'Schiaparelli and the Trace Gas Orbiter.' It sounds like an experimental Italian jazz band doesn't it? It's actually a ground breaking European mission - part of a small fleet of them, titled 'ExoMars.'
The European Space Agecy has gotten spacecraft into orbit around Mars before, and on one occasion a British team tried to put a lander onto the surface - it was never heard from again, although it was found by the MRO spacecraft last year.
But they've never managed to get a working lander on the surface - yet. This afternoon they hope to change that.
ESA is aiming to land a rover and an automated science platform in the early 2020's. That's where the Schiaparelli lander comes in: Although it's science payload is modest, it will give ESA a chance to practice getting something safely onto Martiian soil.
Meanwhile the Trace Gas Orbiter will do a double mission, studying Mars' atmosphere (and looking for any biomarker gases like methane in particular) and acting as a relay satellite for future missions.
But don't just take my word for it* - take these ESA video's word for it instead.
The descent to Mars:
A flyover of the landing site:
The lander should (hopefully) be on the surface by 1500 GMT. You can follow the landing live, here.
*Because I'm some random on the internet.