The Moon, Mercury, large asteroids, and satellites of other planets have enough gravity to hold on to molecules, including water, in their “exosphere.” The dynamics of the molecules may determine whether they could accumulate at the surface. A researcher in the U.S. has proposed a new model that simplifies the calculation of how molecules hop and migrate within a planet’s exosphere. The formalism, based on a combination of random-walk and diffusion theories, can calculate the distribution of the surface concentration of volatile water molecules and is computationally advantageous compared to existing models.

Norbert Schorghofer, “Two-Dimensional Description of Surface-Bounded Exospheres with Application to the Migration of Water Molecules on the Moon,” to appear in Physical Review E [].

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