We present Hubble Space Telescope ultraviolet spectroscopy of the white dwarfs PG 0843+516 , PG 1015+161 , SDSS 1228+1040 , and GALEX 1931+0117 , which accrete circumstellar planetary debris formed from the destruction of asteroids .
Combined with optical data , a minimum of five and a maximum of eleven different metals are detected in their photospheres .
With metal sinking time scales of only a few days , these stars are in accretion/diffusion equilibrium , and the photospheric abundances closely reflect those of the circumstellar material .
We find C/Si ratios that are consistent with that of the bulk Earth , corroborating the rocky nature of the debris .
Their C/O values are also very similar to those of bulk Earth , implying that the planetary debris is dominated by Mg and Fe silicates .
The abundances found for the debris at the four white dwarfs show substantial diversity , comparable at least to that seen across different meteorite classes in the solar system .
PG 0843+516 exhibits significant over-abundances of Fe and Ni , as well as of S and Cr , which suggests the accretion of material that has undergone melting , and possibly differentiation .
PG 1015+161 stands out by having the lowest Si abundance relative to all other detected elements .
The Al/Ca ratio determined for the planetary debris around different white dwarfs is remarkably similar .
This is analogous to the nearly constant abundance ratio of these two refractory lithophile elements found among most bodies in the solar system .

Based on the detection of all major elements of the circumstellar debris , we calculate accretion rates of \simeq 1.7 \times 10 ^ { 8 } \mathrm { g s ^ { -1 } } to \simeq 1.5 \times 10 ^ { 9 } \mathrm { g s ^ { -1 } } .
Finally , we detect additional circumstellar absorption in the Si iv 1394,1403 Å doublet in PG 0843+516 and SDSS 1228+1040 , reminiscent to similar high-ionisation lines seen in the HST spectra of white dwarfs in cataclysmic variables .
We suspect that these lines originate in hot gas close to the white dwarf , well within the sublimation radius .