Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: On the anomalous secular increase of the eccentricity of the orbit of
  the Moon   A recent analysis of a Lunar Laser Ranging (LLR) data record spanning 38.7 yr
revealed an anomalous increase of the eccentricity of the lunar orbit amounting
to de/dt_meas = (9 +/- 3) 10^-12 yr^-1. The present-day models of the
dissipative phenomena occurring in the interiors of both the Earth and the Moon
are not able to explain it. We examine several dynamical effects, not modeled
in the data analysis, in the framework of long-range modified models of gravity
and of the standard Newtonian/Einsteinian paradigm. It turns out that none of
them can accommodate de/dt_meas. Many of them do not even induce long-term
changes in e; other models do, instead, yield such an effect, but the resulting
magnitudes are in disagreement with de/dt_meas. In particular, the general
relativistic gravitomagnetic acceleration of the Moon due to the Earth's
angular momentum has the right order of magnitude, but the resulting
Lense-Thirring secular effect for the eccentricity vanishes. A potentially
viable Newtonian candidate would be a trans-Plutonian massive object (Planet
X/Nemesis/Tyche) since it, actually, would affect e with a non-vanishing
long-term variation. On the other hand, the values for the physical and orbital
parameters of such a hypothetical body required to obtain the right order of
magnitude for de/dt are completely unrealistic. Moreover, they are in neat
disagreement with both the most recent theoretical scenarios envisaging the
existence of a distant, planetary-sized body and with the model-independent
constraints on them dynamically inferred from planetary motions. Thus, the
issue of finding a satisfactorily explanation for the anomalous behavior of the
Moon's eccentricity remains open.

23
The categories of this paper are: solv-int
19
The categories of this paper are: eess
29
The categories of this paper are: funct-an
25
The categories of this paper are: patt-sol
16
The categories of this paper are: stat
35
The categories of this paper are: mtrl-th
18
The categories of this paper are: econ
20
The categories of this paper are: acc-phys
12
The categories of this paper are: nucl-th
13
The categories of this paper are: quant-ph
21
The categories of this paper are: adap-org
34
The categories of this paper are: chem-ph
22
The categories of this paper are: chao-dyn
17
The categories of this paper are: q-fin
36
The categories of this paper are: cmp-lg
28
The categories of this paper are: alg-geom