Given that big and uneroded crater on Charon, I suspect it will end up being a heavily cratered body with limited to no resurfacing that looks rather similar to Oberon.

I have circled the feature on Charon in this image. It has to be speculation at these resolutions, but one also never knows. Personally, it looks very much like a textbook impact crater, but the heat generated must have resulted in some Cryovolcanic activity.

https://www.flickr.com/photos/124013840@N06...eposted-public/

I wonder if Charon has a mainly-ancient surface with most of its internal heat having vented through the north polar area, just as Enceladus has a mainly-ancient surface with most of its internal heat venting near its south pole.

It seems like too much of a coincidence for Charon's biggest impact basin to have hit its north pole so squarely, so I would guess that the dark spot is volcanic. Another possibility is that it is impact-related and some sort of tidal dynamic moved the rotational pole from another place to that location. Or, it could be purely the result of volatile transport.

Obviously there must have been some local melting after the impact, but impossible to say if cryovolcanic activity would result. Much better imagery will be required to determine that.

I would prefer to bet on a climate origin of the dark spot. As Charon rotates at the current season, the dark spot occupies most of the area that is permanently illuminated and therefore a bit warmer than lower latitudes. Any ice (whatever its composition) which can sublime off that region and condense further south will be removed. As seasons change the dark spot may expand and contract, possibly leaving some of those concentric dark fringes.

Phil

Charon could have reoriented so that a large impact basin could shift to one of the poles. IIRC, that's one of the theories for why Enceladus's plumes are at the south pole (the basin they're in reoriented so that it's at the south pole)

I may be mistaken did I hear from today’s media briefing there a less than expected lower atmospheric density and greater ionized Nitrogen further out from Pluto? I wonder how this fits with Pluto’s seasonal atmospheric behavior as measured by past and recent star occultation data (suggesting the atmospheric density is still increasing). To expand on Mercure’s post #90, the paper of Olkin and Young http://arxiv.org/abs/1309.0841 and Emily’s nice discussion here http://www.planetary.org/blogs/emily-lakda...www.google.com/ are 2 years old but are likely to be refined, constrained or refuted in the next few weeks of observations. Also one wonders if the equator looks different because it has been facing the sun for some 40+ years during the perihelion portion of Pluto’s orbit.

Is that really a "polar cap" we're seeing on Charon, or is it a block of dark terrain that happens to be at the north pole? The edges of it look suspiciously angular to me in the highest resolution image, as if it's bounded by faults (a la Ganymede Dark Terrain, or one of those patchwork blocks on Miranda).

And yeah, as soon as I saw Charon at higher resolution I was reminded of Oberon and Titania!

It might be difficult for polar flops to occur on a body already so egg-shaped due to tidal forces. (I have no theories at the moment - just looking at the pictures. )

Is it very egg-shaped though? Not sure what the expected tidal bulge on Charon is supposed to be.

One science team member refers to the large crater as "fresh rayed", and that large crater could indeed be relatively new.

Here is Ceres, for the most part a heavily cratered body, at a slightly lower resolution: http://dawnblog.jpl.nasa.gov/wp-content/up...Nav3_MPS_sm.gif

I am not sure how well the viewing geometries compare (though both disks are close to full phase). There is one place on the Cerean disk that you can see craters: the bottom half, and there you can see many of them. So why don't we see more similarly obvious crater candidates on Charon in a large area around the big bright crater?

There is definitely one such candidate just above and to the right of it; but given how obvious the big crater is, I'm surprised we don't see more obvious craters elsewhere. There is that other really obvious crater candidate much further north, so latitude does not appear to be able to explain it all, as far as viewing geometry goes (though it doesn't actually look that much like a crater in the last release - false positive?). Given that both features are obvious candidates even as Charon has rotated significantly indicates that longitude cannot explain it all, either.


I suspect many craters on Charon have been significantly eroded - perhaps by freezing-thawing cycles and/or thermal stress due to the Pluto system's elliptical orbit around the sun. Erosion could explain why not more craters are obvious from this vantage point.

I think we should know more in a little more than 13 hours from now. Then we might see an image of Charon where it is 170 pixels across.

Hi(gh)!



You are aware that you are always looking at less than 50 % of its surface when viewing a spherical object? So the distance from limb to limb measured from photographs would always be somewhat smaller than the actual diameter - the closer, the smaller. The results closest to the real value should be obtained when viewing from a great distance and using a high magnification...

See you in Khyberspace!

Yadgar

The cratering record may be quite different on Pluto & Charon than what we've seen on other bodies. If the massive impact that formed the Plutonian satellite system occurred after the late heavy bombardment period (Nice model), or even in the late stages, there may not have been enough impactors to saturate the surfaces. It will be interesting to see if there are relatively few craters on an otherwise ancient surface of Charon.

With Pluto, on the other hand, other processes may have altered the cratering record, so all bets are off....

NH has passed the 400,000 mile mark now. LORRI is taking pics.

Pedantic note.... whilst Ralph and Alice are not acronyms... LORRI is.

I took Bjorn Johnson's (awesome) map from this post and used a template based off the image in this post to produce a map comparison.

I have to admit I'm a bit surprised at how well it matches.

Yadgar: "The results closest to the real value should be obtained when viewing from a great distance and using a high magnification..."


So, pretty much what LORRI has in fact been doing!

But Yadgar, make a sketch of the geometry you are describing. If you project the two tangents out to the distance of the centre of the body you are measuring... the angle plus that distance give you a diameter larger than the true value, not smaller.

(Presumably, if you forget the fact that the limb is not at 90 degrees from the line of sight, you would also forget to correct for the change in distance of the apparent limb!)

Phil

Looking at the color image Pluto appears redder to my eyes from the mid-latitude gray terrain and farther north.

And taking another look at the Triton images I don't see any craters visible until around closest approach, although with it retrograde orbit which is decaying, Triton may have been geologically active more recently than Pluto.

I suspect the impact that formed or captured Charon would have happened before the instability in the Nice model when the relative velocities were smaller.

I found this interesting article regarding craters on Pluto and Charon, originally published in Icarus Jan. 2015.

Their models suggest that Kuiper Belt Objects will have a different crater pattern than moons around, say Jupiter or Saturn.

For one thing, primary craters on Pluto and Charon will have a smaller diameter. For example, starting with a 1km diameter impactor:

Click to view attachment

The authors attribute this to the "gravitational focusing that may occur due to a large central body".

Their models also predict:

- Ejecta from Pluto and Charon escape more efficiently from the combined system, relative to ejecta from a satellite in orbit around a giant planet, due to the absence of a large central body.

- We estimate that Kuiper Belt Objects (KBOs) with diameters larger than 1 km should strike Pluto and Charon on (nominal) timescales of 2.2 and 10 million years, respectively.

So there should be some craters, but they will be smaller. It will be interesting to see how closely their current models match this strange region of the Solar System.

Full article: Craters and ejecta on Pluto and Charon: Anticipated results from the New Horizons flyby

I wonder if they are calderas are they darker because the erupted material is darker or could the lower elevation be acting as a trap for dark dust or sand.

This image was just posted on the NH SOC site.
As you can see the perspective has changed. NH is crossing in front of the pole.
Click to view attachment

Wrote down my own ramblings on the encounter from the SOC http://planetimages.blogspot.com/2015/07/r...y-personal.html

Looking at this map: http://www.unmannedspaceflight.com/index.p...st&id=36806 it looks like a lot of the high res imagery will be of the "heart" which doesn't yet appear to have nearly as many surface features as other areas. There will be some good shots of the border between the heart and the whale though. Does anyone know how the flyby was planned? Is it just based best logistics for the trajectory, or were the Hubble maps used? It makes sense that they would target the high albedo areas, but there was an awful lot of interesting stuff on the hemisphere that is turning away from us now.

-kap

If there were an objective scale for "interestingness" and someone had posted odds on Pluto's interestingness, the people who bet high would have won.

Triton was always the comparison case, and Triton's pretty interesting in its own right, but Pluto is looking very interesting without being a Triton clone. Or, at least it's hard to tell how much the things we are seeing are like Triton. There are signs of Titan, maybe signs of Mars.

I keep seeing these images and imagining Wayne and Garth from Wayne's World saying, "We're not worthy!"

Yes, I was expecting (for not particular reason) that the terrain would be a lot more uniform, so I was much less concerned about only imaging one hemisphere in great detail than I am now. We may need to launch a follow-up pretty quickly

I'm watching Nasa's Eyes now, we are getting a lot of Alice measurements.

-kap

A major planning consideration was to have Charon in the right position to light up the "far" side of Pluto with Charonshine. That determines the state of rotation of Pluto at flyby time. I'm not sure about the choice of longitude to overfly, but that was in large part a blind guess, anyway.

I think the high res imaging path is just about perfect, actually. I really like that we'll get the interface between the heart and the darkest material.

"A major planning consideration was to have Charon in the right position to light up the "far" side of Pluto with Charonshine. That determines the state of rotation of Pluto at flyby time. I'm not sure about the choice of longitude to overfly, but that was in large part a blind guess, anyway. "

The desire for a double occultation would have superseded both of those considerations. Then let the Charonshine fall where it may.

Phil

Hey Phil,
In the image I post above, think of it as an analog clock, is the limb from about 1:00 to 4:00 lit up by Charonshine?
Karle

Well this is quite interesting. In the latest images, I think (dangerous for me, I know) we may be seeing some atmospheric effects here at the lower and right edges.

-----------------------------------
2015-7-12 (S1) Pluto blink
-----------------------------------
Click to view attachment
(click to animate)


And here is the processed still frame.
Click to view attachment

Indeed. Not only will it capture some heart (1) and whale terrain (2), it will cover some of the mottled/swirly stuff (3) and the relatively smooth northern 'cap' (4).

Click to view attachment

I do wonder if the mosaic will be adjusted slightly southward to capture more of the whale terrain.

I don't think so. C-shine will be very faint. To see it at all we would need a long exposure, overexposing the rest of the disk.

Phil

Out of 15 shots, it looks like three are filled with the "heart", the other 12 are of very interesting looking boarder or relief enhancing terminator regions. The "heart" is, to me, an enigmatic feature and it may take an entire view of it at high resolution to figure it out.

just saw a posting of an old 1979 painting of pluto on the twitter feed thats really quite amazing.
The whole image is at http://www.cosmographica.com/spaceart/pluto-predicted.html

I'm hard pressed to think of a trajectory that would provide better coverage of a greater diversity of terrain as well.

I think that we should give the mission planners that have lived and breathed this mission for years the benefit of the doubt, eh?

Ted, that's a great blog about your personal history with Pluto.

Phil, thanks for posting that link to an informative and moving account of the naming of Charon. I'm a fan of "fun facts to know and tell," and that one's a gem.

Don't get me wrong, I think we are going to get amazing data, I probably just have a 'grass is always greener' feeling going on. In a perfect world, we could map the whole new world in high resolution, but we don't live in such a world and what we get will greatly advance our knowledge. Also watching the Eyes preview, there are several sweeps of the LORRI to other interesting areas, they just aren't included in the initial downlink.

-kap

Well now I know why everybody mispronounces Charon. Being interested in Greek mythology, it clashed when people always pronounced it Sharon. Interesting story.

Ted, nice story - but I think you mean 56 years since Luna 3!

Phil

Below are the three Pluto images from 7/12/2015. They have been enlarged 2x.

There is only 30 seconds between each image, so not surprisingly there is no change between the three other than Pluto's very very slight rotation (maybe).

The 2 o'clock position circular feature continues to look to me as a crater that froze before it had a chance to fully form. Then other times it looks like a large mountain with a depression below it extending quite a ways.

Click to view attachment

Hopefully everyone knows by now that the best is yet to come...

Andy

Looks like some of the dark areas are elevated terrain
Release Date: July 13, 2015
http://pluto.jhuapl.edu/Multimedia/Science...JHUAPL-SWRI.png

Update of "map animation" to the latest image:
Click to view attachment
I guess this will be the last update before we see a huge jump in resolution!

July 13, 2015 11:45 pm Eastern Time Zone in the USA
250,000 miles to go (the approximate distance to our Moon)
8 hours to closest approach ( 31,000 mph closing speed)
unbelievable!

NH is now completely within the perigee of the Earth's Moon at < 225,309mi.

Just over 1 light second. EOTSS shows observations of the small moons proceeding one by one.

Pluto, 12 of July 08:45, factor x3.
Click to view attachment

Charon, 12 of July 08:50, x3.
Click to view attachment

Turning towards Earth now. That's gotta be the 'insurance' data coming in now, right?

I've modified a capture from the approach animation to show a gibbous-phase Pluto illuminated by Charon alone during the solar eclipse. The only other possible light source will be a ring of light scattered forward by the exosphere at the limb, so that might be the best opportunity to see the Charon-facing side again, in addition to the otherwise hidden southern hemisphere.
Click to view attachment
Regarding the trajectory design, the solar and radio occultations for both bodies was no doubt a primary objective and probably ruled out a close approach pass on the Charon-facing side.

This page is nice for keeping up with what's going on, you can just refresh it if you don't want to scroll around to find where you are:

http://pluto.jhuapl.edu/Mission/The-Flyby.php

Edit:
And of course anybody who is keeping up with this thread should have this open if they can:

http://eyes.jpl.nasa.gov/eyes-on-pluto.html

Currently 7 DSN antenas pointing in NH direction