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The various dynamical classes in the trans-Neptunian region record the history of Neptune’s migration early in solar system history. The low-inclination, low-eccentricity cold classical objects are thought to be the remnants of the outer primordial disk of minor bodies, left undisturbed by the migration of Neptune, while all other classes were implanted on their current orbits from smaller heliocentric distances through interaction with Neptune. Many other trans-Neptunian objects (TNOs) were lost from the solar system entirely or transferred onto crossing orbits that resulted in collisions. Not unexpectedly, two very different populations of TNO binary systems are observed: (1) large TNOs with small satellites on relatively tight orbits and (2) small TNOs, mostly cold classicals, with roughly equal-sized components and relatively large separations. This stark contrast points to two very different formation mechanisms—giant impacts and co-formation—and corresponding expectations for the compositions of the components. Giant impacts are more likely to result in different compositions for the primary and secondary, while co-formation implies similar compositions. Observations with the JWST NIRSpec IFU provide sufficient spatial resolution to resolve TNO binaries and sufficient sensitivity to obtain spectra of both components. We have examined data for both large and small TNO binaries from GTO and GO programs and present spectral comparisons of the primaries and secondaries. The results of this work have implications for the early dynamical history and collisional environment in our own outer solar system, with links to other planetary systems with observed debris disks.

This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited., This work presents the analysis of seven mutual events of the Patroclus–Menoetius system (PMS) observed during the last season of mutual events, in 2017–2018. We compare the obtained light curves with those predicted using Grundy et al. and discuss the differences in the timing of the events and the drop of magnitude. Based on models of these observations, we present a collection of orbital parameters that provide the best fit for the observed events and compare the new solutions for the orbit of the system with solutions provided in the literature. Furthermore, we also discuss an interesting finding in the light curve of the only superior event in our collection. This light curve (the one with the best signal-to-noise ratio in our data set) shows the imprint of a possible crater in the south pole of Menoetius as deep as a fourth of its radius. © 2022. The Author(s). Published by the American Astronomical Society., his work is partially based on observations made with the Gran Telescopio Canarias (GTC), in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, Spain, under Director's Discretionary Time. Partially based on observations obtained with the SARA Observatory 0.9 m telescope at Kitt Peak, which is owned and operated by the Southeastern Association for Research in Astronomy. This research is partially based on observations collected at Sierra Nevada Observatory (OSN) in Granada, Spain, which is operated by Instituto de Astrofísica de Andalucía (CSIC). This article is based on observations made with the Carlos Sánchez Telescope located at the island of Tenerife and operated by the Instituto de Astrofísica de Canarias in the Spanish Observatorio del Teide. N.P.-A. and E.F.-V. acknowledge support from SRI/FSI funds through the project "Earth- and Space-Based Studies in Support of NASA Space Missions." M.P. acknowledges support from AYA2015-67772-R (MINECO, Spain). E.F.-V. acknowledges support from the 2017 Preeminent Postdoctoral Program (P3) of the University of Central Florida. R.D. acknowledges funding from Spanish project AYA2017-89637-R, from FEDER. We would like to acknowledge financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa award for the Instituto de Astrofísica de Andalucía" (SEV-2017-0709). We are grateful to the OSN staff for the excellent work done during the observational campaigns.

The stellar occultation technique is a very powerful tool to obtain the size and shape of Solar System bodies with high accuracy [6]. Size determination allows to obtain geometric albedos and, in the case of binary/multiple objects, even the mass density can be derived [3]. Satellites, atmospheres, and rings can also be detected and characterized [1,2,3]. The observation of stellar occultations produced by Kuiper Belt Objects (KBOs) and Centaurs with the James Webb Space Telescope (JWST) offers a unique possibility to extend our knowledge of these bodies [4] by providing key information on the body's ability to retain volatiles, surface thermal properties, roughness, porosity, etc.We will present our Target of Opportunity (ToO) program [5] accepted within Heidi Hammel's JWST Guaranteed Time Observations (GTO), dedicated to observing stellar occultations by trans-Neptunian objects (TNO) and distant dwarf planets or particularly interesting centaurs (such as the ringed centaurs Chariklo [1] or Chiron [2]). Predictions of such events visible from JWST are challenging due to the chaotic motion of the space telescope around the Lagrange 2 (L2) point. Statistically, we expect there to be approximately a 50% chance of such an occultation of a star brighter than K=19 by a numbered TNO observable from JWST in Cycle 1. We will discuss the possible candidates for Cycle 1 occultations that we have identified so far. As JWST station-keeping maneuvers are executed, the list of possible occultations and their uncertainties will be revised. Very accurate relative astrometry will be performed using the latest releases of the Gaia catalog for particularly promising occultation events through established ground-based programs. Suppose a stellar occultation event is confirmed through such an astrometric revision to have a predicted impact parameter less than 3 times the estimated target radius and to have a 1 sigma uncertainty in prediction less than 2 times the target radius. In that case, the ToO observation will be triggered. JWST station-keeping and trajectory-prediction operations have been studied in the context of stellar occultations by solar system bodies [4]. The accuracy of the trajectory predictions is adequate to support this triggering mechanism up to roughly 30 days before an occultation event: the ToO response time is set to 14 days, the minimum value for a non-disruptive ToO.The observations will be made with NIRCam and the F070W and F277W filters. These filters were chosen to maximize the flux from the star while minimizing the reflected flux from the TNO or Centaur. This filter combination could change based on the properties of the occulted star and the occulting TNO/Centaur. Other technical aspects and updates on this project will be provided during the presentation.Acknowledgments. We acknowledge financial support from the Spanish grant AYA-RTI2018-098657-J-I00 “LEO-SBNAF” (MCIU/AEI/FEDER, UE) and from the State Agency for Research of the Spanish MCIU through the “Center of Excellence Severo Ochoa” award to the Instituto de Astrofísica de Andalucía (SEV-2017-0709). Funding from Spanish projects PID2020-112789GB-I00 from AEI and Proyecto de Excelencia de la Junta de Andalucía PY20-01309 is also acknowledged. Part of this work has received funding from the European Research Council under the European Community’s H2020 (2014-2020/ERC Grant Agreement no. 669416 “LUCKY STAR”). M.V-L. acknowledges funding from Spanish project AYA2017-89637-R (FEDER/MICINN).References[1] Braga-Ribas et al., Nature 508, 72 (2014)[2] Ortiz et al., A&A 576, id.A18 (2015)[3] Ortiz, Santos-Sanz et al., Nature 550, 219 (2017)[4] Santos-Sanz et al., PASP 128, 959 (2016)[5] Santos-Sanz, JWST Proposal. Cycle 1, ID. #1271[6] Sicardy et al., Nature 439, 52 (2006)