> Our own "Indy" (Going into the ocean at 600 mph? B-o) wrote:
> ...and I indicated some asteroids range out as far as 5.2 AU from the
these asteroids are part of the Kirkwood Gap phenomenon, and are called Trojan
Asteroids, something some of you may have heard of before, in some dim faint
distant memory from a basic astronomy class. <<
To which Sturart replied:
> I think there are Trojan point asteroids described in the
<
I'm no physics expert, but my understanding of the Trojan point concept is
that it's a quirk of gravitation. If you have two large masses (does one have
to be
much bigger than the other?) orbiting each other -- or, for simplicity,
let's
consider one of them orbiting the other -- then points in the orbit 60
degrees ahead and behind the mass are gravitationally stable, i.e., another
mass (and this time I think it has to be much smaller than either of the first
two) located at one of those points will stay there and won't be pulled out of
position by gravity (of course, you do have to deal with gravitational effects
from any other bodies in the system, but they will hopefully be small).
Which makes the Trojan points a really good place to put a space station or an
O'Neill colony. It also means that, given enough time, asteroids that drift
through
these points may collect there -- which can mean that there's a ready
supply of raw material to make that O'Neill colony! Also that you need a good
asteroid
defence for when the next Trojan-wannabe drifts through...
> (ps: knowing the above, I did run a PBeM FT game last year that took
So you were fighting in and around a Trojan point! They're prime locations for
battles, because they're where raw material collects.
I hope no-one is going to tear my "explanation" apart, but whether they
do or
not, could some of the _real_ astrophysics buffs answer these:
-- Are the Trojans the same as the L-4 and L-5 Lagrange points?
-- Are points 120 degrees ahead and behind the orbiting mass stable? (I
know 180 is!)
I should know this stuff! I did once, but, like Rabbit, I've forgotten.
<g>
[some may thing this is drifting off-topic, but if you want to deal with
'real', as opposed to fake Hollywood asteroid fields, it helps to understand
them ;-) ]
[earlier I wrote:]
> ...and I indicated some asteroids range out as far as 5.2 AU from
<
> [quoted text omitted]
Where Phil then pops in with:
> I'm no physics expert, but my understanding of the Trojan point concept
Yep, you essentially got it right. The Trojan points are indeed 60 degrees
ahead/behind Jupiter's orbit, and are stable areas in and of themselves.
This is one aspect of the Kirkwood gaps. The Kirkwood Gap phenomenon takes
place where you have resonances with Jupiter's (or any other sufficiently
large-massed body) orbit. These resonances are simple fractions of
Jupiter's
orbit (eg, 3/5, 1/2, 2/3, 1/1, etc). The further away (closer 'in' the
orbital plane) from Jupiter's orbit, the more the gaps are *gaps* and cause
the asteroids to form orbital 'rings' (these gaps would correspond to orbital
ratios with Jupiter of 3:1, 5:2, 7:3, 2:1, and 5:3). The closer you get to
Jupiter's orbit the gaps go from being rings to clumps or groups (these occur
at 3:2, 4:3, and 1:1, where the 1:1 groups are the Trojans).
Now...did that make any sense, or did I just confuse everybody?
> Which makes the Trojan points a really good place to put a space
Welllll, yeah, it's a stable spot in space in the overall scheme of things,
but within that little area there is a lot of oscillation. You'll need to be
set for fending off constant potential collisions. This has been a concern for
one of the possible NGST (Next Generation Space Telescope) orbits. Some are
wanting to put it at one of the Lagrange points, but others are concerned
about some of the debris that may have collected there colliding into the
telescope (no, I don't know how they deal with this with the TDRSS satellites,
but I do know they have some limited capability to manually move those guys)
> (ps: knowing the above, I did run a PBeM FT game last year that took
Works for me. :-)
> I hope no-one is going to tear my "explanation" apart, but whether they
Essentially, yes (though I'd have to go look up exactly where the L-4
and
L-5 points are in orbit wrt each other).
> -- Are points 120 degrees ahead and behind the orbiting mass stable? (I
They are, but I don't *think* quite as stable as 60 degrees
ahead/behind.
> I should know this stuff! I did once, but, like Rabbit, I've forgotten.
<g>
S'okay. I knew it all once, too, long ago, then my job has taken me more into
running a spacecraft than keeping up with things. I've been digging through
all my books (and the library upstairs) as time has allowed me to refresh
myself on this stuff again. Some I actually remember still...
Mk