Starship Asterisk*

by **BMAONE23** » Wed Jul 29, 2015 5:19 pm

A view of a portion of Charon from 100k away

: Click to view full size image

by **neufer** » Wed Jul 29, 2015 12:19 pm

ta152h0 wrote:
Now that NH is out there in the vast ocean of nothingness,
are the cameras taking images of the nothingness ahead of
the spacecract [sic] and maybe catch something simply by golly ?

bystander wrote:New Horizons

What if New Horizons hits my car? — Robin Sheat

by **ta152h0** » Wed Jul 29, 2015 1:23 am

Now that NH is out there in the vast ocean of nothingness, are the cameras taking images of the nothingness ahead of the spacecract and maybe catch something simply by golly ?

by **Beyond** » Wed Jul 22, 2015 7:40 pm

BMAONE23 wrote:Well Ed, I guess that makes you the slightly off center of the universe

Click to play embedded YouTube video.

by **BMAONE23** » Wed Jul 22, 2015 6:51 pm

emc wrote:
Craine wrote:
emc wrote: So Canton, GA isn’t the center of the universe!? Dang again! Now I feel even less important. If I were any lower I would be inside a black hole...
Not Canton. Austell, GA is.
Well that is not bad news... Austell is only a Hercules's stone's throw from Canton! In cosmic resolution, that's as good as dead on.

Well Ed, I guess that makes you the slightly off center of the universe

by **emc** » Wed Jul 22, 2015 12:50 pm

Craine wrote:
emc wrote: So Canton, GA isn’t the center of the universe!? Dang again! Now I feel even less important. If I were any lower I would be inside a black hole...
Not Canton. Austell, GA is.

Well that is not bad news... Austell is only a Hercules's stone's throw from Canton! In cosmic resolution, that's as good as dead on.

by **Nitpicker** » Tue Jul 21, 2015 5:05 am

Bradford wrote:It's misleading and confusing to say "1/10th the size of planet Earth."
You should say 1/10 the diameter, which is closer to 1/1000 the size.

Both 1/10th the size and 1/1000th the size are somewhat ambiguous, but I wouldn't go so far as to say misleading.

More precise to say that Charon's size is 1/10th the diameter, or 1/100th the surface area, or 1/1000th the volume, of Earth. They are all sizes.

by **Bradford** » Tue Jul 21, 2015 12:55 am

It's misleading and confusing to say "1/10th the size of planet Earth."
You should say 1/10 the diameter, which is closer to 1/1000 the size.

by **Chris Peterson** » Sat Jul 18, 2015 2:32 pm

Ann wrote:Well, what do you think of the possibility that an atmosphere might contribute to a reddish color of an outer solar system planet or moon? If Charon itself has an atmosphere, that might just possibly explain this planet/minor planet/moon's slightly reddish hue near its dark pole.

I generally avoid speculation in the absence of evidence. We see color and surface structure on cold, icy, airless (or nearly airless) bodies caused by sublimation, by internal outgasing, by space weather, by impacts. If Pluto has some sort of internal activity of unknown origin, Charon may, as well.

I guess we'll just see when more data arrives, especially from some of the other instruments (which are less glamorous than the imagers, but provide essential information that we simply can't get from images alone).

by **Ann** » Sat Jul 18, 2015 6:35 am

Chris Peterson wrote:
BMAONE23 wrote:Siphoning isn't required to transfer atmospheric gasses between the two bodies. Solar winds strip some atmospheric gasses and blows them back away from Pluto in a type of tail pointing away from the sun. In just 62 years Charon's orbit will be passing between the sun and Pluto so that, out of every 201 hour orbital period, 24 hours will be spent in the atmospheric tail caused by the solar winds
Right, as noted previously Charon can intercept material that diffuses from Pluto. But at that distance, I doubt we're going to have much blown off by the Sun. The atmosphere is already close to a vacuum. Charon's gravity isn't going to retain any stray gas molecules that come its way, so we'd be looking at some sort of adhesion process, I'd think, if anything. But Charon itself is icy. I wouldn't be surprised if it also has an extremely tenuous atmosphere- it may be outgasing more than it receives from Pluto.

Well, what do you think of the possibility that an atmosphere might contribute to a reddish color of an outer solar system planet or moon? If Charon itself has an atmosphere, that might just possibly explain this planet/minor planet/moon's slightly reddish hue near its dark pole.

Saturday's APOD shows a Plutonian landscape with cracks, where dark material has gathered in some places. I'm reminded of both Jupiter's Galilean moon Europa and Saturn's small moon Hyperion. We know that on Europa at least, the dark material in and around cracks is reddish.

Ann

by **Chris Peterson** » Sat Jul 18, 2015 6:04 am

geckzilla wrote:It doesn't matter, at least, until you get a committee on the job, it seems.
https://en.wikipedia.org/wiki/Parkinson ... triviality

Committees tend to be very good at that.

by **geckzilla** » Sat Jul 18, 2015 6:03 am

It doesn't matter, at least, until you get a committee on the job, it seems.
https://en.wikipedia.org/wiki/Parkinson ... triviality

by **Chris Peterson** » Sat Jul 18, 2015 5:59 am

BMAONE23 wrote:Siphoning isn't required to transfer atmospheric gasses between the two bodies. Solar winds strip some atmospheric gasses and blows them back away from Pluto in a type of tail pointing away from the sun. In just 62 years Charon's orbit will be passing between the sun and Pluto so that, out of every 201 hour orbital period, 24 hours will be spent in the atmospheric tail caused by the solar winds

Right, as noted previously Charon can intercept material that diffuses from Pluto. But at that distance, I doubt we're going to have much blown off by the Sun. The atmosphere is already close to a vacuum. Charon's gravity isn't going to retain any stray gas molecules that come its way, so we'd be looking at some sort of adhesion process, I'd think, if anything. But Charon itself is icy. I wouldn't be surprised if it also has an extremely tenuous atmosphere- it may be outgasing more than it receives from Pluto.

by **BMAONE23** » Sat Jul 18, 2015 5:55 am

There is the possibility of transfer through solar interaction by traveling through the atmospheric wake tail of gasses that have been stripped from the solar winds during Pluto fall and spring

by **Chris Peterson** » Sat Jul 18, 2015 5:51 am

Pianosorplanets wrote:Students need not be told it doesn't matter but be told just how grand the scheme of things really is and that we have to draw the line someplace.

Actually, students need to understand that some lines make no sense. It doesn't matter what we call planets. It doesn't matter if there are 9 of them or 1000 of them. Nobody really cares. The definition isn't very important. Whether something on Earth is a "hill" or a "mountain" doesn't interest geologists. What's interesting is if some bump is the product of uplift, or deposition, or extrusion. "Hill" and "mountain" are more useful as informal designations understood in context. The same is true for "planet", which is, in fact, how most astronomers use the word in practice. We care about the physical nature of these bodies, and classify them based on that (terrestrial, gas giant). We care about their origin and formation history, and classify them based on that. We care about their orbital dynamics, and classify them based on that. Lots of categories. Those are what matter, not the loose designation that we can safely use without concern over technicalities.

by **Chris Peterson** » Sat Jul 18, 2015 5:43 am

Pianosorplanets wrote:
Chris Peterson wrote: I can't think of any mechanism for one body to "siphon off" the atmosphere of the other. No gas molecule on Pluto feels any net gravitational force except downwards, towards the center of Pluto.
Can't think of any mechanism for one body to "siphon off" atmosphere? Maybe I can help. How about a double star system with a white dwarf?

Nope, not even close. Material transfers between the components of a close binary star system because the two objects overlap- in particular, the surface of one extends beyond the apex of the Roche lobe, allowing transfer across the L₁ point. This is only possible with fluid bodies. Rigid bodies can't possibly be that close without tidally disrupting each other.

Pluto and Charon are separated by 20,000 km or so, and Pluto has a tenuous atmosphere extending at most a few hundred kilometers, probably much less.

So there's really no mechanism for material to transfer between the two bodies.

by **BMAONE23** » Sat Jul 18, 2015 5:39 am

Siphoning isn't required to transfer atmospheric gasses between the two bodies. Solar winds strip some atmospheric gasses and blows them back away from Pluto in a type of tail pointing away from the sun. In just 62 years Charon's orbit will be passing between the sun and Pluto so that, out of every 201 hour orbital period, 24 hours will be spent in the atmospheric tail caused by the solar winds
http://cseligman.com/text/planets/plutorot.htm

by **Pianosorplanets** » Sat Jul 18, 2015 4:22 am

Milky Waster wrote:As I understand it, the term "binary planets" is used when two bodies orbit a point outside either of their masses which is what I understand Pluto and Charon do. Students everywhere will no doubt be pleased to learn that it doesn't matter what terms they use. "Everyone gets 100%," said Alison Tudorland.

Meteors, Oort cloud objects, binary stars and space dust no doubt find themselves in a dance with a nearby object. We can't name them all "planets" just because their center of gravity is outside the physical form of either object.

No doubt, the Keiper belt is filled to the brim with multiple objects rotating around each other in a manner similar to Pluto and Charon. Students need not be told it doesn't matter but be told just how grand the scheme of things really is and that we have to draw the line someplace. And, being normal, intelligent humans, we'll never agree as to where to put that line.

by **Pianosorplanets** » Sat Jul 18, 2015 4:10 am

geckzilla wrote:
Pianosorplanets wrote:Can't think of any mechanism for one body to "siphon off" atmosphere? Maybe I can help. How about a double star system with a white dwarf?
This type of star system includes a very dense, small member (the white dwarf) and a much larger but less dense member that has begun to swell up and only tenuously holds on to its outer atmosphere (a red giant). The situation is... quite different!

Yes, of course it is. Sorry, I was being a bit glib. Hence my use of the word "Microcosm". More to the point is what space gases might the system pass through as a group and which bodies can and can't hang onto some of it. It seems more likely that that is the mechanism for a commonality in any atmosphere discovered than the chance of Charon actually drafting gas off of Pluto. Quite the long shot, no?

by **Pianosorplanets** » Sat Jul 18, 2015 4:06 am

Chris Peterson wrote:No such agreement is likely, because none of these terms are well enough defined to eliminate ambiguity. Both are reasonably called planets (in which case they are a binary system), Pluto is reasonably called a planet and Charon a moon. It really depends on context. And frankly, it's not all that important which terms we use.

A cheer for Chris! It's fun and interesting to learn the intricate details of how the universe works. Thanks to Chris, just the other day I learned the true solar system escape velocity at Jupiter's orbit. But picking nits just because you can doesn't get us anywhere and getting nowhere does get dull after a while (anybody who's spent a week in the hospital knows how that feels). It's nice to have a grounding force (kind of like gravity) to keep one's thinking and one's speculation in the realms of that which is either productive, build's friendships or is good for a nice chuckle once and again.

by **geckzilla** » Sat Jul 18, 2015 4:01 am

Pianosorplanets wrote:Can't think of any mechanism for one body to "siphon off" atmosphere? Maybe I can help. How about a double star system with a white dwarf?

This type of star system includes a very dense, small member (the white dwarf) and a much larger but less dense member that has begun to swell up and only tenuously holds on to its outer atmosphere (a red giant). The situation is... quite different!

by **Pianosorplanets** » Sat Jul 18, 2015 3:56 am

Chris Peterson wrote: I can't think of any mechanism for one body to "siphon off" the atmosphere of the other. No gas molecule on Pluto feels any net gravitational force except downwards, towards the center of Pluto.

Charon certainly encounters gas which has dissipated away from Pluto, in the same way that moons around Jupiter and Saturn encounter and collect material. With the moons, that shows up as differences on the leading and trailing hemispheres. But we don't really have leading and trailing hemispheres in the same way with Pluto and Charon, so any visible effects are likely to be much more subtle.

Can't think of any mechanism for one body to "siphon off" atmosphere? Maybe I can help. How about a double star system with a white dwarf?

Granted I'm picking nits and this would only be in microcosm in comparison. Let's not forget that Pluto and Charon and all their friends have been orbiting along through the same pathway of space as the others. If any one of them (other than Pluto) is capable of retaining gas near their surfaces without the solar wind blowing it off, it only stands to reason it would be the same gases they all encounter just as you said.

While I'm at it, they suggested the naming of the dark patch "Mordor". Then I suggest that the ridge we see to the west and south (assuming true north is up in the photo...) be named Ephel Dúath. Some of the features are not clear enough to me to tell if I'm seeing crater or mountain. However, if one of those bright patches are a mountain peek in that northern dark feature, then it stands to reason the largest be named Orodruin or Mt. Doom...

We hear of space objects being steeped in mystery and mythology. Nice to consider a little pop culture. Tolkien, Popeye, Pluto (woof, woof), Valentines, Bluto. All in all, this whole thing has been well worth it.

by **MarkBour** » Sat Jul 18, 2015 1:16 am

Chris Peterson wrote:
Craine wrote:But with Pluto and Charon in such close orbits I figured Charon should be able to siphon off some of that atmosphere. In which case the surface of Charon would also be covered in the same ice. Unless the weight of the different components of the atmosphere makes a difference. Methane gas is lighter then Nitrogen (N2). It may be that Charon is siphoning of the lighter gases, giving it a different colored surface.
I can't think of any mechanism for one body to "siphon off" the atmosphere of the other. No gas molecule on Pluto feels any net gravitational force except downwards, towards the center of Pluto.

Charon certainly encounters gas which has dissipated away from Pluto, in the same way that moons around Jupiter and Saturn encounter and collect material. With the moons, that shows up as differences on the leading and trailing hemispheres. But we don't really have leading and trailing hemispheres in the same way with Pluto and Charon, so any visible effects are likely to be much more subtle.

It's interesting to think about. I guess there are multiple competing theories about the formation of the Pluto-Charon pairing. Perhaps there was a collision that both survived. And they remained gravitationally bound together. Presumably at first they were not yet tidally locked. During that initial period, since Charon is so close and so relatively large compared to Pluto, I assume the tidal forces on the atmospheres would have been quite impressive. Once they became tidally locked, there are no more tides in the atmosphere of Pluto, but it must be noticeably stretched (in density) along the mutual axis of the bodies. I suppose the other smaller moons are at least able to "stir up" the mixture to some extent. I can see the sense of the statement that there is no "siphoning" going on, but with all of that history, it seems there would likely have been a fair amount of sharing, and possibly there is still some noticeable random transfer of gas molecules between the two bodies, just from the random motions of gas.

I often come away from such a thought process thinking I should get some hard numbers and do a careful computer simulation. It feels like mental laziness to stop after a little imprecise musing. But it's also often time to just stop at this point and see if someone else has already done it and will give an educated answer. Heck, 10 years ago, somebody knew enough to put instruments on this baby that will hopefully tell us a great deal about these very questions. I hope the data is good!

by **Chris Peterson** » Fri Jul 17, 2015 9:44 pm

Donnageddon wrote:Just to get this straight in my head: If you traced the Moon's (our moon) orbital path around the sun, it would be a wave pattern, getting slightly closer to the sun, and then farther away as it orbits the Earth, then back again, right?

Now if the Earth suddenly disappeared, would the Moon continue this oscillating path? Would it not settle into a more steady elliptical path?

The wiggle would go away. Think of the Moon's orbit like this: when it is in the part of its path around the Earth where it is traveling in the same direction as its orbit around the Sun, it is essentially moving a little faster than a body at Earth's orbital radius can move, so it moves a little closer to the Sun. When it is in the part of its path around the Earth where it is traveling in the opposite direction as its orbit around the Sun, it has slowed down a bit, and so it moves outward. This monthly motion is what generates the wiggle in its path around the Sun. Without the Earth, its orbital speed would not change (except according to Kepler's Second Law). Depending on where the Moon was in its orbit around the Earth when the Earth vanished, the distance of the Moon from the Sun would vary just a tiny bit. And then it would be on that smooth path forever.

by **Donnageddon** » Fri Jul 17, 2015 9:22 pm

Just to get this straight in my head: If you traced the Moon's (our moon) orbital path around the sun, it would be a wave pattern, getting slightly closer to the sun, and then farther away as it orbits the Earth, then back again, right?

Now if the Earth suddenly disappeared, would the Moon continue this oscillating path? Would it not settle into a more steady elliptical path?

Starship Asterisk*

APOD: Charon (2015 Jul 17)

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