or at least write their press releases.

Though the ban on my participation in HZ ended 7 September, that was all I could get Robert to agree to. I've simply found that its much better for me to use my time in other ways.

(I suppose that in my absence Doug Ellison will just have to explain CAPS to Mr Vance. Or perhaps one of Gary's many people who shied away from the HabitableZone because of my prescence here will do it. As I have not seen any of them show up yet, I think I should at least give them another month to do so, or two, or three, or four, or five...)

However, since I was so rude to you over that very nice image from Mars of that blob which you spotted, and as I'm down today with a really terrible cold and just wasting time on the net this afternoon, I am going to make an exception and spare you a few minutes of my time.

The remains of the core of a cometissimal were recovered at Chiemgau. What happens is that over billions and billions of years the heavier metallic elements in the Ur dust of the solar system are precipitated by gravity to the cometissimal's core. Sometimes these cometissimals combine into larger comets, but usually these larger comets break back up into their component cometissimals when they encounter planetary gravity fields.

How big can comets get? Pretty big. The Chixulub crater was formed by the impact of a comet, not an asteroid. We know that both from recovered samples as well as the scaling laws for nuclear explosions. How powerful are they? Pretty powerful. They move much faster then asteroids. How dangerous are they? Shoemaker thought that they presented the bulk of the impact hazard we now face.

So the next time someone tells you that the dinosaurs were killed by an asteroid, just remember to ask them what a carbonaceous chondrite is. Then ask them what the albedo (reflectivity) of a carbonaceous chondrite is.

I wonder if that blob you spotted was organic, Jacob. If so, the detection of any life on Mars is going to make manned flight there much much more difficult. But that's probably a moot point as most people do not want to spend a large amount of money on manned Mars flight anyway.

bye,
ep