Organic matter in interstellar dust lost at the approach to the
  heliosphere: Exothermic chemical reactions of free radicals ignited by the
  Sun
  Aims. We tackle the conundrums of organic materials missing from interstellar
dust when measured inside the Solar System, while undoubtedly existing in the
local interstellar cloud (LIC), which surrounds the Solar System.
  Methods. We present a theoretical argument that organic compounds sublimate
almost instantaneously by exothermic reactions, when solar insolation triggers
the recombination of free radicals or the rearrangement of carbon bonds in the
compounds.
  Results. It turns out that the triggering temperature lies in the range of
20$-$50 K by considering that sublimation of organic materials takes place
beyond the so-called filtration region of interstellar neutral atoms. We find
that in-situ measurements of LIC dust in the Solar System result in an
overestimate for the gas-to-dust mass ratio of the LIC, unless the sublimation
of organic materials is taken into account. We also find that previous
measurements of interstellar pickup ions have determined the total elemental
abundances of gas and organic materials, instead of interstellar gas alone.
  Conclusions. We conclude that LIC organic matter suffers from sublimation en
route to the heliosphere, implying that our understanding of LIC dust from
space missions is incomplete. Since space missions inside the orbit of Saturn
cannot give any information on the organic substances of LIC dust, one must
await a future exploration mission to the inner edge of the Oort cloud for a
thorough understanding of organic substances in the LIC. Once our model for the
sublimation of interstellar organic matter by exothermic chemical reactions of
free radicals is confirmed, the hypothesis of panspermia from the diffuse
interstellar medium is ruled out.
