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Charon among the stars Stellar occultations, when a Solar System object passes between us and a star and blocks its light, are eagerly awaited by astronomers as they provide a chance to make measurements that are not normally possible. It had been 25 years since a solitary observation of a stellar occultation by Pluto's moon Charon. But on 11 July 2005 another occurred and this time observatories across South America were ideally placed to track it. The resulting haul of data has been used to obtain an accurate measure of Charon's radius, of close to 605 km, and to establish an upper limit (a rather low one) on the density of its atmosphere. Visit tinyurl.com/9c56s for a QuickTime movie of the event. Pluto and its satellite, Charon (discovered in 1978; ref. 1 ), appear to form a double planet, rather than a hierarchical planet/satellite couple. Charon is about half Pluto's size and about one-eighth its mass. The precise radii of Pluto and Charon have remained uncertain, leading to large uncertainties on their densities 2 . Although stellar occultations by Charon are in principle a powerful way of measuring its size, they are rare, as the satellite subtends less than 0.3 microradians (0.06 arcsec) on the sky. One occultation (in 1980) yielded a lower limit of 600 km for the satellite's radius 3 , which was later refined to 601.5 km (ref. 4 ). Here we report observations from a multi-station stellar occultation by Charon, which we use to derive a radius, R C = 603.6 ± 1.4 km (1 σ ), and a density of ρ = 1.71 ± 0.08 g cm -3 . This occultation also provides upper limits of 110 and 15 (3 σ ) nanobar for an atmosphere around Charon, assuming respectively a pure nitrogen or pure methane atmosphere.

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.

The icy dwarf planet Makemake has projected axes of 1,430 ± 9 and 1,502 ± 45 km and a V-band geometric albedo larger than Pluto’s but smaller than Eris’s, with no global Pluto-like atmosphere. Makemake shapes up against Pluto and Eris Makemake is thought to be the third-largest dwarf planet in our Solar System, a little smaller than Pluto and Eris, but until now knowledge of its size and albedo were only approximate. This paper reports the results of observations of the occultation of a faint star known as NOMAD 1181-0235723 by Makemake on 23 April 2011. The data confirm that Makemake is smaller than Pluto and Eris, with axes of 1,430±9 km and 1,502±45 km. Makemake's mean geometric albedo — the ratio of light reflected to light received — is intermediate between that of Pluto and that of Eris. All three are icy, making them among the most reflective objects in the Solar System. And the occultation light curves rule out the presence of a global Pluto-like atmosphere on Makemake, although the presence of dark terrain might imply the presence of a localized atmosphere. Pluto and Eris are icy dwarf planets with nearly identical sizes, comparable densities and similar surface compositions as revealed by spectroscopic studies 1 , 2 . Pluto possesses an atmosphere whereas Eris does not; the difference probably arises from their differing distances from the Sun, and explains their different albedos 3 . Makemake is another icy dwarf planet with a spectrum similar to Eris and Pluto 4 , and is currently at a distance to the Sun intermediate between the two. Although Makemake’s size (1,420 ± 60 km) and albedo are roughly known 5 , 6 , there has been no constraint on its density and there were expectations that it could have a Pluto-like atmosphere 4 , 7 , 8 . Here we report the results from a stellar occultation by Makemake on 2011 April 23. Our preferred solution that fits the occultation chords corresponds to a body with projected axes of 1,430 ± 9 km (1 σ ) and 1,502 ± 45 km, implying a V-band geometric albedo p V = 0.77 ± 0.03. This albedo is larger than that of Pluto, but smaller than that of Eris. The disappearances and reappearances of the star were abrupt, showing that Makemake has no global Pluto-like atmosphere at an upper limit of 4–12 nanobar (1 σ ) for the surface pressure, although a localized atmosphere is possible. A density of 1.7 ± 0.3 g cm −3 is inferred from the data.

Pluto's tenuous nitrogen atmosphere was first detected by the imprint left on the light curve of a star that was occulted by the planet in 1985 (ref. 1 ), and studied more extensively during a second occultation event in 1988 (refs 2–6 ). These events are, however, quite rare and Pluto's atmosphere remains poorly understood, as in particular the planet has not yet been visited by a spacecraft. Here we report data from the first occultations by Pluto since 1988. We find that, during the intervening 14 years, there seems to have been a doubling of the atmospheric pressure, a probable seasonal effect on Pluto.

TOI-1695 is a V-mag=13 M-dwarf star from the northern hemisphere at 45\\(\\,\\)pc from the Sun, around which a 3.134-day periodic transit signal from a super-Earth candidate was identified in TESS photometry. With a transit depth of 1.3\\(\\,\\)mmag, the radius of candidate TOI-1695.01 was estimated by the TESS pipeline to be 1.82\\(\\,\\)R\\(_\\oplus\\) with an equilibrium temperature of \\(\\sim 620\\,\\)K. We successfully detect a reflex motion of the star and establish it is due to a planetary companion at an orbital period consistent with the photometric transit period thanks to a year-long radial-velocity monitoring of TOI-1695 by the SPIRou infrared spectropolarimeter. We use and compare different methods to reduce and analyse those data. We report a 5.5-\\(\\sigma\\) detection of the planetary signal, giving a mass of \\(5.5 \\pm 1.0\\,\\)M\\(_\\oplus\\) and a radius of \\(2.03 \\pm 0.18\\,\\)R\\(_\\oplus\\). We derive a mean equilibrium planet temperature of \\(590 \\pm 90\\,\\)K. The mean density of this small planet of \\(3.6 \\pm 1.1\\,\\)g\\(\\,\\)cm\\(^{-3}\\) is similar (1.7-\\(\\sigma\\) lower) than that of the Earth. It leads to a non-negligible fraction of volatiles in its atmosphere with \\(f_{H,He}=0.28^{+0.46}_{-0.23}\\)% or \\(f_\\text{water}=23 \\pm 12\\)%. TOI-1695\\(\\,\\)b is a new sub-Neptune planet at the border of the M-dwarf radius valley that can help test formation scenarios for super-Earth/sub-Neptune-like planets.

A stellar occultation by Neptune's main satellite, Triton, was observed on 5 October 2017 from Europe, North Africa, and the USA. We derived 90 light curves from this event, 42 of which yielded a central flash detection. We aimed at constraining Triton's atmospheric structure and the seasonal variations of its atmospheric pressure since the Voyager 2 epoch (1989). We also derived the shape of the lower atmosphere from central flash analysis. We used Abel inversions and direct ray-tracing code to provide the density, pressure, and temperature profiles in the altitude range \\(\\sim\\)8 km to \\(\\sim\\)190 km, corresponding to pressure levels from 9 {\\mu}bar down to a few nanobars. Results. (i) A pressure of 1.18\\(\\pm\\)0.03 {\\mu}bar is found at a reference radius of 1400 km (47 km altitude). (ii) A new analysis of the Voyager 2 radio science occultation shows that this is consistent with an extrapolation of pressure down to the surface pressure obtained in 1989. (iii) A survey of occultations obtained between 1989 and 2017 suggests that an enhancement in surface pressure as reported during the 1990s might be real, but debatable, due to very few high S/N light curves and data accessible for reanalysis. The volatile transport model analysed supports a moderate increase in surface pressure, with a maximum value around 2005-2015 no higher than 23 {\\mu}bar. The pressures observed in 1995-1997 and 2017 appear mutually inconsistent with the volatile transport model presented here. (iv) The central flash structure does not show evidence of an atmospheric distortion. We find an upper limit of 0.0011 for the apparent oblateness of the atmosphere near the 8 km altitude.

Following the announcement of the detection of phosphine (PH\\(_3\\)) in the cloud deck of Venus at millimeter wavelengths, we have searched for other possible signatures of this molecule in the infrared range. Since 2012, we have been observing Venus in the thermal infrared at various wavelengths to monitor the behavior of SO\\(_2\\) and H\\(_2\\)O at the cloud top. We have identified a spectral interval recorded in March 2015 around 950 cm\\(^{-1}\\) where a PH\\(_3\\) transition is present. From the absence of any feature at this frequency, we derive, on the disk-integrated spectrum, a 3-\\(\\sigma\\) upper limit of 5 ppbv for the PH\\(_3\\) mixing ratio, assumed to be constant throughout the atmosphere. This limit is 4 times lower than the disk-integrated mixing ratio derived at millimeter wavelengths. Our result brings a strong constraint on the maximum PH\\(_3\\) abundance at the cloud top and in the lower mesosphere of Venus.

Context. Pluto's tenuous nitrogen (N2) atmosphere undergoes strong seasonal effects due to high obliquity and orbital eccentricity, and has been recently (July 2015) observed by the New Horizons spacecraft. Goals are (i) construct a well calibrated record of the seasonal evolution of surface pressure on Pluto and (ii) constrain the structure of the lower atmosphere using a central flash observed in 2015. Method: eleven stellar occultations by Pluto observed between 2002 and 2016 are used to retrieve atmospheric profiles (density, pressure, temperature) between \\(\\sim\\)5 km and \\(\\sim\\)380 km altitude levels (i.e. pressures from about 10 microbar to 10 nanobar). Results: (i) Pressure has suffered a monotonic increase from 1988 to 2016, that is compared to a seasonal volatile transport model, from which tight constraints on a combination of albedo and emissivity of N2 ice are derived; (ii) A central flash observed on 2015 June 29 is consistent with New Horizons REX profiles, provided that (a) large diurnal temperature variations (not expected by current models) occur over Sputnik Planitia and/or (b) hazes with tangential optical depth of about 0.3 are present at 4-7 km altitude levels and/or (c) the nominal REX density values are overestimated by an implausibly large factor of about 20% and/or (d) higher terrains block part of the flash in the Charon facing hemisphere.

This article presents XML-based tools for parser generation and data binding generation. The underlying concept is that of transformation between formal languages, which is a form of meta-programming. We discuss the benefits of such a declarative approach with well-defined semantics: productivity, maintainability, verifiability, performance and safety.

We present results derived from four stellar occultations by the plutino object (208996) 2003~AZ\\(_{84}\\), detected at January 8, 2011 (single-chord event), February 3, 2012 (multi-chord), December 2, 2013 (single-chord) and November 15, 2014 (multi-chord). Our observations rule out an oblate spheroid solution for 2003~AZ\\(_{84}\\)'s shape. Instead, assuming hydrostatic equilibrium, we find that a Jacobi triaxial solution with semi axes \\((470 \\pm 20) \\times (383 \\pm 10) \\times (245 \\pm 8)\\)~km % axis ratios \\(b/a= 0.82 \\pm 0.05\\) and \\(c/a= 0.52 \\pm 0.02\\), can better account for all our occultation observations. Combining these dimensions with the rotation period of the body (6.75~h) and the amplitude of its rotation light curve, we derive a density \\(\\rho=0.87 \\pm 0.01\\)~g~cm\\(^{-3}\\) a geometric albedo \\(p_V= 0.097 \\pm 0.009\\). A grazing chord observed during the 2014 occultation reveals a topographic feature along 2003~AZ\\(_{84}\\)'s limb, that can be interpreted as an abrupt chasm of width \\(\\sim 23\\)~km and depth \\(> 8\\)~km or a smooth depression of width \\(\\sim 80\\)~km and depth \\(\\sim 13\\)~km (or an intermediate feature between those two extremes).