Solar radiation balances significantly affect Earth's surface energy balance and climate change. Studying top-of-the-atmosphere (TOA) albedo changes is of great significance for understanding Earth's energy budget and atmospheric circulation. The Loess Plateau (LP), located in the middle reaches of the Yellow River in China, is one of the most severely eroded areas in the world. In this paper, long-term remote sensing data were used to analyze the changes in the TOA albedo in the LP from 1982 to 2016. The results showed that the TOA albedo, its atmospheric contribution (AC), and surface contribution (SC) exhibited decreasing trends: -0.0012, -0.0010, and -0.0003 a-1. The spatial pattern of the TOA albedo was similar to AC, which indicates that AC dominates the change in the TOA albedo. We detected driving factors for AC and SC and found that the cloud fraction (CF) was the main driving factor of the AC, whereas the soil moisture (SM) dominated the SC. The driving factors of two typical regions with a significantly decreasing trend in the TOA albedo were also detected. The Mu Us Desert, where vegetation improved significantly, showed a decreasing trend in the TOA albedo, and we found that NDVI was the main driving factor for the change in the SC of the TOA albedo. However, the Eastern Qilian Mountains, where snow cover decreased in recent years, also showed a significant decreasing trend in the TOA albedo; the SC here was mainly driven by the changes in snow cover days (SCD). These results indicate that changes in the surface environment alter the radiation balance. SIGNIFICANCE STATEMENT: The Loess Plateau in China is one of the most severe cases of soil erosion in the world, and ecological restoration projects have been carried out to recover the fragile ecological environment. Our study was designed to explore changes in the top-of-the-atmosphere (TOA) albedo of the Loess Plateau between 1982 and 2016 using a long time series of multisource satellite products, and driving factors in the atmosphere and at the surface were analyzed. We concluded that the TOA albedo of the Loess Plateau decreased over 35 years, and its atmospheric contribution dominated the change in the TOA albedo. However, the significant ecological improvement in the Loess Plateau, especially in the central vegetation recovery region, such as the Mu Us Desert, was also strongly related to the regional changes in the surface contribution of the TOA albedo. The climate changes had a considerable impact on the eastern branch of the Qilian Mountains in the Qinghai region, where the decline in snow cover days affected the local Alpine meadow ecosystems; therefore, snow cover days also played a decisive role in the local variation of the surface contribution of the TOA albedo.

A latitudinal and radial study of the lunar sodium exosphere has been performed utilizing observations made from two different methods: (1) observations made at targeted altitudes using a Fabry-Perot Spectrometer (FPS) and (2) observations made from a coronagraph. The FPS observations made from the National Solar Observatory McMath-Pierce Solar Telescope, Kitt Peak, Arizona and the coronagraph observations were made at the Winer Observatory, Sonoita, Arizona. A small subset of the high resolution FPS observations were made concurrently with coronagraph measurements. Measured linewidths and linewidth-derived temperatures from FPS observa-tions were compared to temperatures derived from the coronagraphic intensity altitude profiles, with FPS linewidth-derived temperatures shown to be consistently lower. We suggest that the coronagraph method samples a velocity distribution perpendicular to the FPS's LOS, while the FPS samples a velocity distribution tangential to the lunar limb (i.e., along the FPS LOS). We also suggest that the coronagraph measurements may be more sensitive to the escaping population of atoms as the population close to the surface is not observed. The concurrent FPS measurements sit below the occulting disk of the coronagraph and measure the atoms closer to the surface. Furthermore, both the FPS linewidth-derived temperatures and the coronagraph scale heights show an increase towards high latitudes, an effect which is attributed to particle transport and/or contributions from a source like meteoroid impact vaporization. FPS linewidths decrease as a function of altitude, a result confirmed through a simulation of velocity distributions from nonthermal source mechanisms. And, finally, Linewidths are largest when looking over the dawn/dusk terminator. These results will enable improved characterization of the sources for the lunar sodium exosphere.

Numerical models of the lunar exosphere have been available for several decades to allow investigations of the Moon's tenuous atmosphere beyond the few measurements made by satellite or ground-based experiments. We present a novel approach to modeling a system of elements, namely the hydrogen-bearing species H, H2, OH, and H2O, in a multi-element simulation, implementing exospheric and geochemical conversion reactions to connect the different species through their loss and source processes. The model resembles the lunar water cycle, including several source and sink mechanisms like the solar wind proton influx and the eventual loss through Jean's escape, photodissociation, or cold trapping. Unknown and uncertain parameters have been modeled using probability distributions that propagate their uncertainty through the system to allow subsequent statistical analysis of the predictions. In eight studies we varied the reactivity of the lunar environment and investigated the response of the exosphere's densities and dynamics. The results show that the new framework is able to reproduce many published values for the surface number densities and reported dynamics like the H2 dawn-dusk asymmetry, even with a very simple approach to many of the complex input parameters. The most diverging results can be found for the hydroxyl and water predictions. Nonetheless, we show that the multi-element approach using conversion reactions offers an alternative explanation to the observed H and H2 exosphere without having to assume these volatiles as condensable species.

Surface-bound exospheres facilitate volatile migration across the surfaces of nearly airless bodies. However, such transport requires that the body can both form and retain an exosphere. To form a sublimation exosphere requires the surface of a body to be sufficiently warm for surface volatiles to sublime; to retain an exosphere, the ballistic escape and photodestruction rates and other loss mechanisms must be sufficiently low. Here we construct a simple free molecular model of exospheres formed by volatile desorption or sublimation. We consider the conditions for forming and retaining exospheres for common volatile species across the Solar System, and explore how three processes (desorption/sublimation, ballistic loss, and photodestruction) shape exospheric dynamics on airless bodies. Our model finds that the CO2 exosphere of Callisto is much too dense to be sustained by impact-delivered volatiles, but could be maintained by only-7 ha (-0.07 km(2)) of exposed CO2 ice distributed across Callisto (and refreshed through mass wasting). We use our model to predict the peak surface locations of Callisto's CO2 exosphere along with other Galilean moons, which could be tested by JUICE observations. Our model finds that to maintain Iapetus' two-tone appearance, its dark Cassini Regio likely has unresolved exposures of water ice, perhaps in sub-resolution impact craters, that amount to up to approximately-0.06% of its surface. In the Uranian system, we find that the CO2 deposits on Ariel, Umbriel, Titania, and Oberon are unlikely to have been delivered via impacts, but are consistent with both a magnetospheric origin, (as has been previously suggested) or sourced endogenously. We suggest that the leading/trailing CO2 asymmetries on these moons could result from exosphere-mediated volatile transport, and may be a seasonal equinox feature that could be largely erased by pole-to-pole volatile migration during the Uranian solstices. We calculate that-2.4-6.4 mm thick layer of CO2 (depending the moon) could migrate about the surface of Uranus' large moons during a seasonal cycle. Our model also confirms that water migration to Mercury's polar cold traps is inefficient without self-shield against photodestroying UV light, and that Callisto's bright spires could be formed/maintained by exospherically deposited H2O.

Remote observations of the lunar sodium corona have been obtained with the Goddard Lunar Coronagraph located at the Winer Observatory in Sonoita, Arizona. We previously reported the results of observations in the spring, 2017, observing season (Killen et al., 2019). We report herein the results of the 2018-2019 observing campaign. We show definitive effects on the corona - the extended lunar sodium exosphere above 150 km from the surface - of enhanced ion flux onto the Moon as measured by the ARTEMIS ElectroStatic Analyzer. The three observations in this dataset with the largest column abundances are associated with entrance of the Moon into the magnetosheath. The enhancement in the exosphere due to ion flux is not long-lived after the enhanced ion influx decreases, confirming the findings of Killen et al., 2012. The column abundance is greatest at both the dawn and dusk terminators as predicted and simulated by Smyth and Marconi, 1995. The cause of the increased scale height at the terminators is consistent with radiation pressure acceleration anti-sunward. We report a shallow decline of column abundance with increasing latitude which is also consistent with radiation pressure acceleration. Most of our measured scale heights are on the order of 800-1800 km, increasing at high latitudes, consistent with the data set published in Killen et al., 2019. Although the intensity extrapolated to the surface decreases with latitude, the scale height increases with latitude, so that the exospheric column decreases more slowly with increasing latitude than does a cosine function.

Ganymede's surface is subject to constant bombardment by Jovian magnetospheric and Ganymede's ionospheric ions. These populations sputter the surface and contribute to the replenishment of the moon's exosphere. Thus far, estimates for sputtering on the moon's surface have included only the contribution from Jovian ions. In this work, we have used our recent model of Ganymede's ionosphere Carnielli et al., 2019 to evaluate the contribution of ionospheric ions for the first time. In addition, we have made new estimates for the contribution from Jovian ions, including both thermal and energetic components. For Jovian ions, we find a total sputtering rate of 2.2 x 10(27) s(-1), typically an order of magnitude higher compared to previous estimates. For ionospheric ions, produced through photo- and electron-impact ionization, we find values in the range 2.7 x 10(26)-5.2 x 10(27) s(-1) when the moon is located above the Jovian plasma sheet. Hence, Ganymede's ionospheric ions provide a contribution of at least 10% to the sputtering rate, and under certain conditions they dominate the process. This finding indicates that the ionospheric population is an important source to consider in the context of exospheric models.

In this chapter, we review the contribution of space missions to the determination of the elemental and isotopic composition of Earth, Moon and the terrestrial planets, with special emphasis on currently planned and future missions. We show how these missions are going to significantly contribute to, or sometimes revolutionise, our understanding of planetary evolution, from formation to the possible emergence of life. We start with the Earth, which is a unique habitable body with actual life, and that is strongly related to its atmosphere. The new wave of missions to the Moon is then reviewed, which are going to study its formation history, the structure and dynamics of its tenuous exosphere and the interaction of the Moon's surface and exosphere with the different sources of plasma and radiation of its environment, including the solar wind and the escaping Earth's upper atmosphere. Missions to study the noble gas atmospheres of the terrestrial planets, Venus and Mars, are then examined. These missions are expected to trace the evolutionary paths of these two noble gas atmospheres, with a special emphasis on understanding the effect of atmospheric escape on the fate of water. Future missions to these planets will be key to help us establishing a comparative view of the evolution of climates and habitability at Earth, Venus and Mars, one of the most important and challenging open questions of planetary science. Finally, as the detection and characterisation of exoplanets is currently revolutionising the scope of planetary science, we review the missions aiming to characterise the internal structure and the atmospheres of these exoplanets.

In order to observe the lunar sodium exosphere out to one-half degree around the Moon, we designed, built and installed a small robotically controlled coronagraph at the Winer Observatory in Sonoita, Arizona. Observations are obtained remotely every available clear night from our home base at Goddard Space Flight Center or from Prescott, Arizona. We employ an And over temperature-controlled 1.5 angstrom wide narrow-band filter centered on the sodium D-2 line, and a similar 1.5 angstrom filter centered blueward of the D-2 line by 3 angstrom for continuum observations. Our data encompass lunation in 2015, 2016, and 2017, thus we have a long baseline of sodium exospheric calibrated images, During the course of three years we have refined the observational sequence in many respects. Therefore this paper only presents the results of the spring, 2017, observing season. We present limb profiles from the south pole to the north pole for many lunar phases. Our data do not fit any power of cosine model as a function of lunar phase or with latitude. The extended Na exosphere has a characteristic temperature of about 2250-6750 K, indicative of a partially escaping exosphere. The hot escaping component may be indicative of a mixture of impact vaporization and a sputtered component.

The outcome of efforts to detect He-4 in the sunlit lunar exosphere as evinced by the CHACE mass spectrometer aboard the Moon Impact Probe in Chandrayaan-1 is reported. The in situ observations by CHACE were carried out in the lunar dayside, covering a broad range of lunar latitudes, when the Moon was on the verge of exiting the Earth's magnetotail. A combination of daytime He depletion and decrease during magnetotail passage of the Moon, along with low flux of alpha particles in the solar wind at the time of CHACE observations present a case when the He abundance in the Moon had hit one of its lowest values. CHACE, thus had the opportunity to explore the lunar exosphere in an extreme combination of the factors that control the lunar He abundance. Based on the observations and instrument sensitivity, an upper limit of similar to 8.0 x 10(2) cm(-3) for the surface density of lunar He-4 in the sunlit hemisphere is proposed. This result is expected to provide realistic constraints to the lunar He exosphere models under similar extreme conditions. (C) 2017 Elsevier Inc. All rights reserved.

The gas giant planets in the Solar System have a retinue of icy moons, and we expect giant exoplanets to have similar satellite systems. If a Jupiter-like planet were to migrate toward its parent star the icy moons orbiting it would evaporate, creating atmospheres and possible habitable surface oceans. Here, we examine how long the surface ice and possible oceans would last before being hydrodynamically lost to space. The hydrodynamic loss rate from the moons is determined, in large part, by the stellar flux available for absorption, which increases as the giant planet and icy moons migrate closer to the star. At some planet-star distance the stellar flux incident on the icy moons becomes so great that they enter a runaway greenhouse state. This runaway greenhouse state rapidly transfers all available surface water to the atmosphere as vapor, where it is easily lost from the small moons. However, for icy moons of Ganymede's size around a Sun-like star we found that surface water (either ice or liquid) can persist indefinitely outside the runaway greenhouse orbital distance. In contrast, the surface water on smaller moons of Europa's size will only persist on timescales greater than 1 Gyr at distances ranging 1.49-0.74 au around a Sun-like star for Bond albedos of 0.2 and 0.8, where the lower albedo becomes relevant if ice melts. Consequently, small moons can lose their icy shells, which would create a torus of H atoms around their host planet that might be detectable in future observations.