Mike Brown's Planets, season 4: sabbatical Options

[ngunn]

Now on sabbatical, Mike Brown has recently reactivated his mainly Transneptunian blog. Here is a tasty two-parter on Sedna for starters: http://www.mikebrownsplanets.com/2010/10/t...ere-part-2.html

[ElkGroveDan]

I like Brown's writing style.

[cbcnasa]

Excellent blog and mind stimulating

[Gsnorgathon]

And now, we interrupt your regularly scheduled program, to announce that Eris ain't so big after all.

[ngunn]

The consequences of which discovery could be far reaching indeed: http://www.mikebrownsplanets.com/2010/11/d...-are-crazy.html

[ngunn]

After some plutonic intrusions, the next instalment of the Sedna story: http://www.mikebrownsplanets.com/2010/11/t...ere-part-3.html

[Greg Hullender]

Mike's back. This time he's talking about Snow White.

http://www.mikebrownsplanets.com/

--Greg

[ngunn]

After another long lull, obsessive-compulsive rechecking of Mike's blog site is rewarded:
http://www.mikebrownsplanets.com/2013/11/s...s-in-space.html

[ngunn]

The essence of that article and the linked paper is that you can't make a large rocky body by assembling many small icy ones.

Here's a go at that problem. Start with a population of small particles, mostly silicate (rockdust), some ice. Suppose that rock-rock collisions are very bad at resulting in coalescence whereas ice-ice and ice-rock collisions do so more easily due to the absorption of energy by plastic deformation and partial melting. The rock particles would never find a permanent home until they ran into an already formed icy object. As the object grows it becomes better and better at trapping the ubiquitous rockdust.

[djellison]

Suppose that rock-rock collisions are very bad at resulting in coalescence whereas ice-ice and ice-rock collisions do so more easily due to the absorption of energy by plastic deformation and partial melting.

Is there anything in the literature to suggest those suppositions are true.

[ngunn]

Probably not, but does there have to be? Maybe there is but I don't know about it. It seems to me self-evident that the ice/water phase change would facilitate coalescence.

[djellison]

It seems to me self-evident that the ice/water phase change would facilitate coalescence.

Many many things in deep space are the inverse of self-evident.

And yes - there does have to be something...some sort of evidence that your theory holds water. Experimentation, simulation etc to lend it validity.

[ngunn]

Many many things in deep space are the inverse of self-evident.

Experimentation, simulation etc

1/ Very true!

2/ OK here's my winter project, following up on Mike Brown's entertaining terrestrial snowball anecdotes. I will try to make two snowballs collide and coalesce in mid-air. I expect it will require many attempts and I will need some help from the family.

If anyone would like to volunteer for the control group your task is to make it happen with two stones.

[Xcalibrator]

Is there anything in the literature to suggest those suppositions are true.

I'm sure ngunn's suggestion is on Mike Brown's list of possibilities, but no, there probably isn't any solid info to support it at the moment. As I understand it, we know how to form "pebbles" up to around 1 cm (from lab experiments and some theory), and then how to form larger bodies once you've gotten up to 1 km planetesimals (from bulk material properties), but in between is full of question marks. I can't remember the proper buzzwords for a good ADS search but one recent example paper is "Growth and fragmentation of centimetre-sized dust aggregates: the dependence on aggregate size and porosity," Farzana Meru, et al., MNRAS 435, 2371 (2013).

[alan]

I suspect the solution to the problem will turn out to be surprisingly simple.