  Comparing compositional models of the terrestrial planets provides insights
into physicochemical processes that produced planet-scale similarities and
differences. The widely accepted compositional model for Mars assumes Mn and
more refractory elements are in CI chondrite proportions in the planet,
including Fe, Mg, and Si, which along with O make up $>$90\% of the mass of
Mars. However, recent improvements in our understandings on the composition of
the solar photosphere and meteorites challenge the use of CI chondrite as an
analog of Mars. Here we present an alternative model composition for Mars that
avoids such an assumption and is based on data from Martian meteorites and
spacecraft observations. Our modeling method was previously applied to predict
the Earth's composition. The model establishes the absolute abundances of
refractory lithophile elements in the bulk silicate Mars (BSM) at 2.26 times
higher than that in CI carbonaceous chondrites. Relative to this chondritic
composition, Mars has a systematic depletion in moderately volatile lithophile
elements as a function of their condensation temperatures. Given this finding,
we constrain the abundances of siderophile and chalcophile elements in the bulk
Mars and its core. The Martian volatility trend is consistent with $ \leq $7
wt\% S in its core, which is significantly lower than that assumed in most core
models (i.e., $ > $10 wt\% S). Furthermore, the occurrence of ringwoodite at
the Martian core-mantle boundary might have contributed to the partitioning of
O and H into the Martian core.
