Looking at the instrument fit of the new Mars Trace Gas Orbiter - and in particular at MATMOS - I can't but notice a similarity to the MARVEL mission proposed back in 2002. There's precious little available about MARVEL online, but this description covers it quickly:
MARVEL would have taken an occultation FTIR much like MATMOS along with a limb photography camera to spot dust. It also would have brought along a submillimeter spectrometer.
So here's the question I ask (discuss away...):
Given the recent popularity of Martian methane, was it a mistake not to fly MARVEL? How much further along would we be if it had flown in 2007 with an instrument suite that included an instrument so similar to the TGO's flagship tool? And does anyone have any more information about this mission?