Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Number of near-Earth objects and formation of lunar craters over the
  last billion years   We compare the number of lunar craters larger than 15 km across and younger
than 1.1 Ga to the estimates of the number of craters that could have been
formed for 1.1 Ga if the number of near-Earth objects and their orbital
elements during that time were close to the corresponding current values. The
comparison was performed for craters over the entire lunar surface and in the
region of the Oceanus Procellarum and maria on the near side of the Moon. In
these estimates, we used the values of collision probabilities of near-Earth
objects with the Moon and the dependences of the crater diameters on the
impactor sizes. According to the estimates made by different authors, the
number density of known Copernican craters with diameters D>15 km in mare
regions is at least double the corresponding number for the remaining lunar
surface. Our estimates do not contradict the growth in the number of near-Earth
objects after probable catastrophic fragmentations of large main-belt
asteroids, which may have occurred over the recent 300 Ma; however, they do not
prove this increase. Particularly, they do not conflict with the inference made
by Mazrouei et al. (2019) that 290 Ma ago the frequency of collisions of
near-Earth asteroids with the Moon increased by 2.6 times. For a probability of
a collision of an Earth-crossing object (ECO) with the Earth in a year equaled
to 10^-8, our estimates of the number of craters agree with the model,
according to which the number densities of the 15-km Copernican craters for the
whole lunar surface would have been the same as that for mare regions if the
data by Losiak et al. (2015) for D<30 km were as complete as those for D>30 km.
With this collision probability of ECOs with the Earth and for this model, the
cratering rate may have been constant over the recent 1.1 Ga.

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The categories of this paper are: cmp-lg
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The categories of this paper are: q-alg
14
The categories of this paper are: math-ph
0
The categories of this paper are: hep-ph
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The categories of this paper are: eess
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The categories of this paper are: supr-con
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The categories of this paper are: funct-an
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The categories of this paper are: solv-int
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The categories of this paper are: ao-sci
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The categories of this paper are: math
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The categories of this paper are: nucl-th
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The categories of this paper are: hep-lat
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The categories of this paper are: atom-ph
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The categories of this paper are: hep-th
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The categories of this paper are: mtrl-th
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The categories of this paper are: bayes-an