Context: Pluto possesses a thin atmosphere, primarily composed of nitrogen, in which the detection of methane has been reported.
Aims: The goal is to constrain essential but so far unknown parameters of Pluto's atmosphere such as the surface pressure, lower atmosphere thermal stucture, and methane mixing ratio.
Methods: We use high-resolution spectroscopic observations of gaseous methane, and a novel analysis of occultation light-curves.
Results: We show that (i) Pluto's surface pressure is currently in the 6.5-24 microbar range (ii) the methane mixing ratio is 0.5+/-0.1 %, adequate to explain Pluto's inverted thermal structure and ~100 K upper atmosphere temperature (iii) a troposphere is not required by our data, but if present, it has a depth of at most 17 km, i.e. less than one pressure scale height; in this case methane is supersaturated in most of it. The atmospheric and bulk surface abundance of methane are strikingly similar, a possible consequence of the presence of a CH4-rich top surface layer.
We apply scintillation theory to stellar signal fluctuations in the high-resolution, high signal/noise, dual-wavelength data from the MMT observation of the 2007 March 18 occultation of P445.3 by Pluto. A well-defined high wavenumber cutoff in the fluctuations is consistent with viscous-thermal dissipation of buoyancy waves (internal gravity waves) in Pluto's high atmosphere, and provides strong evidence that the underlying density fluctuations are governed by the gravity-wave dispersion relation.
On 6 Jun 2020, Pluto's stellar occultation was successfully observed at a ground-based observatory and Pluto's atmospheric parameters were investigated. We used an atmospheric model of Pluto (DO15), assuming a spherical and transparent pure N2 atmosphere. Using ray-tracing code the stellar occultation light curve was satisfactorily fitted to this model. We found that Pluto's atmospheric pressure at the reference radius of 1215 km is 6.72+_0.21 μbar. Our estimated pressure shows a continuation of the increasing pressure studied in 2016 consistent with a seasonal volatile transport model. We con…
A stellar occultation by Pluto was observed on 6 June 2020 with the 1.3-m and 3.6-m telescopes located at Devasthal, Nainital, India, using imaging systems in the I and H bands, respectively. From this event, we derive a surface pressure for Pluto's atmosphere of $p_{\rm surf}= 12.23^{+0.65}_{-0.38} $~$μ$bar. This shows that Pluto's atmosphere is in a plateau phase since mid-2015, a result which is in excellent agreement with the Pluto volatile transport model of Meza et al. (2019}. This value does not support the pressure decrease reported by independent teams, based on occultations observed …
From 1988 to 2016, several stellar occultations have been observed to characterize Pluto's atmosphere and its evolution (Meza et al, 2019). From each stellar occultation, an accurate astrometric position of Pluto at the observation epoch is derived. These positions mainly depend on the position of the occulted star and the precision of the timing. We present Pluto's astrometric positions derived from 19 occultations from 1988 to 2016 (11 from Meza et al. (2019) and 8 from other publications). Using Gaia DR2 for the positions of the occulted stars, the accuracy of these positions is estimated t…
We present spectra of Eris from the MMT 6.5 meter telescope and Red Channel Spectrograph (5700-9800 angstroms; 5 angstroms per pix) on Mt. Hopkins, AZ, and of Pluto from the Steward Observatory 2.3 meter telescope and Boller and Chivens spectrograph (7100-9400 angstroms; 2 angstroms per pix) on Kitt Peak, AZ. In addition, we present laboratory transmission spectra of methane-nitrogen and methane-argon ice mixtures. By anchoring our analysis in methane and nitrogen solubilities in one another as expressed in the phase diagram of Prokhvatilov and Yantsevich (1983), and comparing methane bands in…
The methane-nitrogen phase diagram of Prokhvatilov and Yantsevich (1983) indicates that at temperatures relevant to the surfaces of icy dwarf planets like Pluto, two phases contribute to the methane absorptions: nitrogen saturated with methane $\bf{\bar{N_{2}}}$:CH$_{4}$ and methane saturated with nitrogen $\bf{\bar{CH_{4}}}$:N$_{2}$. No optical constants are available so far for the latter component limiting construction of a proper model, in compliance with thermodynamic equilibrium considerations. New optical constants for solid solutions of methane diluted in nitrogen (N$_{2}$:CH$_{4}$) an…
Since the last Pluto volatile transport models were published (Hansen and Paige 1996), we have (i) new stellar occultation data from 2002 and 2006-2012 that have roughly twice the pressure as the discovery occultation of 1988, (ii) new information about the surface properties of Pluto, (iii) a spacecraft due to arrive at Pluto in 2015, and (iv) a new volatile transport model that is rapid enough to allow a large parameter-space search. Such a parameter-space search coarsely constrained by occultation results reveals three broad solutions: a high-thermal inertia, large volatile inventory soluti…
High-resolution spectra of Pluto in the 1.66 um region, recorded with the VLT/CRIRES instrument in 2008 (2 spectra) and 2012 (5 spectra), are analyzed to constrain the spatial and vertical distribution of methane in Pluto's atmosphere and to search for mid-term (4 year) variability. A sensitivity study to model assumptions (temperature structure, surface pressure, Pluto's radius) is performed. Results indicate that (i) no variation of the CH4 atmospheric content (column-density or mixing ratio) with Pluto rotational phase is present in excess of 20 % (ii) CH4 column densities show at most marg…
We present three near-infrared spectra of Pluto taken with the IRTF and SpeX, an optical spectrum of Triton taken with the MMT and the Red Channel Spectrograph, and previously published spectra of Pluto, Triton, and Eris. We combine these observations with a two-phase Hapke model, and gain insight into the ice mineralogy on Pluto, Triton, and Eris. Specifically, we measure the methane-nitrogen mixing ratio across and into the surfaces of these icy dwarf planets. In addition, we present a laboratory experiment that demonstrates it is essential to model methane bands in spectra of icy dwarf plan…
Combining stellar occultation observations probing Pluto's atmosphere from 1988 to 2013 and models of energy balance between Pluto's surface and atmosphere, we conclude that Pluto's atmosphere does not collapse at any point in its 248-year orbit. The occultation results show an increasing atmospheric pressure with time in the current epoch, a trend present only in models with a high thermal inertia and a permanent N2 ice cap at Pluto's north rotational pole.
Pluto's atmospheric profiles (temperature and pressure) have been studied for decades from stellar occultation lightcurves. In this paper, we look at recent Pluto Global Climate Model (GCM) results (3D temperature, pressure, and density fields) from Bertrand et al. (2020) and use the results to generate model observer's plane intensity fields (OPIF) and lightcurves by using a Fourier optics scheme to model light passing through Pluto's atmosphere (Young, 2012). This approach can accommodate arbitrary atmospheric structures and 3D distributions of haze. We compared the GCM model lightcurves wit…
We report observations of a stellar occultation by Pluto on 2019 July 17. A single-chord high-speed (time resolution $= 2\,$s) photometry dataset was obtained with a CMOS camera mounted on the Tohoku University 60 cm telescope (Haleakala, Hawaii). The occultation light curve is satisfactorily fitted to an existing Pluto's atmospheric model. We find the lowest pressure value at a reference radius of $r = 1215~{\rm km}$ among those reported after 2012, indicating a possible rapid (approximately $21^{+4}_{-5} \%$ of the previous value) pressure drop between 2016 (the latest reported estimate) and…
We present results from a multi-chord Pluto stellar occultation observed on 29 June 2015 from New Zealand and Australia. This occurred only two weeks before the NASA New Horizons flyby of the Pluto system and serves as a useful comparison between ground-based and space results. We find that Pluto's atmosphere is still expanding, with a significant pressure increase of 5$\pm$2\% since 2013 and a factor of almost three since 1988. This trend rules out, as of today, an atmospheric collapse associated with Pluto's recession from the Sun. A central flash, a rare occurrence, was observed from severa…
Reconciling results of 2019 and 2020 stellar occultations on Pluto's atmosphere. New constraints from both the 5 September 2019 event and consistency analysis
Changes in Pluto's Atmosphere Based on Stellar Occultation Data from 2017 to 2023
Planetary Science Institute（行星科学研究所）；Massachusetts Institute of Technology（麻省理工学院）；Lowell Observatory（洛厄尔天文台）；Universität Stuttgart（斯图加特大学）；SOFIA Science Center NASA Ames Research Center（NASA艾姆斯研究中心索菲亚科学中心）；Las Cumbres Observatory（拉斯孔布雷斯天文台）
On July 14th 2015, NASA's New Horizons mission gave us an unprecedented detailed view of the Pluto system. The complex compositional diversity of Pluto's encounter hemisphere was revealed by the Ralph/LEISA infrared spectrometer on board of New Horizons. We present compositional maps of Pluto defining the spatial distribution of the abundance and textural properties of the volatiles methane and nitrogen ices and non-volatiles water ice and tholin. These results are obtained by applying a pixel-by-pixel Hapke radiative transfer model to the LEISA scans. Our analysis focuses mainly on the large …
Context. During the last 30 years the surface of Pluto has been characterized, and its variability has been monitored, through continuous near-infrared spectroscopic observations. But in the visible range only few data are available. Aims. The aim of this work is to define the Pluto's relative reflectance in the visible range to characterize the different components of its surface, and to provide ground based observations in support of the New Horizons mission. Methods. We observed Pluto on six nights between May and July 2014, with the imager/spectrograph ACAM at the William Herschel Telescop…
Lindal et al. (1987, J. Geophys. Res. 92, 14987-15001) presented a range of temperature and CH4 profiles for Uranus that were consistent with 1986 Voyager radio occultation measurements. A localized refractivity slope variation near 1.2 bars was interpreted to be the result of a condensed CH4 cloud layer. However, models fit to near-IR spectra found particle concentrations in the 1.5-3 bar range (Sromovsky et al. 2006, Icarus 182, 577-593, Sromovsky and Fry 2008, Icarus 193, 211-229, Irwin et al. 2010, Icarus 208, 913-926), and a recent analysis of STIS spectra argued that aerosol particles fo…
We analyze two multi-chord stellar occultations by Pluto observed on July 18th, 2012 and May 4th, 2013, and monitored respectively from five and six sites. They provide a total of fifteen light-curves, twelve of them being used for a simultaneous fit that uses a unique temperature profile, assuming a clear (no-haze) and pure N_2 atmosphere, but allowing for a possible pressure variation between the two dates. We find a solution that fits satisfactorily (i.e. within the noise level) all the twelve light-curves, providing atmospheric constraints between ~1,190 km (pressure ~ 11 \mubar) and ~ 1,4…
The Alice instrument on NASA's New Horizons spacecraft observed an ultraviolet solar occultation by Pluto's atmosphere on 2015 July 14. The transmission vs. altitude was sensitive to the presence of N2, CH4, C2H2, C2H4, C2H6, and haze. We derived line-of-sight abundances and local number densities for the 5 molecular species, and line-of-sight optical depth and extinction coefficients for the haze. We found the following major conclusions: 1) We confirmed temperatures in Pluto's upper atmosphere that were colder than expected before the New Horizons flyby, with upper atmospheric temperatures n…
Results are presented from a 3-D Pluto general circulation model (GCM) that includes conductive heating and cooling, non-local thermodynamic equilibrium (non-LTE) heating by methane at 2.3 and 3.3 microns, non-LTE cooling by cooling by methane at 7.6 microns, and LTE CO rotational line cooling. The GCM also includes a treatment of the subsurface temperature and surface-atmosphere mass exchange. An initially 1 m thick layer of surface nitrogen frost was assumed such that it was large enough to act as a large heat sink (compared with the solar heating term) but small enough that the water ice su…
Constraints on the Atmospheric Composition of 2002 XV$_{93}$ from JWST Spectroscopy
Space Telescope Science Institute（太空望远镜科学研究所）；Southwest Research Institute（西南研究院）；LIRA, Observatoire de Paris, Université PSL, CNRS, Sorbonne Université, Université Paris Cité（拉格朗日天体物理实验室，巴黎天文台，巴黎文理研究大学，法国国家科学研究中心，索邦大学，巴黎西岱大学）
We report observations of a stellar occultation by the classical Kuiper belt object (50000) Quaoar occurred on 28 June 2019. A single-chord high-cadence (2 Hz) photometry dataset was obtained with the Tomo-e Gozen CMOS camera mounted on the 1.05 m Schmidt telescope at Kiso Observatory. The obtained ingress and egress data do not show any indication of atmospheric refraction and allow to set new $1σ$ and $3σ$ upper limits of 6 and 16 nbar, respectively, for the surface pressure of a pure methane atmosphere. These upper limits are lower than the saturation vapor pressure of methane at Quaoar's e…
The New Horizons spacecraft's nominal trajectory crosses the planet's satellite plane at $\sim 10,000\ \rm{km}$ from the barycenter, between the orbits of Pluto and Charon. I have investigated the risk to the spacecraft based on observational limits of rings and dust within this region, assuming various particle size distributions. The best limits are placed by 2011 and 2012 HST observations, which significantly improve on the limits from stellar occultations, although they do not go as close to the planet. From the HST data and assuming a `reasonable worst case' for the size distribution, we …
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 altit…
On 1998 November 14, Saturn and its rings occulted the star GSC 0622-00345. We observed atmospheric immersion with NSFCAM at the National Aeronautics and Space Administration's Infrared Telescope Facility on Mauna Kea, Hawaii. Immersion occurred at 55.5\circ S planetocentric latitude. A 2.3 μm, methane-band filter suppressed reflected sunlight. Atmospheric emersion and ring data were not successfully obtained. We describe our observation, light-curve production, and timing techniques, including improvements in aperture positioning, removal of telluric scintillation effects, and timing. Many of…
The Nadir and Occultation for MArs Discovery instrument (NOMAD), onboard the ExoMars Trace Gas Orbiter (TGO) spacecraft was conceived to observe Mars in solar occultation, nadir, and limb geometries, and will be able to produce an outstanding amount of diverse data, mostly focused on properties of the atmosphere. The infrared channels of the instrument operate by combining an echelle grating spectrometer with an Acousto-Optical Tunable Filter (AOTF). Using in-flight data, we characterized the instrument performance and parameterized its calibration. In particular: an accurate frequency calibra…
We present a 3D general circulation model of Pluto and Triton's atmospheres, which uses radiative-conductive-convective forcing. In both the Pluto and Triton models, an easterly (prograde) jet is present at the equator with a maximum magnitude of 10-12 m/s and 4 m/s, respectively. Neither atmosphere shows any significant overturning circulation in the meridional and vertical directions. Rather, it is horizontal motions (mean circulation and transient waves) that transport heat meridionally at a magnitude of 1 and 3 x 10^7 W at Pluto's autumn equinox and winter solstice, respectively (seasons r…
Observations made during the New Horizons flyby provide a detailed snapshot of the current state of Pluto's atmosphere. While the lower atmosphere (at altitudes <200 km) is consistent with ground-based stellar occultations, the upper atmosphere is much colder and more compact than indicated by pre-encounter models. Molecular nitrogen (N$_2$) dominates the atmosphere (at altitudes <1800 km or so), while methane (CH$_4$), acetylene (C$_2$H$_2$), ethylene (C$_2$H$_4$), and ethane (C$_2$H$_6$) are abundant minor species, and likely feed the production of an extensive haze which encompasses Pluto. …
In terms of scientific output, the best way to study solar system bodies is sending spacecraft to make in-situ measurements or to observe at close distance. Probably, the second best means to learn about important physical properties of solar system objects is through stellar occultations. By combining occultation observations from several sites, size and shape can be derived with kilometric accuracy. Also, atmospheric properties can be derived if the body has an atmosphere. Furthermore, the technique can detect rings and even satellites (although rarely) around the main body. Except for the v…
The surprising discovery by the Rosetta spacecraft of molecular oxygen (O$_2$) in the coma of comet 67P/Churyumov-Gerasimenko (Bieler et al. 2015) challenged our understanding of the inventory of this volatile species on and inside bodies from the Kuiper Belt. That discovery motivated our search for oxygen in the atmosphere of Kuiper Belt planet Pluto, because O$_2$ is volatile even at Pluto's surface temperatures. During the New Horizons flyby of Pluto in July 2015, the spacecraft probed the composition of Pluto's atmosphere using a variety of observations, including an ultraviolet solar occu…
During the New Horizons spacecraft's encounter with Pluto, the Alice ultraviolet spectrograph conducted a series of observations that detected emissions from both the interplanetary medium (IPM) and Pluto. In the direction of Pluto, the IPM was found to be 133.4$\pm$0.6R at Lyman $α$, 0.24$\pm$0.02R at Lyman $β$, and <0.10R at He I 584Å. We analyzed 3,900s of data obtained shortly before closest approach to Pluto and detect airglow emissions from H I, N I, N II, N$_2$, and CO above the disk of Pluto. We find Pluto's brightness at Lyman $α$ to be $29.3\pm1.9$R, in good agreement with pre-encoun…
Central flashes during stellar occultations. Effects of diffraction, interferences, and stellar diameter
Observatoire de Paris, Université PSL, CNRS UMR 8255, Sorbonne Université（巴黎天文台，巴黎文理研究大学，法国国家科学研究中心）；Université Jean Monnet Saint-Etienne, CNRS, Institut d Optique Graduate School, Laboratoire Hubert Curien UMR 5516（让·莫内圣艾蒂安大学，法国国家科学研究中心，光学研究生院）
HST/STIS observations of Uranus in 2015 show that the depletion of upper tropospheric methane has been relatively stable and that the polar region has been brightening over time as a result of increased aerosol scattering. This interpretation is confirmed by near-IR imaging from HST and from the Keck telescope using NIRC2 adaptive optics imaging. Our analysis of the 2015 spectra, as well as prior spectra from 2012, shows that there is a factor of three decrease in the effective upper tropospheric methane mixing ratio between 30°N and 70°N. The absolute value of the deep methane mixing ratio, w…
The Voyager 1 and 2 Ultraviolet Spectrometer (UVS) solar and stellar occultation dataset represents one of the primary, pre-Cassini sources of information that we have on the neutral upper atmosphere of Saturn. Despite its importance, however, the full set of occultations has never received a consistent, nor complete, analysis, and the results derived from the initial analyses over thirty years ago left questions about the temperature and density profiles unanswered. We have reanalyzed all six of the UVS occultations (three solar and three stellar) to provide an up-to-date, pre-Cassini view of…
In this work we present the results of a spectral observing campaign of Pluto to search for temporal changes in surface composition on 1- to 3-year timescales. Near-infrared spectra of Pluto were obtained from June 2014 to August 2017 with the TripleSpec cross-dispersed spectrograph at the Apache Point Observatory's 3.5-meter Astrophysical Research Consortium (ARC) telescope. Observations were requested in order to obtain spectra of approximately the same sub-observer hemisphere $\sim$14 months apart, thus removing the effects of viewing geometry and rotation phase. Comparison of the CH$_4$ (m…
We study large trans-neptunian objects (TNOs) using stellar occultations. We derive precise astrometric predictions for stellar occultations by Eris, Haumea, Ixion, Makemake, Orcus, Quaoar, Sedna, Varuna, 2002 TX300, and 2003 AZ84 for 2011-2015. We construct local astrometric catalogs of stars in the UCAC2 (Second US Naval Observatory CCD Astrograph Catalog) frame covering the sky path of these objects. For that purpose, during 2007-2009, we carried out an observational program at the ESO2p2/WFI (2.2 m Max-Planck ESO telescope with the Wide Field Imager) instrument. Astrometric catalogs with p…
Observations of the Pluto-Charon system, acquired with the ALMA interferometer on June 12-13, 2015, have yielded a detection of the CO(3-2) and HCN(4-3) rotational transitions from Pluto, providing a strong confirmation of the presence of CO, and the first observation of HCN, in Pluto's atmosphere. The CO and HCN lines probe Pluto's atmosphere up to ~450 km and ~900 km altitude, respectively. The CO detection yields (i) a much improved determination of the CO mole fraction, as 515+/-40 ppm for a 12 ubar surface pressure (ii) clear evidence for a well-marked temperature decrease (i.e., mesosphe…
Understanding the trans-Neptunian Solar system: Reconciling the results of serendipitous stellar occultations and the inferences from the cratering record
The PHOT (Portable High-Speed Occultation Telescope) systems were developed for the specific purpose of observing stellar occultations by solar system objects. Stellar occultations have unique observing constraints: they may only be observable from certain parts of the globe; they often require a rapid observing cadence; and they require accurate timestamp information for each exposure. The PHOT systems consist of 14" telescopes, CCD cameras, camera mounting plates, GPS-based time standards, and data acquisition computers. The PHOT systems are similar in principle to the POETS systems (Portabl…
High altitude clouds and hazes are integral to understanding exoplanet observations, and are proposed to explain observed featureless transit spectra. However, it is difficult to make inferences from these data because of the need to disentangle effects of gas absorption from haze extinction. Here, we turn to the quintessential hazy world -- Titan -- to clarify how high altitude hazes influence transit spectra. We use solar occultation observations of Titan's atmosphere from the Visual and Infrared Mapping Spectrometer (VIMS) aboard NASA's Cassini spacecraft to generate transit spectra. Data s…
A recent occultation measurement of the dwarf planet Haumea (Ortiz et al. 2017) revealed an elongated shape with the longest axis comparable to Pluto's mean diameter. The chords also indicate a ring around Haumea's equatorial plane, where its largest moon, Hi'iaka, is also located. The Haumea occultation size estimate (equivalent diameter 1595 km) is larger than previous radiometric solutions (in the range between 1150 and 1350 km), which lowers the object's density to about 1.8 gcm-3, a value closer to the densities of other large TNOs. We present unpublished and also reprocessed Herschel and…
Stellar occultation is a powerful technique that allows the determination of some physical parameters of the occulting object. The result depends on the photometric accuracy, the temporal resolution, and the number of chords obtained. Space telescopes can achieve high photometric accuracy as they are not affected by atmospheric scintillation. Using ESA's CHEOPS space telescope, we observed a stellar occultation by the Transneptunian object (50000) Quaoar. We compare the obtained chord with previous occultations by this object and determine its astrometry with sub-milliarcsecond precision. Also…
Orcus is an intermediate-size 1000km-scale Kuiper Belt Object in 3:2 mean-motion resonance with Neptune, in an orbit very similar to that of Pluto. We present visible and near-infrared photometry and spectroscopy obtained with the Keck 10m-telescope and the Gemini 8m-telescope . We confirm the unambiguous detection of crystalline water ice as well as absorption in the 2.2μm region. Both in the visible and near-infrared Orcus' spectral properties appear to be homogeneous over time (and probably rotation) at the resolution available. From Hapke radiative transfer models involving intimate mixtur…
The vast, deep, volatile-ice-filled basin informally named Sputnik Planum is central to Pluto's geological activity[1,2]. Composed of molecular nitrogen, methane, and carbon monoxide ices[3], but dominated by N2-ice, this ice layer is organized into cells or polygons, typically ~10-40 km across, that resemble the surface manifestation of solid state convection[1,2]. Here we report, based on available rheological measurements[4], that solid layers of N2 ice approximately greater than 1 km thick should convect for estimated present-day heat flow conditions on Pluto. More importantly, we show num…
Triton is the largest moon of the Neptune system and possesses a thin nitrogen atmosphere with trace amounts of carbon monoxide and methane, making it of similar composition to that of the dwarf planet Pluto. Like Pluto and Saturn's moon Titan, Triton has a haze layer thought to be composed of organics formed through photochemistry. Here, we perform atmospheric chamber experiments of 0.5% carbon monoxide and 0.2% methane in molecular nitrogen at 90 K and 1 mbar to generate Triton haze analogues. We then characterize the physical and chemical properties of these particles. We measure their prod…
We present an analysis of the VIMS solar occultations dataset, which allows us to extract vertically resolved information on the characteristics of Titan's atmosphere between 100-700 km with a characteristic vertical resolution of 10 km. After a series of data treatment procedures, 4 occultations out of 10 are retained. This sample covers different seasons and latitudes of Titan. The transmittances show clearly the evolution of the haze and detect the detached layer at 310 km in Sept. 2011 at mid-northern latitudes. Through the inversion of the transmission spectra with a line-by-line radiativ…
On 28th January 2018, the large Trans-Neptunian Object (TNO) 2002TC302 occulted a m$_v= $15.3 star with ID 130957813463146112 in the Gaia DR2 stellar catalog. 12 positive occultation chords were obtained from Italy, France, Slovenia and Switzerland. Also, 4 negative detections were obtained near the north and south limbs. This represents the best observed stellar occultation by a TNO other than Pluto, in terms of the number of chords published thus far. From the 12 chords, an accurate elliptical fit to the instantaneous projection of the body, compatible with the near misses, can be obtained. …
Observations of Pluto's companion planet Charon have so far yielded no compelling evidence for a persistent atmosphere. However, with the upcoming encounter of New Horizons at the Pluto-Charon system, sensitivity to detection of a possible Charon atmosphere will increase by orders of magnitude. In particular, it has long been planned for New Horizons to use its Alice ultraviolet spectrograph during solar occultation observations of Charon on July 14, 2015, for this purpose. But in the days before closest encounter, the Alice instrument will also acquire spectra of reflected sunlight from Charo…
We report on a variety of standard techniques used by New Horizons including a solar ultraviolet occultation, ultraviolet airglow observations, and high-phase look-back particulate search imaging to search for an atmosphere around Pluto's large moon Charon during its flyby in July 2015. Analyzing these datasets, no evidence for a present day atmosphere has been found for 14 potential atomic and molecular species, all of which are now constrained to have pressures below 0.3 nanobar, as we describe below, these are much more stringent upper limits than the previously available 15-110 nanobar con…
Hydrocarbon species, and in particular CH$_4$, play a key role in the stratosphere--thermosphere boundary of Jupiter, which occurs around the $μ$-bar pressure level. Previous analyses of solar occultation, He and Ly-$α$ airglow, and ISO/SWS measurements of the radiance around 3.3 $μ$m have inferred significantly different methane concentrations. Here we aim to accurately model the CH$_4$ radiance at 3.3 $μ$m measured by ISO/SWS by using a comprehensive non-local thermodynamic equilibrium model and the most recent collisional rates measured in the laboratory for CH$_4$ to shed new light onto th…
On 2007 December 16-17, spectra were acquired of the disk of Uranus by the Spitzer Infrared Spectrometer (IRS) when its equator was close to the sub-earth point. This spectrum provides the highest-resolution broad-band spectrum ever obtained for Uranus from space, allowing a determination of the disk-averaged temperature and molecule composition to a greater degree of accuracy than ever before. The temperature profiles derived from the Voyager radio occultation experiments that match these data best are those that assume a high abundance of methane in the deep atmosphere, but none of these mod…
Neptune's moon Triton shares many similarities with Pluto, including volatile cycles of N2, CH4 and CO, and represents a benchmark case for the study of surface-atmosphere interactions on volatile-rich KBOs. Within the context of New Horizons observations of Pluto as well as recent Earth-based observations of Triton, we adapt a Plutonian VTM to Triton, and test its ability to simulate its volatile cycles, thereby aiding our understanding of its climate. We present VTM simulations exploring the volatile cycles on Triton over long-term and seasonal timescales for varying model parameters. We exp…
Within our international program to obtain accurate physical properties of trans-Neptunian objects (TNOs) we predicted a stellar occultation by the TNO (38628) Huya of the star Gaia DR2 4352760586390566400 (mG = 11.5 mag.) for March 18, 2019. After an extensive observational campaign, we updated the prediction and it turned out to be favorable to central Europe. Therefore, we mobilized half a hundred professional and amateur astronomers, and the occultation was finally detected from 21 telescopes located at 18 sites. This makes the Huya event one of the best ever observed stellar occultation b…
Context. GJ 436b is one of the few transiting warm Neptunes for which a detailed characterisation of the atmosphere is possible, whereas its non-negligible orbital eccentricity calls for further investigation. Independent analyses of several individual datasets obtained with Spitzer have led to contradicting results attributed to the different techniques used to treat the instrumental effects. Aims. We aim at investigating these previous controversial results and developing our knowledge of the system based on the full Spitzer photometry dataset combined with new Doppler measurements obtained …
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 t…
Triton possesses a thin atmosphere, primarily composed of nitrogen, sustained by the sublimation of surface ices. The goal is to determine the composition of Triton's atmosphere and to constrain the nature of surface-atmosphere interactions. We perform high-resolution spectroscopic observations in the 2.32-2.37 $μ$m range, using CRIRES at the VLT. From this first spectroscopic detection of Triton's atmosphere in the infrared, we report (i) the first observation of gaseous methane since its discovery in the ultraviolet by Voyager in 1989 and (ii) the first ever detection of gaseous CO in the sa…
