As for the mechanism bringing the bodies back together after a major impact, tidal dissipation immediately comes to mind. If the impact energy was enough to make one body at least partially plastic the dissipation would be greatly increased.

However explicitly calculating the effect on two highly irregular (and possibly inhomogenous) rotating bodies in probably very eccentric orbits would be quite challenging. Qualitatively I would guess that the tidal effects would first slow down rotation of both bodies until they became tidally locked, and probably simultaneously decrease eccentricity of the orbits. Once tidal rotational lock is reached any further dissipation would very slowly bring the bodies together.

Of course they could also have re-collided physically long before this. It all depends on the orbits.

It seems to me that an impact as large as the one on Thule would create enough momentum to separate the lobes, at least temporarily. Could the "ring" be a previous "attachment point"?

A tip. The papers are available at sci-hub.tw. Just input the DOI-numbers.

Yes. The process has actually been rather extensively discussed in the literature in connection with Archaean/Proterozoic glaciations ("Snowball Earth") since there is evidence for oxic conditions immediately after the glaciations. And hydrogen peroxide is actually found in measurable amounts in snow in Antarctica. Incidentally the quantity deposited increases in early summer when ozone is low.

http://rstb.royalsocietypublishing.org/content/363/1504/2755

http://www.pnas.org/content/103/50/18896

https://www.academia.edu/15042568/Productio..._photosynthesis

http://web.gps.caltech.edu/~jkirschvink/pd...iewAndModel.pdf

"The mention of "oxic conditions" is interesting. Anoxic conditions are not surprising on a planet with a CO2 atmosphere. However, what produced the oxic conditions? Where did the oxygen come from?"


There is actually an abiotic mechanism for producing appreciable amounts of oxygen photochemically in a cold glacial/interglacial environment. UV light will produce small quantities of hydrogen peroxide which will be stable enough at low temperatures to be stored in ice. When an interglacial arrives and the ice melts the hydrogen peroxide decomposes into water and oxygen.

Sci-Fi enthusiasts will note that if those observations in Zacatecas were really a fragmented comet it means that the scenario in S. M. Stirling's "The Peshawar Lancers" very, very nearly came true.

Some nice noctilucent clouds over southern Sweden last night. Tonight it's raining and solid clouds unfortunately.

The largest (known) young meteor craters are

Kara-Kul, 52 km, c. 5 million years
El'gygytgyn, 18 km, 3-4 milllion years
Zhamanshin, 14 km, 1 million years
Lake Bosumtwi, 10 km, 1 million year

It seems that at least Kara-Kul might be large enough for ejecta to reach escape velocity, particularly as it is at 3900 meters altitude, that means a lot less atmospheric drag (though I guess it was probably rather lower back then). Interestingly it is situated inside the Tien-Shan, so any ejected rocks would be fairly young sedimentary stuff (though I suppose the impact would turn them into instant metamorphics).

As for really old terran meteorites, I've pointed out before that the best (only?) chance to find out anything about what happened on Earth during the first 500 million years or so is probably to look for terran meteorites on the Moon. It seems that the Late Heavy Bombardment wiped out almost every trace of what happened before c. 3800 million years ago.

It is quite interesting to compare the Tithonius dome with Mount Sedom near the Dead Sea, which is also an evaporite dome with karst topography (though in rock salt rather than gypsum), and also situated in a rift valley. You can see it in Google Earth at 31 deg 4 min N and 35 deg 23 min East. Here on Earth a salt dome can of course only survive long enough to develop karst topography in an extremely dry area, it would literally melt anywhere else.

By the way it's Acta Carsologica, not Carstologica. It's an Croatian journal. Karst is originally a croat word: "krs", however a vowel was added when it became an international word, non-croatians tend to find word like krs, grk and krk difficult to pronounce.

Another large fireball. This one over southern Norway and parts of Sweden. It probably impacted near Oslo in southern Norway. Details here (Norwegian):


http://www.bangirommet.no/pages/news/ildkule10.html


They are calling for more observations to try to pin down the impact site. I don't know if UMSF have any members in the area, but just in case....

There is actually 87 versions of UMSF from April 2005 to August 2008 at archive.org:

http://web.archive.org/web/*/http://www.un...paceflight.com/

A rock ejected from a large impact doesn't have to go into a stable orbit that subsequently decays to end up almost anywhere on a planet. A lot of the ejected rocks go into very excentric "orbits" with a perigeum (or periwhatever) below the surface of the planet and therefore re-enters after less than one orbit.
This can occur almost anywhere since the planet rotates while the rock is in orbit. Computer modelling usually shows a marked concentration of re-entries near the antipodal point of the impact with a westward "trail" (if the planet rotates eastwards) but some rocks will impact almost anywhere on the globe.

It has actually been suggested that the Earth had a temporary ring system in the early Oligocene:

http://www.nature.com/nature/journal/v285/...s/285309a0.html

The problem is that even if there were low-latitude icecaps in the past, they would almost certainly have been "cold-based", i. e. frozen to the ground. Such icecaps leave very little trace of their existence, certainly none of the "classical" signs like striae, drumlins, eskers etc. There might be a some glacial erratics, left behind when the icecaps melted.

The best chance of finding traces would probably be in volcanic areas. Subglacial volcanoes have a number of peculiarities and geothermic energy in such areas might even raise subglacial temperatures to the pressure melting point in which case "classic" glacial landforms might occur.

Since these impacts are apparently fairly frequent (since we have observed two in a short time) and the "gunk" produced should be fairly stable in the low temperatures prevailing in the upper atmosphere one wonders how much "gunk" accumulates and to what extent it contributes to Jupiter's colourful atmosphere.
I would expect that the molecules will ultimately sink deep enough into the atmosphere for the heat to break them up into simple molecules again, but that should be a slow process.

Some were visible over southern Sweden last night. None tonight though, at least not yet.

Is there any way to reduce the aperture external to the camera? There is unlikely to be any structure with a suitable pinhole to look through, but it might be possible to place the MI so that part of the aperture is blocked by the MER structure. Would this work? Most camera apertures become rather asymmetric at small apertures, but this does not seem to have much of an impact on the image quality.

Low humidity has a very strong impact on the reliability of electronics (and on mechanical components too, as a matter of fact). The Swedish armed forces have decreased down-time and maintenance costs dramatically by keeping aircraft and vehicles in humidity-controlled environments when they are not in use.

Also I would imagine that MER electronivs were not constructed for long-term viability in humid conditions.

For all UMSF readers whose Hollywood careers have been stymied because you have green skin, tusks and four arms: here at last is your chance!

I hope so. There is at least four old beach levels in that picture, and possibly a fifth.

That is not a very strong argument against it being an old shoreline. Old shorelines are often deformed by subsequent earth movements. Even the shorelines of Lake Bonneville that you mention are about 150 feet higher in the central part of the basin compared to the edges because of isostatic rebound after the lake disappeared, though this is not obvious because the change is very gradual.
In a more seismically active area like Italy the level of the shoreline from the prevous interglacial (just 125,000 years ago) varies from +170 to -130 meters.

Even a little better than that. During the early Eocene (c. 50 million years ago) there were alligators on Ellesmere Island (about 79 degrees north, and about the same then). This suggests that arctic temperatures were a bit over 30 degrees warmer than at present. Oddly enough equatorial temperatures were only slightly warmer than now.

The "Japanese version of the Me 163 rocket plane" is actually a Mitsubishi J8M1 Shusui, and while closely based on the Me 163B was actually to a large extent a new aircraft since the japanese had only partial technical data on the Me 163.

To return to nprevs suggestion about rocking, this is the preferred way of getting yourself loose when stuck in snow here in Sweden: You gun the car for a moment, then unclutch and let it fall back. However it will move a little bit past the equilibrum position, so you catch it on the return and gun it again and so on. If you time it right the oscillation will gradually build until the car gets loose. I was taught the technique for snow, but it works just as well for desert sand and laterite clay (I've tried both). Surprisingly the technique does not seem to be generally known in other parts of the World.
I don't know if such short bursts of power are practical for MER, and the timing as I said, must be precise. Possibly it could be tried in the test-bed.

Also I would like to comment on the possible use of the IDD for pushing. It might make a difference. I remember a case when two people pushing (I was one of them) was enough to get a ten-ton truck unstuck.

A difficulty would be how early it would be possible to calculate the orbit with enough precision to know whether an incoming comet would be a threat. If the comet makes a tight turn around the sun a very minor error might become very large, so you might have to consider quite a few comets as threatening initially, though the number would decrease as they come closer in. Also comets can break up and spread out as we have all seen.