  There is a wealth of evidence to suggest that planetary systems can survive
beyond the main sequence. Most commonly, white dwarfs are found to be accreting
material from tidally disrupted asteroids, whose bulk compositions are
reflected by the metals polluting the stellar photospheres. While many examples
are known, most lack the deep, high-resolution data required to detect multiple
elements, and thus characterise the planetesimals that orbit them. Here,
spectra of seven DZ white dwarfs observed with Keck HIRES are analysed, where
up to nine metals are measured per star. Their compositions are compared
against those of solar system objects, working in a Bayesian framework to infer
or marginalise over the accretion history. All of the stars have been accreting
primitive material, similar to chondrites, with hints of a Mercury-like
composition at one star. The most polluted star is observed several Myr after
its last major accretion episode, in which a Moon-sized object met its demise.
