5 moons accounted for (Charon was seen earlier):

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Latest release:

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They have this one with three images combined, two more recent and from different faces. It looks like Pluto will have a feature rich surface. I'm giddy with excitement.

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NASA will host a media teleconference at 1 p.m. EDT on Wednesday, June 3, to discuss the Hubble Space Telescope’s surprising observations of how Pluto’s moons behave, and how these new discoveries are being used in the planning for the New Horizons Pluto flyby in July.

NASA news audio page: http://www.nasa.gov/news/media/newsaudio/index.html

Slides from the talk (inc. youtube of Nix's chaotic orbit):
http://www.nasa.gov/content/goddard/bri ... to-s-moons

So if the barycentre of the Pluto-Charon system is above Pluto's surface, how many G's would I feel if I were standing on Pluto, with Charon overhead? Would I be almost weightless?

http://nssdc.gsfc.nasa.gov/planetary/fa ... ofact.html

very roughly, 1/20 g, so you'd weigh 5kg for every 100kg on Earth...

newolder wrote:http://nssdc.gsfc.nasa.gov/planetary/factsheet/plutofact.html

very roughly, 1/20 g, so you'd weigh 5kg for every 100kg on Earth...

Thanks, but I read that as the mean surface gravitation for Pluto, not the gravitation under the Charon-Pluto axis. My question is really what subtraction from Pluto's gravitation would standing under Charon provide? I could figure out the gravitation from Charon at that radius and subtract it, if I could be arsed.

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.

Ah well, I'll have to look elsewhere to try weightlessness on the surface of a world.

Interesting question. If the center of mass is above you, why wouldn't you feel negative total weight?

It is because you are closer to the mass at your feet than the mass in Charon above you. So when close to Pluto (as standing on the surface) you are far more influenced by Pluto's gravity. But as you approach the center of mass above, it switches to Charon having more influence.

If you were not standing on the surface of Pluto but were still at the same distance from the center of mass, you would then be attracted to the center of mass.

So it is your proximity to Pluto that keeps you attached to Pluto.

CdesignProponentsist wrote:Interesting question. If the center of mass is above you, why wouldn't you feel negative total weight?

It is because you are closer to the mass at your feet than the mass in Charon above you. So when close to Pluto (as standing on the surface) you are far more influenced by Pluto's gravity. But as you approach the center of mass above, it switches to Charon having more influence.

If you were not standing on the surface of Pluto but were still at the same distance from the center of mass, you would then be attracted to the center of mass.

So it is your proximity to Pluto that keeps you attached to Pluto.

That and my Velcro booties.

Is the surface the hooks or fuzz?

Definitely the fuzz. You'll see - New Horizons will reveal all, and if it doesn't, I can just blame the high flyby velocity.

Are we there yet?

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".

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".

I don't understand your question. Sorry.

newolder wrote:

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".

I don't understand your question. Sorry.

It wasn't a question, newolder, I was building on Cdesign...'s earlier point.

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...

Newolder, do you appreciate that net g is not constant over Pluto's surface, due to the proximity of Charon.