Evidence for longitudinal variability of ethane ice on the surface of Pluto

Abstract

a b s t r a c tWe present the results of an investigation using near-infrared spectra of Pluto taken on 72 separate nights using SpeX/IRTF. These data were obtained between 2001 and 2013 at various sub-observer longitudes. The aim of this work was to confirm the presence of ethane ice and to determine any longitudinal trends on the surface of Pluto. We computed models of the continuum near the 2.405 lm band using Hapke theory and calculated an equivalent width of the ethane absorption feature for six evenly-spaced longitude bins and a grand average spectrum. The 2.405 lm band on Pluto was detected at the 7.5-r level from the grand average spectrum. Additionally, the band was found to vary longitudinally with the highest absorption occurring in the N 2 -rich region and the lowest absorption occurring in the visibly dark region. The longitudinal variability of 12 CO does not match that of the 2.405 lm band, suggesting a minimal contribution to the band by 13 CO. We argue for ethane production in the atmosphere and present a theory of volatile transport to explain the observed longitudinal trend.

Pluto's haze as a surface material

“…They also found evidence for absorption by C 2 H 6 ice, especially in eastern Cthulhu, including the region where the Schmitt et al (2017) LEISA compositional maps place the Cthulhu "core". Ethane was proposed as representative of all alkanes heavier than methane, but confidence in that interpretation is boosted by its identification in higher spectral resolution ground-based observations around the same longitude (Holler et al 2014). Interestingly, Cook et al also found tentative evidence for methanol ice (CH 3 OH), also mostly in eastern Cthulhu.…”

COMPLEX HYDROCARBON CHEMISTRY IN INTERSTELLAR AND SOLAR SYSTEM ICES REVEALED: A COMBINED INFRARED SPECTROSCOPY AND REFLECTRON TIME-OF-FLIGHT MASS SPECTROMETRY ANALYSIS OF ETHANE (C2H6) AND D6-ETHANE (C2D6) ICES EXPOSED TO IONIZING RADIATION

“…Methane and ethane have been probed on Titan (Griffith et al 2006), Pluto (Holler et al 2014), Makemake (Brown et al 2015), and Quaoar (Dalle Ore et al 2009). Also, low-temperature interstellar ices have been shown to primarily contain water (H 2 O), ammonia (NH 3 ), carbon dioxide (CO 2 ), carbon monoxide (CO), methanol (CH 3 OH), and even methane (CH 4 ), with the latter at a level of a few percent (Boogert et al 2015).…”

“…The detection of ethane (C 2 H 6 ) in the atmospheres of the planetsJupiter, Saturn, Uranus, and Neptune (Gillett & Forrest 1974;Ridgway 1974;Hammel et al 2006) as well as inTitan, Pluto, Quaoar, Makemake (Nakamura et al 2000;Niemann et al 2005;Griffith et al 2006;Dalle Ore et al 2009;Holler et al 2014;Brown et al 2015), and comets including C/ 1996 B2 Hyakutake, 153P/Ikeya -Zhang, C/2001A2, and C/ 1999H1 (DiSanti & Mumma 2008, shows that ethane is a common molecule that deserves the attention of the astrochemistry community. According to Mumma et al (1996), ethane detected in comet C/1996 B2 Hyakutake is likely of interstellar origin based upon its relative abundance to water and can be traced back to the energetic processing of methane ice (Boogert et al 2015) in interstellar clouds, as shown in laboratory experiments simulating the irradiation of pure methane ice (Gerakines et al 1996;Kaiser & Roessler 1998;Bennett et al 2006;Jones & Kaiser 2013), and inmixtures of methane with water (Moore & Hudson 1998) by ionizing radiation.…”

Irradiation Products on Dwarf Planet Makemake

“…Evidence for the presence of intermediate products between methane and the presumed long-chain hydrocarbons that produce the red visible colors has been scant, however. Ethane, one of the first irradiation products of methane, has been detected robustly on Makemake (Brown et al 2007) and more weakly on Quaoar (Schaller & Brown 2007a) and Pluto (DeMeo et al 2010;Holler et al 2014).…”