  A series of astronomical observations obtained over the period 1986 to 2018
supports the idea that life is a cosmic rather than a purely terrestrial or
planetary phenomenon. These include (1) the detection of biologically relevant
molecules in interstellar clouds and in comets, (2) mid-infrared spectra of
interstellar grains and the dust from comets, (3) a diverse set of data from
comets including the Rosetta mission showing consistency with biology and (4)
the frequency of Earth-like or habitable planets in the Galaxy. We argue that
the conjunction of all the available data suggests the operation of cometary
biology and interstellar panspermia rather than the much weaker hypothesis of
comets being only the source of the chemical building blocks of life. We
conclude with specific predictions on the properties expected of
extra-terrestrial life if it is discovered on Enceladus, Europa or beyond. A
radically different biochemistry elsewhere can be considered as a falsification
of the theory of interstellar panspermia.
