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Extreme debris disks (EDDs) are rare systems with peculiarly large amounts ofwarm dust that may stem from recent giant impacts between planetary embryosduring the final phases of terrestrial planet growth. Here we report on theidentification and characterization of six new EDDs. These disks surround F5-G9type main-sequence stars with ages >100 Myr, have dust temperatures higher than300K and fractional luminosities between 0.01 and 0.07. Using time-domainphotometric data at 3.4 and 4.6$\mu$m from the WISE all sky surveys, weconclude that four of these disks exhibited variable mid-infrared emissionbetween 2010 and 2019. Analyzing the sample of all known EDDs, now expanded to17 objects, we find that 14 of them showed changes at 3-5$\mu$m over the pastdecade suggesting that mid-infrared variability is an inherent characteristicof EDDs. We also report that wide-orbit pairs are significantly more common inEDD systems than in the normal stellar population. While current models ofrocky planet formation predict that the majority of giant collisions occur inthe first 100 Myr, we find that the sample of EDDs is dominated by systemsolder than this age. This raises the possibility that the era of giant impactsmay be longer than we think, or that some other mechanism(s) can also produceEDDs. We examine a scenario where the observed warm dust stems from thedisruption and/or collisions of comets delivered from an outer reservoir intothe inner regions, and explore what role the wide companions could play in thisprocess.

A new sample of warm extreme debris disks from the ALLWISE catalog