New Horizons: Near Encounter Phase Options

[Eric H.]

Thirded! I haven't been this excited since Voyager 2 encountered Neptune back in 1989!

[TheAnt]

Thank you for letting us get an insight via your "Observation Playbook".
I can only echo what already been said, that this will indeed be one interesting encounter.

Now I hope you give NH another good workout so she wont sprain a muscle during that intense cosmic ballet performance. =)

[tedstryk]

I will chime in and say that a major part in New Horizons success thus far has been its team dynamic. I have been amazed, given the competing priorities, at the cooperative spirit with which things are dealt with.

[nprev]

Good morning from Los Angeles! Today marks the beginning of the near encounter phase. NASA TV will air the pre-flyby briefing at 1430 GMT today (13 Jul). Note that all times are subject to change as events unfold.

Please utilize this thread for all New Horizons commentary for the next several days. Here we go!!!

[Nafnlaus]

One thing that was being discussed in the last thread, about all of the features that look like "rivers" or "lakes" and the criticism that Pluto's pressure is too low for, say, liquid nitrogen to flow:

Given a triple point pressure of around 12kPa and a solid density of 1027 kg/m^3, 3,2kPa surface pressure, and 0,655m/s^2 pluto surface gravity, Pluto's triple point could be hit underneath as little as 13 meters of nitrogen ice (a bit more, as it would have to have at least a tiny bit of "fluff" to it to float, but that's to be expected). Other ices floating on it such as methane ice could have the same effect. And note that this ice wouldn't be heavily packed due to Pluto's weak gravity, it's the equivalent of less than one meter of nitrogen ice under Earth's gravity. Picture how much a meter of water snow (roughly the same density) packs down on Earth; I'd expect something roughly in the same ballpark - perhaps a situation like arctic sea ice.

Basically, even if there's not liquids flowing on the surface (eutectics or whatnot), there could still be liquids at a shallow depth with a weak ice pack on top of them. And iced-over rivers still flow and move things around.

[Webscientist]

Thanks for the analysis and the calculations Nafnlaus. That's the relevant problem. I was intersted in peforming that kind of simulations. No need to dig deep for the future lander if you're right.

[Nafnlaus]

An interesting thing is that there's a lot of potential liquids and mixtures of liquids / slushes / etc at different (shallow) depths that could be involved here, going through a wide range of dynamic changes as Pluto moves through its seasons. There could be some very complex processes involved in shaping this landscape. I'm sure whatever data comes back, it's going to lead to some very interesting papers down the road

[nprev]

Briefing placard now up on NASA TV.

[Explorer1]

Starting now....

[Bjorn Jonsson]

I have been attempting to measure Pluto's radius from the images that have been obtained in the past few days. I have consistently been getting a values of 1190-1195 km in most cases (1194 km for the latest image). This is close to the radius that SPICE uses (1195 km) but I have seen smaller values elsewhere. Wikipedia gives two values, 1184 km and "1161 km (solid)". The PDS Rings Node Pluto Viewer seems to use a value of 1153 km (selectable in "Field of View" but I'm not completely sure this is the value used to render the Pluto diagrams - I suspect that value may be bigger).

I haven't measured Charon as thoroughly and not in the latest images but I have usually gotten values of 590-600 km. This isn't very far from the SPICE value (605 km).

[nprev]

Pluto's polar cap confirmed as N2 & CH4 ices.

Alan states radius as 1185 km +/- 10.

[Bjorn Jonsson]

Alan states radius as 1185 km +/- 10.

Saw this on NASA TV, nice to see measurements from the NH team only minutes after I posted my (much more crude) measurements here.

[nprev]

By my count, we now have three different pronunciations of "Charon".

[Paolo]

given how it's written in Greek, "kharon" is the correct one

[alk3997]

given how it's written in Greek, "kharon" is the correct one

However, the discoverer's wife's name is Charlene. Therefore the pronunciation is similar to Sharon (or Charlene). Wives usually win...