Combining findings from New Horizons' suite of instruments reveals a bimodal haze particle distribution within Pluto's atmosphere, which haze models have not been able to reproduce. We employ the photochemical and microphysics KINAERO model to simulate seasonal cycles and their impact on the haze distribution. We find that the smaller spherical particle mode can be generated through photochemistry and coagulation, while the larger aggregate mode are formed by surface volatile deposits sublimating and subsequently lofting such particles upwards.
Pluto, Titan, and Triton make up a unique class of solar system bodies, with icy surfaces and chemically reducing atmospheres rich in organic photochemistry and haze formation. Hazes play important roles in these atmospheres, with physical and chemical processes highly dependent on particle sizes, but the haze size distribution in reducing atmospheres is currently poorly understood. Here we report observational evidence that Pluto's haze particles are bimodally distributed, which successfully reproduces the full phase scattering observations from New Horizons. Combined with previous simulation…
Haze in Pluto's atmosphere was detected in images by both the Long Range Reconnaissance Imager (LORRI) and the Multispectral Visible Imaging Camera (MVIC) on New Horizons. LORRI observed haze up to altitudes of at least 200 km above Pluto's surface at solar phase angles from ~20° to ~169°. The haze is structured with about ~20 layers, and the extinction due to haze is greater in the northern hemisphere than at equatorial or southern latitudes. However, more haze layers are discerned at equatorial latitudes. A search for temporal variations found no evidence for motions of haze layers (temporal…
The New Horizons spacecraft, which flew by Pluto on July 14, 2015, revealed the presence of haze in Pluto's atmosphere that were formed by CH4/N2 photochemistry at high altitudes in Pluto's atmosphere, as on Titan and Triton. In order to help the analysis of the observations and further investigate the formation of organic haze and its evolution at global scales, we have implemented a simple parametrization of the formation of organic haze in our Pluto General Circulation Model. The production of haze in our model is based on the different steps of aerosol formation as understood on Titan and …
The New Horizons flyby of Pluto confirmed the existence of hazes in its atmosphere. Observations of a large high- to low- phase brightness ratio, combined with the blue color of the haze, suggest that the haze particles are fractal aggregates, analogous to the photochemical hazes on Titan. Therefore, studying the Pluto hazes can shed light on the similarities and differences between the Pluto and Titan atmospheres. We model the haze distribution using the Community Aerosol and Radiation Model for Atmospheres assuming that the distribution is shaped by sedimentation and coagulation of particles…
Pluto's atmospheric haze settles out rapidly compared with geological timescales. It needs to be accounted for as a surface material, distinct from Pluto's icy bedrock and from the volatile ices that migrate via sublimation and condensation on seasonal timescales. This paper explores how a steady supply of atmospheric haze might affect three distinct provinces on Pluto. We pose the question of why they each look so different from one another if the same haze material is settling out onto all of them. Cthulhu is a more ancient region with comparatively little present-day geological activity, wh…
Seasonal Variability of Pluto's Haze Formation Revealed by Laboratory Simulations
University of Science and Technology of China（中国科学技术大学）；Johns Hopkins University（约翰斯·霍普金斯大学）；Space Telescope Science Institute（太空望远镜科学研究所）；NASA Goddard Space Flight Center（美国宇航局戈达德太空飞行中心）；Univ. Grenoble Alpes, CNRS, IPAG（格勒诺布尔阿尔卑斯大学，法国国家科学研究中心，IPAG）；Department of Materials Science and Engineering, Johns Hopkins University（约翰斯·霍普金斯大学材料科学与工程系）
Pluto has a heterogeneous surface, despite a global haze deposition rate of ~1 micrometer per orbit (Cheng et al., 2017; Grundy et al., 2018). While there could be spatial variation in the deposition rate, this has not yet been rigorously quantified, and naively the haze should coat the surface more uniformly than was observed. One way (among many) to explain this contradiction is for atmospheric pressure at the surface to drop low enough to interrupt haze production and stop the deposition of particles onto part of the surface, driving heterogeneity. If the surface pressure drops to less than…
Refractive indices of photochemical haze analogs for Solar System and exoplanet applications : a cross-laboratory comparative study between the PAMPRE and COSmIC experimental set-ups
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…
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）
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…
Numerous solar system atmospheres possess aerosols including the characteristic organic hazes of Titan and Pluto. Haze particles substantially impact atmospheric temperatures structures and may provide organic material to the surface of a world, thereby affecting its habitability. Observations of exoplanet atmospheres suggest the presence of aerosols, especially in cooler (<800 K), smaller (<0.3 times Jupiter's mass) exoplanets. It remains unclear if the aerosols muting the spectroscopic features of exoplanet atmospheres are condensate clouds or photochemical hazes, which is difficult to predi…
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. …
The Pluto-Charon system provides a broad variety of constraints on planetary formation, composition, chemistry, and evolution. Pluto was the first body to be discovered in what is now known as the Kuiper belt, its orbit ultimately becoming a major clue that the giant planets underwent substantial orbital migration early in Solar System history. This migration has been linked to an early instability in the orbits of the giant planets and the formation of the Kuiper belt itself, from an ancestral trans-Neptunian planetesimal disk that included Pluto. Pluto-Charon is emblematic of what are now re…
Using Chandra ACIS-S, we have obtained imaging Xray spectrophotometry of the Pluto system in support of the New Horizons flyby on 14 July 2015. 174 ksec of observations were obtained on 4 visits in Feb 2014 to Aug 2015. We measured a net signal of 6.8 counts and a noise level of 1.2 counts in a comoving 11 x 11 pixel box (100 x 100 R_Pluto) in the 0.31 to 0.60 keV passband for a detection at > 99.95 C.L. The Pluto photons do not match the background spectrum, are coincident with a 90% flux aperture comoving with Pluto, and are not sky source confused. The mean 0.31 to 0.60 keV Xray power from …
Optical Constants of Photochemical Haze Analogs in N2-CH4-CO Atmospheres from 0.4 to 28.6 μm
National Key Laboratory of Deep Space Exploration/School of Earth and Space Sciences, University of Science and Technology of China（中国科学技术大学地球与空间科学学院深空探测重点实验室）；Department of Earth and Planetary Sciences, Johns Hopkins University（约翰斯·霍普金斯大学地球与行星科学系）；Space Telescope Science Institute（太空望远镜科学研究所）
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 Pluto system was recently explored by NASA's New Horizons spacecraft, making closest approach on 14 July 2015. Pluto's surface displays diverse landforms, terrain ages, albedos, colors, and composition gradients. Evidence is found for a water-ice crust, geologically young surface units, surface ice convection, wind streaks, volatile transport, and glacial flow. Pluto's atmosphere is highly extended, with trace hydrocarbons, a global haze layer, and a surface pressure near 10 microbars. Pluto's diverse surface geology and long-term activity raise fundamental questions about how small planet…
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…
