Do giant-planet cores grow mainly by pebble accretion?
In plain words
A growing core can sweep up drifting pebbles efficiently because gas drag slows them as they pass. Whether this, or collisions with kilometer bodies, built the cores of Jupiter and Saturn is debated.
Precise statement
For cores reaching $\sim 10\,M_{\mathrm{earth}}$ within a disk lifetime of $\sim 3\,\mathrm{Myr}$ at $5-10\,\mathrm{AU}$, determine whether accretion of pebbles with $\mathrm{St} \sim 10^{-3}-10^{-1}$ dominates over accretion of planetesimals. Tests include the isotopic split between non-carbonaceous and carbonaceous meteorites (attributed to early Jupiter blocking pebble drift), disk dust masses and the composition of giant-planet envelopes.
What would settle it
Disk-evolution and core-growth models that match the meteorite isotope chronology, ALMA disk dust masses and the heavy-element content of Jupiter.