Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Mars Express/ASPERA-3/NPI and IMAGE/LENA observations of energetic
  neutral atoms in Earth and Mars orbit   The low energy neutral atom imagers on Mars Express and IMAGE have revealed
that the neutral atom populations in interplanetary space come from a variety
of sources and challenge our current understanding of heliospheric physics. For
example, both in cruise phase and at Mars, the neutral particle instrument NPD
on Mars Express observed "unexplained neutral beams" unrelated to Mars which
appear to be either of heliospheric or solar wind origin. Likewise, the NPI
instrument on Mars Express has revealed streams of neutral atoms with different
properties than those observed by NPD. Independently, IMAGE/LENA has reported
neutral atom observations that may be interpreted as a "secondary stream"
having different characteristics and flowing from a higher ecliptic longitude
than the nominal upstream direction. Both sets of observations do not appear to
fit in easily with the neutral atom environment from 1.0-1.57 AU as it is
currently understood. In this paper we examine some highly suggestive
similarities in the IMAGE/LENA and Mars Express/ASPERA-3/NPI data to try to
determine potential origins for the observed signal.

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The categories of this paper are: q-alg
0
The categories of this paper are: hep-ph
33
The categories of this paper are: plasm-ph
32
The categories of this paper are: atom-ph
4
The categories of this paper are: cond-mat
10
The categories of this paper are: q-bio
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The categories of this paper are: math-ph
19
The categories of this paper are: eess
20
The categories of this paper are: acc-phys
29
The categories of this paper are: funct-an
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The categories of this paper are: chao-dyn
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The categories of this paper are: hep-ex
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The categories of this paper are: math
1
The categories of this paper are: cs
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The categories of this paper are: alg-geom
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The categories of this paper are: stat