beta Pic dust

From: Amara Graps (
Date: Sun Nov 26 2000 - 10:43:58 MST

From: "Michael M. Butler" <>, Sat, 25 Nov 2000

>Beta Pic has a dust disk around it, doesn't it?

Yup. Edge-on.. ~1000 AU extended from the star.

>Pretty trippy to think of a star fifty light years away as a clear
>dust source here.

See, I thought it would boggle the mind, once given the thought :-).

Think: it's the first interstellar contact (even if they are just
dust particles ...)

>What are typical speeds of these particles when they arrive in our

They travel at speeds up to 75 km/sec (45 km/sec with respect to the

>I see that some folks claim dust rings in the disk might have been
>formed by a star passing beta Pic only 100kyears ago. Is that enough
>time for dust to arrive here? What I'm trying to get at is, has the
>dust been arriving all along from the disk, or is it a result of
>recent "swirls" associated with ring formation? Hmm.

Until someone finds some other kinds of data, we only have our current
radar meteor observations to know, so I don't know.

The mechanisms are fascinating though. I would love to have it as
my thesis topic, if I didn't already have a thesis topic (below).

For a dust particle to escape from beta Pic, it would have to be
accelerated to greater than beta Pic's escape velocity. What might do
that? If the dust particles are small enough, then the Lorentz force
(from beta Pic's magnetic field) would do it.

For example, dust from Io's volcanoes in the Jovian system is
accelerated enough by Lorentz forces (Jupiter's magnetic field) to
escape Jupiter and be detected outside Jupiter's magnetosphere by
the Ulysses, Galileo, and Cassini spacecraft. The picture that we
have for the Io dust ("Jovian dust streams") is a little like a
"dust sprinkler system", spewing the dust in all orientations (here
is my thesis topic). The magnetic field of Jupiter can act as a mass
spectrometer, selecting the smallest particles to be accelerated the
most, so then the spacecraft see mostly the tiny nanometer-sized

But the beta Pic particles are 40 microns... rather large to be
dominated by Lorentz forces, which dominate submicron sized

So what other force mechanism? Can gravity accelerate 40 micron
sized particles from there to here? Can radiation pressure force? I
don't know.

Also, the interstellar beta Pic dust particles have to be the right
the size and velocity (and charge and other bulk properties) to
enter our solar sytem. The particles are too big to be embedded in
the interstellar gas flow that flows through our solar system. The
dust particles' optical (etc.) properties are such that they can
penetrate deep into our heliosphere, to Earth, which means that
radiation pressure force from our Sun is not blowing them out. Or
perhaps it is, but on different sized particles than the ones that
we are detecting (duh).

OK, so thinking out loud. I haven't worked out any of this, however,
probably Jack Baggaley, the New Zealand radar researcher who
reported the results, has, no doubt, considered these things.

Still mind boggling.


Amara Graps email:
Computational Physics vita: finger
Multiplex Answers URL:
"Sometimes I think I understand everything. Then I regain
consciousness." --Ashleigh Brilliant

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