Early Activity in Comet C/2014 UN271 Bernardinelli–Bernstein as Observed by TESS

We used long duration observations from the Transient Exoplanet Survey Satellite (TESS) to investigate the behavior of comet C/2014 UN271 Bernardinelli–Bernstein at large heliocentric distances. By combining data from sector 03 (976 30 minute exposures from 2018), and sectors 29 and 30 (3585 and 3410 10 minute exposures, respectively, from 2020), we produced deep coadded images of the comet. A comparison of these results with similarly processed images of inactive Kuiper Belt objects and asteroids reveals that the comet was already exhibiting coma at heliocentric distances 23.8 and 21.2 au, making this one of the most distant comets for which preperihelion activity has been directly detected. A simple syndyne analysis of asymmetries in the coma suggests that activity probably started several years prior to these observations, and likely arose from emission in roughly the sunward direction. The images were used to produce photometric lightcurves, though no rotational variability was detected. We used NEOWISE observations from 2020 November 26–28 to place an upper limit of 2 × 1028 molecules s−1 (3σ) on the CO production rate.

The fast rotation of Orcus obtained from TESS measurements

<p>(90482) Orcus is one of the largest Kuiper belt objects, with one known, relatively large satellite, Vanth. There have been several ~10-20h rotation periods reported in the literature for Orcus, with considerable uncertainty. Here we report on recent measurements of Orcus with the TESS Space Telescope providing a light curve period of 7 h, the fastest rotation among those large trans-Neptunian objects for which the rotation is not expected to cause a distorted, triaxial ellipsoid shape, like in the case of Haumea. While moons of large Kuiper belt objects are usually assumed to be formed from an original large body via collisions, the fast rotation may point to a scenario in which Vanth was captured from a nearby heliocentric orbit early in the history of the Solar system, and subsequent tidal evolution led to the present, nearly circular orbit. In this sense the Orcus-Vanth system is peculiar, as the present rotational characteristics and satellite orbits of all other large Kuiper belt objects are consistent with a collisional origin. </p>