The Market module contains the logic for atomic swaps between Terra currencies (e.g. UST<>KRT), as well as between Terra and Luna (e.g. SDT<>Luna).
The ability to guarantee an available, liquid market with fair exchange rates between different Terra denominations and between Terra and Luna is critical for user-adoption and price-stability.
The price stability of TerraSDR's peg to the SDR is achieved through Terra<>Luna arbitrage activity against the protocol's algorithmic market-maker which expands and contracts Terra supply to maintain the peg.