Examining the dust of the tailless Oort-cloud comet C/2020 T2

We report our latest analysis of the Oort-cloud comet C/2020 T2 (also named Palomar or T2) observed at 2.06 au from the Sun (phase angle of 28.degrees 5) roughly two weeks before perihelion. It lacks a significant dust tail in scattered light, showing a strong central condensation of the coma throughout the apparition that is reminiscent of so-called Manx comets. Its spectral slope of polarized light increases and decreases in the J (1.25 mu m) and H (1.65 mu m) bands, respectively, resulting in an overall negative (blue) slope (-0.31 +/- 0.14% mu m(-1) ) in contrast to the red polarimetric color of active comets observed at similar geometries. The average polarization degree of T2 is 2.86 +/- 0.17% for the J and 2.75 +/- 0.16% for the H bands. Given that near-infrared wavelengths are sensitive to the intermediate-scale structure of cometary dust (i.e., dust aggregates), our light-scattering modeling of ballistic aggregates with different porosities and compositions shows that the polarimetric properties of T2 are compatible with low-porosity (similar to 66%), absorbing dust aggregates with negligible ice contents on a scale of 10-100 mu m (density of similar to 652 kg m(-3)). This is supported by the coma morphology of T2 which has a viable beta (the relative importance of solar radiation pressure on dust particles) range of less than or similar to 10(-4). The secular evolution of r-band activity of T2 from archival data reveals that the increase in its brightness accelerates around 2.4 au pre-perihelion, with its overall dust production rate that is about 100 times smaller than those of active Oort-cloud comets. We also found an apparent concentration of T2 and Manx comets toward ecliptic orbits. This paper underlines the heterogeneous nature of Oort-cloud comets, which may be investigated in the near future with dedicated studies of their dust characteristics.