Benjamin D. Boatwright & James W. Head

"Inverted fluvial channels"-Speaker

Great news. This one has timestamps embedded already. Better news, the slides are beautiful and packed with knowledge-bombs.

In the southern Noachian Highlands where the most ancient craters have not been wiped-out by erosion, they've still been eroded a bit. The rims are low and the basins are infilled. Some have a channel leading into them with an alluvial fan, some alluvial fans don't have a channel, but essentially most Noachian craters have an inlet of some kind, and quite a few have an outlet too. Classically people have assumed rain to be the erosive element, albeit very rare rain. But you don't need rain to explain things, and with each probe regular-rain becomes less and less a possibility. 

• The slide at 5:55 has an example of lake features in a crater that has no obvious inlet. The implication is that groundwater seepage was involved since there is no inlet, but there are alluvial fans.
• At 8:50 the speaker is still building up to the overall point, but that's because it is a HUGE point. Still I wanted to call attention to slide since it displays these inverted fluvial channels so well.
• At 10:30 the speaker begins to make the argument that the crater features, were most likely formed in cold conditions. RSL's, recurring slope lineae, those are the "water-steaks" that have been noted forming and disappearing currently in the late Amazonian era. The suggestion is that the mechanics are the same.
• At 13:45 the overall question is asked. 'are the features we see explicable by episodic melting events.' And where the climate models have always said that's what has to be, the geological evidence had been lacking, until this.
• The whole lecture, including the Q&A is entertaining. Great questions come up.

These inverted fluvial channels are best explained as brine flowing under an icecap. Activity under the glaciers. That's why the cliff-facing-scarps have that backwards curve, and why the fluvial channels are inverted. You know how you see river beds on Mars and assume they are depressions instead of highlands because they look like dendritic rivers, but for some reason they usually aren't braided streams? That's because it's a cold fluid brine acting like a fluid brine, and not a river not acting like a river.