Nightside ionosphere of Mars: Modeling the effects of crustal magnetic fields and electron pitch angle distributions on electron impact ionization

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/95654/1/jgre2678.pd

Observations of Ionospheric Oxygen in the Vicinity of the Moon

Using data from the ARTEMIS spacecraft, we report on observations consistent with the detection of ionospheric oxygen ions in the terrestrial magnetosphere at lunar altitudes. Since there is no mass spectrometer onboard the spacecraft, oxygen can only be detected when the outflow velocities are sufficient to separate oxygen from hydrogen in energy (for the same velocity, oxygen will appear to have a higher energy). We catalog the occurrence of such signatures and relate the detection, number density, and energy of ionospheric oxygen ions to geomagnetic activity parameters. These observations shed light on the amount of ionospheric plasma that reaches the Moon in the magnetotail and how this plasma may participate in and contribute to magnetospheric activity and lunar exosphere production

Inverted-V Electron Acceleration Events Concurring With Localized Auroral Observations at Mars by MAVEN

International audienceFrom February to March 2019, the Mars Atmosphere and Volatile EvolutioN (MAVEN) spacecraft repeatedly observed aurora near periapsis over Mars' southern strong crustal fields. During these orbits, the Solar Wind Electron Analyzer observed accelerated electrons at similar locations to where the auroras were observed, resembling the inverted-V structure observed near Earth's auroral region. In this study, we present a case study of such an acceleration event, where we estimate a field-aligned electrostatic potential drop of ∼440 V. We determine the field-aligned current from the observed magnetic perturbation reaches 1.1 μA/m2, agreeing reasonably well with the estimated net electron current carried by acceleration electrons with a maximum of 2.5 μA/m2. Similar to Earth, the potential drop develops when the ambient plasma cannot sustain the imposed field-aligned current. We also estimate the potential layer to be located above 750- to 850-km altitude and the associated electric field to be ∼0.6 V/m

Early MAVEN Deep Dip campaign reveals thermosphere and ionosphere variability

International audienceThe Mars Atmosphere and Volatile Evolution (MAVEN) mission, during the second of its Deep Dip campaigns, made comprehensive measurements of martian thermosphere and ionosphere composition, structure, and variability at altitudes down to ~130 kilometers in the subsolar region. This altitude range contains the diffusively separated upper atmosphere just above the well-mixed atmosphere, the layer of peak extreme ultraviolet heating and primary reservoir for atmospheric escape. In situ measurements of the upper atmosphere reveal previously unmeasured populations of neutral and charged particles, the homopause altitude at approximately 130 kilometers, and an unexpected level of variability both on an orbit-to-orbit basis and within individual orbits. These observations help constrain volatile escape processes controlled by thermosphere and ionosphere structure and variability

MAVEN observations of the response of Mars to an interplanetary coronal mass ejection

International audienceCoupling between the lower and upper atmosphere, combined with loss of gas from the upper atmosphere to space, likely contributed to the thin, cold, dry atmosphere of modern Mars. To help understand ongoing ion loss to space, the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft made comprehensive measurements of the Mars upper atmosphere, ionosphere, and interactions with the Sun and solar wind during an interplanetary coronal mass ejection impact in March 2015. Responses include changes in the bow shock and magnetosheath, formation of widespread diffuse aurora, and enhancement of pick-up ions. Observations and models both show an enhancement in escape rate of ions to space during the event. Ion loss during solar events early in Mars history may have been a major contributor to the long-term evolution of the Mars atmosphere

Loss of the Martian atmosphere to space: Present-day loss rates determined from MAVEN observations and integrated loss through time

International audienceObservations of the Mars upper atmosphere made from the Mars Atmosphere and Volatile Evolution (MAVEN) spacecraft have been used to determine the loss rates of gas from the upper atmosphere to space for a complete Mars year (16 Nov 2014 – 3 Oct 2016). Loss rates for H and O are sufficient to remove ∼2-3 kg/s to space. By itself, this loss would be significant over the history of the planet. In addition, loss rates would have been greater early in history due to the enhanced solar EUV and more-active Sun. Integrated loss, based on current processes whose escape rates in the past are adjusted according to expected solar evolution, would have been as much as 0.8 bar CO2 or 23 m global equivalent layer of H2O; these losses are likely to be lower limits due to the nature of the extrapolation of loss rates to the earliest times. Combined with the lack of surface or subsurface reservoirs for CO2 that could hold remnants of an early, thick atmosphere, these results suggest that loss of gas to space has been the dominant process responsible for changing the climate of Mars from an early, warmer environment to the cold, dry one that we see today