And it's believed that the high chemical reactivity of the surface is due to the deposition of chemically active gases from the atmosphere onto the surface, gases like hydrogen peroxide and ozone.

NPR: Revisiting the Viking Missions to Mars

It will study chemically active gases.

NPR: Revisiting the Viking Missions to Mars

Greenhouse gases are not the only climatically active ingredients that industry, farming and land clearance add to the atmosphere.

ECONOMIST: The science of climate change