there are some astronomical observations that indicate the presence of millimeter-sized cosmic dust grains. Such is the case of comet 67P/Churyumov-Gerasimenko (Fulle et al. 2015, Rotundi et al. 2015), circumstellar disks (e.g., Andrews & Williams 2005; Canovas et al. 2015, 2016; Kataoka et al. 2016), in particular, the circumstellar disk orbiting Fomalhaut and HR 4796A (Kalas et al. 2005, Milli et al. 2017, Min et al. 2010)
reqV=2.5 mm (volume-equivalent sphere radius)
oblate spheroid, irregularly highly porous
imaginary part higher than that of the White Porous Ball In Fixed Orientation
Muñoz O, Moreno F, Gómez-Martín JC et al. Experimental Phase Function and Degree of Linear Polarization Curves of Millimetersized Cosmic Dust Analogs. The Astrophysical Journal Supplement Series, vol. 247, pp. 19-32, 2020