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Arecibo radar observations of near-Earth asteroid (3200) Phaethon during the 2017 apparition

Bhiravarasu, Sriram S.; Benner, Lance A. M.; Giorgini, Jon D. +8 more

We report Arecibo S-band (2380 MHz; 12.6 cm) radar observations of near-Earth asteroid (3200) Phaethon during the December 2017 apparition when Phaethon passed within 0.07 au of Earth. Radar images with a resolution of 75 m per pixel reveal a roughly spheroidal shape more than 6 km in diameter at the equator with several discernible surface featur…

Dusk over dawn O₂ asymmetry in Europa's near-surface atmosphere

Johnson, Robert E.; Chaufray, Jean-Yves; Oza, Apurva V. +4 more

The evolution of Europa's water-product exosphere over its 85-h day, based on current models, has not been shown to exhibit any diurnal asymmetries. Here we simulate Europa's exosphere using a 3-D Monte Carlo routine including, for the first time, the role of Europa's rotation on the evolution of exospheric molecules tracked throughout the orbit. …