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The exosphere, the tenuous collisionless cloud of gas surrounding Mercury is still a poorly known object because it is the result of many various interactions between the surface, the interplanetary medium (Solar wind, photons and meteoroids), the planetary and the interplanetary magnetic fields. Many ground-based observations have allowed the detection of intense and variable sodium emissions at global and local spatial scales, the latter being mostly concentrated in the polarmid latitude regions. These regions are indeed the preferred location of solar wind precipitation on the surface of the planet. In the present paper, by using high resolution Na observations obtained at the Canary Islands with the THEMIS solar telescope, we analyze the variability of the sodium exosphere on time-scale of 1 hour and investigate the possible mechanisms that could explain the exospheric sodium emission distribution and its dynamics. Our interpretation relates the observed sodium asymmetries to the combined effects of plasma and photons impacts onto the Mercurys surface and of sodium diffusion through the upper layer of the surface. The comparison between data and simulations seems to evidence that, similarly to what occurs at the Earth, both the magnetic reconnection regimes of pulsed or quasi-steady reconnection could occur on Mercury, and be responsible for the observed Na short term variations. In addition to this, a progressive broadening of the peak regions together with an increase of the equatorial region seem to corroborate the idea of the role of photon stimulated desorption, in association with ion sputtering and with global sodium migration around Mercury as the cause of the observed evolution of the Na exosphere.
A determination of the dynamical evolution of the asteroid belt is difficult because the asteroid belt has evolved since the time of asteroid formation through mechanisms that include: (1) catastrophic collisions, (2) rotational disruption, (3) chaot
We report new near ultraviolet HST/STIS observations of atmospheric absorptions during the planetary transit of HD209458b. We detect absorption in atomic magnesium (MgI), while no signal has been detected in the lines of singly ionized magnesium (MgI
The asteroid belt was dynamically shaped during and after planet formation. Despite representing a broad ring of stable orbits, the belt contains less than one one-thousandth of an Earth mass. The asteroid orbits are dynamically excited with a wide r
The orbit of the Chelyabinsk object is calculated, applying the least-squares method directly to astrometric positions. The dynamical evolution of this object in the past is studied by integrating equations of motion for particles with orbits from th
Boulders on the surfaces of planets, satellites and small bodies, as well as their geological associations, provide important information about surface processes. We analyzed all available images of the surface of Mercury that have sufficient resolut