Statistical analysis of the reflection of incident O<sup>+</sup> pickup ions at Mars: MAVEN observations

Masunaga, Kei; Seki, K.; Brain, David; Fang, Xiaohua; Dong, Y.; Jakosky, B. M.; McFadden, J. P.; Halekas, J. S.; Connerney, J. E. P.; Mitchell, David; Eparvier, F. G.

doi:10.1002/2016ja023516

Cited by 12 publications

(12 citation statements)

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“…However, the lack of energetic neutral oxygen flux over the sensitivity level of the energetic neutral particle instruments on MEX suggests that the sputtering rate may be lower than theoretical predictions (Futaana et al, ). It is also currently unclear how the sputtering estimates under a primordial solar wind conform to the strong dependence of pickup O + reflection ratios on p dyn (caused by stronger magnetic fields/smaller gyroradii in the sheath) recently reported by Masunaga et al ().…”

Section: Discussionmentioning

confidence: 88%

Ion Escape From Mars Through Time: An Extrapolation of Atmospheric Loss Based on 10 Years of Mars Express Measurements

et al. 2018

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Solar wind-driven atmospheric ion escape has long been hypothesized as a major influence on the evolution of the Martian atmosphere due to the lack of a Martian global dipole magnetic field. We use 10 years (2007)(2008)(2009)(2010)(2011)(2012)(2013)(2014)(2015)(2016)(2017) of Mars Express data to quantify the ion escape rate over the fully sampled parameter space of upstream solar wind dynamic pressure, p dyn , and solar photoionizing flux, F XUV . The modeled dependence on the upstream parameters indicates a near-linear dependence on F XUV and weak negative correlation with p dyn . Integrating total heavy ion escape back through time, considering the evolution of the upstream parameters and the modeled trends, can only account for an estimated 4.8 ± 1.1 mbar of atmosphere lost as ions since the middle to late Hesperian (∼3.3 Ga ago). Accounting for the recently reported stability of ion escape through the energetic oxygen ion plume provides an upper estimate of ∼6 mbar lost. Extending the extrapolation to the late Noachian (3.9 Ga ago) accounts for 6.3 ± 1.9 mbar, and analogously up to ∼9 mbar, lost through ion escape since that time. Thus, the ion escape trends observed by Mars Express indicate that atmospheric ion escape contributed only a minor role in the evolution of the Martian atmosphere. We also report solar wind control of the cold ion outflow channel, providing a tentative explanation for the low response of the ion escape rate to upstream solar wind. Plain Language SummaryThere is plentiful evidence that liquid water was standing, flowing, and precipitating on the surface of Mars early in the planet's geological history. About 3.3 billion years ago the climate that allowed such a wet environment on Mars changed and turned the planet into its present-day cold and dry state. It is commonly thought that a strong greenhouse effect, sustained by an initially thick atmosphere, collapsed as the atmosphere gradually escaped to space, a process that can be driven by interaction with the solar wind, among other mechanisms. We estimate how much atmosphere has been removed by the solar wind by studying measurements of escaping atmospheric ions as the planet is subjected to varying solar conditions. We find that the solar wind is not a strong driver for the rate of atmospheric ion escape, which is rather driven by solar ionizing radiation. Adding up the estimated ion escape rate over 4 billion years, accounting for the stronger solar wind and solar radiation from the younger Sun, we find that at most roughly 9 mbar surface pressure has been removed by the solar wind through ion escape. This amount is alone too small to explain the removal of the early Martian atmosphere.

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Section: Discussionmentioning

confidence: 88%

Ion Escape From Mars Through Time: An Extrapolation of Atmospheric Loss Based on 10 Years of Mars Express Measurements

et al. 2018

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“…Numerical simulations have predicted this hemispheric asymmetry of precipitating ions along the solar wind electric field (e.g., Chaufray et al, ; Curry et al, ; Fang et al, ; Luhmann & Kozyra, ). Recently, such a hemispheric asymmetry of precipitating ion fluxes with respect to the direction of the upstream solar wind electric field was observationally confirmed by MAVEN (e.g., Brain et al, ; Hara, Luhmann, et al, ; Masunaga et al, ).…”

Section: Introductionmentioning

confidence: 81%

Evidence for Crustal Magnetic Field Control of Ions Precipitating Into the Upper Atmosphere of Mars

et al. 2018

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We present the effects of the local magnetic field configurations on ions precipitating into the upper atmosphere of Mars using Mars Atmosphere and Volatile EvolutioN (MAVEN) observations. Precipitating pickup planetary heavy ions (O + , O + 2 , and CO + 2 ) are of particular interest in the Martian plasma environment because they potentially enhance the sputtering loss of ambient neutral particles. In addition, solar wind protons (and H + pickup ions) penetrate into the dayside atmosphere due to the direct interaction with the Martian obstacle. We present a statistical study showing that precipitating ion fluxes are typically enhanced by a factor of 2-3 under radial field configurations. We also show that the crustal fields have a shielding effect; the precipitating fluxes are significantly reduced by ∼50% under the strong crustal fields (≳ 100 nT), where the local magnetic field is oriented with a more horizontal component to the surface. These trends are seen consistently regardless of ion species, as well as the observed locations including dayside/nightside, subsolar longitudes, and ±E hemispheres in the Mars-centered solar electric (MSE) coordinates. In particular, the local magnetic field configurations control precipitating ions with energies lower than a few keV, while precipitating high-energy ion fluxes are likely independent of the local magnetic field configurations. Precipitating ion fluxes are known to vary by at least an order of magnitude depending on the upstream solar wind. Therefore, the local magnetic field configurations turn out to be the secondary factor in modulating precipitating ion fluxes at Mars.

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“…One of the major sputter sources at Mars are incident O + pick up ions that were ionized by the solar wind but re-entered the Martian atmosphere (e.g., . Masunaga et al (2017) found that the rate of O + that do not re-enter the Martian atmosphere is strongly dependent on IMF, solar wind dynamic pressure and the gyroradius of the O + ions, but rather not on the EUV flux. Under extreme solar wind conditions, Masunaga et al (2017), therefore, deduce, sputtering might even be reduced due to an increase of O + reflection into the solar wind.…”

Section: Non-thermal Escape Processes Over the Last ~4 Gyrmentioning

confidence: 98%

Did Mars Possess a Dense Atmosphere During the First $\sim400$ Million Years?

Scherf

Lämmer

2020

Space Sci Rev

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It is not yet entirely clear whether Mars began as a warm and wet planet that evolved towards the present-day cold and dry body or if it always was cold and dry with just some sporadic episodes of liquid water on its surface. An important clue into this question can be gained by studying the earliest evolution of the Martian atmosphere and whether it was dense and stable to maintain a warm and wet climate or tenuous and susceptible to strong atmospheric escape. In this review we therefore discuss relevant aspects for the evolution and stability of a potential early Martian atmosphere. This contains the EUV flux evolution of the young Sun, the formation timescale and volatile inventory of the planet including volcanic degassing, impact delivery and removal, the loss of the catastrophically outgassed steam atmosphere, atmosphere-surface interactions, as well as thermal and non-thermal escape processes affecting a potential secondary atmosphere at early Mars. While early non-thermal escape at Mars before 4 billion years ago is poorly understood, in particular in view of its ancient intrinsic magnetic field, research on thermal escape processes and the stability of a CO2-dominated atmosphere around Mars against high EUV fluxes indicate that volatile delivery and volcanic degassing cannot counterbalance the strong thermal escape. Therefore, a catastrophically

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Statistical analysis of the reflection of incident O⁺ pickup ions at Mars: MAVEN observations

Cited by 12 publications

References 31 publications

Ion Escape From Mars Through Time: An Extrapolation of Atmospheric Loss Based on 10 Years of Mars Express Measurements

Ion Escape From Mars Through Time: An Extrapolation of Atmospheric Loss Based on 10 Years of Mars Express Measurements

Evidence for Crustal Magnetic Field Control of Ions Precipitating Into the Upper Atmosphere of Mars

Did Mars Possess a Dense Atmosphere During the First $\sim400$ Million Years?

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Statistical analysis of the reflection of incident O+ pickup ions at Mars: MAVEN observations

Cited by 12 publications

References 31 publications

Ion Escape From Mars Through Time: An Extrapolation of Atmospheric Loss Based on 10 Years of Mars Express Measurements

Ion Escape From Mars Through Time: An Extrapolation of Atmospheric Loss Based on 10 Years of Mars Express Measurements

Evidence for Crustal Magnetic Field Control of Ions Precipitating Into the Upper Atmosphere of Mars

Did Mars Possess a Dense Atmosphere During the First $\sim400$ Million Years?

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Statistical analysis of the reflection of incident O⁺ pickup ions at Mars: MAVEN observations