I have to admit, when I saw the Blackstar story, that West Wing plot line came to mind. Amazing, how sideways-prescient some pieces of fiction end up being...

It's really a moot point, since everyone at Houston had convinced themselves that Columbia just couldn't have been seriously injured by a little foam -- and since, even if the bird was damaged beyond a safe return, they didn't think there were any options. I just wonder how much more careful they might have been if they thought there *were* options...

-the other Doug

I'm not trying to imply conspiracies -- though it seems to me that AW&ST has already done so, in saying that such a thing as Blackstar may have existed for as long as 15 years and *no one* has said anything serious about it until now.

All I was trying to do was invite y'all to consider the consequences if Blackstar was a manned SSTO that actually worked, and that was in operational service during the final flight of Columbia. I suggest nothing except that y'all use your own imaginations as to what kind of recriminations could come out of something like that...

-the other Doug

Good point, Alex -- NRO probably would run such an asset, not NSA.

-the other Doug

You also have to remember that NASA HQ has ben steeling themselves to cancel a mission that's blown its cost cap for a while, now. Recall that HQ told Steve Squyres that Spirit and Opportunity would look great sitting in a museum -- it came very close on the MERs.

It was bound to happen to someone, eventually. NASA HQ was looking to make an example of someone, and now they have.

-the other Doug

Amen to that, brother. It's a testament to this place that I've never even had the urge to look and see if it's possible to filter someone out, here.

-the other Doug

Just a little gedankenexperiment, here -- anyone care to ponder the ramifications, if the NSA had a manned SSTO vehicle, capable of detailed reconaissance from low orbit, operating at the same time that NASA had an injured bird in orbit?

I grant you, NASA failed to realize that their bird was injured... and failed to even request the kind of NSA imaging that Blackstar might have been able to provide. Much less been *aware* that such imaging, or such a potential rescue vehicle, might even be available.

But, if Blackstar *does* exist, *was* able to fly into orbit, and *was* capable of being manned -- that opens up a whole new can of worms when it comes to decisions made affecting Columbia's condition and the perceived lack of options the NASA managers thought they had in the event their bird *was* injured.

-the other Doug

And don't forget, ESA will claim in every picture they release that they have made the exciting new discovery that the Moon's craters get smaller and smaller as you get closer and closer...



-the other Doug

Come now, Watson, you know my methods -- simply apply them.

First, we observe rocks on the surface, which have obviously been eroded by aeolian forces for millions, if not billions of years. Second, we see massive erosion of landforms -- upon which sit rocks which seem not to have moved for millions, if not billions, of years.

By process of elimination, we can see that aeolian forces, even over billions of years, could not have been the sole erosive force acting upon Martian landforms.

Whatever remains, however unlikely, must be the truth...

-the other Doug

Hmmm... I've seen Mars directly, with my own eye, through a 3-inch reflector and a 10-inch reflector. In both cases, the dark markings I could make out really looked distinctly greenish. No filters involved, and I don't think the mirrors in question failed to reflect any given wavelengths, or emphasized any others.

Is it possible that there *is* a certain greenish tinge to the dark-colored regions of Mars?

-the other Doug

If we're going to delve into the realm of Looney Tunes physics, the answer for *any* lander is perfectly obvious.

You put your lander on a scale automobile. You put a very precisely measured amoutn of gas int he automobile. The car runs out of gas just an inch before crashing into the surface, stops dead (but perfectly intact) that one inch above the ground, your lander hops off, and the car *then* continues on to crash into smithereens.

I think we're researching the wrong propulsion fields -- we need to investigate alternate physics, concentrating on Looney Tunes physics. There are so many things to take advantage of there!

-the other Doug

Just for y'all to chew on -- Opportunity spent more time at Olympia than it was originally scheduled to survive for its *entire* primary mission.

Boy, it seems like there's something wrong with that -- but it's the truth.

-the other Doug

Scarp retreat is exactly what I think we're seeing at Mogollon and Payson. It's my belief that the original Erebus was only about twice as large as Endurance, and that it struck into the western side of the bowl of an even older, larger crater (Terra Nova) that had already been mostly filled with dunes, evaporite and sediments. (If Terra Nova had been an unfilled crater at the time of the Erebus impact, I would imagine that you wouldn't see such a pronounced east rim on Erebus, which lies roughly on top of what would have been the deepest portion of Terra Nova.)

Because the evaporite and weakly cemented sandstones are rather friable, scarp retreat ensued rather quickly, and continued even as Erebus' own bowl was filled with sand, sediments and evaporite. It probably continues slowly to this day -- Mogollon and Payson might be moving away from the center of Erebus at the rate of a few centimeters every hundred thousand years or so...

Remember, too, that most evaporites *shrink* a tiny bit as they completely dry out (think of the cracking you see in dried-out lakebeds). This process is complicated if the last stages of dessication involve ice as opposed to liquid water. There would be a tendency for an evaporite "cap" on the crater fill to shrink away from the crater rim a bit, encouraging a final subsidence along the rim line.

I think all of those factors are at work here...

-the other Doug

Well, Phil, I hope knowing that your work is extremely and thoroughly appreciated by people like me makes it worthwhile for you.

Though I imagine that, at the core of it, you're doing these for yourself, so you can see the Surveyor sites as they truly appeared.

But, whatever the reason you are doing it -- the work is appreciated.

-the other Doug

See, this is where we need some better modeling of the Big Whack to see what behaviors the models predict, over a set of possible variables.

For example, the energy of such a collision would obviously have been enough to vaporize a large amount of the impactor (which, at the size of Mars, is no mean feat). Would the proto-Earth have been completely re-melted and remixed, and thus proceeded through an either complete or partial re-differentiation? The core of the impactor is supposed to have "sunk" to the Earth's core and added its mass of (presumably) nickel and iron to our own -- wouldn't that require a significant, if not total, re-melting of Earth?

How much of the debris ring/disk that formed around the new Earth was composed of the impactor, and how much of materials from the proto-Earth? What materials would have been thrown farthest, and why? What materials would have re-impacted the new Earth, and what would have been pulled into the newly forming Moon? Is there some "magic line" in the size, shape and mass of the debris disk below which its water would be shared between the two new worlds, and above which the lucky Earth retained it all? (Remember, there is no hint that *any* water was ever retained by the Moon in its formation; its polar water ice seems to have been accumulated over the eons from subsequent ice-body impacts.)

Just how discrete would the impactor and terrestrial materials have remained after the impact? How thoroughly would the materials have been mixed? If the impactor had originally accreted in a different part of the solar nebula and had a different oxygen isotope ratio than the proto-Earth's, would the mixing be complete enough to create an amalgam isotope ratio that would, by necessity, be the same between the Moon and the new Earth?

Recall, too, that the Moon formed relatively close to the new Earth (something like 12,000 miles away when it accreted, IIRC), and that a tremendous amount of angular momentum was imparted into the system by the collision. The new Earth was rotating every 10 hours or so at that point. What effect would such angular momentum have on the gravity field, the magnetic field, etc.? And how would partial or total re-melting have affected the Earth's magnetic field, anyway? And how would magnetic field fluctuations and gravity field perturbations (especially as the new Earth was in the process of "swallowing" the impactor's core) have affected the materials in the debris disk?

Since the Moon formed so close to the new Earth, wouldn't it have orbited within the outer van Allen belt? How long did it take for the Moon to traverse the outer Belt? Or did Earth's disrupted core even generate a magnetic field for thousands, or even millions, of years after the impact? What affect would the total disruption of Earth's magnetic field (if that's what happened) have had on the re-accretion of water onto Earth from the debris disk?

Did all of this happen before or after the Sun hit its T-Tauri stage and sent powerful winds out to strip all of the rocky planets of their primordial atmospheres? If the Big Whack occurred before the T-Tauri winds, then could water on Earth have survived the stripping of the primordial atmosphere? If not, wouldn't that mean that Earth had to have accumulated all of its water well *after* the Big Whack?

Questions, questions, questions... I see all of these factors floating in front of me, provocative -- and I don't have the tools available to me to investigate the probabilities. It's frustrating!

-the other Doug

No, no, no -- the *ball* has to cross the plane of the ellipse line. That's all that's required.

Oppy is a pretty good running back, she's rushed for well over a thousand yards in this, her rookie season. But who are we going to get to kick the extra point?

-the other Doug

I just did a quick search, and it was actually nearly two years ago that I made the comment:

Post

If we want to keep talking about Meridiani craters being sinkholes vs. impact craters, maybe we ought to move the discussion over to the Opportunity forum...?

-the other Doug

Actually, since we're speaking of Mars, it's more like the ochre side... which sounds somewhat unappetizingly like a side of okra, if you're not careful.



-the other Doug

Doug, if you look back about a year or so ago, I believe I was suggesting that Eagle crater may well have been a sinkhole. Ever seen a sinkhole? They're not far from perfectly circular, and they're similar to many other round-impactey-type-features, and if you leave one in a dusty place for a few million years, aeolian deposition will raise an irregular rim around it...

That said, I think the odds of Eagle being an impact crater as opposed to a sinkhole are in the range of 80-20.

-the other Doug

Speaking of naming conventions for KBOs, we need to remember that there might be *thousands* of them out there.

There aren't thousands of names related to the Underworld out there. Heck, there aren't thousands of names of deities, period -- even if you add up all of the pantheons of all the religions from the dawn of civilization.

And most of the names of the deities from all of those pantheons have already been used to name at least one sky object.

I think it's possible we may be on the verge of seeing people being allowed to name objects they discover after whatever and whoever they want, as long as the names aren't obscene or offensive. So, how long will it be, I wonder, before we see bodies that are *really* named Xena and Gabrielle? Or Fred and Barney, for that matter...?

-the other Doug

The Messenger posted an interesting comment over on the asteroid/comet board, in a discussion about how comets are turning out to have much less water in them than we once thought:


Now then -- something with a mass like a large outer-planet moon hitting Earth most likely *did* happen -- it's called the Big Whack theory.

I have never seen any speculations on the *composition* of the impactor that created the Moon -- the only comments I have seen are those relating to oxygen isotope abundances which indicate that Moon rocks formed from roughly the same solar nebula composition as Earth did (which I've always thought could be in doubt, since the material that made up the Moon must have a pretty large admixture of material from the proto-Earth).

If the impactor (which had a mass roughly equivalent to Mars) was something like an oversized Ganymede, with a large percentage of ice around a chondritic rocky core, is it possible that *all* of the water ended up back on Earth, while the ring from which the Moon formed lost all of it?

I don't have the proper education or tools, myself, to model a Big Whack with an impactor composed of, say, 25% water ice by mass, to see where the water ends up and how it can be disassociated from the materials that made up the Moon. But it seems to me that the question of how water in the debris cloud could have been so thoroughly removed before the Moon formed must be answered, in any event, since there had to have been terrestrial water involved -- unless we postulate that neither proto-Earth nor impactor had any water. And *that* means we have to postulate no ice-body impacts onto Earth before the Big Whack and a whole bunch afterwards, to explain where the oceans came from.

Assuming, of course, that the oceans came from impacts of ice-body objects in the first place...

-the other Doug

Very provocative... I'm going to respond to this over on the Moon board, I think, for reasons that will become clear when y'all get there...

-the other Doug

I don't entirely agree. First off, Erebus is several times larger than Endurance. It would not have had a small rim when it formed. It would have had a very pronounced rim, a bowl shape, and a deep floor. As time went on, it would have suffered collapse along the outer rim, as the very steep faces of the inner walls of the crater are not stable over long periods. You get a characteristic scalloped rim as a result of the edges of the rim falling into the crater, widening and shallowing it.

According to my understanding of lunar crater development and aging, it takes the better part of a billion years for a crater the size of Erebus to become as wide and as shallow as mass wasting is going to make it.

Note, too, how Endurance has been partially filled with dust, but is nowhere near "filled" to the extent that Erebus is. And Endurance may well be more than a billion years old.

The problem with Erebus spending eons being worn down to a nub of a crater *before* the evaporites were layed down over it is that, according to curren theory, Mars was only wet enough for the large mass of evaporites we observe to have been laid down for a fairly short period of Mars' early history. My best guess is that there was simply not enough time for an Erebus-sized crater to have been worn down to nearly planar before Mars froze up and standing water was no longer possible.

I would amend your timeline as follows:

First - Deposition of some layered beds (mostly from dune formations)
Second - A shallow sea forms cyclically in the area, laying down layer after layer of evaporite
Third - A cluster of impact craters (including Erebus and Terra Nova) form after some of the local evaporite is laid down
Fourth - Deposition of the rest of the layered Meridiani beds and subsequent groundwater alteration, filling the Erebus-Terra Nova complex with evaporite shot full of hematitic concretions
Fifth - General raising of the land by volcanic uplift of Meridiani Terra south and east of Meridiani Planum, putting an end to standing water by changing the landform and raising it above the then-current "sea level" where seas were able to form
Sixth - Erosion of evaporite, formation of hematite-enriched soils, and dune formation
Seventh - Differential subsidence along old crater rim which offsets evaporite layer along old rim

I just don't think there was time for Erebus and the cluster it's associated with to form and degrade to a filled-in status and *then* have a Mars warm and wet enough to cover that over with evaporite. I think there had to have been evaporite formation both before and after the creation of Erebus.

-the other Doug

Very, very well said, David. I couldn't have said it better myself.

-the other Doug

This image, of the rim of Erebus, showing where the uppermost layers collapsed a la the collapses around the rim of Endurance, but with an almost-level paving of evaporite rock below the rover's wheels, just reinforces my impression that Erebus must have been inundated by standing water *after* it was formed. Perhaps a multitude of times.

Can anyone here say they don't see how it's impossible that the entire crater wasn't inundated by water after it formed? How else can it be *filled* with evaporite?

-the other Doug

Looks more like someone troweled a thin layer of concrete over a rougher surface. In panel-like sections. One panel, for whatever reason, has resisted erosion, but adjacent panels have been flaked off, revealing the pebbly surface below.

Man -- this stuff does look a lot like concrete, doesn't it? A naturally-occurring concrete, of course... which is sort of what sandstone is, I suppose.

-the other Doug