Pluto Surface Observations 1: NH Post-Encounter Phase, 1 Aug 2015- 10 Oct 2015 Options

[Gennady Ionov]

There are images (yet to be downlinked) of Pluto lit by Charon, and the central area lit would be near latitude 0 / longitude 0

I check LORRI trajectories in the NASA's Eyes software and conclude to my big regret, that all post-encounter frames was taken at the limb area and have exposure about 0.1 s, but not at least 10 s which neсessary to obtaining a good night side picture... I'm wrong?

[alan]

I read somewhere that the Charonshine images of Pluto would be MVIC images near close approach and LORRI images at a distance where Pluto would fill most of the frame. Also the LORRI images would be many short images which would be added, this will allow them to avoid smearing of the images and bleeding from the overexposed parts of the images.

[JRehling]

Checking the orbital positions, there were Charonshine opportunities for imaging Pluto on July 14, July 20, etc. and Plutoshine opportunities for imaging Charon on July 17, July 23, etc.

If we get some regional albedo information for the mid-southern latitudes, that would be great. A bonus would be if we get some details and/or could see if Charon has a dark region at the other pole, too. I'd love to see something like the Saturnshine images of Iapetus, but I'm not getting my hopes up.

[Gerald]

I check LORRI trajectories in the NASA's Eyes software and conclude to my big regret, that all post-encounter frames was taken at the limb area and have exposure about 0.1 s, but not at least 10 s which neсessary to obtaining a good night side picture... I'm wrong?

If my memory serves me right, long-exposure 4x4 binned images should have been taken for this purpose. I thought, this has been hinted at in one of the press conferences. We'll know for sure before the end of the year, after the browser images will be downlinked.

[Gennady Ionov]

Alan, Gerald, thank you very much for this encouraging information about night side pictures!!!
Once again I watch my animation of New Horizons FlyBy
https://www.youtube.com/watch?v=GYpw4joQPzo
trying to imagine how those will look like night shots :-)

[alan]

I believe these are the MVIC and LORRI Charonshine images listed in the New Horizon's Full Activity List

July 14 08:08:13 EDT New Horizons is taking an image of Pluto with MVIC from 20323.226 km away at est. resolution 0.40 km/pix.

July 14 21:47:42 EDT New Horizons is taking 180 images of Pluto with LORRI 4x4 from 692198.32 km away at est. resolution 14 km/pix.
July 14 21:57:27 EDT New Horizons is taking 180 images of Pluto with LORRI 4x4 from 700250.68 km away at est. resolution 14 km/pix. New Horizons is 31.9 AU from Earth.
July 14 22:11:53 EDT New Horizons is taking 90 images of Pluto with LORRI 4x4 from 712170.95 km away at est. resolution 14 km/pix.
July 14 22:16:53 EDT New Horizons is taking 90 images of Pluto with LORRI 4x4 from 716300.37 km away at est. resolution 14 km/pix. New Horizons is 31.9 AU from Earth.
July 14 22:21:53 EDT New Horizons is taking 90 images of Pluto with LORRI 4x4 from 720429.80 km away at est. resolution 14 km/pix.
July 14 22:25:00 EDT New Horizons' track ending with Madrid 70 m (DSS-63)
July 14 22:26:53 EDT New Horizons is taking 90 images of Pluto with LORRI 4x4 from 724559.23 km away at est. resolution 14 km/pix. New Horizons is 31.9 AU from Earth.

[JRehling]

According to Solar System Simulator, Charon was at half phase as seen from Pluto during those images, and decreasing with passing time. So those should be Charonshine images – not the best lit, but good resolution. It seems like several hours earlier would have been a better opportunity, but perhaps the thin daylit crescent of Pluto would have been a problem at that time.

[alan]

So roughly half of Pluto in Charonshine then.

[JRehling]

So roughly half of Pluto in Charonshine then.

All of Pluto's Charon-side in the light of a half Charon.

The portion of Pluto facing Charon never changes, so there's no variation in that regard whatsoever. At any point in time that Charon isn't "new" as seen from Pluto, that entire half of Pluto will get some Charonshine. Only the quantity of illumination will vary, not the areas on Pluto that are illuminated.

[scalbers]

A key part of this point is that half of the night side of Pluto will be illuminated by Charon.

[Phil Stooke]

Another point to consider: since the illumination is coming largely from the northern hemisphere of the reflecting body, it will be barely able to illuminate the south pole itself. And the bodies are pretty close to each other. Imagine you are at Pluto's south pole - can you see Charon at all? Or is it below the horizon, as Phobos and Deimos are from Mars's poles? In fact it will be below the horizon out to a certain distance from the pole, and for an additional distance, only the night side of Charon would be above the horizon, so not illuminating anything. It's intriguing to speculate on the appearance of Pluto from Charon's south pole - in some range of latitudes Pluto's night side would be above the horizon, its illuminated portion still below the horizon, but arcs of faintly lit atmospheric haze might reach up from the horizon as we saw in the backlit view. They might not make a full circle because of the geometry.

As for the range of longitudes, as the system rotates the illuminated night half will sometimes be better placed for viewing, sometimes less so. Light bleed from the sunlit crescent will be a problem, so when the Charonshine region is adjacent to the sunlit crescent we should have better viewing geometry but worse light pollution. When it's opposite the sunlit crescent it will be foreshortened but less contaminated. So a lot depends on the timing of imaging. I would like to see some simulations of this.

Phil

[Bill Harris]

half of the night side of Pluto will be illuminated by Charon.

A half-phase Pluto should be illuminated by a half-phase Charon, according to what was said about the Solar System Simulator model.

With the Earth-Moon duo, the phase of the Earth, seen from the Moon, is an inverse-mirror. A Crescent Moon, it "sees" a Gibbous Earth, and a Gibbous Moon sees a Crescent Earth. On our Moon, First or Last Quarter Earthshine is quite dim, and is somewhat overwhelmed by the illuminated half of the Moon. It may show something but my expectations are not high.

--Bill

[ngunn]

All the posters here clearly understand the geometry but not all visitors will. Can anyone provide a simple diagram for the Charonshine imaging showing which parts of the 'planet' will and won't be seen?

[Explorer1]

One could take a map like the ones we already have and outline the Charon-facing hemisphere on it too. That would show exactly how much of the southern hemisphere could be illuminated/imaged.

[scalbers]

Yes the approximate region on the Pluto maps would be between -90 and +90 longitude. On my map (centered on 180 longitude) this would be within 90 degrees of the left and right edges, or the left quarter and the right quarter. The latitude range as Phil pointed out would be not quite all the way to the poles, related to how many Pluto radii Charon lies at. It would be interesting to map this out in terms of the illumination, being proportional to the sine of Charon's angular altitude from each point on Pluto's surface. This altitude reaches a maximum at the zenith at latitude 0 longitude 0.

We could also import a Pluto map into Celestia, position the observer near Charon (on its Pluto facing side) and take a look at what portions of Pluto show up. This Charon illuminated portion will be fixed as a function of time, even though the sunlit phases of Pluto and Charon will vary. Meng-'Po Macula is at the best location.