Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Vapor drainage in the protolunar disk as the cause for the depletion in
  volatile elements of the Moon   Lunar rocks are severely depleted in moderately volatile elements such as Rb,
K, and Zn relative to Earth. Identifying the cause of this depletion is
important for understanding how the Earth-Moon system evolved in the aftermath
of the Moon-forming giant impact. We measured the Rb isotopic compositions of
lunar and terrestrial rocks to understand why moderately volatile elements are
depleted in the Moon. Combining our new measurements with previous data reveals
that the Moon has an 87Rb/85Rb ratio higher than Earth by +0.16 permil. This
isotopic composition is consistent with evaporation of Rb into a vapor medium
that was ~99 percent saturated. Evaporation under this saturation can also
explain the previously documented isotopic fractionations of K, Ga, Cu and Zn
of lunar rocks relative to Earth. We show that a possible setting for achieving
the same saturation upon evaporation of elements with such diverse volatilities
is through viscous drainage of a partially vaporized protolunar disk onto
Earth. In the framework of an alpha-disk model, the alpha-viscosity needed to
explain the ~99% saturation calculated here is 0.001 to 0.01, which is
consistent with a vapor disk where viscosity is controlled by magnetorotational
instability.

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The categories of this paper are: physics
8
The categories of this paper are: hep-ex
14
The categories of this paper are: math-ph
33
The categories of this paper are: plasm-ph
35
The categories of this paper are: mtrl-th
27
The categories of this paper are: comp-gas
10
The categories of this paper are: q-bio
20
The categories of this paper are: acc-phys
12
The categories of this paper are: nucl-th
7
The categories of this paper are: hep-th
26
The categories of this paper are: bayes-an
25
The categories of this paper are: patt-sol
34
The categories of this paper are: chem-ph
9
The categories of this paper are: nlin
29
The categories of this paper are: funct-an
13
The categories of this paper are: quant-ph