Interesting crater on Thebe

vogon13 · May 6, 2006

Thebe (an otherwise obscure inner moon of Jupiter) has a rather largish crater on it. In fact, the moon seems to be little more than a convenient roost for the crater. Any larger an impactor surely would have zorched this little guy. {I am also trying out the picture self-approval thingy} <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

vogon13 · May 6, 2006

Wow, I didn't crash Uplink, or the internet, for that matter. I guess I now have 1 computer skill. <img src="/images/icons/laugh.gif" /> <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

JonClarke · May 7, 2006

Wow! Bit like Phobos and Stickney. <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

qso1 · May 7, 2006

Or the big crater on Saturns moon Mimas. <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

JonClarke · May 7, 2006

Indeed, although I suspect that Thebe is more like Phobos in size, seeing its so irregular. Jon <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

qso1 · May 7, 2006

As I recall, it is pretty small and probably right around the same size as Phobos. <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

thepiper · May 7, 2006

Yes, just like Mimas (left in the photo below) and Tethys (to the right). Presumably, impacts should have shattered the tiny bodies and so the cratering is likely from another source.

qso1 · May 7, 2006

While the crater may be from another source, I wouldn't rule out the possibility of impact because we don't know for sure if there was enough energy to actually destruct the moons affected. Good example of Tethys, I'd forgotten that moon had a large crater. That crater looks like its filled in somewhat over the millinia. <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

brandbll · May 8, 2006

hey if a moon like tethys came in contect with Saturn's rings, what would happen? <div class="Discussion_UserSignature"> You wanna talk some jive? I'll talk some jive. I'll talk some jive like you've never heard! </div>

qso1 · May 8, 2006

Theoretically, since the rings are made up of particles, most of which are probably smaller than cars, Tethys would in effect, be getting snowed on at roughly the equatorial plane of the moon since its diameter is larger than the thickness of the ring plane. There are a lot of variables to consider however, such as the angle at which Tethys would enter. In most cases, I also suspect Tethys would have a more visible effect on the rings than vice versa. <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

JonClarke · May 8, 2006

Both Stickney and the large crater on Mimas are less than the maximum possible size for a crater on a body, though not by much. Jon <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

vogon13 · May 8, 2006

Depending on the mechanical strength of Tethys, disruption as it passed thru the Saturnian Roche limit on it's way too the main ring system could occur. Might get the rings embiggened. (to use one of Yevaud's favorite words) <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

brandbll · May 8, 2006

So, technically if it crossed at a bad angle it would get destroyed? It would be crazy to see one of the moons after it was briefly in there. Also, is that possible to happen to Tethys while Cassini is there? <div class="Discussion_UserSignature"> You wanna talk some jive? I'll talk some jive. I'll talk some jive like you've never heard! </div>

vogon13 · May 8, 2006

No, it won't happen while Cassini is there. <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

vogon13 · May 8, 2006

Perhaps the formation of the crater occured when Thebe was bigger. The impact fused the materials under and around the crater into a more monolithic form, cone shaped and centered on the crater. Then a subsequent bigger impact on the other side of the original Thebe blew away all the rest of the moon except the consolidated materials around this fascinating crater. Plausibly weird? <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

qso1 · May 8, 2006

Forgot about the Roche limit. That would do Tethys in. <div class="Discussion_UserSignature"> My borrowed quote for the time being:There are three kinds of people in life. Those who make it happen, those who watch it happen...and those who do not know what happened. </div>

mikeemmert · May 9, 2006

Jon: How do you get this "maximum possible size"? Is some velocity assumed for the impactor? What is that velocity? Can you explain why these craters look so similar? Why there are only one or two? I think all these craters came from low-energy impacts from objects formed at the Lagrange points 4 and 5 of the bodies and Saturn. A body coming from a Lagrange point would impact at the escape velocity of the moon in question (or planet, beyond the scope of this post). Mimas, Tethys, and Thebe are small, so the escape velocity is small. Thus, we have very large (compared to the moon) objects traveling at a very slow speed. There are lots of other examples of Lagrangians, for instance Valhalla and Aesgard on Jupiter's Callisto, the "coronae" on Uranus's moon Miranda, and two craters on Neptune's Proteus. There is also another 1:1 resonance, called a "horseshoe orbit", in which a large body could form. That would create a single object. Lagrangians are much more common.

rfoshaug · May 9, 2006

That's not a moon - that's a space station! <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> ----------------------------------My minds have many opinions </div>

JonClarke · May 9, 2006

Crater size is proportional to the energy released (which varies) according to the mass of the impactor and its velocity) and the strength of the target body. I have read papers discuussing the maximum size (as in energy release) impact a body such as Pobos or Mimas can sustain without getting disrupted. In each case the large craters are below this threshold. It would take a lot of hunting to find these references, I am afraid! Jon <div class="Discussion_UserSignature"> Whether we become a multi-planet species with unlimited horizons, or are forever confined to Earth will be decided in the twenty-first century amid the vast plains, rugged canyons and lofty mountains of Mars Arthur Clarke </div>

vogon13 · May 9, 2006

Due to Thebe being so deep in Jupiter's gravity well, the impactor for our crater was quite small and hit at very high velocity. <div class="Discussion_UserSignature"> TPTB went to Dallas and all I got was Plucked !!So many people, so few recipes !!Let's clean up this stinkhole !! </div>

bonzelite · May 15, 2006

i think the issue over impactors is their size versus how large the impact basin is left versus structural integrity of the small body being hit. an impactor the size of a truck could render a gigantic impact basin several orders of magnitude larger than the actual meteoroid. the molten ejecta is then vaporized and/or dispersed back to the surface. the low gravity of these small moons cannot retain the non-vaporized ejecta, so no debris field is seen. this builds a case in favor of impactors despite no debris fields. however, this has not yet been observed directly, so we are left with conjecture. a factor against impactors is the myriad "impacts" seen throughout the solar system all the way down to very tiny, nearly microscopically small, bodies. why? how can rogue impactors find such tiny bodies in the void? i find it difficult to believe that all basins we see are of impact origin with so vast a distance between bodies. even during the "early bombardment phase" there must have been, then wall-to-wall debirs every few meters in space to render such diverse and myriad "impact" sites everywhere. something is missing from the picture. but i sure as hell don't know what!

CalliArcale · May 15, 2006

<blockquote>In reply to:<hr />how can rogue impactors find such tiny bodies in the void?<hr /></blockquote> Chance encounters. The thinking goes that while space seems very empty, given enough time (and the majority of these objects are billions of years old), impacts are inevitable. <div class="Discussion_UserSignature"> "People assume that time is a strict progression of cause to effect, but actually from a non-linear, non-subjective viewpoint it's more like a big ball of wibbly wobbly . . . timey wimey . . . stuff." -- The Tenth Doctor, "Blink" </div>

silylene old · May 15, 2006

Here is what happened to Thebe: Ever heard of the EPH Theory? The Exploded Planet Hypothesis is well documented on the internet, and also has more support than any other hypothesis in this forum, as proven by post counts. Well, sometimes a planet *almost* explodes. In an abortive explosion, a huge piece of a planet is ripped asunder from the mother body, and hurled into space, to never be seen again. What is left of the mother body is a giant maw, which partially collapses to leave a big hole behind. This is what happened to Thebe. PEPH. Partially Exploded Planet Hypothesis. Exploded planet (or moon, in this case) gone sub-critical. Happens a lot. <img src="/images/icons/wink.gif" /> <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center">- - - - - - - - - - - - - - - - - - - - - - </div><div class="Discussion_UserSignature" align="center">I really, really, really miss the "first unread post" function. </div> </div>

robnissen · May 15, 2006

"Chance encounters. The thinking goes that while space seems very empty, given enough time (and the majority of these objects are billions of years old), impacts are inevitable. " I don't know. Over 5 billion years, there is time for a lot of random chance events. But the problem is, according to theory, the vast, vast majority of these impacts took place during a few hundred million years. That would seem to me to require almost wall-to-wall space debris.

bonzelite · May 16, 2006

yes, chance encounters are inevitable. but we're talking a need for wall to wall debris nearly everywhere, then. billions of years or not. you just cannot attribute all of the blemishes and bad complexions of these bodies to be solely from impactors. it just cannot be. sure, impactors are there. and we've even seen some in our lifetimes. but you just got to be kidding me that they're accountable for all we see. i would not invest in such a stock were it traded on the exchange. an all-impact investment would shy me away.

Interesting crater on Thebe

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