He3 on asteroids?

Is there any known or guessed quantity of He3 on asteroids or dead
comets? If an object has been orbitting for 4+ billion years, it
should have collected some from the solar wind. It seems that He3
would be easier to obtain from something like Eros than the Moon, if
it existed in similar density. If there was a supply, collecting and
separating He3 could be much simpler in the micro-G environment.

I did a quick Google and found little, but am wondering what you
think?

Josh

In article ,
Josh Gigantino wrote:
Is there any known or guessed quantity of He3 on asteroids or dead
comets? If an object has been orbitting for 4+ billion years, it
should have collected some from the solar wind.

The big uncertainty is that we know essentially nothing about the depth
and age of the regolith on asteroids.

Yeah, there'd probably be some, but whether it's worth exploiting is
another question.

...If there was a supply, collecting and
separating He3 could be much simpler in the micro-G environment.

Or not, as the case may be. Handling fine powders may well be easier
in gravity.
--
MOST launched 30 June; science observations running | Henry Spencer
since Oct; first surprises seen; papers pending. |

Josh Gigantino wrote:
Is there any known or guessed quantity of He3 on asteroids or dead
comets? If an object has been orbitting for 4+ billion years, it
should have collected some from the solar wind. It seems that He3
would be easier to obtain from something like Eros than the Moon, if
it existed in similar density. If there was a supply, collecting and
separating He3 could be much simpler in the micro-G environment.

I did a quick Google and found little, but am wondering what you
think?

Josh

From pages 204 and 205 of _Mining The Sky_ by John S Lewis

"But the circumstances of the asteroids differ from those we have
studied on the Moon. First, the intensity of the solar wind drops off
roughly with the square of the distance from the Sun. Therefore an
asteroid near 3.2 AU from the Sun experiences a solar wind flux that is
only a tenth that felt by the Moon. Second, accumulation of solar wind
gases on the Moon is aided by 'gardening' of the lunar surface by small
impacts, which constantly expose fresh material to the solar wind and
constantly bury gas-saturated surface grains out of harm's way. On
asteroids, even small impact events can remove regolith material by
ejecting it at speeds greater than the asteroid's tiny escape velocity.
Thus, "mature" surface grains with high contents of implanted gases are
preferentially lost, not preserved. Finally, the total exposed surface
area of the asteroids is less than the surface area of the Moon. For all
these reasons, extraction of helium-3 from the surfaces of asteroids is
not likely to be competitive with that from the Moon."

An excellent book in my opinion.
http://www.amazon.com/exec/obidos/tg...92717?v=glance

Although I think the last part of the paragraph must be in error. Surely
the surface area of the asteroids is greater than the Moon's (even
though the Moon outmasses the asteroids).


--
Hop David
http://clowder.net/hop/index.html

Josh Gigantino wrote:
Is there any known or guessed quantity of He3 on asteroids or dead
comets? If an object has been orbitting for 4+ billion years, it
should have collected some from the solar wind. It seems that He3
would be easier to obtain from something like Eros than the Moon, if
it existed in similar density. If there was a supply, collecting and
separating He3 could be much simpler in the micro-G environment.

I did a quick Google and found little, but am wondering what you
think?

Josh

From pages 204 and 205 of _Mining The Sky_ by John S Lewis

"But the circumstances of the asteroids differ from those we have
studied on the Moon. First, the intensity of the solar wind drops off
roughly with the square of the distance from the Sun. Therefore an
asteroid near 3.2 AU from the Sun experiences a solar wind flux that is
only a tenth that felt by the Moon. Second, accumulation of solar wind
gases on the Moon is aided by 'gardening' of the lunar surface by small
impacts, which constantly expose fresh material to the solar wind and
constantly bury gas-saturated surface grains out of harm's way. On
asteroids, even small impact events can remove regolith material by
ejecting it at speeds greater than the asteroid's tiny escape velocity.
Thus, "mature" surface grains with high contents of implanted gases are
preferentially lost, not preserved. Finally, the total exposed surface
area of the asteroids is less than the surface area of the Moon. For all
these reasons, extraction of helium-3 from the surfaces of asteroids is
not likely to be competitive with that from the Moon."

An excellent book in my opinion.
http://www.amazon.com/exec/obidos/tg...92717?v=glance

Although I think the last part of the paragraph must be in error. Surely
the surface area of the asteroids is greater than the Moon's (even
though the Moon outmasses the asteroids).

--
Hop David
http://clowder.net/hop/index.html

Hop David wrote:

From pages 204 and 205 of _Mining The Sky_ by John S Lewis

"[...] For all
these reasons, extraction of helium-3 from the surfaces of asteroids is
not likely to be competitive with that from the Moon."


I wonder if comets may have a larger amount of 3He. This would
not be implanted from the solar wind, but trapped in ices as the
comets formed in the protostellar nebula.

Paul

"Paul F. Dietz" wrote in message ...
Hop David wrote:

From pages 204 and 205 of _Mining The Sky_ by John S Lewis

"[...] For all
these reasons, extraction of helium-3 from the surfaces of asteroids is
not likely to be competitive with that from the Moon."


I wonder if comets may have a larger amount of 3He. This would
not be implanted from the solar wind, but trapped in ices as the
comets formed in the protostellar nebula.

Paul

That could be.
There is an excess of He-3 in interplanetary dust particles, many of
which are from comets.
He-3 trapped in comets would then not suffer the surface loss
mentioned in connection with asteroids.
But that makes me wonder about the amount of He-3 in the protostellar
nebula, maybe that could be trapped inside asteroids too?

Al Jackson wrote:

But that makes me wonder about the amount of He-3 in the protostellar
nebula, maybe that could be trapped inside asteroids too?

Possibly, but much asteroidal material has been extensively thermally
processed. Maybe carbonaceous chondrites? This could be tested
by examining meteorites, if it hasn't been already.

Paul

Paul F. Dietz wrote:
Hop David wrote:

From pages 204 and 205 of _Mining The Sky_ by John S Lewis

"[...] For all these reasons, extraction of helium-3 from the surfaces
of asteroids is not likely to be competitive with that from the Moon."



I wonder if comets may have a larger amount of 3He. This would
not be implanted from the solar wind, but trapped in ices as the
comets formed in the protostellar nebula.

Paul

As I understand it ordinary 4He is a product of uranium decay and 3He is
from stellar fusion. I'd expect the accretion disk from which the solar
system was formed to have more of the lighter isotope than what we see
on earth (since its thought the disk was remnants of earlier stars).

It seems to me our 4 gas giants would have lots of 3He. Helium is a gas
at Neptune distances. How would the lighter bodies in the Kuiper Belt
accrete a gas?

--
Hop David
http://clowder.net/hop/index.html

Hop David wrote:

It seems to me our 4 gas giants would have lots of 3He. Helium is a gas
at Neptune distances. How would the lighter bodies in the Kuiper Belt
accrete a gas?

They wouldn't; it might be trapped in growing ice grains.

Alternately, 3He is produced in situ by spallation. IIUC, the trapped
helium in some meteorites is about 2% 3He (the rest 4He, much of that
from radioactive decay.) I don't know the absolute concentration of
these isotopes, unfortunately.

Paul

Hop David wrote in message ...

From pages 204 and 205 of _Mining The Sky_ by John S Lewis

snip MTS quote


Although I think the last part of the paragraph must be in error. Surely
the surface area of the asteroids is greater than the Moon's (even
though the Moon outmasses the asteroids).

Thanks Hop! I sometimes forget there are these strange, rectangular
things called "books" next to my computer desk. I've got both "Rain of
Iron & Ice" and "Mining the Sky", I'll brush up on what Mr. Lewis
says.

I agree on the surface area issue. Thousands of roughly spherical
objects all rotating slowly should have a vast collective surface. For
the NEOs that are "rubble piles", there would be that much more
surface area, and a method for trapping He3.

Josh