages, 13 figures, accepted for publication in ApJ Supplemen

Mars atmospheric escape and isotopic fractionation: Synthesis of data and models

The present Mars atmosphere is relatively thin and cold. It is not at all like that which is presumed to have been responsible for the formation of valley networks and the heavy erosion of craters during the earliest epochs of martian history. An important goal of Mars exploration is to try to understand the properties of the early atmosphere, the initial inventory of volatiles at the planet's surface, the processes by which the atmosphere and climate have evolved over time, and the current location of volatiles presumed to have been in the atmosphere in the earlier times. The current status of understanding of the escape of volatiles to space over geologic time and the resulting fractionation of isotopes of stable atoms remaining in the atmosphere are described, and a scenario for volatile abundance and evolution that is consistent with the available information on the escape and fractionation of each species is constructed. In particular, the evolution of hydrogen, carbon, oxygen, and nitrogen, as contained in atmospheric (and non-atmospheric) water, carbon dioxide, and molecular nitrogen, is examined

Poker Flat MST radar observations of high latitude neutral winds at the mesopause during and after solar proton events

Observations with the Poker Flat, Alaska, MST radar during and after solar proton events in 1982 and 1984 suggest that winds in the altitude range of ~ 80-90 km were altered as a consequence of the influx of energetic charged particles and large electric fields at high latitudes. The atmospheric changes accompanying these events appear to result in a reduction of the semidiurnal tide and an enhancement in the diurnal tide. It is suggested that these changes could result from the alteration of the local tidal heating distribution produced by the particle precipitation, either through changes in the local ozone distribution or as a result of mesospheric Joule heating.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30726/1/0000375.pd

Formation and Evolution of the Large‐Scale Magnetic Fields in Venus’ Ionosphere: Results From a Three Dimensional Global Multispecies MHD Model

Large‐scale magnetic fields have been observed in Venus’ ionosphere by both the Pioneer Venus Orbiter (PVO) and Venus Express spacecraft. In this study, we examine the formation and evolution of the large‐scale magnetic field in the Venus ionosphere using a sophisticated global multispecies Magnetohydrodynamics (MHD) model that has been developed for Venus (Ma et al., 2013, https://doi.org/10.1029/2012JA018265). A time‐dependent model run is performed under varying solar wind dynamic pressure. Based on model results, we find that (1) the initial response of the induced magnetosphere is fast (~min), (2) a large‐scale magnetic field gradually forms in the ionosphere when the solar wind dynamic pressure suddenly exceeds the ionospheric thermal pressure, (3) both the penetration and decay of the large‐scale magnetic field in the ionosphere are slow (~hr), and (4) the ion escape rate has a nonlinear response to the change of solar wind dynamic pressure.Plain language SummaryLarge‐scale magnetic fields have been observed at Venus’ ionosphere by previous Venus missions. In this study, we examine the formation and evolution of the large‐scale magnetic field in the Venus ionosphere using a sophisticated global model. A time‐dependent model run is performed under varying solar wind dynamic pressure (density). Model results show that the outside interaction region responds quickly (~min) to the solar wind variation, while the response time of the ionosphere is long (~hr). We also found that the ion escape rate has a nonlinear response to the change of solar wind dynamic pressure.Key PointsThe global MHD model self‐consistently reproduces the formation and evolution of the large‐scale magnetic fields in the Venus ionosphereModel results show that it takes quite long time (~hr) for the magnetic field to penetrate into and decay in the ionosphereThe large‐scale magnetic fields in the ionosphere act as an additional obstacle to the solar windPeer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/155482/1/grl60596.pdfhttps://deepblue.lib.umich.edu/bitstream/2027.42/155482/2/grl60596_am.pd