Silverpit, Chicxulub, Miranda, & variable speed craters

[mikeemmert]

A reply to this post from silylene:<blockquote><font class="small">In reply to:</font><hr /><p>I am particularly interested in if you can find any chances for slow motion collisions. By this, I mean two moons which collide with a delta-v that is minimal Perhaps a delta-v of just a few tens of km/hr or less?). I think that the two moons would need to be nearly co-orbital for this to happen (not orbiting each other, but rather sharing almost the same orbit around the planet). As you know, Saturn has currently three pairs of nearly co-orbital moonlets. Is there any way to perturb these into a slow motion collision?<p><hr /></p></p></blockquote>I certainly do believe so. A picture of what I think is the result of a slow-motion collision is posted below.<br /><br />The three pairs of co-orbital (Lagrange) moons you mention prove that moons can form at Lagrange points L4 and L5. I believe that early in the history of the Solar system, objects formed at <i>every</i> Lagrange point in the Solar system; two each for all eight planets (Pluto's not a planet, <i>it</i> is a Lagrangian) and two each for the moons of the gas giant's planets. Let me concentrate for now on the moons of the gas giants. Since there are several photos on public websites I will need to make more than one post. I have a lull in my job with the Census Bureau right now while they decide what to do about nonresponse, so I'll try to get these in pretty quick here.<br /><br />I came up with this idea looking at a map of the orbits around the Sun/Earth Lagrange points L4 and L5. These points are about 60 degrees ahead of and 60 degrees behind the Earth in it's orbit around the Sun; more precisely, in the case of a perfectly circular orbit (of course Earth doesn't have one) the Sun, the Earth, and the Lagrange points L4 and L4 would form equilateral triang

 

[mikeemmert]

More from silylene's post:<blockquote><font class="small">In reply to:</font><hr /><p>(I have wondered if Iapetus could be the result of a slow motion collision) <p><hr /></p></p></blockquote>Ah, the bizzare walnut moon of Saturn! OK, I went to GravitySimulator, divided the mass of Iapetus in half (actually, I used 10^21 kg for each object, which is slightly greater than half of 1.9739×10^21 kg) and multiplied Iapetus' diameter by 0.8 (the cube root of 1/2, approx) and let them fall for 100,000,000 km. The collision speed was 420 meters per second. That would be about Mach 1.2 in our atmosphere. <br /><br />Make of that what you will, obviously it would make a pretty big mess. That will just about give you the escape velocity of the two objects with respect to each other.

 

[yevaud]

That's well below the binding energy for a mass that size. However, it may have caused a great deal of plastic deformation.<br /><br />Interesting. <div class="Discussion_UserSignature"> <p><em>Differential Diagnosis:  </em>"<strong><em>I am both amused and annoyed that you think I should be less stubborn than you are</em></strong>."<br /> </p> </div>

 

[silylene old]

Mike, very interesting.<br /><br />You may remember my more unusual posts when we first saw the unusual belly-band around Iapetus. I proposed that Iapetus formed by the very slow motion collision of two similar sized mini-moons...and subsequent plastic deformation during the collision gave us the moon belly band morphology we see today. Think of two scoops of ice cream mushed together.<br /><br />Yes I know this is probably incorrect. But it's a fun hypothesis to speculate about! <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[brandbll]

So your saying our moon was one of the parts of this trifecta of planets? <div class="Discussion_UserSignature"> <p><font size="3">You wanna talk some jive? I'll talk some jive. I'll talk some jive like you've never heard!</font></p> </div>

 

[mikeemmert]

<blockquote><font class="small">In reply to:</font><hr /><p>when we first saw the unusual belly-band around Iapetus. I proposed that Iapetus formed by the very slow motion collision of two similar sized mini-moons...<p><hr /></p></p></blockquote>I remember that post. I had the same impression, too, because I had done simulations of binaries past Neptune and sometimes got collisions.<blockquote><font class="small">In reply to:</font><hr /><p> Yes I know this is probably incorrect.<p><hr /></p></p></blockquote>Not neccessarily. At this point it's certainly a viable hypothesis.<br /><br />Another idea might be that Iapetus almost, but not quite, got ripped apart and this created the belly band.<br /><br />The collision velocity I got (420 meters per second) might be lower if the progenitors were in a close orbit. It could be as low as 294 meters per second that way.<br /><br />How about that it got ripped apart and then collided on a second pass by Titan?<br /><br />Wikipedia says Iapetus is pretty mis-shapen.

 

[mikeemmert]

I don't know if any of you have ever heard of Silverpit CraterIt's in the North Sea off the coast of Britain. I found it in an idle search for the town of Chicxulub out of vulgar curiosity. I wondered if they had an impact museum there. But the Wikipedia article was very short. It's a village of about 3,500 and they are probably engaged in the agricultural industry (goathearding? who knows?).<br /><br />Moving on to the famous impact crater I discovered that there are other craters on Earth dated to the same time, 65,000,000 years ago. For instance, there is the Boltysh Crater in Ukraine, which due to the local geological circumstance can be very accurately dated. This astrobleme is very well known and easy to study. Then there is the Shiva]http://en.wikipedia.org/wiki/Shiva_crater]Shiva crater on the floor of the Indian Ocean[/url] which is hard to study and is not well known. It's bigger than Chicxulub, they think. It's been broken up into sections, which have been scrambled by plate tectonics; some has subsided beneath the crust.<br /><br />All these locations are very interesting in their own right so I provided links for your leisure entertainment. The entire concept of multiple impacts is also extremely interesting. This might even be tied to the "Nemesis" Death Star, but that's another thread. But the theme of this thread is impacts on the moons of the outer planets. Silverpit is germane to the discussion of two of them.<br /><br />This link: http://en.wikipedia.org/wiki/Silverpit_crater<br />has so many connections that I'm going to make quotes germane to all of them and deal with why it'

 

[silylene old]

Mike: More interesting thoughts to ponder. thanks! <div class="Discussion_UserSignature"> <div class="Discussion_UserSignature" align="center"><em><font color="#0000ff">- - - - - - - - - - - - - - - - - - - - - -</font></em> </div><div class="Discussion_UserSignature" align="center"><font color="#0000ff"><em>I really, really, really miss the "first unread post" function.</em></font> </div> </div>

 

[brandbll]

So wait, are you saying that the moon was captured instead of something that possibly split off from early Earth from a collision?(That's what i've was always told in my history of the Earth geology class) <div class="Discussion_UserSignature"> <p><font size="3">You wanna talk some jive? I'll talk some jive. I'll talk some jive like you've never heard!</font></p> </div>

 

[mikeemmert]

Here is a picture of Asgard crater on Jupiter's moon, Callisto. Another crater, Valhalla, is larger but did not fit on the file attachment. So I used this one. Too bad, the other photo is quite striking: http://en.wikipedia.org/wiki/Image:Valhalla_crater_on_Callisto.jpg#file<br /><br /><br />Callisto is the third largest moon in the solar system and has an escape velocity of 2.44 km/sec.