tokens: K are highlighted. The inset summarizes the distribution of all shown planets over temperature. Overlaid are two lines of constant temperature. The 1000 K line corresponds to a change in aggregation observed in our work (see below). 1500 K is approximately the upper limit of the condensation region for typical silicates. The database is still one with low statistics, and detailed dependencies on temperature might be discussed. There is, e.g., a maximum at about 500 K, but the distribution might just as well be considered flat in a wide range. None of these statements are statistically significant at the moment. Nevertheless, there is a clear gap in the occurrence of planets between about 1000 K and 1500 K. For a planet forming at a larger distance from the star, the inward drift would not need to stop at the 1000 K line. Also, from a more general perspective of late planet formation phases there is no obvious reason why planets should not form, e.g., at 1100 K as likely as at 900 K. That leaves the question whether this temperature gap is inherited from the early phases of planet formation by aggregation at elevated temperatures. More often than not, planet formation and its limits are considered in light of radial distance. It might be argued that the lack of planets at higher temperatures might be due to a closer distance and a related lack of material for planet formation. Certainly, temperature and distance are related, but we note that they are not the same. Small changes in stellar mass already lead to large luminosity and significant temperature variations. However, the local material available will not significantly change. Also, it is currently often argued that inner planetary systems are formed from material drifting inward (Boley Ford 2013 ; Wurm et al. 2013 ; Hu et al. 2014 ). Inward drift is a classical mechanism for redistribution of matter (Weidenschilling 1977 ). As a special aspect, e.g., Ebel Alexander ( 2011 ) suggested that Mercury might have formed from dusty matter (chondritic porous interplanetary particles) drifting inward that were reprocessed in a region of higher temperatures with a composition that is then very different from solar composition. Considering such work, one motivation for our experiments is a radial inward drift of a mix of materials (see below). The mass of material available for planet formation does not necessarily depend only on the radial distance to the star. We also note that current planet temperatures and temperatures at the time of dust aggregation might not be the same. They might be comparable if the relevant aggregation occurred in a passive disk. They might have been higher in a still actively accreting disk. However, accretion of dust at these active times might have removed these aggregates again. In any case, we do not claim to have the only answer to planet formation in the inner disk at high temperature, but we think it is curious that there is a temperature limit in the exoplanet
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