New Horizons at Pluto

The question I'd have for a recent collision is how likely that makes the current configuration; in particular, how circular is Charon's orbit (or rather, the mutual orbit) as well as how long it would take for the two to become tidally locked after such a collision.

In any event, as the data comes in from NH we may get better clues.
 
grmcdorman said:
The question I'd have for a recent collision is how likely that makes the current configuration; in particular, how circular is Charon's orbit (or rather, the mutual orbit) as well as how long it would take for the two to become tidally locked after such a collision.
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Good point. Does anyone know?

On another matter, surely the relative recency of the end-Cretaceous impact, which involved a body a mere few miles in diameter, tells us nothing about the probability of a recent much larger impact, splitting a dwarf planet apart to produce Charon, which must have involved a vastly larger impactor.
 
Craig B said:
Good point. Does anyone know?

On another matter, surely the relative recency of the end-Cretaceous impact, which involved a body a mere few miles in diameter, tells us nothing about the probability of a recent much larger impact, splitting a dwarf planet apart to produce Charon, which must have involved a vastly larger impactor.
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It doesn't directly, but it does show that fairly large impacts are not outside the realm of possible. We're dealing with a geophysicist as well--which means that the argument has special significance (it references a series of issues raised during the 1990s in geology).
 
Craig B said:
Good point. Does anyone know?
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Humm... well the earth-moon system was created 4.5 gya, and the Earth won't be tidally-locked with the moon for another couple billion years1. Earth is bigger relative to the moon than Pluto to Charon, of course.



1: By that time the sun may have engulfed us anyway.
 
Gawdzilla Sama said:
grmcdorman said:
The question I'd have for a recent collision is how likely that makes the current configuration; in particular, how circular is Charon's orbit (or rather, the mutual orbit) as well as how long it would take for the two to become tidally locked after such a collision.
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It could have happened immediately?
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While I am by no means an expert, I don't think so. All of the angular momentum of the bodies needs to be dissipated; especially in a glancing collision I'd think the collision would add angular momentum to the individual bodies, not remove it.

As I mentioned, the other question is how circular the orbit is; the more circular the orbit the more likely that the collision is not recent. In particular, I'd expect a young pair to have a rather eccentric orbit, as the original path intersected the two. Given that Charon's listed orbital eccentricity is a mere 0.0022 (see http://solarsystem.nasa.gov/planets/profile.cfm?Object=Plu_Charon&Display=Facts&System=Metric), I - again, as a non-expert - would take this as an indication that the collision is not recent. For comparison, the eccentricity of Venus - which is said to have a nearly circular orbit - is about 3 times higher, at 0.0067.

According to Wiki, the current theoryWP for the formation of Charon is a collision 4.5 billion years ago.

Mind you, if you're a Velikovskyian, the low eccentricity doesn't mean anything.
 
grmcdorman said:
The question I'd have for a recent collision is how likely that makes the current configuration; in particular, how circular is Charon's orbit (or rather, the mutual orbit) as well as how long it would take for the two to become tidally locked after such a collision.
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According to this article, once Charon has coalesced from the collision debris, it would have take for Charon only 50 years (no, not a typo) to become tide-locked, and several million years for Pluto to become also tide-locked.

An eyeblink on the scale of Solar System.
 
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Interesting; apparently the relatively close masses of the two bodies speeds up the process. I wonder if the same applies to the orbit.
 
Mark6 said:
According to this article, once Charon has coalesced from the collision debris, it would have take for Charon only 50 years (no, not a typo) to become tide-locked, and several million years for Pluto to become also tide-locked.

An eyeblink on the scale of Solar System.
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So it could have possibly happened when they were still molten--and certainly well within the 100 ma timeframe we're working with.

Mark6 said:
Some of Pluto's terrain appears to be billions of years old.
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It's evidence against it, but not proof. It may not have been completely melted--chunks of it may have been, but other chunks may have been blasted off before they could have melted.

Though this does rather more strongly support the notion of the white stuff coming after the crators formed (you can see it infilling the craters, which pretty much proves it). You can even see it filling different craters to different degrees.

Could the planet have been hit by a small comet? Or a series thereof? Think a snowball--Suzie's head retains a bit of the snow even if the snowball is completely destroyed or glances off (Calvin and Hobbs references, if anyone has to ask).
 
Dinwar said:
It's evidence against it, but not proof. It may not have been completely melted--chunks of it may have been, but other chunks may have been blasted off before they could have melted.
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I find that most improbable. A very large moon is created by the disruption of a dwarf planet; but the impact leaves some mountains on that body (composed of water ice!) looking perfectly normal and undisturbed.
 
Craig B said:
I find that most improbable. A very large moon is created by the disruption of a dwarf planet; but the impact leaves some mountains on that body (composed of water ice!) looking perfectly normal and undisturbed.
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What I'm thinking is this: Something (possibly the moon) smashes into the planet. Bits of both are blown into space--and some of them are pretty large, because the material is pretty weak (it's ice). While the stuff condenses into the Pluto/moon system, some of the chunks fall back into the system and are large enough to survive the impact.

It would explain the mountain in a moat: a chunk of material hit th planet and stuck. It may explain the dischordant facets of the planet as well.

Unlikely? Sure. But not impossible. Planets don't blow up uniformely, and if there were fractures (if Pluto had been softened up previously by collisions with things orbiting the impactor, perhaps?) they could easily be re-activated, lessing the amount of stress necessary to toss the chunk into space wholesale.
 
Dinwar said:
What I'm thinking is this: Something (possibly the moon) smashes into the planet. Bits of both are blown into space--and some of them are pretty large, because the material is pretty weak (it's ice). While the stuff condenses into the Pluto/moon system, some of the chunks fall back into the system and are large enough to survive the impact.

It would explain the mountain in a moat: a chunk of material hit th planet and stuck. It may explain the dischordant facets of the planet as well.

Unlikely? Sure. But not impossible. Planets don't blow up uniformely, and if there were fractures (if Pluto had been softened up previously by collisions with things orbiting the impactor, perhaps?) they could easily be re-activated, lessing the amount of stress necessary to toss the chunk into space wholesale.
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What would make it even better is if it was a glancing blow at low speed. Enough to melt part of Pluto. The body that hit it would melt completely, forming its main moon. It would also create the other smaller moons. Where was this body before the collision? Maybe at a relatively stable point like L1, L2 or whatever. It would also explain why it was late in the solar system's evolution. Those points would be much more stable than Earth's points, having less to disrupt the object.
 
grmcdorman said:
Cool. It's especially interesting to see the moons become worlds in their own right, when prior to this they were just single pixels in images.
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The idea that we can see an object that is 25 miles across out by Pluto is mind-boggling. That is a LONG way out in space.
 
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