Context :

Aims : Collisional growth of dust occurs in all regions of protoplanetary disks with certain materials dominating between various condensation lines .
The sticking properties of the prevalent dust species depend on the specific temperatures .
The inner disk is the realm of silicates spanning a wide range of temperatures from room temperature up to sublimation beyond 1500 \mathrm { K } .

Methods : For the first time , we carried out laboratory collision experiments with hot levitated basalt dust aggregates of 1 mm in size .
The aggregates are compact with a filling factor of 0.37 \pm 0.06 .
The constituent grains have a wide size distribution that peaks at about 0.6 \mu \mathrm { m } .
Temperatures in the experiments are varied between approximately 600 \mathrm { K } and 1100 \mathrm { K } .

Results : Collisions are slow with velocities between 0.002 \mathrm { m } \mathrm { s } ^ { -1 } and 0.15 \mathrm { m } \mathrm { s } ^ { -1 } , i.e. , relevant for protoplanetary disks .
Aside from variations of the coefficients of restitution due to varying collision velocities , the experiments show low sticking probability below 900 \mathrm { K } and an increasing sticking probability starting at 900 \mathrm { K } .

Conclusions : This implies that dust can grow to larger size in hot regions , which might change planet formation .
One scenario is an enhanced probability for local planetesimal formation .
Another scenario is a reduction of planetesimal formation as larger grains are more readily removed as a consequence of radial drift .
However , the increased growth at high temperatures likely changes planetesimal formation one way or the other .