On Wednesday, NASA's Cassini spacecraft will fly super close to Saturn's icy moon Enceladus, passing within 30 miles of its South Pole. That’s a little more than two times the length of Manhattan. It's the second of three final flybys the space probe is conducting by the end of the year, before it leaves the area around Enceladus for good. NASA researchers are particularly excited about this close encounter though, as it will bring Cassini through a giant plume that continually spews out materials from underneath the moon's crust. NASA hopes Cassini will get a taste of what this plume is made of, helping to determine whether or not Enceladus is likely to harbor alien life.
Astronomers have become increasingly intrigued with Enceladus, as it's turning into one of the best candidates in our Solar System for the search for extraterrestrials. The Saturn moon is known to eject icy plumes across its surface, and just recently, NASA scientists confirmed that those plumes are likely coming from a global subsurface ocean underneath the moon's icy exterior. Liquid water is essential for life here on Earth, and it could be essential for lifeforms on Enceladus, too.
NASA researchers are particularly excited about this close encounter
Researchers are also pretty sure that hydrothermal activity is occurring on the sea floor of this ocean, meaning the hot rock of Enceladus is chemically reacting with the liquid water. This kind of hydrothermal activity is also seen here on Earth, in the form of vents on the sea floor. These vents provide heat and energy for diverse ecosystems to exist at the bottom of frigid oceans, leading scientists to wonder if something similar may be happening on Enceladus as well.
With this flyby, NASA scientists hope to confirm that hydrothermal activity is indeed happening on Enceladus, as well as characterize the likelihood that the moon is habitable. To do this, Cassini will fly through an incredibly large plume erupting from the moon's south pole region, which ejects about 440 pounds of water vapor every second. This plume is filled with materials originating from the moon’s ocean, and Cassini's instruments will attempt to figure out their chemical composition when it zooms through the geyser. The spacecraft can't detect life directly, but it will provide insight into the conditions that might support life.
Most of all, NASA scientists hope that Cassini will find the presence of molecular hydrogen in the plume. That would help confirm that hydrothermal activity is happening on the ocean's sea floor as expected. Hydrothermal vents here on Earth produce fluids with very high concentrations of hydrogen, so the molecule's presence would be a strong indicator. Cassini will also try to get a better understanding of the chemistry of the plumes in general. A dust analyzer and spectrometer will observe all the particles ejecting from Enceladus, which are usually about 30 microns thick. NASA is expecting to find organic molecules such as methane, ethane, hydrocarbons, and more.
If NASA researchers find Enceladus to be a somewhat hospitable place, they say it's possible any alien life forms there could be similar to deep sea creatures found on our planet. "If you use the analogy to Earth's oceans and hydrothermal vents on the sea floor, perhaps you have a very diverse kind of life, similar to what we see here — from small diatoms and individual celled creatures to things that are more complex," said Linda Spilker, a Cassini project scientist at NASA's Jet Propulsion Laboratory. "You probably don’t get advanced life; there's no sunlight there, so not to the advancement of human beings."
Cassini's time flying through the plume will be incredibly short
This Cassini trip may also solve a mystery about Enceladus that has plagued astronomers: where these icy plumes are coming from. Some believe that the geysers originate from tight column-like jets around the south pole, while others believe that the plumes are spewing from curtain-like cracks that run across the surface. "There's an ongoing source of debate about just what this emission looks like," said Spilker.
Cassini will make its closest approach to Enceladus at 11:22AM ET tomorrow. It's time flying through the plume will be incredibly short; the spacecraft will be moving 19,000 miles per hour, so the plume dive will be over in an instant. Cassini will also be snapping some pictures of Enceladus along the way, though they'll likely be a bit blurry. NASA is relying on the light reflected off Saturn to illuminate Enceladus, which isn't very bright, so the camera on Cassini will have its aperture open to let in the most light possible. So spotting any aliens probably won’t happen either. But if the truth is out there, we may see it in the data this go around.
An artist’s rendering of the interior of Enceladus, as well as the plume of ice particles spraying from the moon's south polar region. (NASA)