JRS: In article , seen in
news:sci.space.policy, Henry Spencer posted at
Sun, 15 Feb 2004 23:04:56 :-
In article ,
Dr John Stockton wrote:
A close encounter with a planet can split a rubble pile
into a pair of rubble piles, by tidal interaction. (In fact, one of the
points offered in support of the rubble-pile hypothesis is precisely that
we see a suspiciously large number of double asteroids, which ought to be
fairly rare unless there is some specific mechanism that creates them.)

Why a pair of rubble piles? Half a rubble pile is still a rubble pile,
and should itself be split (ignoring the presumably improbable case of
an encounter virtually tangent to the Roche limit).

If memory serves -- I didn't pay close attention to the details -- the
two-way split of a rubble pile is a non-trivial interaction between tidal
forces and the rotation of the original rubble pile, and generally does
not involve further splitting of the resulting two piles.

Multi-way splits of fragile bodies are certainly possible, as witness SL9,
but they generally don't leave the fragments in orbit around each other.

OK, I can easily enough believe that if the spin rate gives a
centrifugal effect non-negligible in comparison with surface gravity,
then the break-up will occur at a greater distance, and that the
subsequent distribution of angular momentum from spin into spin + spin +
orbital will leave the new spins insufficient for further break-up.

"The satellite is here assumed not to be spinning." is now added to my
Roche material in gravity3.htm.

--
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