<”Teresa Segura offered an interesting new slant on the early Mars atmosphere. Based on a freshly-published paper, she described how large impacts would blast rock and ice into the atmosphere, vapourising them, and delivering a pulse of heat to the air and ground, as rock fragments fell back to the ground.
Since Mars odyssey has shown that much of Mars is covered in shallow permafrost, there is plenty of ice available to melt and boil by this process. She proposed that each giant impact made Mars hot and wet for a few decades, before the rain poured out of the skies again, eroded channels, and refroze.
There was intense debate on this issue. Mike Carr showed that the size of impactors that Teresa had modelled were too large for the time when the river channels were formed.
There certainly had been such giant impacts earlier in Mars history but these had been almost completely erased, perhaps by processes as described by Teresa, but that during the formation of the river channels we see now, impacts were much smaller.
Others noted that Teresa had modelled only the contribution of water, and not that possible from Carbon Dioxide, and that if Mars had more CO2 available at that time, then her model would work for smaller impacts.

Well, I wasn’t entirely off the mark...

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