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.

Exploring the Solar System with the NOIRLab Source Catalog I: Detecting Objects with CANFind

Despite extensive searches and the relative proximity of solar system objects (SSOs) to Earth, many remain undiscovered and there is still much to learn about their properties and interactions. This work is the first in a series dedicated to detecting and analyzing SSOs in the all-sky NOIRLab Source Catalog (NSC). We search the first data release of the NSC with CANFind, a Computationally Automated NSC tracklet Finder. NSC DR1 contains 34 billion measurements of 2.9 billion unique objects, which CANFind categorizes as belonging to “stationary” (distant stars, galaxies) or moving (SSOs) objects via an iterative clustering method. Detections of stationary bodies for proper-motion μ ≤ 2.″5 hr−1 (0.°017 day−1) are identified and analyzed separately. Remaining detections belonging to high-μ objects are clustered together over single nights to form “tracklets.” Each tracklet contains detections of an individual moving object, and is validated based on spatial linearity and motion through time. Proper motions are then calculated and used to connect tracklets and other unassociated measurements over multiple nights by predicting their locations at common times, forming “tracks.” This method extracted 527,055 tracklets from NSC DR1 in an area covering 29,971 square degrees of the sky. The data show distinct groups of objects with similar observed μ in ecliptic coordinates, namely Main Belt Asteroids, Jupiter Trojans, and Kuiper Belt Objects. Apparent magnitudes range from 10 to 25 mag in the ugrizY and VR bands. Color–color diagrams show a bimodality of tracklets between primarily carbonaceous and siliceous groups, supporting prior studies.

Constraints on the Occurrence of ‘Oumuamua-Like Objects

At present, there exists no consensus in the astronomical community regarding either the bulk composition or the formation mechanism for the interstellar object 1I/2017 U1 (‘Oumuamua). With the goal of assessing the merits of the various scenarios that have been suggested to explain ‘Oumuamua's appearance and observed properties, we report a number of new analyses and provide an up-to-date review of the current hypotheses. We consider the interpretations that can reconcile ‘Oumuamua's observed non-Keplerian trajectory with the nondetection of traditional cometary volatiles. We examine the ability of these proposed formation pathways to populate the galaxy with sufficient interstellar objects such that the detection of ‘Oumuamua by Pan-STARRS would be statistically favored. We consider two exotic ices, hydrogen and nitrogen, showing that the frigid temperature requirement for the former and the necessary formation efficiency of the latter pose serious difficulties for these interpretations. Via order-of-magnitude arguments and hydrodynamical cratering simulations, we show that impacts on extrasolar Kuiper Belt analogues are not expected to generate N2 ice fragments as large as ‘Oumuamua. In addition, we discuss observational tests to confirm the presence of these ices in future interstellar objects. Next, we examine the explanations that attribute ‘Oumuamua's properties to other compositions: ultraporous dust aggregates and thin membranes powered by solar radiation pressure, among others. While none of these hypotheses are perfectly satisfactory, we make predictions that will be testable by the Vera Rubin Observatory to resolve the tension introduced by ‘Oumuamua.

Transneptunian Space

We provide a nonspecialist overview of the current state of understanding of the structure and origin of our Solar System's transneptunian region (often called the Kuiper Belt), highlighting perspectives on planetesimal formation, planet migration, and the contextual relationship with protoplanetary disks. We review the dynamical features of the transneptunian populations and their associated differences in physical properties. We describe aspects of our knowledge that have advanced in the past two decades and then move on to current issues of research interest (which thus still have unclear resolution). ▪ The current transneptunian population consists of both implanted and primordial objects. ▪ The primordial (aka cold) population is a largely unaltered remnant of the population that formed in situ. ▪ The reason for the primordial cold population's current outer edge is unexplained. ▪ The large semimajor-axis population now dynamically detached from Neptune is critical for understanding the Solar System's history. ▪ Observational constraints on the number and orbits of distant objects remain poor.

Triton: Topography and Geology of a Probable Ocean World with Comparison to Pluto and Charon

The topography of Neptune’s large icy moon Triton could reveal important clues to its internal evolution, but has been difficult to determine. New global digital color maps for Triton have been produced as well as topographic data for <40% of the surface using stereogrammetry and photoclinometry. Triton is most likely a captured Kuiper Belt dwarf planet, similar though slightly larger in size and density to Pluto, and a likely ocean moon that exhibited plume activity during Voyager 2′s visit in 1989. No surface features or regional deviations of greater than ±1 km amplitude are found. Volatile ices in the southern terrains may take the form of extended lobate deposits 300–500 km across as well as dispersed bright materials that appear to embay local topography. Limb hazes may correlate with these deposits, indicating possible surface–atmosphere exchange. Triton’s topography contrasts with high relief up to 6 km observed by New Horizons on Pluto. Low relief of (cryo)volcanic features on Triton contrasts with high-standing massifs on Pluto, implying different viscosity materials. Solid-state convection occurs on both and at similar horizontal scales but in very different materials. Triton’s low relief is consistent with evolution of an ice shell subjected to high heat flow levels and may strengthen the case of an internal ocean on this active body.