Then, as spring progresses, the remaining slabs warm up, de-gas and travel down the dune face. Because of the thin air on Mars, dry ice above its freezing temperature there does the same thing as on Earth: it sublimates, which means it goes directly from solid to gas, without a liquid phase between. This outgassing of the slabs appears to help lubricate them as they slip downhill.
The dry ice explanation of the seasonal channels could also solve the puzzle of why the dune-side channels end abruptly, often with small pits at the end of them. This makes little sense if they were caused by flowing water. However, if there were chunks of dry ice sitting there, subliming away, they make a lot of sense, said Hansen.
The narrow channels, are among many kinds of channels and streambed-like features on Mars that have been imaged by orbiting spacecraft for decades, and have puzzled scientists for just as long. Twelve years ago Australian geologist Nick Hoffman stirred things up with what he called the "White Mars" hypothesis, which ascribed most of the major erosional features of Mars to dry ice lubricating flows of rocks. Today the view of Mars processes seems to be one of a very mixed planet.