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Observations of a stellar occultation by (10199) Chariklo, a minor body that orbits the Sun between Jupiter and Neptune, reveal that it has a ring system, a property previously observed only for the four giant planets of the Solar System. Tiny Chariklo has its own ring system Observations of a stellar occultation by (10199) Chariklo, a Centaur-class outer-system asteroid orbiting between Saturn and Uranus, reveal that it has a ring system, a feature previously observed only for the four giant planets. Chariklo, with a diameter of about 250 km, has two narrow and dense rings separated by a small gap, probably due to the presence of a (yet-to-be-found) kilometre-sized satellite. The discovery of these rings raises questions about the formation and dynamical evolution of planetary rings. For one thing, it seems likely that planetary rings are much more common than previously thought. Hitherto, rings have been found exclusively around the four giant planets in the Solar System 1 . Rings are natural laboratories in which to study dynamical processes analogous to those that take place during the formation of planetary systems and galaxies. Their presence also tells us about the origin and evolution of the body they encircle. Here we report observations of a multichord stellar occultation that revealed the presence of a ring system around (10199) Chariklo, which is a Centaur—that is, one of a class of small objects orbiting primarily between Jupiter and Neptune—with an equivalent radius of 124   9 kilometres (ref. 2 ). There are two dense rings, with respective widths of about 7 and 3 kilometres, optical depths of 0.4 and 0.06, and orbital radii of 391 and 405 kilometres. The present orientation of the ring is consistent with an edge-on geometry in 2008, which provides a simple explanation for the dimming 3 of the Chariklo system between 1997 and 2008, and for the gradual disappearance of ice and other absorption features in its spectrum over the same period 4 , 5 . This implies that the rings are partly composed of water ice. They may be the remnants of a debris disk, possibly confined by embedded, kilometre-sized satellites.

Evidence suggests the existence of a ninth planet in the Solar System, with an orbit far beyond Neptune. This so-called “Planet 9” has not yet been directly observed, but gravitational effects can be noticed in objects known as trans-Neptunian objects (TNOs), those with a semi-major axis orbital greater than that of Neptune. Some of them present a clustering in relation to the perihelion argument, and from these data, numerical simulations were performed by Brown and Batygin (Astron J 162:219, 2021. https://doi.org/10.3847/1538-3881/ac2056 ) indicating some orbital elements for Planet 9 so that, in the near future, the body may be detected. For a better understanding of the evolution and origin of the Solar System, a physical characterization of the body becomes necessary. One powerful observational technique for the study of TNOs is stellar occultation. A technique in which a body generates a shadow over the Earth as it passes in front of a background star, allowing it to determine, with kilometer accuracy, the shape, size, albedo and to sound for the existence of atmosphere, rings and satellites around the body. Thus, a code in Python was developed to simulate stellar occultation light curves by the Planet 9. The results are analyzed to understand the main parameters that influence the light curve construction so we can be better prepared for a future occultation by the body.

Stellar occultations provide a powerful tool to explore objects of the outer solar system. The Gaia mission now provides milli-arcsec accuracy on the predictions of these events and makes possible observations that were previously unthinkable. Occultations return kilometric accuracies on the three-dimensional shape of bodies irrespective of their geocentric distances, with the potential of detecting topographic features along the limb. From the shape, accurate values of albedo can be derived, and if the mass is known, the bulk density is pinned down, thus constraining the internal structure and equilibrium state of the object. Occultations are also extremely sensitive to tenuous atmospheres, down to the nanobar level. They allowed the monitoring of Pluto’s and Triton’s atmospheres in the last three decades, constraining their seasonal evolution. They may unveil in the near future atmospheres around other remote bodies of the solar system. Since 2013, occultations have led to the surprising discovery of ring systems around the Centaur object Chariklo, the dwarf planet Haumea and the large trans-Neptunian object Quaoar, while revealing dense material around the Centaur Chiron. This suggests that rings are probably much more common features than previously thought. Meanwhile, they have raised new dynamical questions concerning the confining effect of resonances forced by irregular objects on ring particles. Serendipitous occultations by km-sized trans-Neptunian or Oort objects have the potential to provide the size distribution of a population that suffered few collisions until now, thus constraining the history of primordial planetesimals in the 1–100 km range.

Stellar occultations, when a distant object passes in front of a star and casts a shadow on Earth, are a powerful tool to probe the physical properties of solar system bodies. They enable precise size and shape measurements and can reveal rings, satellites, atmospheres, or surface features. Here we present results from two stellar occultations by Hi'iaka, dwarf planet Haumea's largest satellite, observed in April 2021. The second event yielded the first documented multi-chord occultation involving a trans-Neptunian satellite other than Charon. Combining these data with photometric observations, we find that Hi'iaka is a triaxial ellipsoid with a volume-equivalent diameter of 370 ± 20 km and a density of 640 ± 80 kg/m³, indicating a porous interior. The visible geometric albedo is , (∼ higher than Haumea's). The combination of low density and rapid rotation (9.68 ± 0.02 hours), under the assumption of a homogeneous body, indicates that Hi'iaka deviates from hydrostatic equilibrium.

This paper presents early results from and prospects for exoplanet science using a citizen science private/public partnership observer network managed by the SETI Institute in collaboration with Unistellar. The network launched in 2020 January and includes 163 citizen scientist observers across 21 countries. These observers can access a citizen science mentoring service developed by the SETI Institute and are also equipped with Unistellar Enhanced Vision Telescopes. Unistellar technology and the campaign’s associated photometric reduction pipeline enable each telescope to readily obtain and communicate light curves to observers with signal-to-noise ratio suitable for publication in research journals. Citizen astronomers of the Unistellar Exoplanet (UE) Campaign routinely measure transit depths of ≳1% and contribute their results to the exoplanet research community. The match of the detection system, targets, and scientific and educational goals is robust. Results to date include 281 transit detections out of 651 processed observations. In addition to this campaign’s capability to contribute to the professional field of exoplanet research, UE endeavors to drive improved science, technology, engineering, and mathematics education outcomes by engaging students and teachers as participants in science investigations, that is, learning science by doing science.

Transneptunian objects (TNOs) are a source of invaluable information to access the history and evolution of the outer solar system. However, observing these faint objects is a difficult task. As a consequence, important properties such as size and albedo are known for only a small fraction of them. Now, with the results from deep sky surveys and the Gaia space mission, a new exciting era is within reach as accurate predictions of stellar occultations by numerous distant small solar system bodies become available. From them, diameters with kilometer accuracies can be determined. Albedos, in turn, can be obtained from diameters and absolute magnitudes. We use observations from the Dark Energy Survey (DES) from November 2012 until February 2016, amounting to 4292847 CCD frames. We searched them for all known small solar system bodies and recovered a total of 202 TNOs and Centaurs, 63 of which have been discovered by the DES collaboration until the date of this writing. Their positions were determined using the Gaia Data Release 2 as reference and their orbits were refined. Stellar occultations were then predicted using these refined orbits plus stellar positions from Gaia. These predictions are maintained, and updated, in a dedicated web service. The techniques developed here are also part of an ambitious preparation to use the data from the Large Synoptic Survey Telescope (LSST), that expects to obtain accurate positions and multifilter photometry for tens of thousands of TNOs.

Stellar occultations are a unique technique to access physical characteristics of distant solar system objects from the ground. They allow the measure of the size and the shape at kilometric level, the detection of tenuous atmospheres (few nanobars), and the investigation of close vicinity (satellites, rings) of Transneptunian objects and Centaurs. This technique is made successful thanks to accurate predictions of occultations. Accuracy of the predictions depends on the uncertainty in the position of the occulted star and the object's orbit. The Gaia stellar catalogue (Gaia Collaboration (2017)) now allows to get accurate astrometric stellar positions (to the mas level). The main uncertainty remains on the orbit. In this context, we now take advantage of the NIMA method (Desmars et al.(2015)) for the orbit determination and of the Gaia DR1 catalogue for the astrometry. In this document, we show how the orbit determination is improved by reducing current and some past observations with Gaia DR1. Moreover, we also use more than 45 past positive occultations observed in the 2009-2017 period to derive very accurate astrometric positions only depending on the position of the occulted stars (about few mas with Gaia DR1). We use the case of (10199) Chariklo as an illustration. The main limitation lies in the imprecision of the proper motions which is going to be solved by the Gaia DR2 release.

The history of the outer solar system is intrinsically related to the Giant Planets migration. A massive disk of material within a radius of 30~au was scattered during the planetary migration, creating different dynamic populations in the Transneptunian region. They were formed in a collisional environment when massive collisions allowed them to grow and form much smaller moons than the primary body. The dynamical group, known as the Cold Classicals, was formed in a sparse disk from 42 to about 47~au and did not suffer much from planet migration. Observations show that many of Cold Classical are binary, consistent with the streaming instability process. The stellar occultation technique, with a spatial resolution of a few kilometres, can be used to search for binaries where other techniques are unable to do so, and to characterise the known satellites of Trans-Neptunian Objects (TNO), constraining their formation scenarios. We review here the first stellar occultations by TNO's satellites (besides Charon), discuss the methods used to detect these events. We also fit new orbital elements and system mass for Vanth (Orcus/1) and Weywot (Quaoar/1), finding reasonable solutions for pure Keplerian orbits. Finally, we discuss the prospects regarding the stellar occultations by TNO binaries and their implications for the study of the history of the Solar System.

Stellar occultations provide a powerful tool to explore objects of the outer solar system. The Gaia mission now provides milli-arcsec accuracy on the predictions of these events and makes possible observations that were previously unthinkable. Occultations return kilometric accuracies on the three-dimensional shape of bodies irrespective of their geocentric distances, with the potential of detecting topographic features along the limb. From the shape, accurate values of albedo can be derived, and if the mass is known, the bulk density is pinned down, thus constraining the internal structure and equilibrium state of the object. Occultations are also extremely sensitive to tenuous atmospheres, down to the nanobar level. They allowed the monitoring of Pluto's and Triton's atmospheres in the last three decades, constraining their seasonal evolution. They may unveil in the near future atmospheres around other remote bodies of the solar system. Since 2013, occultations have led to the surprising discovery of ring systems around the Centaur object Chariklo, the dwarf planet Haumea and the large trans-Neptunian object Quaoar, while revealing dense material around the Centaur Chiron. This suggests that rings are probably much more common features than previously thought. Meanwhile, they have raised new dynamical questions concerning the confining effect of resonances forced by irregular objects on ring particles. Serendipitous occultations by km-sized trans-Neptunian or Oort objects has the potential to provide the size distribution of a population that suffered few collisions until now, thus constraining the history of primordial planetesimals in the 1-100 km range.

At 30-50 K, the temperatures typical for surfaces in the Kuiper Belt (e.g. Stern & Trafton 2008), only seven species have sublimation pressures higher than 1 nbar (Fray & Schmitt 2009): Ne, N\\(_2\\), CO, Ar, O\\(_2\\), CH\\(_4\\), and Kr. Of these, N\\(_2\\), CO, and CH\\(_4\\) have been detected or inferred on the surfaces of Trans-Neptunian Objects (TNOs). The presence of tenuous atmospheres above these volatile ices depends on the sublimation pressures, which are very sensitive to the composition, temperatures, and mixing states of the volatile ices. Therefore, the retention of volatiles on a TNO is related to its formation environment and thermal history. The surface volatiles may be transported via seasonally varying atmospheres and their condensation might be responsible for the high surface albedos of some of these bodies. The most sensitive searches for tenuous atmospheres are made by the method of stellar occultation, which have been vital for the study of the atmospheres of Triton and Pluto, and has to-date placed upper limits on the atmospheres of 11 other bodies. The recent release of the Gaia astrometric catalog has led to a \"golden age\" in the ability to predict TNO occultations in order to increase the observational data base.