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Radiation in the form of solar energetic particles (SEPs) presents a severe risk to the short-term health of astronauts and the success of human exploration missions beyond Earth’s protective shielding. Modeling how shielding mitigates the dose accumulated by astronauts is an essential step toward reducing these risks. PREDICCS (Predictions of radiation from REleASE, EMMREM, and Data Incorporating the CRaTER, COSTEP, and other SEP measurements) is an online tool for the near real-time prediction of radiation exposure at Earth, the Moon, and Mars behind various levels of shielding. We compare shielded dose rates from PREDICCS with dose rates from the Cosmic Ray Telescope for the Effects of Radiation (CRaTER) onboard the Lunar Reconnaissance Orbiter (LRO) at the Moon and from the Radiation Assessment Detector (RAD) on the Mars Science Laboratory (MSL) during its cruise phase to Mars for five solar events in 2012 when Earth, MSL, and Mars were magnetically well connected. Calculations of the accumulated dose demonstrate a reasonable agreement between PREDICCS and RAD ranging from as little as 2% difference to 54%. We determine mathematical relationships between shielding levels and accumulated dose. Lastly, the gradient of accumulated dose between Earth and Mars shows that for the largest of the five solar events, lunar missions require aluminum shielding between 1.0 g cm−2 and 5.0 g cm−2 to prevent radiation exposure from exceeding the 30-day limits for lens and skin. The limits were not exceeded near Mars.

Io's sodium clouds result mostly from a combination of two atmospheric escape processes at Io. Neutralization of [Na.sup.+] and/or Na[X.sup.+] pickup ions produces the 'stream' and the 'jet' and results in a rectangular-shaped sodium nebula around Jupiter. Atmospheric sputtering of Na by plasma torus ions produces the 'banana cloud' near Io and a diamond-shaped sodium nebula. Charge exchange of thermal [Na.sup.+] with Na in Io's atmosphere does not appear to be a major atmospheric ejection process. The total ejection rate of sodium from Io varied from 3 x [10.sup.26] to 25 x [10.sup.26] atoms/s over seven years of observations. Our results provide further evidence that Io's atmospheric escape is driven from collisionally thick regions of the atmosphere rather than from the exosphere. Key Words: Io; atmospheric dynamics; satellite atmospheres; magnetospheres.

Observational studies using Monte-Carlo model of fast sodium production to investigate high-resolution images of sodium emission obtained from ground-based spectroscopes indicate that the Io plasma torus consists of sodium-bearing molecular ions. A considerable part of the exobase of Io is molecular in nature and consists of several of sodium-bearing molecules. The spectroscopic images reveal the slow-down in the speed of co-rotation of the plasma in Io.