  The effective potential in universal like coordinates$(U, V, \theta, \phi)$,
which are smooth across the event horizon is derived and investigated the
ISCO(Innermost Stable Circular Orbits) explicitly in these coordinates for
extremal Kerr spacetime. Extremization of the effective potential for timelike
circular orbit shows that the existence of a stable circular geodesics in the
extremal spacetime for direct orbit, precisely {\it on} the event horizon in
terms of the radial coordinate which coincides with the \emph{principal null
geodesic congruences} of the event horizon. These null geodesic congruences
mold themselves to the spacetime curvature in such a way that Weyl conformal
tensor and its dual are vanished, that is why they are in fact \emph{doubly
degenerate principal null congruences}.
