[extropy-chat] Pluto New Horizons launch -getting ready

[Amara Graps]

Robert Bradbury
>It took me a while to understand this (particularly when they called
>it "hot plasma").  If I understand it correctly now this is because
>astronomers are relating temperature to the ionization state of the
>atoms/molecules (yes???).

Physicists too. Well, they might have been there first. Almost every
astrophysicist realizes at some point in their life, that if they
didn't take that plasma physics course while in university, they were
going to pay for it at some point later on. I think every astronomer
is also a plasma physicist at heart.

My plasma physics books are at work, but here is a beginning:
http://en.wikipedia.org/wiki/Plasma_(physics) 

>  However I question the number of 99% as I'm
>not under the impression that most material at stellar cores is in a
>plasma state (though I'm willing to be corrected).

A star's center is one of the best examples of a hot plasma: very
dense and very hot. It is at the top right of the
temperature/number-density chart: http://www.amara.com/E-4thstate.jpg

(I could only find this pretty chart, but I've seen others in the past
that are more detailed)

Us liquid/solid humans on our little cool (but still very dense) rock,
are a rare non-plasma phenomena in the universe.

>Of course one thing that has always bothered me about "hot"
>interstellar ions/molecules is *where* the hell are all of the
>electrons?

They are there. They _must_ be there (almost by definition) because
plasmas are (statistically) neutral. For evidence: we can look at
lightning and at our auroras (or our neon lights). In space, there
are different plasma probes flying on spacecraft in our solar
system measuring all of  the components of the plasma. One of the
most successful line of plasma instruments came out of the
group founded by James Van Allen:

http://www-pw.physics.uiowa.edu/

(don't forget to check out their fantastic space sounds page:
http://www-pw.physics.uiowa.edu/space-audio/)

Dust particles are a  kind plasma probe too because they
collect ions and electrons on their  surfaces which cause
the dust to charge up. The trajectories of the smallest
dust follow exactly as predicted for a charged particle
influenced/dominated by Lorentz forces

http://www.mpi-hd.mpg.de/dustgroup/~graps/earth/charging.html

>I thought I saw a paper recently that attributed at least the iron
>meteorites to having a limited set of sources (planetesimals) which
>were large enough to have undergone gravitational compression.

A limited set of planetesimals being the source of all/most of
the meteorites collected on Earth?  Given the 5 billion year
collisional history of our solar system, this sounds fishy to me.

Amara