Icarus 287 (2017) - 124–130 - Pluto Charon Atmospheres - New Horizons constraints on Charon’s present day atmosphere

Aug 28, 2026

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The paper reports multiple New Horizons observational techniques used to search for a present-day atmosphere around Pluto’s moon Charon during the July 2015 flyby, including a solar ultraviolet occultation, ultraviolet airglow measurements, and high-phase look-back particulate search imaging. Analysis of returned datasets yields no atmospheric detection for 14 candidate atomic and molecular species. Upper limits constrain possible atmospheric pressures below 0.3 nanobar, providing substantially more stringent results than earlier studies, including an N2 3σ pressure limit of 4.2 picobars and a haze brightness limit of I/F = 2.6 × 10−5.

LanguageEnglish

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Introduction

Atmospheric solar ultraviolet occultation search

Atmospheric solar ultraviolet occultation search instrument and method

Icarus 287 (2017) 124–130 Contents lists available at ScienceDirect Icarus journal [homepage:](homepage: www.elsevier.com/locate/icarus)[ www.elsevier.com/locate/icarus](homepage: www.elsevier.com/locate/icarus) | New Horizons constraints on Charon’s present day atmosphere
S.A. Stern∗, J.A. Kammer, G.R. Gladstone, A.J. Steﬄ, A.F. Cheng, L.A. Young, H.A. Weaver, C.B. Olkin, K. Ennico, J. Wm. Parker, A.H. Parker, T.R. Lauer, A. Zangari, M. Summers, the New Horizons Atmospheres Team | | | | | --- | --- | --- | --- | | Southwest Research Institute, 1050 Walnut Street Suite 300, Boulder, CO 80302, United States. | | | | | a r t i c l e i n f o | | a b s t r a c t | | | Article history:
Received 23 March 2016
Revised 1 September 2016
Accepted 10 September 2016
Available online 29 September 2016 | | 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 constraints (e.g., Sicardyet al., 2006); for example, we ﬁnd a 3σ upper limit for an N2 atmosphere on Charon is 4.2 picobarsand a 3σ upper limit for the brightness of any atmospheric haze on Charon of I/F = 2.6 × 10−5 . A radio occultation search for an atmosphere around Charon was also conducted by New Horizons but will be published separately by other authors.
© 2016 Elsevier Inc. All rights reserved. | | | Keywords: Pluto Charon Atmospheres | | | | 1. Introduction Pluto’s largest satellite, Charon, is very close to half of Pluto’s diameter and has a surface gravity that is also close to half of Pluto’s. Although the surface composition of Charon has long been known to only display involatile materials (water ice, ammonia/ammonium hydrate, and tholins; e.g., Stern 1992; Stern et al. 2015a,b; Grundy et al. 2016 and references therein), searches for an atmosphere around Charon have nonetheless been conducted almost since it was discovered (e.g., Stern, 1992 and Sicardy et al., 2006). The exploration of the Pluto system by New Horizons (Stern et al., 2015a) employed a variety of techniques to search for an atmosphere around Charon. These included: (1) a search for the absorption of ultraviolet (UV) sunlight by key molecular species candidates during a solar occultation; (2) searches for far/extreme UV airglow emissions form a variety of possible molecular and atomic species; (3) high phase, panchromatic imaging above the limb by the New Horizons Long range Reconnaissance Imager (LORRI; Cheng et al., 2008) camera after closest approach: and (4) searches for refractive atmospheric refraction and an ionosphere using the New Horizons Radio Experiment (REX; Tyler et al., 2008) via radio occultation. Data from searches (1)–(3) have been returned to Earth and are the subject of this paper. They allow us constrain ∗ Corresponding author. E-mail address: [astern2010@aol.com](astern2010@aol.com) (S.A. Stern). abundances for 14 relevant atomic and molecular neutral species that could potentially be present in Charon’s atmosphere, notably including N2 , CO, CH4 , H2 , Ne, and Ar, and to also constrain forward scattering above Charon due to hazes or other optical effects. Results from search (4) have not yet been analyzed and so will be reported on separately in a subsequent paper; however, we note that these results are not expected to be more sensitive than techniques (1)-(2) for the species we discuss here. We now discuss results from searches (1)–(3) in turn, and then present summary conclusions. 2. Atmospheric so

FAQs

Which New Horizons techniques were used to search for an atmosphere around Charon?

The study used a solar ultraviolet occultation, ultraviolet airglow observations, and high-phase particulate search imaging, while a radio occultation search was handled separately by other authors.

Did the datasets show evidence of a present-day atmosphere on Charon?

No evidence was found for a present-day atmosphere for 14 candidate atomic and molecular species.

What upper limits were derived for possible atmospheric gases or haze?

The results constrain pressures below 0.3 nanobar for relevant species; for example, the N2 3σ upper limit is 4.2 picobars, and the 3σ upper limit for any atmospheric haze brightness is I/F = 2.6 × 10−5.

Aug 28, 2026

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