> On 24 Nov 2014, at 23:57, Tim <xxxxxx@little-possums.net> wrote:
>
> On Mon, Nov 24, 2014 at 07:16:53PM +0000, Timothy Collinson wrote:
>>> On 24 Nov 2014, at 12:07, Tim <xxxxxx@little-possums.net> wrote:
>>> From much of
>>> Triton's surface, Neptune would never be visible at all.
>>
>> "Much"?  Is it not simply 'half'?
>
> Slightly less, since Neptune is rather large in Triton's sky.  From
> some parts just inside the back half, part of Neptune would still be
> visible above the horizon.

That's true.  Had forgotten its size.

>  Then again from others just inside the
> near half, an inconvenient terrain feature may obscure Neptune.

Good point.
>
>
>
> I think that's enough to be visible, though much of the time they
> might be lost in the millions of times brighter glare from Neptune
> itself or worse, the Sun.

Ok
>> !
>>
>> Sounds, however, if there's enough wiggle room for a bit of fiction
>> if desired.
>
> Yes, always some room for that.

Phew!

>
>
>> - would the frozen Nitrogen layer sit on the rock or water (etc)
>>  below, or would there be any kind of gap (I'm specifically
>>  thinking human sized!)
>
> I'm not a planetary scientist or even a geologist, but I would expect
> that the temperature would fairly gradually increase with depth, and
> cause some sort of stratification.  My guess would be a surface crust
> of solid nitrogen, water ice, and CO2 on top, giving way to mostly
> water and CO2 ice with liquid nitrogen in pockets and crevices, and
> maybe some slush mixture.  Going down further, any nitrogen would be
> confined to pockets of high-pressure gas under ice,

Ooooh, high pressure and PCs drilling... that sounds like what Orbital might refer to as a 'complication'!

>
>
>> - roughly how deep is the Nitrogen layer?
>
> I don't think we have enough information to tell.  I would guess at
> least 20-50 km,

Ah, ok.  Some what deeper than I'd imagined...

> else the thermal gradient would significantly heat the
> surface, which isn't observed.  The flow of interior heat reaching the
> surface must average at most about 10 milliwatts per square metre
> (Earth averages about 90 mW/m^2).  A thinner crust would mean a
> greater temperature gradient and hence more heat flow.
>
> Then again that thickness range is based on data I have for thermal
> conductivity of relatively pure substances under lab conditions, not
> some messy mixture in Triton's crust.

Hah!  Noted. :-)
>
>
>> - how long would it take to drill though (I'm thinking of a hole
>> wide enough to take a human sized capsule)?  Or are we now in the
>> realm of make up something that sounds reasonable?!
>
> It would depend entirely upon the technology

Hmmm, No idea on that actually.  Except Orbital is generally TL9ish so not much beyond what we have now.  A bit maybe - I was thinking in terms of hours, not months.  Dramatic licence.

> and economic resources
> available in the setting.  Although the gravity is much less and
> consequently the pressure does not increase nearly as fast as on
> Earth, it's still a very long way down and an enormous amount of ice
> to drill through.

But 'a while' clearly!

Many thanks for the pointers.  Really appreciated.  And even if you don't claim to be a planetologist, you'd be more than capable of playing one in the adventure... :-)

tc