At the poster session I bumped into John Murray from the Open University, Milton Keynes, UK. John and his colleagues from the Mars Express team caused quite a stir last year when they announced they had found a frozen sea on Mars. Nature papers followed soon after, but since then arguments have raged between those who support the idea, and others who claim the features they saw are in fact lava flows …

A presentation yesterday by Susan Sakimoto, a vulcanologist at the University of Notre Dame, Illinois, seems to have brought the issue to a head. She’s doubtful about John’s interpretation, and she and two other pro-lava scientists (or at least, not-convinced-it’s-ice scientists) engaged John and his OU partner David Page in some robust debate about their new research poster, which unveils even more bits of Mars that look like ice floes. More of their work in this area has just come out in the journal Icarus.

John maintains that as a vulcanologist himself, he’s been looking at lava flows for more than twenty years – and the plates, ridges and wiggles they are finding are definitely not produced by lava.

But Susan, along with Laszlo Keszthelyi, an astrogeologist with the US Geological Survey, disagrees. “We’re saying that all the plates and surface features here, we can show you examples on Earth that come from lava,” she says, adding that some of John’s proposed flow directions for the ice actually go uphill.

So how will this (very good-natured) argument be settled? “Go drill it?” she suggests brightly. Sadly, both sides agree that remote observations are unlikely to give a definitive answer. “We’ll be waving our arms about this for years,” she smiles.