Video: The Cassini spacecraft will fly closer to the moon Enceladus on 12 March than ever before in an attempt to scoop up particles from the moon鈥檚 mysterious icy jets (Courtesy of NASA)
The Cassini spacecraft will fly into mysterious icy plumes erupting from Saturn鈥檚 moon Enceladus on Wednesday. The flyby, the spacecraft鈥檚 closest approach to any object so far, could shed light on whether a liquid water ocean 鈥� and possibly life 鈥� lies beneath the moon鈥檚 icy surface.
In July 2005, Cassini flew within 175 kilometres of Enceladus鈥檚 surface, discovering a dozen or so jets spraying water vapour and ice crystals out of warm fissures near the south pole.
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That was surprising because moons as small as Enceladus, which is just 500 km wide, do not usually boast enough internal heat to foster such violent volcanic activity. Nonetheless, the existence of the plumes hinted that there might be a liquid water ocean beneath the surface that could provide a toehold for life.
To find out more about the plumes and their origin, mission managers devised a plan to send Cassini flying into the icy jets. On Wednesday, it will carry out the bold mission, passing just 50 km above the moon鈥檚 equatorial region before flying down the length of the plumes鈥� outer regions, beginning at an altitude of about 200 km (scroll down to see its trajectory).
鈥淭his daring flyby requires exquisite technical finesse, but it has the potential to revolutionise our knowledge of the geysers of Enceladus,鈥� says Alan Stern, NASA鈥檚 science chief.
Plume composition
Particle analysers, such as the INMS (Ion and Neutral Mass Spectrometer) and the CDA (Cosmic Dust Analyzer), will study the plumes, collecting data on the density, size, composition and speed of the gas and particles within them.
The plumes鈥� composition might shed light on their source. Eberhard Gruen at the Max Planck Institute for Nuclear Physics in Heidelberg, Germany, says the small moon may be heated as it is squeezed and stretched by Saturn鈥檚 gravity 鈥� a phenomenon called tidal heating.
This heating could either power a hot core inside the moon that is in contact with a deep reservoir of liquid water, or it could simply melt pockets of ice, forming smaller pools of liquid water, in the moon鈥檚 icy shell.
鈥淭he question is, do the vents from which the plumes emanate reach down to the rocky core or not,鈥� he told New 杏吧原创. He says this may be the case 鈥渋f only plume particles carry silicates and other impurities while particles from other parts of the surface consist of pure water ice鈥�.
Sascha Kempf, deputy principal investigator for the CDA who also works at Max Planck, agrees. 鈥淭he composition of the impurities tells a lot about the geological processes below the ice crust of the moon,鈥� he told New 杏吧原创.
North pole
During the flyby, a magnetometer on the spacecraft will also determine if the moon generates an induced magnetic field from a subsurface ocean.
Several gases, including water vapour, carbon dioxide and methane have been detected in the vicinity of the plumes. During the flyby, scientists hope to determine the differences in composition between the plumes鈥� own gas and the gas released from the moon鈥檚 surface when it is hit by particles from micrometeoroids and Saturn鈥檚 E-ring 鈥� which is densest at Enceladus鈥檚 orbit.
Cassini鈥檚 imagers will not be pointed at Enceladus when the spacecraft is closest to the moon, but they will take the first good images of the moon鈥檚 north polar region when Cassini begins its approach.
This will reveal whether the north pole has remnant 鈥渢iger stripe鈥� fissures like those on the south pole, which could help solve the mystery of why the plumes erupt only from the south pole.
The closest approach will take place at 2015 GMT on Wednesday. About six hours later, the spacecraft will begin beaming the flyby data back to Earth, a process expected to take 9 hours.
Cassini: Mission to Saturn 鈥� Learn more in our continually updated .
