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Aims. We tackle the conundrums of organic materials missing from interstellardust when measured inside the Solar System, while undoubtedly existing in thelocal interstellar cloud (LIC), which surrounds the Solar System.  Methods. We present a theoretical argument that organic compounds sublimatealmost instantaneously by exothermic reactions, when solar insolation triggersthe recombination of free radicals or the rearrangement of carbon bonds in thecompounds.  Results. It turns out that the triggering temperature lies in the range of20$-$50 K by considering that sublimation of organic materials takes placebeyond the so-called filtration region of interstellar neutral atoms. We findthat in-situ measurements of LIC dust in the Solar System result in anoverestimate for the gas-to-dust mass ratio of the LIC, unless the sublimationof organic materials is taken into account. We also find that previousmeasurements of interstellar pickup ions have determined the total elementalabundances of gas and organic materials, instead of interstellar gas alone.  Conclusions. We conclude that LIC organic matter suffers from sublimation enroute to the heliosphere, implying that our understanding of LIC dust fromspace missions is incomplete. Since space missions inside the orbit of Saturncannot give any information on the organic substances of LIC dust, one mustawait a future exploration mission to the inner edge of the Oort cloud for athorough understanding of organic substances in the LIC. Once our model for thesublimation of interstellar organic matter by exothermic chemical reactions offree radicals is confirmed, the hypothesis of panspermia from the diffuseinterstellar medium is ruled out.

Organic matter in interstellar dust lost at the approach to the heliosphere: Exothermic chemical reactions of free radicals ignited by the Sun