Planetary accretion idea

[bobvanx]

I noticed some things about the Earth's surface in satellite imagery that caused me to wonder about small panets grouping up to form larger planets. The recent images of Tempel1 are also fascinating. I see what looks like a few small objects mashed together into a larger object; as though I were to take different types of modelling clay and gently smoosh them together.<br /><br />So here's the thing:<br /><br />Suppose differentiated bodies about the moon's size (and smaller) "landed" on proto-Earth. Impact speeds are a function of orbital mechanics, so if these things were co-orbital, they could have a (relatively) slow contact. The crust of the small body would certainly collapse, spilling its interior into the interior of the Earth. The shell would get left behind, floating on the Earth's surface, severely distorted as the sphere flattened into a pancake. Imagine the peel of an orange (intact but without the slices inside) flattening down. If the Earth were just viscous enough, the roundness along the edge would be preserved, but the shapes on the surface of the small body would get distorted.<br /><br />I know there are myriad processes shaping Earth's surface, so this alternate explanation is possibly unnecessary.<br /><br />However, the Rocky Mountains are roughly circular, with the Yellowstone hotspot somewhat offcenter (as though the core of the small body drifted some as it sank). The San Joaquin Valley in California is the remains of a very large crater that was on the rim of the small body, so it's been squashed and arched.<br /><br />China has three of these sorts of large, round areas, and the Indian Sub-continent pushes up along a portion of a circle against the Himalyas, so that mountain range was once a planetesimal as well.<br /><br />That's my theory in a few paragraphs. Here it is in a sentence: Small bodies merged at low enough speeds that we can still see remnants of their surface morphologies even today, even after billions of years of tectonic activity, b

 

[nexium]

Even objects with the mass of Earth's moon rarely collide with speeds less than 30,000 feet per second because their gravety causes them to speed up just before impact. Lower mass objects than Tempel 1 sometimes smoosh together gently, so your hypothesis may work for very low mass objects.<br />If the crust decelerates from 30,000 feet per sec to zero with respect to Earths crust, in ten seconds over a distance of 200,000 feet: S = 1/2 at squared. 200,000 = 1/2 a times 100 a = 200,000 times 2 divided by 100 a = 4000 feet per second per second = 124g which would disrupt even grossly cohesive and grossly adhesive crust. Worse the 124g is average; the peak g is much higher. Please correct, embellish and/or work the problem in meteric. Neil

 

[vogon13]

Sorry, there are no low speed collisions possible in the mass range you're considering. In the Newtonian (Isaac not the SDC poster <img src="/images/icons/wink.gif" />) scheme of things, the reverse, a low speed seperation trajectory doesn't exist either, for the same reason.<br /><br /> <div class="Discussion_UserSignature"> <p><font color="#ff0000"><strong>TPTB went to Dallas and all I got was Plucked !!</strong></font></p><p><font color="#339966"><strong>So many people, so few recipes !!</strong></font></p><p><font color="#0000ff"><strong>Let's clean up this stinkhole !!</strong></font> </p> </div>

 

[silylene old]

<font color="yellow">Sorry, there are no low speed collisions possible in the mass range you're considering.</font><br /><br /><b>Actually I do think there is one possible mechanism for an extremely low speed collision between moons.</b> I proposed this on a thread about 3 or 4 months ago. Hopefully one day a researcher can model the possibility and publish an analysis of this hypothesis (I don't have the time with my present job to pursue this).<br /><br />I think that it's possible for <i>co-orbital</i> moons to have a <i>very low speed</i> collision. For examples of co-orbital moons consider the following: Janus and Epimetheus, S1 and S3, Tethys has 4 co-orbital moonlets, and Dione has 2 co-orbital moonlets.<br /><br />In these cases, both moons are moving in nearly circular orbits. They are not moving at exactly the same speed. The faster moon slowly gains on the slower moon. The faster moon is faster because it is in a slightly lower orbit. They approach each other very slowly, and are close to each other for a long period of time. The gravity of the trailing moon pulls on the leading moon, and the gravity of the leading moon pulls on the trailing moon. This adds energy to the trailing moon and takes energy from the leading moon. This does not speed up the trailing moon, but instead tugs it into a higher orbit. In this higher orbit, the trailing moon has more energy, and a slower speed. Similarly, the leading moon loses energy and is pulled into a lower, faster orbit.<br /><br />I do think it is possible that co-orbital moons could conceivably collide someday due to gravtitational interactions with other bodies which bring them slowly closer to each other millenia after millenia. Someday, the passing distance of the two moons becomes closer than the intersections of their surfaces. At this time, The two moons would have an extremely low speed collision, perhaps with a closing velocity of only a few km/hr difference (or less!).<br /><br />In such a case, <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>

 

[nexium]

Are there any co-orbital moons with more than ten times the mass of Templel 1? Likely the low mass co-orbital moons take a long time to pass each other, but the more massive pass each other much like a sling shot manuver. Perhaps the distributed mass of the rings plus the concentrated mass of a gas giant planet, make co-orbital moons more probable? I suppose identifing co-orbital asteroids and comets would be difficult, but that does not prove their non-existance. Neil

 

[silylene old]

Vogon, thank you for finding the original thread, where I proposed this idea:<br />http://uplink.space.com/showflat.php?Cat=&Board=sciastro&Number=118640&page=0&view=collapsed&sb=5&o=0&fpart=11<br /><br />AlexBlackwell, I again searched the references you suggested and others, but found no (obvious) discussions of my hypothesis.<br /><br />Nexium, I very much doubt this mechanism could ever apply to comets or asteroids such as Tempel1. Their orbits just are unlikely to have the co-orbital dynamics I suggested. Similarly bobvanx, I also do not think that the early Earth had a co-orbital companion in the distant past from which a collision could have created a lumpy aggregation (and if anything, the long-ago collision with a Mars-like body which formed the moon would've wiped the crust clean).<br /><br />I basically just wanted to point out that I think there is one mechanism which could give an extremely low impact collision resulting in an unusual fused body. But I think this is rather rare, and if it ever did occur, it's more likely to occur among co-orbital satellites. <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>