When NASA sent a spacecraft to Saturn, they were excited to learn about the planet, its largest moon Titan, and the rings. They didn't expect its sixth-largest moon, Enceladus, to take center stage and become a prime target for the search for life, but it did. Now, three years after Casinni performed its swan-dive into Saturn, new value is still being rung out of images the craft took of this endlessly surprising body.
The 2005 discovery of jets spouting from Enceladus' south pole changed the way we view the world, indicating it has liquid ocean within that might support life. Moreover, while Europa's ocean is (probably) buried deep inside, and thus inaccessible for future missions, Enceladus sprays so much material it is the source of Saturn's E ring and changes Titan's atmospheric chemistry. Collecting some for analysis is under consideration for future missions.
All the interesting aspects of Enceladus initially appeared to be around its south pole, where “tiger stripes” look like a set of giant claws were raked across the ice. From these stripes, geysers spew water vapor and ice grains 0.1 mm (0.004 inches) across. Carbon dioxide and organic molecules have been deposited nearby. Nothing similar has been found in the northern hemisphere, until now.
Dr Gabriel Tobie of the University of Nantes is part of a team that stitched together images of 23 flybys of Enceladus using Cassini's Visible and Infrared Mapping Spectrometer (VIMS). As its name suggests, VIMS' vision extends well into the infrared, and geological activity was highly visible at certain wavelengths.
Similar, but less striking infrared signals can also be seen in an area around 30 North 90 West, Tobie reports in Icarus, suggesting something similar may have occurred there quite recently.
"The infrared shows us that the surface of the south pole is young, which is not a surprise because we knew about the jets that blast icy material there," said Tobie in a statement. "Now, thanks to these infrared eyes, you can go back in time and say that one large region in the northern hemisphere appears also young and was probably active not that long ago, in geologic timelines."
Whether the fresh ice comes from gradual movement through fissures or now-extinguished jets depositing material is unknown.
Enceladus is so active because the gravitational tug of other moons constantly pull it out of shape, creating enough heat to melt its innards and sometimes breaking through the icy surface. Tobie and co-authors speculate the northern hotspot existed during a time when Enceladus' orbit was more elongated, and therefore the inner heat engine was more powerful.
Tobie has recently collaborated on a case to send an orbiter to Titan, but notes a craft orbiting Enceladus would fill gaps Cassini left. Perhaps a combined mission could manage both.
2