I don't know -- the dune we got stuck in is only about 30cm tall, after all. Not tall enough for Oppy to bottom out or anything.

From what I read of the analysis of Oppy getting stuck in the first place, they thought that the problem was not that Oppy ran into a dune that was too soft to support it -- it was that we got into a position where the three wheels on one side were on one side of the dune crest, and the other three wheels were on the other side of the dune crest. They didn't see any real compositional or textural differences between the dunes Oppy had climbed over with no problem and the one they got stuck in, except for the positioning of the wheels astride the crest.

I'm not an engineer, but I can "feel" how the rocker-bogey system would suddenly be less effective if the slopes suddenly sloped away from the vehicle on both sides.

In other words, it's possible that all we have to do is avoid driving over dunes at a shallow angle to their crests. I bet we'll be able to cross the dunes easily as long as we approach them transverse to their crests...

-the other Doug

According to the latest description I've seen of the planned back-out maneuver, they're supposed to be moving back *not* in a straight line, but in a leftward arc (leaving the stuck front wheel at its seven-degree toe-in position). It would make sense, then, that the left side would move a little more than the right.

Remember, according to the plan, they're only going to spin the wheels a few meters' worth each day and see what happens. They think it'll take days, if not a week or more, for Oppy to actually back out.

In other words, don't panic -- the maneuver isn't supposed to have gotten us very far yet.

-the other Doug

Rings very true with me. Especially where Freire says "The dark streaks observed at the edge of Cassini Regio indicate that it was a wind blowing from the equator that deposited the 'dust'. We can be certain of this because Cassini imagery shows clearly that the dust is deposited downward from the crater rims."

The first close approach images of Iapetus from Cassini sure looked to me like they showed material literally piled into craters, especially along the edge of Cassini Regio. And the material appears to be piled against the *far* walls of the craters in relation to Cassini Regio -- in other words, the material was blown from the direction of the dark area, which means that it settled on the far inside rims, leaving the near inside rims uncovered (and therefore retaining their bright surfaces).

I don't recall if I mentioned here my perception of how the material collected against the far rims of the craters along the edge of the dark area, but I sure noticed it... and then, when several members of the forum suggested that no material was deposited but, instead, icy coverings were being stripped to create the dark albedo, I decided that my eyes must have lied to me.

It's nice to know somneone else saw the same things I did!

-the other Doug

No problem. I enjoyed it.

Looking at Jibsheet some more, though, I'm reminded that breccias aren't the only kinds of rocks that have clasts embedded in a matrix. Conglomerate rocks can be simple sandstones and mudstones that have embedded stones or pebbles, and a congolmerate will often have a softer and more easily eroded matrix than harder stones embedded within it. Which is what we see at Jibsheet.

Breccias and ashflow tuffs can also have soft (the geological term is "friable," meaning soft and crumbly) matrices compared to their clasts... it all depends on the minerals that make up the rocks and the speed with which melted rock cooled and solidified. But whichever kind of rock Jibsheet is made up of, it's definitely shedding clumps onto the ground. Which, if nothing else, is different from most of the rocks we've seen at Gusev. Looks a little like Pot of Gold and others like that, with harder material surviving the erosion of softer pieces of a rock, but we haven't seen the shedding of uniform little clumps like this before, really...

Now, at Meridiani, on the other hand, soft rocks shedding fairly uniform-sized harder bits are the most common... so, go fig!

-the other Doug

I think you're exactly right, Phil. Though the exposed, eroded evaporite in the actual etched terrain is, I think, not crater-rim excavations but ridges in the ejecta blanket created by the ancient crater cluster of which Erebus and Terra Nova are a part...

-the other Doug

Well, I'm nothing more than an enthusiastic amateur, but sure, I can give a description of breccia (pronounced BRETCH-yah), here.

Breccia is a multi-rock kind of rock. It has what are called clasts within a matrix. It's sort of like concrete, in which you have gravel "suspended" in a matrix of cement, which is itself composed of crushed rock grains and other chemicals that make it harden.

A clast in a breccia is a small rock or stone that's been embedded in another kind of rock. In concrete, people make up that "other kind of rock" as a slushy cement mix, and it hardens because of chemical changes (polymerization) that occur within the cement. In a breccia, the matrix is often rock that is molten or semi-molten that has surged across the landscape, picking up stones as it goes -- it hardens as it cools. The outsides of the stones are heated, often shocked, and sometimes partially melted, but they retain their original minerology and gross structure. As the molten or semi-molten rock that "picked up" the clasts cools, it forms rock with these inclusions, or clasts, within it. That rock is called breccia. A landscape that has been altered by multiple impacts that have created thick layers of such breccia is referred to as "brecciated."

On the Moon and on Mars (and on any other rocky body where impact has had a large hand in shaping the landscape), an impact event melts the target rocks, creating what's called an impact melt sheet. This sheet ends up (roughly) lining the crater and gets splashed outside of the crater.

In the center of the melt sheet (thickest in the bottom of the crater itself), it's pretty pure melt -- it gets melted thoroughly and cools into what looks exactly like igneous rock (because, except for being melted by an impact instead of being melted deep within the planet's crust, it formed the same way, as molten rock that cooled). At the edges of the melt sheet, the molten rock begins to cool even before it hits the ground, and as it strikes other rocks it embeds them rather than simply melting or vaporizing them.

Sometimes, the impact melt picks up rocks from the surface, but the molten rock can also accrete around cooler pieces of non-molten rock within the ejecta cloud as it flies away from the impact crater. Sometimes the clasts are partically molten themselves and recrystallize within the melt matrix.

So, every impact creates a certain amount of impact melt, and some of that melt will pile into unmelted or partially melted rock and incorporate it into the new rock. This new rock is breccia.

On Earth (and I suppose, on Mars as well), breccias can also be formed during pyroclastic flows from volcanic eruptions, when extremely hot ash created by the eruption flows away from the vent and incorporates cool surface rocks as it goes. These breccias are called ashflow tuff, since the ash is usually not hot enough to melt completely and the resulting rock looks less crystalline than does rock that cooled from a pure melt. From orbit, there are a lot of places on Mars that look like they have ashflow tuff deposits, so finding ashflow tuff at some places on Mars is quite likely.

But impact has carved Mars' landscape at least as pervasively as has volcanics. Especially in the ancient cratered southern highlands. So the vast majority of breccia found on Mars is probably going to be impact-created.

Now, the really interesting thing about impact melt is that when the impact melts the target rocks (i.e., the rocks that make up the ground where a meteor or asteroid strikes), the minerals that make up the target rocks get homogenized and the new impact melt is made up of the minerals that had been in all of the rocks. So, for example, if a meteor hits a layered rock bed that includes layers of granite and layers of iron-rich basalt and even layers of sandstone, the resulting melt will include the *average* chemical and mineral composition of *all* of the rock layers that were melted. So impact melt from a large crater (like Gusev, for example) hints at the composition of not just the rocks that had been on the surface when the impact happened, but also the rocks excavated from the deepest part of the crater.

So, for example, if the surface rocks are mostly low-magnesium, high-titanium basalts but the impact melt from a nearby deep crater includes a noticeably higher proportion of magnesium and a lower proportion of titanium than the surface rocks, you can tell that there are layers of rock underlying the current surface that are higher in magnesium and lower in titanium than what you're standing on. Even if there aren't any pristine examples of that high-magnesium, low-titanium rock lying around anywhere on the surface.

Finally, impact melt is valuable when you can use it for radio-isotopic dating, since the melting and recrystallization of the rock resets its "radiological clock" and you can tell from it when the impact event occurred.

Which is why it's interesting to see something that looks like it might be impact melt in Gusev. Even though we don't have the instruments to perform radiological dating on the MERs, it's important to know if we can find and recognize impact melt on Mars, for when we actually have the capability of selecting samples for such dating.

I hope the explanation wasn't worse than the stuff you wanted explained... And I'm sure that there are *real* professional geologists in our little forum who could correct me on terminology here and there... but I think I've got the concepts down fairly well.

-the other Doug

Looks like the "popcorn" assembled at the base of the rock are pieces that dropped out of, or at places peeled off of, the rock face. To me, it looks like a breccia with dense clasts and a softer matrix has been eroding there, and the clasts are lying on the ground.

This is the first thing I've seen that looks like it might be impact melt. That's just a WAG, but the appearance just reminds me of something like that. I think it's interesting that a breccia with a melt matrix would have harder clasts than the matrix, though...

-the other Doug

I could be wrong, but it may be because MGS, Odyssey and MRO are all designed to use aerobraking to achieve their final orbital parameters. The concave part of a parabolic antenna makes a really good air brake, something that would probably make the things less controllable during the aerobraking sequences.

-the other Doug

This is a family forum, sir, and any further reference to Gigi's "bits," as you call them, will be most unfavorably viewed...



-the other Doug

See, this is why I think the hills are *not* composed of the original crater floor, uplifted by faulting. The floor of Gusev would have been a melt sheet covering a highly shocked and probably brecciated underfloor. Methuselah looks like sandstone -- whether deposited by wind or water, it's some type of layered sandstone. Which is why I'm convinced that Gusev developed a nice thick floor of layered sediments on top of the melt sheet before the upthrust fault created the hills, which was then followed by one or more lava inundations.

And the larger-scale landforms (the "feed river" formation and delta landforms on the floor) would suggest that the layered sediments were water-laid. I don't insist that the sediments *must* have been water-laid, but I think the evidence is pointing to that conclusion...

-the other Doug

Um, yeah... well, actually, the "problem wheel" *can* be turned (according to the initial reports I read), just not through its entire designed range of motion. Though I don't think I'd risk turning it much from the closest they can get it to straight-forward, that seven-degree "toe-in" it's set on now. I'd be afraid it would get stuck in a far worse position.

-the other Doug

Yeah -- when they speak of the glories of exploring the Moon, they never talk about things like space adaptation syndrome, which made at least one guy on most every flight queasy enough to vomit. They never talk about the indignities of bowel movements in a capsule no larger than the inside of a Volkswagen Beetle, for which, according to Wally Schirra, the only way to proceed was to get entirely naked and leave yourself a good hour for preparation and clean-up. They never talk about less-than-palatable food, total lack of warm water and food while on the Moon, or struggling into pressure suits that are designed to fit so snugly that, until you actually pressurized them, the neck ring would bite into your shoulders.

Even on the ISS, they never talk about how the only drinking water temperature choices are lukewarm and sort-of-hot, or how the noise level in some parts of the station is such that it could cause permanent hearing degradation if endured for as long as six months at a time.

I always thought SkyLab was on the right track. Hot showers, a refrigerator and freezer for food, an oven and table-top heaters with which to cook their food (making available such meals as lobster thermidor and prime rib), and a nice, big open space to just plain have fun floating around in. Now that was flying in style!

-the other Doug

Remember, it gets windy up in the hills. I can imagine a sequence of events where a piece of basalt gets lobbed on top of a much softer piece of sandstone and the winds strip the sandstone down to a flat, "floor-tile" appearance (sweeping the eroded dust away) and leaving the denser basalt far less eroded. Now, in such a case, you have to postulate changing wind directions to explain the lack of a "shadow" of non-deflated dust, but it's not hard to believe that winds would vary enough to accomplish the job. Especially over the thousands (maybe millions) of years that basalt has been sitting there, the sandstone underneath it slowly blowing away in the wind...

It can be hard to apply common-sense "gut feelings" about erosion processes to aeolian weathering, especially in such a thin atmosphere, since it takes so *very* long for that thin air to erode the softer rocks down flat. Over the very long time that it takes to erode the sandstone flat, prevailing wind directions can change a lot, especially in a hilly region where we *know* atmospheric vortices are common.

-the other Doug

Yeah, I like it here a lot, too. A very welcome change from the signal-to-noise ratio of the Usenet newsgroups. I hardly ever visit the newsgroups anymore, and I think my blood pressure is the better for it...

Back to topic, the other real issue with either MER rocking itself out of a sand trap is that they don't have the horsepower to get the kind of momentum going that would be needed for such a maneuver. Even at a charitable estimate, the MERs creep along the surface more than they motor along. At the speed we can get the wheels moving, you can't push forward and then let gravity pull you back farther than the distance you pushed forward, which is how the rocking maneuver has to work.

However, unlike the dilemma all of us face when we get a car stuck in the snow, Oppy has an advantage -- not only does it have four-wheel-drive, it has *six*-wheel-drive. And four of the six wheels are independently steerable. That really does open up more possibilities than most of us are familiar with from terrestrial driving experience.

-the other Doug

Tang is an interesting subject, since Tang itself (the exact formulation that was sold commercially) never flew in space. The same people who made Tang formulated the various citrus drinks that NASA included in Apollo meal packs, but the formulation was slightly different from the commercuial product. And yes, after the Apollo 15 situation, in which low potassium levels were identified as a contributing factor to the bigeminal heart rhythms that both Scott and Irwin displayed (Irwin more than Scott), the fruit drinks for the LM crews on the remaining flights were enriched with potassium. Which encouraged stomach acid and intestinal gas production.

The citrus drinks weren't the only culprits for gas production, either. On Apollo 17, Jack Schmitt blamed the corn chowder for a rather pungent episode of gas-passing during translunar coast, and felt he had to warn Cernan about it when the corn chowder showed up on the menu for their first post-landing meal. Since they were going to begin EVA prep right after eating and Schmitt would be cocooned in his own suit (with his own stink) for the next eight hours or so, Cernan didn't seem too worried about it...

But every single American space flight through the end of Apollo ran across some level of problem with intestinal gas. On Apollo, this was partially blamed on leftover hydrogen gas bubbles in the drinking water (the water having been produced by combining hydrogen and oxygen in the electricity-generating fuel cells). One flight surgeon even tried to blame it on the 5 psia cabin pressure -- the rationale was that the intestines always contain a certain amount of gas, and that if you lower the outside pressure, the gas will, in response, increase in volume and push harder to escape. Of course, the body maintains the same pressure against the intestines at 5 psia as it does at sea level, so that argument never made a lot of sense... but it was put forth back in the 60s.

But for whatever reason, early American spaceflights were all flown in a cloud of methane at some point. The issue was made a lot more obvious by the fact that the smell of the gas can't dissipate, like it would even in an indoor room on Earth. With such a relatively small volume of air and limited scrubbing for aroma removal, *any* farting became immediately obvious and stayed around for hours. So even a normal amount of intestinal gas became much more obvious.

-the other Doug

"How do you know it's an abyss and not a shadow? Are you an areologist?"

"No... but I did stay at an Ultreya Inn Express last night."



-the other Doug

Well, why not? I'll only be 129 years old by then...

-the other Doug

It's something of a shame that John Young, one of the most capable astronauts who ever wore the pin, is remembered by most people primarily for two things:

1) The corned-beef sandwich he "smuggled" onto Gemini 3, and

2) The "acid stomach" comments he made on a hot mike (that he had *no* idea was hot) on Apollo 16.

Actually, my favorite moment in re the "acid stomach" incident during Apollo 16 happened the next day, near the end of EVA-2. Young and Duke were lobbying Houston for an EVA extension, so they could finish up their close-out without the need to hurry through it (and perhaps forget something, or screw something up). Since I have the exchange memorized, I can tell you it went like this:


Duke: Tony, how about an extension, you guys? We feelin' good.

Young: Yeah -- you said all we was gonna do tonight was sit around and talk! ((Young spoke the word "talk" like it was the most disgusting thing he could think of.))

CapCom Tony England: Oh, we like to hear you talk. Especially about the orange juice...


((Less than two minutes later, the Flight Director agreed to grant a 15-minute extension, to which Duke replied "Let's here it for ol' Flight! An Attaboy for Flight!" To which Tony added a spontaneous "yea!"))

BTW, I don't know how the otherwise excellent Encyclopedia Astronautica got this so wrong, but the story about Duke is actually about Pete Conrad, and it is an apocryphal story. Conrad, as anyone who ever spoke with him could tell you, used profane words as grace notes. He swore every three or four words, usually. In Bartlett's Quotations, the phrase "swear like a sailor" has a picture of Pete next to it...

Anyway, before Apollo 12, NASA PAO was having conniptions, convinced that their Third Man on the Moon was *never* going to be able to control his language. His LMP, Al Bean, even talked to Pete about it, saying he was really concerned that Pete was going to slip and swear a lot on the Moon. Pete told Al not to worry, he would be fine -- and that, furthermore, it was guys like Al, who rarely swore in everyday life, who would be *more* likely to slip up and swear on a live mike. Sure enough, Pete only swore once or twice, mild things like "damnits" under his breath, and Al slipped up five or six times.

Now, a naturally ebullient Conrad was absolutely ecstatic to be walking on the Moon, so as he went about his business, he hummed and sang little wordless ditties. The apocryphal story was that NASA had convinced Pete to undergo hypnosis, and that he was under a post-hypnotic suggestion forcing him to hum or sing whenever he felt like swearing. But it's not true -- Pete, good to his word, knew how to keep his language fit for a G-rated audience when he was on a live mike.

As for Duke, he was a good ol' Carolina boy, but also a devout Christian who, after his astronaut career, took up a career in the ministry. Charlie was naturally pretty mild-mannered and soft-spoken, with that marvelous deep-South accent that will forever be linked in my mind with the moment men first landed on the Moon (Duke was the CapCom who responded to Armstrong's declaration that Eagle was now Tranquility base with an emotion-choked "Rog, Twan - Tranquility, we copy you on the ground. You got a bunch of guys about to turn blue. We're breathin' again -- thanks a lot.") His swearing, as revealed on the onboard recordings, was always very mild and infrequent. So this entry is a little unfair to Duke.

I need to remember to write Mark Wade an e-mail about this...

-the other Doug

Yeah -- while I really enjoy my Apollo CDs, I miss the commentary a bit. Somewhere on my original cassettes from 33 years ago, I have John Chancellor commenting on the exuberance of Young and Duke, saying "Do you think that when these fellows come home from the office at night, they say things like 'Gee, the key fits in the door! Out-STANDING!'?"

-the other Doug

That's exactly what it sounds like. No wonder she dug in so deep.

If we get out of here, it sounds like we're going to be going a lot slower and with a lot less "blind drive" action...

-the other Doug

Very nice -- but what about those few of us who still have relatively small monitors and are rather forced to use 800x600 resolution? There are still a few of us out here...

-the other Doug

Observing Earth from Mars would manifest the same issues we have observing Venus from Earth, to wit:

1 - When Earth is closest to Mars (and therefore appears larger and, you would think, brighter), it's always going to be in a crescent phase.

2 - It's also going to be relatively close to the Sun, appearing (like Venus does to us) as a morning or evening star. So it will never be as bright as it would be if it were full-disk-illuminated at closest approach.

Because Earth at its closest (and therefore at "best seeing") shows a crescent, you'd have just a small, tantalizing slice of illuminated area to observe. Within that slice, I would think you would see a mottled blue-and-white appearance, with occasional brownish-greenish land masses rotating through.

It would be exceedingly difficult, starting from first principles, to separate the transient cloud formations from the static land mass formations with anything less powerful than a major observatory. The polar ice caps would be pretty easy to pick out, though. So, mapping Earth's surface using telescopic images from Mars would be a challenging exercise.

As for man-made lights on the Earth's unlit side, they would be detectable only by long-period exposures, I think, not visible to the naked eye. Even at its slimmest crescent, the illuminated portion of the Earth would be *so* much brighter that, as long as it was in view, I doubt you'd see any of the relatively dim stretches of man-made light from the cities and towns experiencing planetary night. But a really good telescope and good, discriminating astrophotography software would probably be able to see night-time ights.

All in all, though, trying to characterize the Earth's surface, atmosphere and climate telescopically from Mars would be a challenging and confusing exercise. I think the Martians would probably be highly tempted to send a few probes in, to get better resolution and a better view of the daylit side of the planet.

-the other Doug

Without any APXS, Mossbauer or mini-TES data, just from looking at the rock, I'd guess it's a chunk of basalt that was dropped onto the hills from some nearby impact. It's more resistant to erosion than the softer rock that makes up the bedded unit of which Methuselah is an outcrop (thereby attaining the "perched" appearance after underlying rock has eroded out from under it).

Also, while I don't know what kind of false-color attributes this particular image has, similar false-color images out on the lava plains at Gusev have showed chunks of basalt highlighted in blue tones. So, if this image uses the same false-color assignations, I'd say the color suggests basalt.

-the other Doug

You know, it looks a little like Huygens might have landed on one of the "pebbly"-looking sandbar-like stretches that extend out from the brighter, obviously higher "islands" in the channel areas.

In other words, maybe Huygens didn't land in the channel itself, it landed in a sandbar. So, it's possible that lower, deeper areas of the channels are in fact filled with liquid. We just landed a meter (or less) above the "waterline" on a sandbar...

-the other Doug

Yep, that's the one -- though that's a very reduced version. On a larger version I saw, supposedly full resolution, you can zoom in and make out human figures on the ships and docks. One guy, you could make out the distinctive shape of a Soviet Navy officer's hat on his head.

Let's see, the one-and-a-half-foot resolution they mention is about 50cm, right? So, that's in the ballpark of what I was talking about.

One thing to remember, of course, is that this was a film-based system. DoD could, by the early 1970s, achieve that level of resolution on film that they de-orbited and processed back on the ground. Achieving similar resolution real-time, from electronic imaging sensors (vidicons and later CCDs) took DoD a LOT longer, and I'm sure that the current systems (which are what we really ought to compare to HiRise) are tremendously larger and heavier than the early film-based KH that took the above snapshot... Heck, considering they were using Titan IV's to orbit them, I'd have to say they would *have* to be bigger and heavier. Certainly bigger and heavier than we could even think about sending to Mars right now.

-the other Doug