That seems to be a question but incorrect punctuation makes me hesitant to reply...

newolder wrote:

Wouldn't the result depend on where on the surface you measued it?

This is not a question? Ok, I'll just slide over here and keep quiet...

OK, that bit was a question - a rhetorical one. I thought you would realise that. My thesis in that post, however, was not a question, but building on Cdesign...'s point about floating above Puto.

... There can't be much dust on either Pluto, or Charon, because any such loose material would collect at the gravitational centre.

DavidMcC wrote:

newolder wrote:My sums could be wrong but I calculate the gravitational force of Charon on a test mass (1 kg) on the surface of Pluto (19 600 km away) as fractions of millinewtons. Measurable but tiny.

Wouldn't the result depend on where on the surface you measued it? As Cdesign... pointed out, you would float above the surface of Pluto if you were directly underneath Charon, but this would only happen when you are near the centre of gravity of the system, and can look up at Charon in the (black) "sky".

No, the centre of gravity is an equilibrium point, but it's an unstable equilibrium. If you're slightly closer to Pluto, you'll fall towards Pluto. If you're slightly closer to Charon, you'll fall towards Charon.

The effect of Charon is a tidal force, just like our own Moon, which is proportional to the mass of Charon and the inverse cube of the distance between Pluto and Charon. Since the mass of Charon is 1/10 the mass of Pluto and the distance is more than 10 times the radius of Pluto, the tidal force is about a 10000 times smaller than the surface gravity of Pluto.

Recent addition from the National Space Society...
https://www.youtube.com/watch?t=14&v=aky9FFj4ybE

Nice.

Getting closer

It almost looks like our moon's lunar mare features. Large flooded then frozen crater basins.

June 21st color image of Pluto and Charon

After deconvolution of the latest Charon image data:

Amazing how much detail you can extrapolate from a fuzzy ball.

CdesignProponentsist wrote:Amazing how much detail you can extrapolate from a fuzzy ball.

It's prone to errors, though, because a small error in the undeconvoluted plot leads to a large error in the deconvoluted plot. (I say this from experience of deconvolution in a different context - Rutherford backscattering spectra for determining ion implant profiles in silicon.)

Starting to get some real detail now

^ Interesting write-up on these images by Phil Plait aka BadAstronomer

Interesting article

Enceladus' tiger stripes came to mind when I saw those 4 marks. Also it would be really awesome to find another planet/moon system formed from an impact other than the Earth/Moon system which would indicate that it may be more common then you would think.

Those images still look pretty artefacty, especially the one on the right.

Made of Stars wrote:Those images still look pretty artefacty, especially the one on the right.

There's a lot of guesswork and enhancement going on - the images are only around 25-50 pixels on the probe's camera.

Yeah. Less than 2 weeks till we know for certain. Feels like an eternity though.

NASA reestablish communications with New Horizons after glitch
Phew!1