Elevated atmospheric escape of atomic hydrogen from Mars induced by high-altitude water

Chaffin, Michael; Deighan, Justin; Schneider, Nicholas M.; Stewart, A. I. F.

doi:10.1038/ngeo2887

Cited by 129 publications

(150 citation statements)

References 42 publications

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“…These observations and the modeling of Chaffin et al . [] may provide a link between seasonal variability in the lower atmosphere, high‐altitude water concentration, and elevated escape of hydrogen. Our observations, which provide some of the best coverage of the seasonal variability of the exosphere to date, may help prove or disprove these new models for hydrogen escape.…”

Section: Seasonal Variability Of the Hydrogen Exospherementioning

confidence: 99%

“…However, many of these observations have incomplete temporal coverage, and uncertainties in data inversion make it challenging to translate observations of seasonal variability into quantitative estimates of escape flux. As a result, questions remain about the exact form of the seasonal variability, the mechanism(s) responsible for creating this variability, and the implications for escape [ Chaufray et al ., ; Chaffin et al ., ]. In this manuscript, we present observations from the Solar Wind Ion Analyzer (SWIA) on MAVEN [ Halekas et al ., , ] that provide a sensitive measurement of the high‐altitude hydrogen corona along a different column than UV observations, with good temporal coverage over the Martian year.…”

Section: Introductionmentioning

confidence: 99%

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Seasonal variability of the hydrogen exosphere of Mars

2017

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The Mars Atmosphere and Volatile EvolutioN (MAVEN) mission measures both the upstream solar wind and collisional products from energetic neutral hydrogen atoms that precipitate into the upper atmosphere after their initial formation by charge exchange with exospheric hydrogen. By computing the ratio between the densities of these populations, we derive a robust measurement of the column density of exospheric hydrogen upstream of the Martian bow shock. By comparing with Chamberlain‐type model exospheres, we place new constraints on the structure and escape rates of exospheric hydrogen, derived from observations sensitive to a different and potentially complementary column from most scattered sunlight observations. Our observations provide quantitative estimates of the hydrogen exosphere with nearly complete temporal coverage, revealing order of magnitude seasonal changes in column density and a peak slightly after perihelion, approximately at southern summer solstice. The timing of this peak suggests either a lag in the response of the Martian atmosphere to solar inputs or a seasonal effect driven by lower atmosphere dynamics. The high degree of seasonal variability implied by our observations suggests that the Martian atmosphere and the thermal escape of light elements depend sensitively on solar inputs.

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Section: Seasonal Variability Of the Hydrogen Exospherementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Seasonal variability of the hydrogen exosphere of Mars

2017

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“…Gravity waves can induce mean‐wind acceleration/deceleration via momentum deposition, thereby driving large‐scale vertical transport (e.g., Holton et al, ). P and L are expressed as

P ()(, z) = n_{{CO}_{2}} \int italicdλ (}{, σ ()(, λ) Φ_{0} ()(, λ) \exp (][, - \frac{1}{\cos θ} σ ()(, λ) \int_{z}^{\infty} n_{{CO}_{2}} italicdz)),

L = 2 k n_{O}^{2} n_{{CO}_{2}},

where

n_{{CO}_{2}}

is the CO 2 density, λ is the wavelength of the incoming solar radiation, σ ( λ ) is the absorption cross‐section of CO 2 (Von Zahn et al, ), Φ 0 ( λ ) is the solar spectrum, θ = 45° is the approximate solar zenith angle at the sub‐Earth point, and k = 5.4 × 10 −33 (300/ T ) 3.25 is the rate coefficient for the recombination of O (Chaffin et al, ). The solar spectrum was taken from the American Society for Testing and Materials (https://www.nrel.gov/grid/solar-resource/spectra-astm-e490.html).…”

Section: Modeling Of the Perturbation Of Atomic Oxygen Densitymentioning

confidence: 99%

Vertical Coupling Between the Cloud‐Level Atmosphere and the Thermosphere of Venus Inferred From the Simultaneous Observations by Hisaki and Akatsuki

et al. 2020

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The vertical coupling between the cloud‐level atmosphere and the thermosphere of Venus was investigated using 365 nm images obtained by the Ultraviolet Imager on board Akatsuki and oxygen atom 135.6 nm dayglow intensities obtained by the Extreme Ultraviolet Spectroscope for Exospheric Dynamics on board the space telescope Hisaki. Simultaneous observations revealed a common periodicity of ~3.6 Earth days in the cloud‐tracked velocity, the cloud brightness, and the airglow intensity. The oscillation at the cloud level is attributed to a planetary‐scale Kelvin wave. A one‐dimensional linear wave model showed that the Kelvin wave cannot propagate from the cloud level to the thermosphere because of radiative damping. The modeling also revealed that a small‐scale gravity waves having wavelengths of <1,000 km can reach the thermosphere on the dawnside and that they are strongly attenuated on the duskside because of the difference in the background winds with vertical shears. We further developed a one‐dimensional photochemical model to investigate the response of the airglow intensity to the change of the eddy diffusion coefficient, which is expected to increase with the wave amplitude. The model showed that a 3.6‐day oscillation of the diffusion coefficient with an amplitude of ~300 m2 s−1 explains the observed airglow intensity variation. A possible cause of the 3.6‐day period is the filtering of gravity wave fluxes by the Kelvin wave‐induced wind.

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“…Given the high solubility of O 2 at these low temperatures (Stamenković et al, ), the required pO 2 can be lowered to greater than or equal to ~0.2 mbar for Ca/Mg perchlorate brines at –70 °C (see Figure 1b of Stamenković et al, ). On the other hand, the atmospheric models suggest that pO 2 in a CO 2 ‐rich atmosphere on Mars would have been kept as low as ~10 −3 mbar in the steady state due to the negative feedback mechanism between hydrogen escape and photochemistry (Chaffin et al, ; Zahnle et al, ). Hence, the achievement of long‐term, high pO 2 (~0.2 mbar) in the atmosphere may still be challenging.…”

Section: Implications For Aqueous Environments and Redox States On Eamentioning

confidence: 99%

Highly Oxidizing Aqueous Environments on Early Mars Inferred From Scavenging Pattern of Trace Metals on Manganese Oxides

et al. 2019

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The Curiosity and Opportunity rovers have found depositions of manganese (Mn) (hydr)oxides within the veins of the sedimentary rocks at Gale and Endeavour craters. Since Mn is a redox sensitive element, revealing the chemical form of the Mn (hydr)oxide provides unique information on the redox state of the near‐surface/groundwater at the time of deposition. Here we report results of laboratory experiments that investigated scavenging patterns of trace metals (zinc, nickel, and chromium) on different Mn (hydr)oxides in order to constrain the chemical form of the Mn precipitates found on Mars. Our results show manganese dioxide (MnO2) scavenges zinc and nickel effectively but not for chromium. The agreement of this scavenging pattern with the observations strongly suggests that the Mn (hydr)oxides found on Mars are highly likely to be MnO2. To form MnO2, oxidizing aqueous environments are required (e.g., Eh > 0.5 V at pH ~ 8). The candidates of the oxidant include molecular oxygen, ozone, nitrates, and perchlorate acids; all of which are considered to be produced by photochemical processes. The presence of MnO2 veins in sediments suggests that such atmospheric high‐Eh oxidants may have been supplied to the subsurface, possibly through hydrological cycles activated by transient warming.

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Elevated atmospheric escape of atomic hydrogen from Mars induced by high-altitude water

Cited by 129 publications

References 42 publications

Seasonal variability of the hydrogen exosphere of Mars

Seasonal variability of the hydrogen exosphere of Mars

Vertical Coupling Between the Cloud‐Level Atmosphere and the Thermosphere of Venus Inferred From the Simultaneous Observations by Hisaki and Akatsuki

Highly Oxidizing Aqueous Environments on Early Mars Inferred From Scavenging Pattern of Trace Metals on Manganese Oxides

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