Pickup ion measurements by MAVEN: A diagnostic of photochemical oxygen escape from Mars

Rahmati, Ali; Cravens, T. E.; Nagy, Andrew F.; Fox, Jane L.; Bougher, S. W.; Lillis, R. J.; Ledvina, S. A.; Larson, D. E.; Dunn, P.; Croxell, J. A.

doi:10.1002/2014gl060289

Cited by 24 publications

(66 citation statements)

References 49 publications

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“…For terrestrial atmospheres, increasing the EUV flux to levels estimated for the young Sun (≈1 Gyr; Ayres 1997) can increase the temperature of the thermosphere by a factor of 10 (Tian et al 2008), potentially causing significant and rapid atmospheric mass-loss. Ionization by EUV photons and the subsequent loss of atmospheric ions to stellar wind pick-up can also drive extensive atmospheric mass-loss on geologic timescales (e.g., Rahmati et al 2014 and references therein). Estimates of the incident EUV flux are therefore important for evaluating the long-term stability of an HZ atmosphere; however, a direct measurement of the EUV irradiance from an exoplanetary host star is essentially impossible because interstellar hydrogen removes almost all of the stellar EUV flux for virtually all stars except the Sun.…”

Section: High-energy Spectra As Photochemicalmentioning

confidence: 99%

The Muscles Treasury Survey. I. Motivation and Overview*

Loyd

Youngblood

Brown

et al. 2016

ApJ

401

381

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Ground-and space-based planet searches employing radial velocity techniques and transit photometry have detected thousands of planet-hosting stars in the Milky Way. With so many planets discovered, the next step toward identifying potentially habitable planets is atmospheric characterization. While the Sun-Earth system provides a good framework for understanding the atmospheric chemistry of Earth-like planets around solar-type stars, the observational and theoretical constraints on the atmospheres of rocky planets in the habitable zones (HZs) around low-mass stars (K and M dwarfs) are relatively few. The chemistry of these atmospheres is controlled by the shape and absolute flux of the stellar spectral energy distribution (SED), however, flux distributions of relatively inactive low-mass stars are poorly understood at present. To address this issue, we have executed a panchromatic (X-ray to mid-IR) study of the SEDs of 11 nearby planet-hosting stars, the Measurements of the Ultraviolet Spectral Characteristics of Low-mass Exoplanetary Systems (MUSCLES) Treasury Survey. The MUSCLES program consists visible observations from Hubble and ground-based observatories. Infrared and astrophysically inaccessible wavelengths (EUV and Lyα) are reconstructed using stellar model spectra to fill in gaps in the observational data. In this overview and the companion papers describing the MUSCLES survey, we show that energetic radiation (X-ray and ultraviolet) is present from magnetically active stellar atmospheres at all times for stars as late as M6. The emission line luminosities of C IV and Mg II are strongly correlated with band-integrated luminosities and we present empirical relations that can be used to estimate broadband FUV and XUV (≡X-ray + EUV) fluxes from individual stellar emission line measurements. We find that while the slope of the SED, FUV/NUV, increases by approximately two orders of magnitude form early K to late M dwarfs (≈0.01-1), the absolute FUV and XUV flux levels at their corresponding HZ distances are constant to within factors of a few, spanning the range 10-70 erg cm −2 s −1 in the HZ. Despite the lack of strong stellar activity indicators in their optical spectra, several of the M dwarfs in our sample show spectacular UV flare emission in their light curves. We present an example with flare/quiescent ultraviolet flux ratios of the order of 100:1 where the transition region energy output during the flare is comparable to the total quiescent luminosity of the star E flare (UV) ∼ 0.3 L * Δt (Δt = 1 s). Finally, we interpret enhanced L(line)/L Bol ratios for C IV and N V as tentative observational evidence for the interaction of planets with large planetary mass-to-orbital distance ratios (M plan /a plan ) with the transition regions of their host stars.

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Section: High-energy Spectra As Photochemicalmentioning

confidence: 99%

The Muscles Treasury Survey. I. Motivation and Overview*

Loyd

Youngblood

Brown

et al. 2016

ApJ

401

381

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“…Rahmati et al . [] used a value of 2.5 × 10 −16 cm 2 (Table ), but many other values can be found in the literature. Most modelers use the full differential cross section of Kharchenko et al .…”

Section: Photochemical Hot Oxygen Production and Escapementioning

confidence: 99%

“…Rahmati et al . [, 2016] and other researchers (see section 1 for references) calculated hot oxygen density profiles and oxygen escape rates. Rahmati et al .…”

Section: Comparison Of the Simple Escape Model With A Numerical Modelmentioning

confidence: 99%

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Hot oxygen escape from Mars: Simple scaling with solar EUV irradiance

et al. 2017

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The evolution of the atmosphere of Mars and the loss of volatiles over the lifetime of the solar system is a key topic in planetary science. An important loss process for atomic species, such as oxygen, is ionospheric photochemical escape. Dissociative recombination of O2+ ions (the major ion species) produces fast oxygen atoms, some of which can escape from the planet. Many theoretical hot O models have been constructed over the years, although a number of uncertainties are present in these models, particularly concerning the elastic cross sections of O atoms with CO2. Recently, the Mars Atmosphere and Volatile Evolution mission has been rapidly improving our understanding of the upper atmosphere and ionosphere of Mars and its interaction with the external environment (e.g., solar wind), allowing a new assessment of this important loss process. The purpose of the current paper is to take a simple analytical approach to the oxygen escape problem in order to (1) study the role that variations in solar radiation or solar wind fluxes could have on escape in a transparent fashion and (2) isolate the effects of uncertainties in oxygen cross sections on the derived oxygen escape rates. In agreement with several more elaborate numerical models, we find that the escape flux is directly proportional to the incident solar extreme ultraviolet irradiance and is inversely proportional to the backscatter elastic cross section. The amount of O lost due to ion transport in the topside ionosphere is found to be about 5–10% of the total.

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“…Mars is the best known example of the effect of this kind of aggression eliminating habitability. Recent data from the MAVEN Mission (Rahmati et al 2014;Jakosky et al 2015) areshowing the increased level of importance that SW interaction with the atmosphere has in shaping the evolution of Mars'scapability to have liquid water on its surface (habitability).…”

Section: The Evolution Of Atmospheres As a Key Factor For Assessing Hmentioning

confidence: 99%

Constraining the Radiation and Plasma Environment of the Kepler Circumbinary Habitable-Zone Planets

Zuluaga

Mason

Cuartas-Restrepo

2016

ApJ

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The discovery of many planets using the Kepler telescope includes 10planets orbiting eight binary stars. Three binaries, , have at least one planet in the circumbinary habitable zone (BHZ). We constrain the level of high-energy radiation and the plasma environment in the BHZ of these systems. With this aim, BHZ limits in these Kepler binaries are calculated as a function of time, and the habitability lifetimes are estimated for hypothetical terrestrial planets and/or moons within the BHZ. With the time-dependent BHZ limits established, a self-consistent model is developed describing the evolution of stellar activity and radiation properties as proxies for stellar aggression toward planetary atmospheres. Modeling binary stellar rotation evolution, including the effect of tidal interaction between stars in binaries, is key to establishing the environment around these systems. We find that Kepler-16 and its binary analogsprovide a plasma environment favorable for the survival of atmospheres of putative Mars-sized planets and exomoons. Tides have modified the rotation of the stars in Kepler-47, making its radiation environment less harsh in comparison to the solar system. This is a good example of the mechanism first proposed by has an environment similar to that of the solar system with slightly better than Earth radiation conditions at the inner edge of the BHZ. These results can be reproduced and even reparameterized as stellar evolution and binary tidal models progress, using our online tool http://bhmcalc.net.

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Pickup ion measurements by MAVEN: A diagnostic of photochemical oxygen escape from Mars

Cited by 24 publications

References 49 publications

The Muscles Treasury Survey. I. Motivation and Overview*

The Muscles Treasury Survey. I. Motivation and Overview*

Hot oxygen escape from Mars: Simple scaling with solar EUV irradiance

Constraining the Radiation and Plasma Environment of the Kepler Circumbinary Habitable-Zone Planets

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