Hemisphere of Enceladus

Spectral data gathered by the Visual and Infrared Mapping Spectrometer (VIMS) onboard NASA’s Cassini spacecraft provide strong evidence that the northern hemisphere of Saturn’s moon Enceladus has been resurfaced with ice from its interior.

In these detailed infrared images of Enceladus, reddish areas indicate fresh ice that has been deposited on the surface. Image credit: NASA / JPL-Caltech / University of Arizona / LPG / CNRS / University of Nantes / Space Science Instituto.

In these detailed infrared images of Enceladus, reddish areas indicate fresh ice that has been deposited on the surface. Image credit: NASA / JPL-Caltech / University of Arizona / LPG / CNRS / University of Nantes / Space Science Instituto.

Between 2004 and 2017, the VIMS instrument collected infrared data during 23 Enceladus close encounters, in addition to more distant surveys.

Dr. Gabriel Tobie, a researcher in the Laboratory of Planetology and Geodynamics at the University of Nantes, and colleagues used the VIMS data, combined with detailed images captured by Cassini’s Imaging Science Subsystem (ISS), to make the new global spectral map of Enceladus.

In 2005, the scientists discovered that Enceladus, which looks like a highly reflective, bright white snowball to the naked eye, shoots out enormous plumes of ice grains and vapor from an ocean that lies under the icy crust.

The new spectral map shows that infrared signals clearly correlate with that geologic activity, which is easily seen at the south pole.

That’s where the so-called ‘tiger stripes’ blast ice and vapor from the interior ocean.

But some of the same infrared features also appear in the northern hemisphere.

That tells the researchers not only that the northern area is covered with fresh ice but that the same kind of geologic activity — a resurfacing of the landscape — has occurred in both hemispheres.

The resurfacing in the north may be due either to icy jets or to a more gradual movement of ice through fractures in the crust, from the subsurface ocean to the surface.

“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,” Dr. Tobie said.

“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.”

The findings were published in the journal Icarus.

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R. Robidel et al. 2020. Photometrically-corrected global infrared mosaics of Enceladus: New implications for its spectral diversity and geological activity. Icarus 349: 113848; doi: 10.1016/j.icarus.2020.113848

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