  Planetary systems are born in the disks of gas, dust and rocky fragments that
surround newly formed stars. Solid content assembles into ever-larger rocky
fragments that eventually become planetary embryos. These then continue their
growth by accreting leftover material in the disc. Concurrently, tidal effects
in the disc cause a radial drift in the embryo orbits, a process known as
migration. Fast inward migration is predicted by theory for embryos smaller
than three to five Earth masses. With only inward migration, these embryos can
only rarely become giant planets located at Earth's distance from the Sun and
beyond, in contrast with observations. Here we report that asymmetries in the
temperature rise associated with accreting infalling material produce a force
(which gives rise to an effect that we call "heating torque") that counteracts
inward migration. This provides a channel for the formation of giant planets
and also explains the strong planet-metallicity correlation found between the
incidence of giant planets and the heavy-element abundance of the host stars.
