Landing may be easy, but surviving very long after landing is not. It's not just hot with very high pressures down there on the surface, it's very chemically reactive, too. For such a geologically young surface, have you noticed how nearly all of Venera landing sites feature rocks that have been flattened right down to the ground? The conditions on the surface of Venus grind the very rocks down to flat, even surfaces.

That's what I call a hostile environment.

And exactly how close are we to developing "heat-proof electronics," anyway? It's not like designing a spacecraft to endure solar heating from, say, Mercury's orbit, since any spacecraft in a vacuum has a shadowed side that can be used to dump heat. It's much more difficult to cool something when it's got superheated air or rock on all sides and all exterior surfaces.

I just think it's premature to think about roving vehicles on Venus. The balloon-lifted drop-and-grab probe, however, is an excellent idea and much easier to design -- it lets you store heat temporarily and then get rid of it after the probe ascends to cooler levels of the atmosphere. That's a far less challenging engineering problem than trying to operate continually in such an environment for more than a few hours...

-the other Doug

"Texas has nothing in places that other nothings don't even have places."

-the other Doug

"If I had to give this country an enema, I'd stick the nozzle right here in Texas!"

-Lee Harvey Oswald, from the film "Executive Action"

I wholeheartedly agree -- there may well be other explanations for the magnetic features that we see (even though they are so very poorly resolved) in the southern highlands. It's interesting, though, that there are *no* anomalies (at the current resolution limits) around the easily identifiable impact basins, such as Hellas and Argyre. There is very little remanent magnetism at all in the basin floors and ringwalls. Which argues that Mars' magnetic field died before they were formed.

I'm just afraid that trying to reconstruct ancient landforms in the southern highlands is akin to observing an omelet and trying to reconstruct the chicken that laid the eggs. Impact modification has been so extensive and so drastic that it's nearly impossible to identify pre-impact landforms in the underlying crust. Add to the impact modification the stretching and cracking of much of the surviving ancient southern highlands crust due to tectonic response to the immense, and far younger, lava structures of the Tharsis Bulge, and it becomes nearly impossible to identify with any certainty *any* topographic features in the highlands that might pre-date both the high-impact-flux era and the Tharsis construction era.

I like your idea of powered orbiters. I despair that we'll never see the funding required to fly them, but they would be invaluable in answering some basic questions about Mars' early history. I think it's important to find out whether or not any other planet in the solar system has ever displayed plate tectonic processes, since those processes are so important to the history and ongoing evolution of our own planet.

-the other Doug

So, what Mars (and the Moon, for that matter) seem to lack, in the process of granite development, is plate tectonics, eh?

Now, while Mars lacks any obvious signs of plate tectonics in its current landforms, there is magnetic "striping" observed in some of the ancient cratered southern hemisphere, particularly in the Sirenum region. While it's not as distinct as the striping in, say, the Atlantic Ocean floor, there are definite regions that feature alternating remanent magnetic fields with reversed north/south orientations. That would argue, at least with some force, that crustal spreading occurred in Mars' ancient past. You would think that crustal spreading would require at least two floating plates and a subduction zone somewhere along a plate boundary -- unless you subduct somewhere, you can't spread for very long anywhere else.

On Earth, subduction seems to require an oceanic overlay to work properly. Now, back when Mars had a molten core and generated a global magnetic field (a requirement for the creation of the remanent magnetism observed by orbital sensors), and when this crustal spreading would have been occurring, Mars might well have had a fair amount of standing water. Perhaps even oceans. And since subduction zones naturally form rifts that would collect standing water, you could argue that Mars may well have had all of the processes in place required to make granite.

Perhaps what Mars did *not* have was enough time during which active plate tectonic prcoesses were occurring to form significant amounts of granite. Earth's oldest granites are, what, 2 to 3 billion years old? If it took a billion years of plate tectonics on Earth to build up significant granitic deposits, maybe that tells us that Mars only sported plate tectonics for a relatively brief time, on the order of a half-billion years or less.

Of course, that still doesn't explain why we don't see more quartz on Mars. Since quartz is one of the ingredients of granite, maybe some other factor (possibly simply a compositional difference) limiting quartz formation is also partially responsible for the lack of granite on Mars...

-the other Doug

Can *you* think of a better way to get people to want to go to Mars than by putting Las Vegas up there?



-the other Doug

This is more of a general question/comment about Martian geology, but since Oppy is in such a unique environment (unlike any of the other landing sites we've visited), I figure it belongs here more than anywhere else.

As far as I've been able to tell in my reading of the results of the various Mars probes, there doesn't seem to be much in the way of granite on the surface of Mars. There's a lot of basaltic and andesitic lava-rock (with a lot of olivine, pyroxene and even ilmenite), some ancient feldspathic/anorthositic rock, a lot of sulfates and other salts, a lot of rusted iron -- but little to no granite.

There's almost no granite in any of the lunar samples, either. Quartz also seems to be very rare, both in lunar samples and in what we see on Mars.

Has anyone here heard any good theories on why Earth produced so much granite and neither of the other rocky bodies we've looked at in detail seem to have much, if any?

-the other Doug

Heck, I remember thinking that the plan to drive all the way to the Columbia Hills, with an estimated arrival date of Sol 160, was outrageously optimistic. I never thought Spirit would last anywhere near long enough to reach the hills -- as I recall, my exact words were "Yeah, right. Good luck!"

Boy, am I glad I was wrong!!!

-the other Doug

Not in the current terrain, of course not. But when we get out of this, we'll be traveling out of this terrain into different stuff -- and if they decide to retreat back to "safer" ground and approach Victoria from a different angle, over the darker ground with 5cm drifts as oposed to the 70cm+ dunes in the etched terrain, we could easily get back to 100m blind drives again.

-the other Doug

I wasn't aware of the competition at the time, but in the spirit of Phobos and Deimos, I would have entered the names Fear and Loathing.

Not that I would expect NASA PAO to *ever* select those names...

-the other Doug

That's because Ares Vallis and Chryse Planitia have a lot in common -- both appear to have been carved by catastrophic flooding events. Such events pick up rocks, carry them along for up to hundreds of kilometers, and dump them out in characteristic ways, which are visible at both sites.

The problem, of course, with that is that both sites are littered with rocks picked up somewhat randomly along the flood path, so the surface rocks don't always particularly correlate with the underlying geology. But for a good (if somewhat random) sampling of diverse rocks from different landforms, they were both good landing sites.

-the other Doug

Originally, the 50 flights per year rate was based on 10 flights per year for each vehicle in a 5-orbiter fleet. The idea was that they would turn around each shuttle in about four weeks. When I saw exactly how much tear-down and rebuilding had to be done after each flight, I knew they would never, ever approach that launch rate.

And because they would never even get close to that rate, they couldn't bring the per-flight cost down to where launch costs per pound would have encouraged more and more launches. I don't think the concept that "lower per-pound launch costs will result in more business for space launches" is totally invalid -- in other words, bring the costs down and you'll have more payloads.

The *real* problem is that you'll never generate a need for a high flight rate until you bring the costs down, and no one will spend the money to develop a system that can be rapidly turned around and re-used because you can't demonstrate that there is a need for it. It's a vicious circle.

It also doesn't help that most of the companies capable of building such a launch vehicle have *zero* interest in bringing down launch costs. They're making huge profits by building three or four billion-plus-dollar throwaway rockets per year. They don't want demand to increase -- as long as they keep the launch costs high, they make more money. So they don't even make a decent try at it...

-the other Doug

I would vote for this, too. I always have a lot better luck with the cross-eyed technique, and I currently don't even own a pair of red/blue glasses. (And they don't work very well when you *also* wear real, corrective glasses.) In general, the anaglyphs don't work well for me at all.

-the other Doug

And, let's face it, we have successfully landed probes at five locations on Mars, and four out of those five locations have very, very similar types of terrain -- rock-strewn with windblown dust/sand drifts building up in various places. Only Meridiani has shown a different type of terrain.

Of course, there are a lot of different terrain types on Mars. But I think a lot of the flatter plains units (the places we're most likely to try landing) are going to be rock-strewn. So the rocker-bogey wheel system is probably going to be the best approach for most future rovers.

-the other Doug

Does anyone know if this feature will ever be in proper geometry for the RADAR to take a good look at it?

-the other Doug

There is a suspicious, very dark splotch to the east and somewhat to the south of Oppy's original landing spot. I don't have the images in front of me right now, but my (admittedly non-perfect) memory says that it's something like one-third of the distance we've already traveled to the south, and something like one-quarter to one-half that same distance to the east. Again, I'm reaching with my memory, here, but I seem to recall it's just a little east of straight north of Victoria, and maybe 1 to 1.5 km north of it.

The only other really dark splotches we've seen are the marks made by heatshields hitting the ground at high speed. I know there was a discussion in this forum, back before the trek to Victoria won out as the extended mission objective, that this dark splotch might well be the impact point of the cruise stage, or at least of the largest piece of the cruise stage that survived to the ground. There was a certain amount of sentiment for visiting that feature before going anyywhere else.

Depending on the orientation of the tiny dune craters in relation to this dark splotch, it night be a possibility that whatever made the dark splotch could have ejected a pebble that traveled as far as Oppy's current position...

-the other Doug

The one big problem I have with all the nice math above that calculates the minimum speed of a primary impactor is that, according to those numbers, nothing of *any* size that reaches the surface will be going slowly enough to avoid being vaporized upon impact.

And yet, Oppy found an iron meteorite. Just sitting on the ground. Didn't even dig a hole.

Which means that the numbers above *cannot* describe every possible primary impactor. Those equations fail the test of explaining observed phenomenah.

As I have said on a number of occasions, many objects break up explosively under entry heating conditions. Some of those objects are ejected from the "parent" body in such a way as to reduce their velocity relative to the ground to *much* slower speeds than are calculated above.

For example, on Earth, there is absolutely no trace of the main impactor that creted Meteor Crater in Arizona. However, there were literally hundreds of small (fist-sized, usually) chunks of unvaporized meteorite found *outside* the crater. Some of them don't apear to have been shocked or anything. So, while the main impactor that hit Arizona was vaporized, smaller pieces of it were shed during its descent in such a way as to reduce their impact speed and allow them to strike the ground and remain intact.

In other words, if a medium-sized body enters Mars' atmosphere at a shallow angle, it *can* break up explosively and some of the fragments can be slowed by the energy of the breakup (relative to the main body's motion) such that small pieces can drop to the ground at *much* sower speeds than that of the main body.

It just seems to me that if we observe a meteorite just sitting out on the ground, we have to include in our discussion of impactor sizes and terminal velocities events that will allow what we observe to actually happen.

-the other Doug

Actually, while no one has ever actually said it on the record, I think the MER teams were going to "informally" name MER-A Marvin and MER-B Duck Dodgers (or perhaps just Daffy), but that NASA's PR flacks got the idea it would be *so* much better to have some fifth-grader name them.

In any event, there are indeed mission patches for each rover, with the MER-B patch featuring Daffy Duck as Duck Dodgers (in the twenty-fourth-and-a-halfth-century!) and the MER-A patch featuring Marvin the Martian. Here's a link with a decent view of both patches:

MER mission patches

I sort of wish they had used the cartoon names -- Spirit is an OK name, but Opportunity is just not a proper noun, and never will be. It's a terribly awkward name for a rover...

-the other Doug

Wile E. Coyote is the cartoon character who is always in pursuit of -- and never catches -- the Roadrunner in the many, many Roadrunner cartoons produced by Warner Bros. from the 1950s through the 1970s.

Wile E. uses every hare-brained scheme in the book to try and catch the Roadrunner (often with the help of outlandish products and weapons from the ACME Company), which always backfire on him. Most of the time, he ends up flying off the end of a cliff, hangs in mid-air long enough for a reaction shot, and then falls several thousand feet to make a "splat" on the desert floor below. He then always walks away and lives to pursue another day. It is this ability to survive what would appear to be non-survivable falls and impacts that would lead one to assume that the Deep Space Two mission was relying, to one degree or another, on the Wile E. Coyote theory of physics...

-the other Doug

I don't have the images right at hand, but I have seen a few nearly-erased craters in the dunes, too. If I recall correctly, there is one very good example of a fresh crater and one very good example of a nearly-obliterated circular depression of similar size. Also if I'm not mistaken, they were taken from the same location, so they were located on fairly near-to-each-other dunes.

Unless we sit for months at a time at one of these highly drifted/duned locations and take a bunch of images over a fairly long baseline, I don't think we can state with any kind of certainty the time needed to fill in such a little dimple crater.


Some of the dunes near Oppy's current position show layering, so we know the dunes have built up over some span of time. And, of course, dune/drift formation is by definition a constructive process whereby new material is slowly built up onto the duneforms. So, depending on the speed of dune/drift formation (and dune/drift erosion -- it goes both ways, after all), these tiny craters could be years old or millions of years old. But since we see degradation of tiny craters, I'd have to think that really fresh-appearing tiny craters are probably not ancient.


You can tell from the lower limit of the size of what appear to be primary impact craters the size of impactors that get through the air. On Mars, these *seem* to get as small as a few meters, which can be made by marble-sized to fist-sized chunks traveling at cosmic velocities. The tiny craters we're seeing in the dunes are more likely caused by something smaller than a peanut, probably less than half the size of a shelled peanut, or smaller -- if they are primary impacts.

I'm really not convinced that these are primary craters, though. They look exactly like what I would expect from a pebble or stone ejected from a nearby impact, traveling at relatively slow speed, hitting the side of a powdery-sand dune. I would say the most likely thing to have caused the really fresh one, if it *is* a primary impact, would be a small survivng piece from the cruise stage that broke off and traveled downrange a bit. But again, that would be very, very difficult to prove.

-the other Doug

Yeah -- the theory I heard was that either they buried themselves too deeply to be able to send radio signals back out, or that they hit a hillside or inner crater rim at nearly right angles. While the impact at the semi-grazing angle that was anticipated would not have exceeded its designed G-load survivability, if it hit at more of a right angle, the sudden deceleration could exceed the design limits.

However, the most interesting reason for their failure I ever heard was in the TV series "The West Wing," which dealt with a fictionalized loss of both MPL (called "Galileo V" in the episode) and its two accompanying hard-landing probes. When told of the plan to crash-land two probes with the expectation of gaining telemetered data from them afterwards, the Josh Lyman character responded (quoting from memory), "Hasn't the Wile E. Coyote theory of physics been pretty well disproven?"

-the other Doug

From what I've been able to piece together, the final two candidate landing sites for the Mars Surveyor 2001 lander (which, of course, was canceled after MPL failed) were the Isidis Rim and what was then being called "the Hematite site" in Sinus Meridiani -- in other words, the site eventually selected for MER-B.

Can you imagine what would have happened had they sent an immobile lander to Meridiani and it landed out in the middle of the flat, featureless plains? With no outcrop in direct line of site?

We would have identified the blueberries as the source of the hematite seen from orbit, but would have had little to no clue as to how the blueberries had formed -- we would never even have seen the evaporite with the concretions eroding out of it. We would have no clue whatsoever that the dark mantling was the debris left over from the erosion of the soft, salty evaporite rocks, which would have left us without an all-important context for the soils we could observe from the lander. (Yes, I know the 2001 lander would have carried Marie Curie, Sojourner's back-up, but depending on where it landed, evaporite outcrop could well have been completely out of reach of the second Brave Little Toaster on Mars, as well...)

So, MER-B would have been sent somewhere else, and our understanding of Mars would possibly be a whole lot less developed than it is right now.

I guess the point I'm making is that the failure of MPL might have been a blessing in disguise -- it led to a chain of events that put the right instrument on the ground in the right place, which might well not have happened had MPL worked and the 2001 lander been sent to Meridiani.

-the other Doug

The freshest of the tiny craters we've seen in these dunes *does* have a raised rim, though.

I just have to figure these are little secondary impact craters, caused by small stones ejected from a larger impact somewhere nearby. Either that, or the freshest ones *may* be from stray bolts, nuts or flakes of paint that came off the lander's cruise stage and survived to hit the ground. But that last is *awfully* hard to prove.

-the other Doug

I believe she did wheel turns for about 40 meters of driving without moving at the end of that last blind drive. I also believe I have read that it will likely take more turns than that to get her out -- but the exact number, no one knows.

-the other Doug

Boy -- the "smile" sure looks like a portion of a crater rim to me. Could differential solar heating of the inner rim of a crater wall cause it to heat up enough above its surroundings that other chemical processes would take place and give you a combination of topographic control of heated atmosphere and a noticeable difference in composition?

If the smile is a crater wall, the entire crater has been degraded -- the "upper" portion of the circle is not apparent, and there seems to be dark deposit "ponds" at places where the upper portion of the rim wall ought to be...

-the other Doug