Henry Spencer ) wrote:
: In article ,
: Bruce Sterling Woodcock wrote:
: And Pluto is 57.5 degrees retrograde? The latter is new to me as I had
: not known that we knew the axis tilt of Pluto.
:
: We determined it once we had radar pictures (and the Hubble).

: No, what quickly settled Pluto's axial tilt was the discovery of Charon
: (Pluto's moon) in the early 1980s. With a moon that big and close, the
: two just had to be tide-locked together, so the easily-observable orbit
: of Charon also gave us Pluto's axis.

Wait, doesn't the Moon orbit at an inclination different than that of
the Earth's equitorial plane? Tidal lock is one thing and axis tilt is
another, at least in the Earth/Moon system. Now, since the Earth is 81
times as massive as the moon and Charon is much larger in comparison to
Pluto, you could be right based upon that. But I think I would want to
check the rotation of Pluto compared to its orbital plane based upon
something else to make sure other than rely and Charon's orbital
characteristics.

Eric

: --
: MOST launched 30 June; science observations running | Henry Spencer
: since Oct; first surprises seen; papers pending. |