"The boundary between the northern and southern hemispheres is quite sharp."-Jessica Sunshine.

One concept in planetary science I take particular umbrage with is the very idea of a habitable zone. I don't think they exist. Oh sure, if you force a particular atmospheric mix on the concept you can say it's from some distance to another where liquid water can do whatever, fine. But what if you instead define it by wherever you can engineer life to persist? Europa is arguably more habitable than Earth if you slant your definition that way. Why should an ice-shell not be just as good as an atmosphere? There's liquid water at some depth and that arbitrary distance. Even tying your definition to water seems to display a lack of imagination to me. Water seems to be applicable because it's polar. There are other combinations of polar and non-polar solvents and solids that might sort natural chemicals. 

If we stop presuming and ask a comet what it thinks, what will it reply? Comets say something changes at 2.5AU. Volatiles sublimate and form the comet plasma at that range, roughly the orbit of asteroid 25-Phocaea. And comets cross that line often, from any angle. But they also do similar comet stuff at 15AU. What are comets telling us about the path they travel and what it contains, either because the comet withdrew or deposited there at some point in time.

This lecture is about hyper-active comets. That's to say, comets that have a lot more chemistry going on than normal. Hyper-active comets are a lingering annoyance proving that we don't yet know how comets, the Kuiper Belt, or the Ort Cloud actually work.  

• At 16:30 get the ingredients for a blue comet. 
• At 21:00 comet 64P-Wirtanen is the first hyper-active comet described. 
• Summary at 45:40

There's no great need to call attention to too many slides because the talk is laid out almost in story form. The story being the discovery and study of hyperactive-comets. It ends in test proposals and implications. Is the polished surface of comets literally polished by tumbling particles? Seems plausible. I often wonder if the Solar wind hydrogen, the CO2 of Venus, the dust of Mars, the whatever ejected from IO & Enceladus, are all blown into the solar wind until heliopause where it tumbles along to find some point of aggregation? The odds seem low as things spread apart, yet also inevitable since they may be in something of a closed and irregularly shaped container. That's just speculation for now, but seems to be using similar physics as the mysteries of comet study seem to be leaning.