I have wanted to see impact melt since we first landed on Mars. The matrix of the breccia is the impact melt, of course -- the clasts are pieces of rock that were caught up in the melt. That melt ought to give us a first-order feel for the gross composition of the target where the Victoria impactor struck. If the melt has remained generally unaltered, we have an important clue to the mineralogical nature of the surface 'way back when this hole in the ground formed.

This assumes, of course, that any piece of impact melt we find here is of local origin. As you are fond of pointing out, Herr Doktor, there are an awful lot of impact craters on Mars... *smile*...

-the other Doug

Several interesting statements, here.

First off, the rocks at HP are quite dissimilar to those at Meridiani in everything except their fine layering. They are not shot through with concretions *or* lapilli, they are composed of hard-set basalt and not loose grains assembled into very friable rock by sulfur salts, and they have withstood erosive winds for far longer than Meridiani sulfate rocks have.

Secondly, and I know it's an imperfect analogy, our Moon is covered with tens of thousands of square kilometers of mare lavas for which there are no obvious volcanoes or even obvious vents to point to as origins.

Lavas of very low viscosity can seep up through a brecciated subfloor, "igniting" pockets of volatiles (such as ices) and creating localized violent explosions, but not creating cinder cones, volcanoes or other obvious signs of volcanic landforms. Our Moon is proof of that.

Show me all the dikes and quartz veins that "prove" that, for example, the Mare Imbrium lavas were emplaced by volcanic extrusion, and I'll take my hat off to you, sir...

-the other Doug

So -- if there are nothing but volcanic and/or impact-emplaced materials anywhere in Gusev, including in the Columbia Hills, how does one explain the rather obvious large-scale landforms that argue very, very strongly that a river once flowed into the crater?

I'll also somewhat diffidently point out that Gusev began as a large crater, with a floor presumably paved with impact melt and breccia. Isn't it possible that the Columbia Hills are uplifted remnants of materials that once lay *below* a lakebed? The brecciated nature of at least some of the materials that make up the Hills would support this theory, I think.

Also, it's obvious that a layer of basalt was extruded onto the top of whatever materials made up the floor of Gusev prior to the lava emplacement. There are no obvious large flows that come from outside of Gusev (unless you want to argue that the river valley which debouches into Gusev is actually a lava channel) -- the lava must have escaped from vents within the crater itself.

I see a lot of large-scale morphological evidence for an early crater-lake which dried up and was then modified by relatively benign and non-explosive lava extrusion. Small-scale violent outbursts in the lava emplacement episode (possibly associated with hydrothermal effects) would seem to account for what we see at Home Plate, IMHO.

Then again, I'm just an amateur... *smile*... I think that what I'm seeing is consistent with the "Cornell Theory," here, but of course I could be wrong.

-the other Doug

OK, John -- now you've done it. Your comment made the following pop into my head:

Once there was a silly old rock,
Thought that it would clean Mars' clock.
But with a shove and a pull, that rock's stock
Says it won't go ker-plock!

But it has...
High hopes!
It has...
High hopes!
It has...
High, flying by
Deimos in the sky
Hopes!

So any time you're feeling low,
Feel like letting go,
Just remember that rock!
Ooops, there goes
A megaton of Mars shock!



-the other Doug

It still occurs to me that surface sample return is beyond our capabilities at the moment. Venus has a gravity field very similar to that of Earth -- you would need something more powerful than a Delta II to get a sample off the surface and into an escape trajectory, I would think (especially when you consider how much more atmospheric drag it would encounter on the way up).

That's an awfully big rocket to land on Venus and to engineer such that it will survive any sort of surface stay long enough for teleoperations.

Here's a question, though: just how valuable would a sample of Venusian air, collected at, say, 50km altitude, be? We're still above a lot of the atmosphere at 50km, right? You could design an entry probe to pump a chamber full of Venusian air (complete with dust particles, etc.), or perhaps several chambers at different altitudes. Then, when the vehicle is still moving relatively fast (we're talking Mach 6 to Mach 10 operations, here) all you would really need to boost the sample chamber(s) back to an escape trajectory would be something like one of those air-to-orbit rockets.

I'd think the data on isotope abundances and elemental compositions of dust particles would make the samples worthwhile, and you could collect such samples and then rendezvous the collection chamber(s) with a manned flyby, just as John described.

What do y'all think?

-the other Doug

Wasn't so much an evaporation of the cloud deck as it was the explosive clearing of the deck. I've always loved this particular feature of the Apollo 11 launch. You can actually see that thin cloud deck (more like the top of the humid haze layer -- all of us who have flown on airliners are familiar with it) *rippling* with the shock wave as the Saturn exhaust passed through it and then beat down on top of it. Beyond the relatively small hole punched in that thin deck, the remaining clouds showed rapid parallel-trough rippling shooting out to six "hole diameters" or more past the hole.

-the other Doug

OK -- before y'all get all het up over the topic title, let me emphasize that this is *my* new idea for asteroid defense. I want to know what people think.

My idea deals with the subset of NEOs that are rubble piles. I'm assuming that a rubble pile is made up of numerous small bodies ranging from sub-micron size up to pieces of solid rock as large as 20 or 30 meters across.

My idea is based on the concept that the Earth's atmosphere can handle the impact, over a period of days and weeks, of thousands of tons of meteorites without generating catastrophic atmospheric heating. The reason the entire mass of an asteroid will cook you whether it comes in intact or in millions of pieces is based on the concept that the entire mass enters the atmosphere within a very short time frame.

So -- if you can bust a rubble pile apart such that the rubble enters the atmosphere over a period of days, or weeks, and if you can push the larger frags away from impacting trajectories, you'd be reducing the overall impact of even a large-ish rubble pile. Depending on how much mass is in the entire pile, you could reduce the overall impact of the event to eliminate any serious threat to life on Earth.

So -- the idea is to choose a point in the asteroid's orbit where you can maximize the spread of the rubble into the largest ellipse possible prior to its impacting the Earth. You use whatever means is most efficient to effect a *relatively slow* disassembly of the rubble pile into this disperse ellipse. And here's the point that I don't think I've read or heard anyone come up with before -- you attach propulsion and attitude control systems to the largest remaining chunks and steer them into trajectories that are designed to 1) disperse the remaining rubble even further, and 2) push them onto trajectories that don't impact Earth.

This is why you want the *relatively* slow initial breakup speed. You use the gravity interactions between the large chunks in their planned traverses of the rubble to spread it all out to your specifications.

If you have a good decade to plan and implement such a defense to a given body, I think it might be one of the few strategies that could be done within our current technologies. It would be expensive -- you'd have to jet around within the initial debris field, attaching propulsion modules to the biggest chunks, and you wouldn't be able to design your large-chunk trajectories until after the breakup was effected. It would take a lot of energy for the maneuvering, and you'd have to have rather massive armor to jet around within the rubble field. But it's do-able with current technologies, if not easily.

-the other Doug

Wow is a massive, massive understatement.

No vertical exaggeration?????? I'm speechless.

-the other Doug

Remember, slump effects can be enhanced by seismic shocks. Mass wasting downslope is often driven by seismic activity.

So, one way to observe seismic events is to look at how much change we end up seeing in materials on slopes.

Seems to me Opportunity and Spirit are both sitting on slopes right now...

-the other Doug

I'm with Mike, here, Nick. These look a lot like dust slope streaks, not like the putative water-carved gullies seen elsewhere. You see these slope streaks all over on Mars, in places where liquid water could not possibly exist (i.e., high on the slopes of the Tharsis volcanoes) and they don't seem to share the V-cut morphologies of the gullies.

-the other Doug

From an old Pagan to all of you...

Merry Christmas

Blessed Solstice

Happy Hanukkha

Good Kwanzaa

And if I missed anyone -- y'all have a happy whatever!



-the other Doug

Many of the Apollo astronauts chose to wear sunglasses when doing a lot of "out of the window" stuff both in lunar orbit and on the surface -- and, of course, the LEVVA visor assemblies had built-in sunglasses (the outer gold-coated visor).

Pete Conrad almost landed on the Moon wearing sunglasses inside his bubble helmet, but all of the standard-issue sunglasses back then were the green-tinted kind, and Pete decided rather late that the green shading washed out too many details. But he indeed removed his helmet and took off his sunglasses just prior to descent.

As for Young, recall that 1) the Descartes landing site was in one of the highest albedo terrain units the Moon has to offer, and 2) by the time they lifted off, Young and Duke were sitting under the highest Sun angle anyone in Apollo would ever see from the surface (owing to their three-rev, six-hour landing slip). Add to that the airlessness, which not only gave the pure black sky in contrast to the brightly lit surface but also allowed full unfiltered Sunlight to beat down. Any place on Earth lit with that kind of unfiltered Sunlight would likely make you "snowblind," as well.

-the other Doug

Well -- yes, but. The migration process doesn't require tons of big debris chunks. A long enough transit through gas clouds dense enough to collapse the heliopause inside the orbit of Jupiter could set it going again, I bet. The upcoming collision (in something more than 2 billion years) between the Milky Way and M31 might provide the right conditions for outer planet migration to begin again, after all. And there's some good theories out there that the Magellanic Clouds are remnants of a galactic collision that occurred since our own Solar System formed -- they could have provided a lot of gas and dust clouds through which a lot of systems might have plowed.

Also -- from my best understanding, all these hot Jupiters, if they are indeed gas giants, had to have formed a lot farther from their suns than where they are at present, right? My best understanding of current planet formation theory is that gas giants won't form until it's cold enough for ices to maintain themselves without solar radiation boiling them off into vapor. So, these hot Jupiters must have migrated all the way in to where they are, right? And they're pretty darned abundant, right?

So... seems to me it might be a good idea to start understanding exactly what conditions can cause migrations to start and stop. Just to be on the safe side.

-the other Doug

Watch it there, Nick. You of all people here ought to know better than to be bringing down the wrath of the Robot Santa Claus onto our heads. Might feel like an asteroid just landed on us!

-the other Doug

It's also possible that extensive study of these hot gas giant systems could disclose that every solar system, sooner or later, finds its gas giants migrating in to close orbits and eventually impacting into their stars. Such information would be useful to us, don't you think?

-the other Doug

Actually, depending on the time frame, it doesn't necessarily make sense to alter the LSAM design for this mission (as has been done in the illustration that accompanies the story). You don't really need the same kind of landing gear, etc., to anchor to an asteroid as you would to land on the Moon, so unless you already have LSAMs built and available, it doesn't really make sense to use that design when you are in a position to design a mission module more appropriate to the mission.

Since the crew will have to live in the CEV and the mission module for the entire flight, the asteroid version of the Orion configuration will need to carry more consumables and less propellants than a lunar version. A lot of this will come in the form of food and water -- items that are bulky and (especially in the case of food) not all that easy to just plop into a tank welded onto the outside of an existing descent stage design.

What makes more sense for a mission of this type is an asteroid mission module that likely would resemble an ISS lab module more than it would look like an LSAM. The only landing equipment you need is a flat bus that actually contacts the surface and piton-like grapnels to keep the whole stack attached -- you don't need a specialized descent stage with its own separable propulsion system. You don't need a separable ascent stage at all, the mission module can come back with you as easily as not (since you have almost zero gravity well to climb back out of after your surface explorations are finished).

So, instead of being a several-month mission cramped into the cabins of the CEV and LSAM, you'd be better off dusting off an ISS hab module design, fitting it out with any specialized gear (like grapnels, etc.) for "landing" operations, and using it instead of an LSAM. You're going to need such a hab module for a flight to Mars in any event, might as well get started gaining experience for such a module by designing it to be used on an asteroid recon.

Remember the rationale behind the Constellation architecture -- the CEV (i.e., the Orion capsule) is a common ferry that, with modest changes, can be used for a variety of missions. In each mission, it serves mostly as a transport from the Earth to LEO and then back from LEO or a deep-space trajectory to Earth. The specific mission defines the type(s) of mission modules that the Orion will operate with. For a lunar mission, you use an LSAM. For a Mars mission, you have a much larger complex of mission modules that support transit activities, Mars orbit activities, and of course Mars surface activities. For an asteroid mission, you'd just naturally have a different type and design of mission module, one suited properly to the mission at hand.

-the other Doug

I'd just like to bring into this conversation the experience of the guys who have dealt with something similar -- those who went to the Moon.

Now, the Moon is a lot darker than Venus, by something like an order of magnitude. It reflects a lot less light. But astronauts who operated in orbit around it, or on its surface, regularly wore sunglasses, and skipped the sunglasses at their own peril.

As one example, John Young, on Apollo 16, decided he didn't need sunglasses when preparing for ascent from the lunar surface, and ended up riding into orbit in an almost completely sun-blinded condition. Per his own statements in debriefing, Young couldn't really see anything during ascent, and he blamed it on sun-blinding from the brightly illuminated surface. (Granted, the highlands site where Young and his LMP, Charlie Duke, had landed was of a higher albedo than other landing sites, but not that much higher.)

So, if the Moon can cause sun-blindness in those who don't take the proper precautions, I can just imagine how much greater the problem would be in orbit around Venus.

-the other Doug

You know... don't get me wrong, guys, but, um... one in 75 is still pretty big odds against something happening.

I'm seeing people getting real excited over something that is more than likely not going to happen.

Let's not get ourselves all het up over it and then get all upset when it doesn't happen, okay, folks?



-the other Doug

Io is just a whole order of magnitude more difficult to do, in-close. The radiation environment there is extraordinary. The surface conditions on most of the globe are straight from Dante's Inferno. Orbiters and landers would be fried extremely fast.

You almost have to do your Io science from something of a distance.

-the other Doug

I think that, at this point in time, after what we've seen at both Jupiter and Saturn, we can make the following generic statements:

Rocky bodies with no atmosphere: Predominated by craters.

Solid icy bodies with no atmosphere: Predominated by craters and then cracks (i.e., tectonic formations).

Partially solid (i.e., with liquid water underneath a solid ice crust) icy bodies with no atmosphere: Predominated by cracks and then craters.

The less solid an icy body is, the fewer craters we see and the more cracks we see. But at no point do we seem to lose the tectonic formations -- if it's icy, it's cracked.

So, we seem to have a rough rule of thumb in terms of the potential for subsurface oceans -- the higher the ratio of cracks to craters, the greater the chance of an ocean.

-the other Doug

Sounds like we ought to move this discussion to the "Tiny Craters" thread over in the MER forum...

-the other Doug

That still makes you closer and more knowledgeable than most (if not all) of the rest of us about the specific issue of flying full-scale nuclear reactors on outer planet probes, Ralph.

Sure, it's possible. The technical challenges and risks are just a little higher than can be overcome at the moment, I think.

-the other Doug

And remember, folks, this comes from someone who was a lot closer to the JIMO debacle than most of us.

-the other Doug

You know, any really energetic impact will create secondary projectiles. I can imagine that there would be a "ring" around an impact site where the ejecta would still be red-hot when it landed. That ring could be pretty large, depending on the size of the impact, the characteristics of the target, etc.

Besides, I would think that something coming in at cosmic velocities would shatter a horn or a bone, not burn a hole into it. I don't think the described damage necessarily requires that the objects which hit these beasts to have had the speed of a primary impactor.

-the other Doug

It's not a matter of redundancy. What is being proposed is to use fuel cells as an energy storage system.

Every energy process involves several systems -- collection, storage and distribution being the primary systems. In the proposed process, solar panels are used to collect energy. The energy from the solar panels goes into cracking water into hydrogen and oxygen -- this is a way of storing the solar energy, since the separated hydrogen and oxygen are now fuels for a fuel cell system. You use those fuels on demand to provide power into the distribution system, which delivers it to the people and equipment that need it.

Less sophisticated energy processes, like those used on the ISS, for instance, simply use rechargeable batteries to store the power being collected by solar cells. The problem is that batteries eventually wear out and have to be replaced. In the solar-to-fuel-cell scenario, your energy storage doesn't wear out. (It may need some maintenance as time goes on, but the main elements of energy storage, the reactants, never wear out, they are just re-used over and over again.)

Since the solar panels and the fuel cells are serving very different functions in this energy process, it's not really a redundant system. If you lost the fuel cells, you'd have to replace them with batteries for energy storage, and if you lost the solar panels, you'd have to replace them with some other energy source (nuclear?) to crack the water back into hydrogen and oxygen and recycle the storage system's storage medium. In true redundancy, one element could take over for the other without impact to the overall system.

-the other Doug