We present details of a precision subsampling system (PSS) under development for surface exploration of Mars and possibly other planets. The PSS combines a fine-scale solid powder extraction tool with sample collection, manipulation, and instrument analysis subsystems in a highly compact package. The system offers future landed missions the ability to selectively analyze heterogeneous surface sample composition on millimeter scales. Analysis of subsamples by mass spectrometry and other tools would then permit characterization of highly-localized chemical and mineralogical phases that could be key indicators of past or present habitability on Mars. Systematic measurements along a finely laminated sedimentary sequence would also lead to a greater understanding of surface formation processes. Following subsystem design and test, our breadboard PSS will undergo full end-to-end characterization at Mars ambient pressures using analog rock samples and integrated prototype spaceflight analytical instruments.