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We report our new analysis of Oort-cloud comet C/2020 T2 (Palomar) (T2)observed at 2.06 au from the Sun (phase angle of 28.5 deg) about two weeksbefore perihelion. T2 lacks a significant dust tail in scattered light, showinga strong central condensation of the coma throughout the apparition,reminiscent of so-called Manx comets. Its spectral slope of polarized lightincreases and decreases in the J (1.25 um) and H (1.65 um) bands, respectively,resulting in an overall negative (blue) slope (-0.31+/-0.14 % um^-1) incontrast to the red polarimetric color of active comets observed at similargeometries. The average polarization degree of T2 is 2.86+/-0.17 % for the Jand 2.75+/-0.16 % for the H bands. Given that near-infrared wavelengths aresensitive to the intermediate-scale structure of cometary dust (i.e., dustaggregates), our light-scattering modeling of ballistic aggregates withdifferent porosities and compositions shows that polarimetric properties of T2are compatible with low-porosity (~66 %), absorbing dust aggregates withnegligible ice contents on a scale of 10--100 um (density of ~652 kg m^-3).This is supported by the coma morphology of T2 which has a viable beta (therelative importance of solar radiation pressure on dust) range of <~10^-4.Secular evolution of the r-band activity of T2 from archival data reveals thatthe increase in its brightness accelerates around 2.4 au pre-perihelion, withits overall dust production rate ~100 times smaller than those of activeOort-cloud comets. We also found an apparent concentration of T2 and Manxcomets toward ecliptic orbits. This paper underlines the heterogeneous natureof Oort-cloud comets which can be investigated in the near future withdedicated studies of their dust characteristics.

On the dust of tailless Oort-cloud comet C/2020 T2 (Palomar)