NASA’s Cassini space probe launched in 1997 to study Saturn, its rings and its system of moons. It concluded its voyage of exploration in 2017 with a spectacular final swan dive into Saturn’s atmosphere.
But Cassini is still yielding new discoveries as scientists go through the vast amount of imagery and other data that it sent back to Earth. According to Space.com, its latest posthumous discovery was evidence of fresh ice on the northern surface of Enceladus, Saturn’s moon.
A Little World With an Ocean
Enceladus is a small world, only 314 miles in diameter according to NASA — which is only about a tenth the diameter of Titan, the giant of Saturn’s moon system. Experts already predicted it had geysers, but Cassini was able to capture images of these during close passes.
The images were surprising proof that Enceladus has an internal supply of liquid water. The source of this water supply, as EarthSky.org notes, is believed to be a subsurface ocean layer sandwiched between the moon’s solid core and its icy surface. The gravitation interplay of Saturn’s moon system provides an energy source that keeps this underground ocean from freezing solid.
The geysers originally imaged by Cassini — more than a hundred of them, per Space.com — are clustered around the moon’s south pole. Scientists believe that water from the underground ocean in this region is forced up through cracks in the surface ice. When it breaks through to the surface, it spurts into space, forming the geysers Cassini observed.
Some of the water from the geysers vaporizes in the vacuum of space and is lost, but some falls back to the surface and freezes. This process is gradually “repaving” the surface of Enceladus’ south polar region.
Teasing Secrets Out of Images
All of this was discovered during Cassini’s mission, before its final swan dive into Saturn. But scientists have continued to examine the imagery that Cassini sent back, using image-processing software to tease out subtle details that could not be seen by simply looking at the images.
These techniques led to the latest Cassini discovery: A research team combined visible-light and infrared images to examine the surface of Enceladus and found infrared heat signatures, such as “tiger stripes,” that matched up with the location of the southern polar geysers.
Now, this detailed search has also detected infrared signatures indicative of recent surface “repaving” in the northern hemisphere as well. The researchers do not yet know whether this repaving is produced by additional geysers, less powerful than the southern polar geysers and thus not dramatically visible, or by a more subtle seepage process. This might be equivalent to the hot springs that are commonly associated with geysers here on Earth, such as in Yellowstone Park.
Looking for Life in Unexpected Places
Will future space tourists take selfies standing in front of geysers on Saturn’s moon? We don’t know, but the scientists have more than just tourism prospects in mind. In 2018, as Chemical & Engineering News reported, another research team found that the water spurting from the geysers contains “large, complex organic molecules.”
These molecules resemble the building blocks of life, and while they are not by themselves proof of life , they certainly get the attention of biochemists. As a result, Enceladus has now emerged as one of the solar system’s prime candidates for potential extraterrestrial life.
This in itself is a remarkable discovery. Until recently, no one would have expected to find life anywhere amid the frigid reaches of Saturn’s moon system (with the possible exception of Titan).
A Solar System Full of Surprises
But it gets better. Scientists are finding growing evidence for hidden oceans of liquid water beneath the surfaces of a variety of small- to medium-sized bodies scattered across the solar system, including two dwarf planets: Ceres in the asteroid belt and Pluto in the remote Kuiper Belt.
The search for life, once almost wholly confined to Mars, is now spreading across the solar system. The more we look, the more surprises we continue to find.