  A fundamental astrobiological question is whether life can be transported
between extrasolar systems. We propose a new strategy to answer this question
based on the principle that life which arose via spreading will exhibit more
clustering than life which arose spontaneously. We develop simple statistical
models of panspermia to illustrate observable consequences of these excess
correlations. Future searches for biosignatures in the atmospheres of
exoplanets could test these predictions: a smoking gun signature of panspermia
would be the detection of large regions in the Milky Way where life saturates
its environment interspersed with voids where life is very uncommon. In a
favorable scenario, detection of as few as $\sim 25$ biologically active
exoplanets could yield a $5\sigma$ detection of panspermia. Detectability of
position-space correlations is possible unless the timescale for life to become
observable once seeded is longer than the timescale for stars to redistribute
in the Milky Way.
