I agree, Bill -- the distribution of dark materials just screams to me that it overlies the brighter, cleaner ice surfaces.

I also still believe I can see evidence of dark material piling up in craters, filling and/or deforming the "downwind" sides of some craters, and exhibiting some dune-like striations. I've been really busy and haven't had enough time to annotate images to point out what I think I'm seeing -- but I am certain that I'm seeing it.

To me, it all adds up to dark material covering light material, thickly in some places and more thinly in others.

-the other Doug

For me, the self-portrait thing started with Surveyor 1, and that famous image of the footpad sitting right smack in the center of the field of view, firmly pressed into the lunar surface. Since then, all of the Surveyors and then the Vikings took their first images of their own footpads. So there is a grand old tradition of landing probes imaging themselves before anything else...

-the other Doug

I've revisited the late June and early July discussions and press releases, and it seems that all anyone was prepared to be specific about at that time, in re Oppy's exact preplanned path, was that she would head down to the "bright ring" layer (otherwise referred to as the "bathtub ring") and follow it around, parallel to the crater rim, observing and sampling as it went along. While it would appear that it would be easiest for Oppy to turn to her left and follow the bright layer to Cabo Verde, and while Squyres was very clear that there was a specific path laid out "from which we will not stray," that exact path was never shared with us, the little people...

-the other Doug

The aerodynamic pressures going Mach 5 in the Martian atmosphere, at say 10km above the surface, are quite a bit lower than what you would find on Earth, and while there would be considerable blow-back, it wouldn't be as bad as what you might think.

The biggest problem with the approach to Mars is that you encounter maximum aerodynamic deceleration much closer to the surface than you do on an entry approach to Earth. The time frame between decelerating to a speed at which parachutes and rockets are effective and reaching zero altitude is far, far smaller than that on Earth. But, as has been pointed out, you need to take advantage of that aerodynamic deceleration, or else you need to send four times as much mass as you otherwise would in deceleration propellant.

I think nprev is right, we're going to need something that will maintain altitude through lift as it bleeds off speed, so that we can continue to use aerodynamic deceleration to slow the craft. Of course, that means huge wings (to generate enough lift int he thin air) that have to be strong, since they have to withstand Mach 5 (and above) winds for a decent percentage of an hour, not just four or five minutes. Even in the Martian atmosphere, I have a hard time imagining a deployable wing system that could deploy cleanly and then withstand the heating and shear forces they would encounter in the long, slow decelerating glide.

So, it's a tough nut to crack. We may have to develop entirely new materials and technologies to allow rocket-assisted aerodynamic entries, and/or we may have to assemble gliding vehicles in Martian orbit. In any event, I bet that even if a Mars program aimed at landing humans there by 1980 had been funded, it would have failed when faced with this issue...

-the other Doug

If any Saturnian moon is going to be lumpy, it would be Iapetus. However, it's possible to maintain an orbit around even a very gravitationally lumpy body, if you pay attention on every rev to what your dispersions are. Just like our Moon, it's not possible to maintain such a low orbit for long unattended, but attended (i.e., with constant adjustments) you can orbit such a body indefinitely.

-the other Doug

I'd like to see Spirit limp her way over to the fractures in the Plate that parallel its north-northwest edge. These cracks look constructional, not dessicational, to me. And where better to examine the history of the creation of this feature than along a constructional fracture?

I know I'm getting all excited about volcanic/basaltic rock emplacement, and Squyres et. al. are on record as not being all that interested in "ho-hum, another busted up hunk of lava." But for me, this is the kind of thing geology is all about -- reconstructing the events that caused such an unusual-looking but generically common (as there are certainly a number of similar features scattered throughout these hills) feature as Home Plate. I still don't think the possibility that this could have been part of an active hydrothermal system has yet been put to rest, since I know it had a great deal of support within the MER science team when Spirit first reached the Plate...

-the other Doug

I thought the plan was to turn to Oppy's left (our right), Tom. I recall that the planning team had designed a very specific route over to the exposed Cabo Verde cliff faces, and that no straying off the path was going to be allowed. The path was designed to explore the light-colored "bathtub ring" and to keep Oppy on rocky, non-sandy footing.

As I seem to recall, the plan was for Oppy to enter pretty much where she entered, turn to her left at about the level she's at, and stair-step in a couple of legs down to the base of the Cabo Verde cliffs.

Does anyone have any information indicating that this is no longer the plan?

-the other Doug

Yep -- as someone else here once said, I would absolutely adore to see images from a Barsoom Reconnaisance Orbiter. BRO could resolve the great spires of the city of Helium, after all...

-the other Doug

I think it's worth pointing out, here, that Google has some serious space exploration fans in its upper ranks. Google never fails to commemorate the date of July 20 each year, and at one point (I believe it was on a July 20 several years ago), Google announced it was accepting applications for positions at its new lunar facility which was to be located (IIRC) on the floor of Copernicus. (I actually sent in an application, all in fun, and got a very nice letter stating that they already had enough applications, but to keep them in mind when they begin hiring again for this facility, in about 35 years... *smile*...)

Google would be doing something like this, not for the PR value (although there is that), but just because it appears that the people who run Google *want* to do it! They think space is cool, and even if no one ever knew what they were doing, they'd love being involved in getting new, fresh-off-the-wire views from the lunar surface.

-the other Doug

Yep -- the rendezvous at Mars scene is a direct translation of a Bonestell painting, updated to make Mars look real.

In Saunders' alternate history, btw, Fred Haise becomes the first man to set foot on Mars. I like that idea.

-the other Doug

Hmmm.. that first bootprint was almost certainly overtrodden by both Armstrong *and* Aldrin durng the course of the EVA. It was just off the footpad, after all, on the side of the footpad facing the MESA, and they did a lot of work at the MESA.

But for the whole scene, overall, I think that Tranquility Base ought to remain untouched and "unsullied" for now. I'd have no problems with rovers visiting any of the other five Apollo landing sites -- they're historical, but not so much as that first one. A few more rover tracks wouldn't damage anything at, say, Hadley or Taurus-Littrow. Or even at Fra Mauro.

In fact, I think Fra Mauro would be a great place for an unmanned rover. Work it right and we might *finally* get to look into Cone Crater. I think it would be appropriate to allow Ed Mitchell to drive a rover right up to Cone's rim and be the first to look inside... or maybe, if Ed can't do it, let Jim Lovell and Fred Haise do it!

-the other Doug

Congratulations, Nick!!!!!

Once you finally graduate -- THEN it's time for a few beers! Wish I could join you.

-the other Doug

Must be dependent on your individual ISP. My Comcast DNS servers have never lost the original website, I've been able to get to it all along.

-the other Doug

OK -- for those who feel the bright surface is overlaying a dark substrate, how do you explain the "streams" of dark material which extend hundreds of kilometers into the trailing side? These are linear features made up of mostly contiguous dark material. Sometimes they separate into discrete pits or craters with dark floors, but for the most part they are dark "stains" that do not seem to follow fracture patterns or even organized crater chains.

It looks for all the world like jets of dark material sprayed from the leading edge back to the trailing edge...

-the other Doug

Well, LRO will outdo Kaguya for number of names, anyway. I just signed up for the LRO program and got certificate number one million, one hundred and sixty-nine.



-the other Doug

Seems to be fixed now -- at least I get what looks to be the correct site. No problems. And I've cleaned my cache since the last time I loaded the site, so I know I'm pulling it "fresh"...

-the other Doug

Ooooh -- anyone else notice the arcuate and possibly pentagonal cracking in the upper surface of Home Plate in the latest images?

This used to be a cracked and tortured surface, it's been smoothed out over the megayears but it was as strong and tortured as any volcanic terrain we've ever seen on Earth.

-the other Doug

It looks to me like the extension of the equatorial plane into the bright terrain expresses itself as an almost cahotically fractured terrain -- I certainly don't see the massive constructional landforms seen on the dark, leading hemisphere. Looks like chaotically cratered terrain that expresses itself in large-scale cratering and small-scale tortured surfaces.

What if it wasn't a full ring that impacted Iapetus to form the belly bad -- what if it was a ring arc? A body that disintegrated within Iapetus' Roche limit but impacted the surface before it had a chance to evenly distribute itself into a full ring?

Is it possible that an extremely uneven distribution of mass within the impacting ring, combined with a gravitational "high point" along the leading face of Iapetus could have caused selective accretion along the leading edge and the chaotic disuption of the trailing edge caused by leftover accretion plus seismic and torsional stresses caused by the accretion?

If the vast majority of the accretion event that created the belly band occurred on the leading edge, perhaps this is the singular event that emplaced the dark layer in the first place? Or does the post-formation cratering of the ridge, which itself seems completely mantled by dark material, rule this out and require a later emplacement of exogenous material?

And -- while it could just be a basin formation, there is a formation on the bright-side terminator along the trailing edge that appears to be a bright-side version of the equatorial ridge. Shorter, to be sure, but with similar attendant ridgelines and the same piled-up appearance. Interestingly, this feature doesn't follow an equatorial line at all. It looks like it could follow a great circle line, though...

-the other Doug

You're seeing blanketing, too, tasp? Good, I was beginning to think I was going crazy...

Yeah, I'm seeing debris blanketing at various levels. Some of it seems pretty thick and exhibits mostly parallel striations, some of it seems very thin. But I'm definitely seeing a variety of blanketing processes going on here.

-the other Doug

I'm specifically speaking of this image and the larger composite of this area that has been posted previously by several people.

Look at the pattern of the debris flow here. The rim is degraded, but not all along its extent. The major degradation runs from the left edge, through the floor, and up the right edge (as seen in this image), with a linearity to the debris on the floor that parallels the points on the walls that are most heavily degraded.

If you look closely at the surrounding area, you can see similar "ponding" or "pooling" of debris along the "right" and left" crater rim arcs, not so much on smaller craters but very definitely noticable on the larger craters.

All I have available for image manipulation on my system is your basic MS Paint -- I'll try and annotate one of these images later today and highlight what I'm seeing.

-the other Doug

I don't know about anyone else, but in some of these images I'm seeing very definite evidence of material flow, in a direction that, if the shadows aren't playing tricks on me, seems parallel to Iapetus' orbital motion.

In other words, it looks a lot to me like most of the larger craters have debris on opposite sides, filling in both inner walls to some degree but piled up a bit more on the far sides (in relation to their orientation towards the direction of orbital motion). The debris patterns seem to consistently apply themselves 180 degrees apart on the larger crater rims (i.e., the thickest or most obvious sections of the debris accumulations lie approximately 180 degrees apart along the rims), and the vector through these points in the crater walls seem to align with direction of orbital motion.

I'm getting my concept of the direction of orbital motion from the shadow angles and from my (admittedly extremely rough) concept of where these regions lie in relation to the equatorial ridge. In any event, to make it a little simpler, it looks like the vector defined by the 180-degree-seperated rim distortions points back toward the center of Cassini Regio, i.e., towards the center of the region Iapetus that faces into its direction of orbital motion.

It will be more instructive, and prove more, when I can see exactly where these images are located and where those vectors actually point. After all, you *could* (and, on many Solar System bodies, do) see the same kind of phenomenah emanating from basins. But while some of this looks like ejecta, more of it looks like, well -- duning. To me.

This debris accumulation looks less obvious in the inter-crater "plains" (as rare as they seem to be) than on the rims and floors of the larger craters. But I really do think I see very specific patterns of debris accumulation here. It would seem to support the belief that material is, or has been at some point in the past, very slowly "flowing" from the midpoint of Cassini Regio out in vectors away from the leading face's central point. What's harder to tell is whether the "flow" is more radial to the center of the leading face, or more parallel to the equatorial ridge. It may well be a combination of the two...

I'd have to say it looks like the surface is very ancient, but that that the debris accumulations (which you don't see in such abundance on the other icy moons), while relatively thin in most places, seem to definitely overlay almost all of the craters to the same extent. In other words, this material is younger than the underlying ancient surface, but thin enough that it doesn't resurface the ancient terrain, it just piles dunes and sprays of debris on top of it. It's not enough material to resurface, but it does seem to be enough material to "paint" the cratered terrain a very dark brown.

-the other Doug

To the argument that we can't tell if the dark material is Titanian in origin, since we don't have spectra of Titan's surface:

If the material is being accreted from a Titanian smutz torus (I like that term, Nick!), then that material comes not fromTitan's surface, but from the outer layers of Titan's atmosphere.

Correct me if I'm wrong, but we have a *lot* of spectroscopic information about the outer layers of Titan's atmosphere, don't we? You don't have to look down through Titan's thick atmosphere in order to see its outer layers, do you? You basically just have to look at Titan from a distance and take spectroscopic readings of what the outer layers are made of... right?

According to the best theories I've been reading, if there is a torus of Titanian origin that gets swept back through Saturn's magnetotail, it would be composed of molecules sputtered off the top of the atmosphere by solar wind interactions and by interactions with Saturn's magnetic field. You don't have to postulate some huge impact that lofted megatons of Titan's surface material out beyond its Hill sphere to construct such a torus -- and to be honest, I haven't seen anything in the surface imaging of Titan to hint at such an enormous impact. Unlike several other Saturnian moons, Titan doesn't sport any obvious basins that are a sixth or more the size of the moon itself.

I think that if the dark material on Iapetus is of Titanian origin, it's got to be remnants of Titan's depleted upper atmosphere. Which we have a fair amount of compositional data for.

-the other Doug

Has anyone ever given any serious consideration to David Brin's "energetic arm-waving" concept of a refrigerating laser?

After all, the whole idea is to dump heat outside of the probe, right? To do so, you need to generate it out into heat pulses that are *hotter* than the ambient outside temperature, since you can't dump heat into an environment that's hotter than the dump.

So -- use the heat that leaks through your outer skin to power a laser that's a *lot* hotter than 500C, and then dump the energy by blasting the laser out and away from the probe.

What are the engineering challenges in such a system? And does it violate any basic laws of thermodynamics?

-the other Doug

It's raining here in MN, and while it's only down to about 72, it's supposed to stay at 72 until sometime Friday night, when it's going to drop down into the upper 50s.

The temp here hasn't been below 70 (if it has, it's only been by a degree or two) for about two weeks... at any time of the day. That's really unusual for MN this time of year -- seasonal highs would be in the low to mid 70s.

-the other Doug

OK, OK -- so I was a little off. It's not like the error ended up piling a Mars orbiter deep into the atmosphere or anything...

-the other Doug