5
Implications of M, r for nebula
•Relative amount of H, He (compared to
heavy elements) drop for Saturn
then drop dramatically at Uranus and Neptune
then drop dramatically at Uranus and Neptune
•Why were these outer planets so less
efficient at capturing H, He?
–Their mass is still great enough to do
this, especially given low temperatures
in the outer solar system
in the outer solar system
•May be a problem of timing
–Accretion takes longer in the outer solar
system because
•The velocities of all objects there are
much less
•The distances between objects are
greater
•This is the same reason the periods of
the orbits are so long
–Uranus
and Neptune may have only started to grow to critical size by the time the H, He gas was being driven out
of the solar system
From our text Horizons, by Seeds