by Robin Andrews
Say goodbye to Enceladus: The Cassini spacecraft has finished its final flyby of themysterious icy moon of Saturn. After receiving streams of data over the weekend, NASAhas showcased some of the most beautiful astrophotography taken by the probe. Passing at a distance of 4,999 kilometers (3,106 miles) from the surface of the moon, the final series of images reveals the world’s furrows and ridges in impeccable detail.
“This final Enceladus flyby elicits feelings of both sadness and triumph,” said Earl Maize, Cassini project manager at NASA’s Jet Propulsion Laboratory (JPL), in a statement. “While we're sad to have the close flybys behind us, we've placed the capstone on an incredible decade of investigating one of the most intriguing bodies in the Solar System.”
The final flyby was Cassini’s 22nd, and was by no means its most dramatic. An earlier flybysaw the probe skim just 48 kilometers (30 miles) above the surface of Enceladus’ south pole, a region featuring spectacular plumes breaking through the ice and launching into space. Some have termed these icy jets as an example of cryovolcanism: volcanic eruption columns made entirely of ice.
Image credit: Samarkand Sulci, one of the “tiger stripes” of Enceladus likely formed by very young tectonic activity. This feature is 383 kilometers (238 miles) in length. NASA
This year, Cassini confirmed that there is a global ocean beneath the surface of Enceladus, one which is warm enough to produce these icy plumes. These plumes actually replenish one of Saturn’s famous rings, in this case the E ring. Although the formations on Pluto are more likely to be bonafide ice volcanoes, these plumes are still spectacular, and important: they may contain compounds indicative of biological processes operating beneath the surface.
Some scientists have speculated that this Saturnian moon, therefore, may be a prime candidate in our search for extraterrestrial life. By flying the spacecraft directly into one of these plumes in order to collect samples, NASA hoped to find evidence for this remarkable possibility. The data is still being analyzed, so only time will tell in this respect. Organic molecules, the building blocks of life on Earth, have already been confirmed to be present in these plumes.
Image credit: Enceladus’ northern territory. The terrain in the left part of this image has almost no craters, meaning it must be quite young. NASA
Scientists noted that the moon generates internal heat using the same mechanism that that powers the fiery, hellish volcanism of Jupiter’s moon Io. In Io’s case, the massive pull of Jupiter’s gravity, enhanced by its interaction with two other nearby moons, exerts an incredible gravitation force on its subsurface; this rips apart solid rock, causing it to melt.
In the case of Enceladus, the same mechanism, albeit a weaker variant, comes from its celestial dance with Saturn. This is known as tidal heating, demonstrated in two remarkably different ways in Enceladus and Io’s song of ice and fire.
Enceladus, 1.4 billion kilometers (890 million miles) from Earth, still holds many mysteries, and it’s likely that only a handful will be unraveled by the data streaming back from Cassini as it begins to turn its focus to Saturn itself.
“We bid a poignant goodbye to our close views of this amazing icy world,” said Linda Spilker, the mission's project scientist at JPL. The spacecraft will continue its tour of the Saturnian system until September 2017, whereupon it will complete its Solstice Mission by dramatically entering Saturn’s atmosphere.
