Water vapour jets inside the plume of gas leaving Enceladus

Abstract

A plume of water vapour escapes from fissures crossing the south polar region of the Saturnian moon Enceladus. Tidal deformation of a thin surface crust above an internal ocean could result in tensile and compressive stresses that would affect the width of the fissures; therefore, the quantity of water vapour released at different locations in Enceladus' eccentric orbit is a crucial measurement of tidal control of venting. Here we report observations of an occultation of a star by the plume on 24 October 2007 that revealed four high-density gas jets superimposed on the background plume. The gas jet positions coincide with those of dust jets reported elsewhere inside the plume. The maximum water column density in the plume is about twice the density reported earlier. The density ratio does not agree with predictions-we should have seen less water than was observed in 2005. The ratio of the jets' bulk vertical velocities to their thermal velocities is 1.5 +/- 0.2, which supports the hypothesis that the source of the plume is liquid water, with gas accelerated to supersonic velocity in nozzle-like channels.

The Main Belt Comets and ice in the Solar System

“…Many of the moons of the outer planets and Pluto contain a significant fraction of water, with Tethys possibly consisting almost entirely of water ice (Thomas et al 2007). Some, such as Jupiter's Europa and Saturn's Enceladus, are thought to contain a tidally heated global or local subsurface ocean of liquid water beneath the outer shell of ice (Carr et al 1998;Manga and Wang 2007;Nimmo et al 2007;Hansen et al 2008). …”

Direct detection of the Enceladus water torus withHerschel

“…Water emitted from Enceladus' plumes in jets with 1 km s −1 velocity (Hansen et al 2008(Hansen et al , 2011 initially forms a narrow torus. However, the observed OH distribution (Melin et al 2009) requires acceleration and spreading, for which processes identified early on (Jurac & Richardson 2005;Johnson et al 2006) include the release of kinetic energy under photodissociation and collisions with rapid torus ions.…”

Water masers in the Saturnian system

“…The black line shows the averaged spectrum with a peak antenna temperature of 32 mK and an SNR at the level of 7.0σ. the detection by Hansen et al (2006Hansen et al ( , 2008 of Enceladus' water vapour in UV-absorption. We note that over the preceding 14 months the Medicina telescope did not detect a line exceeding 3σ from Enceladus.…”