Dammit! I leave for lunch and all of this discussion happens. francopoli did a very good job of answering your question, but there is one thing that I'd like to clarify. Pluto swinging inside the orbit of Neptune would not bring it close enough to the sun to outgas significantly enough to cause the atmosphere that we are seeing today. This is the mystery of "what heated up Pluto and caused these gasses to sublimate" that francopoli was talking about in his posts. It didn't get close enough to the sun, so what heated it up? As he pointed out, it isn't tidal interactions with another large body, the usual other source of heating in our solar system. And to expand on this mystery: 1. Pluto has an atmosphere that should have been stripped away by now by the solar wind. This is what is currently happening to it and is creating the tail. The question is, what is replenishing it? 2. Pluto, like any other comet, is full of ices which sublimate into gasses when heated. This is what causes the atmospheres and the tails on comets that venture closer to the sun. This is where that gas is coming from, the question is, what's heating the planet? The three common, go-to sources of heat in a body in our solarsystem are 1. The sun (Pluto is too far away) 2. Tidal forces (Pluto is already tidally locked to Charon, francopoli gave a good description of this) 3. Latent heat of formation (Pluto isn't big enough for this to have stuck around. Source: Mercury's has not stuck around, and it is bigger than Pluto). So what's causing this heat? Well first here are some other facts that I'd like you to consider: With all comets, as the ices sublimate off, they leave the rock behind. With smaller comets, this rock is left behind in an almost "haphazard" fashion. The rock stays where it was, and it might roll a bit downhill towards the comet's center of mass. This leads them to be to porous and misshapen (like 67P). ----Leaving facts behind, entering speculation. Everything below here is an educated guess from someone who has never studied Pluto in particular, but has taken graduate level Planetary Science classes, including (recently) one in geophysics (the relevant subject here). It is very possible that I think that I know more than I do, so take everything below with a grain of salt---- My thoughts/hypothesis/speculation that might be completely wrong (feel free to NOT read this, it might be wrong)? I think that there is something special about Pluto that we haven't seen with other large bodies that makes it take longer to lose its latent heat. And that special thing is its composition and size. The only other object similar to it in both of these respects is Triton, but Triton has tidal heating that might mask this effect. Remember how the other comets are misshapen and porous? Well, Pluto is big enough to pull itself back into a spherical shape (hydrostatic equilibrium). Its gravity is strong enough to pull the rocks back down and close up these porous "gaps" left by the escaping volatiles. Perhaps some event (possibly an impact) imparted a lot of heat into Pluto in the somewhat recent past and caused a lot of ices to sublimate all at once, and now the atmosphere is slowly returning to equilibrium. As Pluto reforms itself into a spherical shape, it would create all sorts of active geology like mountains and canyons and other things that we are seeing there that we weren't expecting. This active geology would also cover up the scars of this event, much like what happens on the Earth, or possibly by the refreezing of these gasses, creating an ice layer that would hide the craters. This isn't too unreasonable. While the Earth has plate tectonics and thus is only geologically active along faults and at hot spot volcanoes, this would be happening to Pluto everywhere, and the surface rock would be being reformed everywhere, because all of Pluto would have been outgassing and all of Pluto would now be compressing. (CAUTION: EXTREME SPECULATION IN THIS PARAGRAPH) Perhaps the "heart" is the impact site, and the heat from impact melted a lot of the ices and created a muddy crater that had a low enough viscosity to flow into becoming flat again (no crater), and even flow some mud into the surrounding areas. I would suspect that the original impact crater was MUCH MUCH smaller than the heart, and the rest of the heart would be caused by this mud flowing out. We already know that this region resembles frozen mud cracks on the Earth, and is rich in Carbon Monoxide. This would fit with liquid Carbon Monoxide mixing with the rocks and dirt on the surface and creating a mud that then refroze. In fact, this feature is so consistent with a freezing mud flow, that I would personally be surprised if it wasn't caused by some sort of local heating, causing what I just described. The hypothesis that I just described fills in a lot of the gaps in knowledge and questions that we currently have about Pluto, BUT keep in mind that I am by no means a Pluto expert. There are definitely things about Pluto that people have studied and that the experts know about that I do not, and it is also very possible that one of those things could throw my whole hypothesis out of the window. I'm mostly just typing this out so that I have a record of what I thought "way back when", so that I can objectively see how right I was later on, and as "food for thought" for you guys. Again, it may all be wrong, so take it with a grain of salt.
Now, wouldn't THAT be a neat thing to find out! Triton is an interesting object that I hope we get a better look at during my lifetime. It is most likely a captured object, orbiting the "wrong way" around Neptune. It is (barely) bigger than Pluto as well. This is why I love science. Last month, we did not even know to ask these questions, yet here we are excited and forced to think outside of a comfort zone. Maybe something odd is going on in the Pluto system! Or maybe the impactor that created the Pluto system was recent! Or maybe there is a weird new chemistry going on here! Maybe a bit of everything? I've been reading up a bit on a proposed sample Return Mission to Pluto. 12 years to get there, a few years to map the place out and possibly make fuel on the surface of Pluto, and due to the small size and weaker gravity maybe multiple landings. Then take off and head back to earth in 12-13 years. I really hope that Pluto turns out to be fantastically weird so that something like this mission becomes a reality. I'm doing the same thing here. It will be neat to come back to this thread a year from now when we have most of not all the data and can laugh at how wrong/right we are.I think that there is something special about Pluto that we haven't seen with other large bodies that makes it take longer to lose its latent heat. And that special thing is its composition and size. The only other object similar to it in both of these respects is Triton, but Triton has tidal heating that might mask this effect.
I'm mostly just typing this out so that I have a record of what I thought "way back when", so that I can objectively see how right I was later on, and as "food for thought" for you guys. Again, it may all be wrong, so take it with a grain of salt.
I have to leave, but want this here to get a reply if you have time today. I'll try to answer more replies Sunday and apologize in advance if I don't get back to you quickly. Mimas is the smallest body in the solar system know to be in hydrostatic equilibrium. Mimas is 200 miles in diameter. Pluto is nearly five times larger. Pluto's density does not suggest that it is porous like a comet or asteroid. Ceres is the closest analog I was expecting and Pluto is over two times as wide. Something is reforming the surface of Pluto! This is something that I was not anticipating at all, and it brings up a multitude of possibilities. Here is hoping that the next two years will answer some questions.Remember how the other comets are misshapen and porous? Well, Pluto is big enough to pull itself back into a spherical shape (hydrostatic equilibrium). Its gravity is strong enough to pull the rocks back down and close up these porous "gaps" left by the escaping volatiles.
Nope, because its gravity is pulling it together enough to compress the rocks together and make it not porous. This is the point that I was trying to make, sorry if it wasn't clear. You get to a point size-wise where eventually you stop just getting bigger, and you start getting denser. This happens when the force of gravity overcomes a force stopping things from compressing. There are many such forces, and thus many such points where "object gets bigger, then starts getting denser, then starts getting bigger again, then denser again, etc" as you add more and more mass. Again! Speculation on my part! Take it with a grain of salt! Please don't use concrete language like "is" or else I'll regret posting my thoughts and will take them down so that people don't get confused. Those aren't facts, that's a hypothesis from me.Pluto's density does not suggest that it is porous like a comet or asteroid.
Something is reforming the surface of Pluto!
dont take them down. i think the warning suffices.
I thought that was what you were saying. This is something neat to point out to people. Jupiter and Saturn are not that different in size; Saturn is 9.5 earths wide and Jupiter is 11.2 earths wide. If you could find three more Jupiters and dump them into our current gas giant, the resulting planet would be SMALLER than the current one! Jupiter size objects don't really start to get bigger until they start fusing deuterium and become brown/red dwarfs. Yea, I'm jumping the gun here. Here is why I said that with certainty, and thank you for making me defend such a definitive statement. We have six "young" surfaces in the explored solar system. Venus, which looks like the whole planet resurfaces itself every few million years, which along with raining METAL and having a surface that can melt lead just adds to the weirdness factor. You have the Earth which resurfaces itself due to tectonic plates moving, water erosion, wind and biology. The impact that finished off the dinosaurs is 200 miles wide, yet was not discovered until the 1980's due to it being eroded away at the surface. Then you have Io and Europa. Io was until this month the youngest surface in the solar system. Io is also the most volcanic body in the solar system. Europa has resurfaced itself "recently" as in the last few 100 million years. Enceladus has a young surface where the geysers are spewing water ice back onto the surface of the moon, and Titan has active weather that is at least masking the age of the surface. All of these ages are mostly determined by crater counts. To not see any craters on Pluto was a shock to me. I was expecting a mix of Triton with its ice geysers and Ceres with its heavily craters surface. The "easy" answer is that there is a mechanic like we have already seen in the solar system reworking the surface. I hope that the real answer is something more odd and interesting!You get to a point size-wise where eventually you stop just getting bigger, and you start getting denser. This happens when the force of gravity overcomes a force stopping things from compressing. There are many such forces, and thus many such points where "object gets bigger, then starts getting denser, then starts getting bigger again, then denser again, etc" as you add more and more mass.
Again! Speculation on my part! Take it with a grain of salt! Please don't use concrete language like "is" or else I'll regret posting my thoughts and will take them down so that people don't get confused.
Is it the case that there are absolutely no craters on Pluto? or is that our best estimate from the particular locations we saw in the media release?
Seems that there are a few in the new images. This is the border of the smooth white area and the darker spots. This reminds me a lot of Iapetus. You can clearly see impact craters at the edges of the "white" area. There is also a larger crater that looks very similar to a lunar maria with a flooded floor. So my initial guess that there is something on Pluto that is causing it to resurface itself may be at least partially correct. Neat.