Radiogenic heating in comets: A computational study from an astrobiological perspective

Abstract Over the past two decades, interstellar dust and cometary material have been found to include a significant content of organic and biogenic molecules. This possibly hints towards a genesis of life in cometary bodies, with comets acting as carriers of microbial life throughout the galaxy. We describe here a computational study of the role of radiogenic heating due to <m:math xmlns:m="http://www.w3.org/1998/Math/MathML"> <m:msup> <m:mrow/> <m:mrow> <m:mn>26</m:mn> </m:mrow> </m:msup> </m:math> {}^{26} Al in the thermal evolution of a cometary interior and thereby delineate zones with possible liquid water content. Thermal evolution calculations are carried out for comets possessing various radii, starting from an initial accretion phase to some 100 million years after the completion of accretion. Our computation shows that comets with radius 6 km and higher can have liquid water interior regions and hence can support zones where microbes can survive. Such microbial survival zones are traced out as regions where the temperature rises above the melting point of water ice and later remain below a sterilizing temperature. The active time available for possible microbial multiplication is also determined. Computations also show that survival zones are not generally found at the centres of comets but at varying radial distances from the centre, depending on the radius of the comet.