Comparative Na and K Mercury and Moon Exospheres

Leblanc, François; Schmidt, Carl; Mangano, V.; Mura, A.; Cremonese, G.; Raines, J. M.; Jasinski, J. M.; Sarantos, M.; Milillo, A.; Killen, R. M.; Massetti, S.; Cassidy, Timothy A.; Vervack, Ronald J.; Kameda, Shingo; Capria, M. T.; Horányi, M.; Janches, Diego; Berezhnoy, A. A.; Christou, Apostolos; Hirai, Takayuki; Lierle, Patrick; Morgenthaler, J. P.

doi:10.1007/s11214-022-00871-w

Cited by 17 publications

(14 citation statements)

References 226 publications

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“…The alkali distribution at Mercury's limb derived from this observation appears in Schmidt et al (2018b) and Leblanc et al (2022). The 27 mÅ Na D2 equivalent width yields a tangent column of 1.6 × 10 11 atoms cm −2 in the densest regions of the exosphere.…”

Section: Solar System Analogs: the Case For Eccentric Exoplanetsmentioning

confidence: 60%

“…This creates a 41′′ by 21′′ field of view per scan, over which the Na doublet was measured at a resolving power of R = 1.4 × 10 5 . This is a provisional file, not the final typeset article The alkali distribution at Mercury's limb derived from this observation appears in Schmidt et al (2018b) and Leblanc et al (2022). The 27mÅ Na D2 equivalent width yields a tangent column of 1.6 x 10 11 atoms cm -2 in the densest regions of the exosphere.…”

Section: Introductionmentioning

confidence: 81%

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Doppler-Shifted Alkali D Absorption as Indirect Evidence for Exomoons

Schmidt

2022

Front. Astron. Space Sci.

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Sodium and potassium signatures in transiting exoplanets can be challenging to isolate from the stellar absorption lines. Here, these challenges are discussed in the framework of Solar System observations, and transits of Mercury in particular. Radiation pressure is important for alkali gas dynamics in close-orbiting exoplanets since the D lines are efficient at resonant scattering. When the star-planet velocity is ≳10 km/s, eccentric exoplanets experience more than an order of magnitude higher radiation pressures, aiding atmospheric escape and producing a larger effective cross-section for absorbing starlight at the phase of transit. The Doppler shift also aids in isolating the planetary signature from the stellar photosphere’s absorption. Only one transiting exoplanet, HD 80606b, is presently thought to have both this requisite Doppler shift and alkali absorption. Radiation pressure on a planetary exosphere naturally produces blue-shifted absorption, but at levels insufficient to account for the extreme Doppler shifts that have been inferred from potassium transit measurements of this system. In the absence of clear mechanisms to generate such a strong wind, it is described how this characteristic could arise from an exomoon-magnetosphere interaction, analogous to Io-Jupiter. At low contrasts presented here, follow-up transit spectra of HD 80606b cannot rule out a potassium jet or atmospheric species with a broad absorption structure. However, it is evident that line absorption within the imaging passbands fails to explain the narrow-band photometry that has been reported in-transit. New observations of energetic alkalis produced by the Io-Jupiter interaction are also presented, which illustrate that energetic sodium Doppler structure offers a more valuable marker for the presence of an exomoon than potassium.

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Section: Solar System Analogs: the Case For Eccentric Exoplanetsmentioning

confidence: 60%

Section: Introductionmentioning

confidence: 81%

Doppler-Shifted Alkali D Absorption as Indirect Evidence for Exomoons

Schmidt

2022

Front. Astron. Space Sci.

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“…Another major release mechanism for volatiles into Mercury's exosphere is photon-stimulated desorption (PSD; McGrath et al 1986;Killen et al 1990;Madey et al 1998;Leblanc et al 2022), a process that is enhanced by ion bombardment (McGrath et al 1986;Mura et al 2009;Leblanc et al 2022). The coupling of these two processes is thought to produce a sodium exosphere in regions typical of ion sputtering but with the high efficiency and lower energy distribution of PSD.…”

Section: Discussionmentioning

confidence: 99%

Maps of Solar Wind Plasma Precipitation onto Mercury’s Surface: A Geographical Perspective

Lavorenti,

Jensen,

Aizawa

et al. 2023

Planet. Sci. J.

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Mercury is the closest planet to the Sun, possesses a weak intrinsic magnetic field, and has only a very tenuous atmosphere (exosphere). These three conditions result in a direct coupling between the plasma emitted from the Sun (namely, the solar wind) and Mercury’s surface. The planet’s magnetic field leads to a nontrivial pattern of plasma precipitation onto the surface that is expected to contribute to the alteration of the regolith over geological timescales. The goal of this work is to study the solar wind plasma precipitation onto the surface of Mercury from a geographical perspective, as opposed to the local time-of-day approach of previous precipitation modeling studies. We employ solar wind precipitation maps for protons and electrons from two fully kinetic numerical simulations of Mercury’s plasma environment. These maps are then integrated over two full Mercury orbits (176 Earth days). We found that the plasma precipitation pattern at the surface is most strongly affected by the upstream solar wind conditions, particularly the interplanetary magnetic field direction, and less by Mercury’s 3:2 spin–orbit resonance. We also found that Mercury’s magnetic field is able to shield the surface from roughly 90% of the incoming solar wind flux. At the surface, protons have a broad energy distribution from below 500 eV to more than 1.5 keV, while electrons are mostly found in the range 0.1–10 keV. These results will help to better constrain space weathering and exosphere source processes at Mercury, as well as interpret observations by the ongoing ESA/JAXA BepiColombo mission.

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“…Usually, a mix of the release processes is occurring and the attribution of the Na signal, or a part of the Na signal, to a single release process is often difficult. The observations of Na and K at Mercury and the Moon, and their interpretation, are discussed in detail by Leblanc et al (2022). Burger et al (2012Burger et al ( , 2014 explained their Ca observations with the UVVS instrument on MESSENGER being the result of MIV.…”

Section: Tablementioning

confidence: 99%

Particles and Photons as Drivers for Particle Release from the Surfaces of the Moon and Mercury

et al. 2022

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The Moon and Mercury are airless bodies, thus they are directly exposed to the ambient plasma (ions and electrons), to photons mostly from the Sun from infrared range all the way to X-rays, and to meteoroid fluxes. Direct exposure to these exogenic sources has important consequences for the formation and evolution of planetary surfaces, including altering their chemical makeup and optical properties, and generating neutral gas exosphere. The formation of a thin atmosphere, more specifically a surface bound exosphere, the relevant physical processes for the particle release, particle loss, and the drivers behind these processes are discussed in this review.

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Comparative Na and K Mercury and Moon Exospheres

Cited by 17 publications

References 226 publications

Doppler-Shifted Alkali D Absorption as Indirect Evidence for Exomoons

Doppler-Shifted Alkali D Absorption as Indirect Evidence for Exomoons

Maps of Solar Wind Plasma Precipitation onto Mercury’s Surface: A Geographical Perspective

Particles and Photons as Drivers for Particle Release from the Surfaces of the Moon and Mercury

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