  The evolution of gravitationally unstable protoplanetary gaseous disks has
been studied with the use of three-dimensional smoothed particle hydrodynamics
simulations with unprecedented resolution. We have considered disks with
initial masses and temperature profiles consistent with those inferred for the
protosolar nebula and for other protoplanetary disks. We show that
long-lasting, self-gravitating protoplanets arise after a few disk orbital
periods if cooling is efficient enough to maintain the temperature close to 50
K. The resulting bodies have masses and orbital eccentricities similar to those
of detected extrasolar planets.
