Journal Article

Ongoing hydrothermal activities within Enceladus

Hsu, Hsiang-Wen, Tachibana, Shogo, Postberg, Frank, Sekine, Yasuhito, Suzuki, Katsuhiko, Srama, Ralf, Moragas-Klostermeyer, Georg, Juhász, Antal, Altobelli, Nicolas, Masaki, Yuka, Kuwatani, Tatsu, Sirono, Sin-iti, Shibuya, Takazo, Horányi, Mihály, Kempf, Sascha

2015

Overview

Analysis of silicon-rich, nanometre-sized dust particles near Saturn shows them to consist of silica, which was initially embedded in icy grains emitted from Enceladus’ subsurface waters and released by sputter erosion in Saturn’s E ring; their properties indicate their ongoing formation and transport by high-temperature hydrothermal reactions from the ocean floor and up into the plume of Enceladus. Evidence of hydrothermal activity on Enceladus Hsiang-Wen Hsu et al . have analysed the silicon-rich, nanometre-sized dust stream particles in the Saturnian system using the Cosmic Dust Analyser (CDA) onboard the Cassini spacecraft. With the help of experiments and modelling, the particles are interpreted as silica grains that were initially embedded in the icy plume emitted from subsurface waters on Enceladus and released by sputter erosion in Saturn's E ring. Their properties indicate their formation and transport by high-temperature hydrothermal reactions from the ocean floor and up into the plume of Enceladus. Detection of sodium-salt-rich ice grains emitted from the plume of the Saturnian moon Enceladus suggests that the grains formed as frozen droplets from a liquid water reservoir that is, or has been, in contact with rock 1 , 2 . Gravitational field measurements suggest a regional south polar subsurface ocean of about 10 kilometres thickness located beneath an ice crust 30 to 40 kilometres thick 3 . These findings imply rock–water interactions in regions surrounding the core of Enceladus. The resulting chemical ‘footprints’ are expected to be preserved in the liquid and subsequently transported upwards to the near-surface plume sources, where they eventually would be ejected and could be measured by a spacecraft 4 . Here we report an analysis of silicon-rich, nanometre-sized dust particles 5 , 6 , 7 , 8 (so-called stream particles) that stand out from the water-ice-dominated objects characteristic of Saturn. We interpret these grains as nanometre-sized SiO 2 (silica) particles, initially embedded in icy grains emitted from Enceladus’ subsurface waters and released by sputter erosion in Saturn’s E ring. The composition and the limited size range (2 to 8 nanometres in radius) of stream particles indicate ongoing high-temperature (>90 °C) hydrothermal reactions associated with global-scale geothermal activity that quickly transports hydrothermal products from the ocean floor at a depth of at least 40 kilometres up to the plume of Enceladus.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 140/58 / 147/135 / 639/33/445/847 / Atoms & subatomic particles / Dust / Enceladus (Satellite) / Fluids / Gravity / High temperature / Humanities and Social Sciences / Hydrothermal systems (Geology) / Ice / letter / Moons / multidisciplinary / Observations / Ocean floor / Salinity / Saturn / Science / Silica / Temperature