(Cassini Imaging Team, SSI, JPL, ESA, NASA) The possibility of alien life thriving somewhere other than Earth is now stronger than ever before.
Underwater hydrothermal vents — the same kind that may have spawned life on our planet — seem to be lining the ocean floors of Saturn's tiny, water-rich moon called Enceladus, according to two recently published papers.
This is the most compelling evidence we have so far for the existence of these vents anywhere other than Earth. The latest discovery is a tantalizing hint that the conditions right for life may be present outside of Earth.
While Enceladus is watery, it is no Earth: It is only about 300 miles across. But under a thick, icy shell lies a water ocean habitat that resembles the conditions on an adolescent Earth, between 3.5 and 4 billion years ago.
Back then, Earth was covered in a single, global ocean. Most of the ocean is thought to have been extremely acidic — to0 acidic to create life — except around certain underwater, hydrothermal vents in which pockets of warm, less-acidic water could have formed. These conditions would have been the ideal place for life to arise on Earth, according to NASA scientist Michael Russell.
With this latest announcement, hydrothermal vents with these pockets of warm water are now believed to exist outside of Earth — at the bottom of Enceladus' oceans.
So how did these researchers find vents under miles of ice? Using the instruments on board the Cassini spacecraft, the team measured the size and number of silicon-rich particles, called silicates, in Saturn's second outer-most ring, the E ring. The E ring is made of particles that came from the moon's plumes and therefore tells scientists something about what is going on underneath the surface.
Once formed, these particles rise to the surface, where they escape to space through plumes off the moon's south polar region, shown in the arresting image below taken by Cassini:
(Cassini Imaging Team, SSI, JPL, ESA, NASA) The silicates' chemical makeup, size, and abundance give an indication of what is forming in the ocean underneath Enceladus' surface. And the result is incredibly exciting.
To show that these particles could come from hydrothermal vents, the team re-created them in the lab. To their surprise, they discovered that particles of this chemical composition, size, and abundance grow only under a very specific set of conditions. The team reported their findings Wednesday in the journal Nature.
What's more shocking is that these conditions are remarkably similar to a unique, underwater environment here on Earth, called the Lost City, which some researchers consider the cradle of life.
A miraculous find
(NOAA Photo Library on Flickr) Lost City Expedition 2005. One of four pinnacles that form the summit of the 200-foot tall carbonate chimney called Poseidon in the Lost City hydrothermal field. The Lost City is a field of hydrothermal vents that was first discovered in the mid-Atlantic ocean in the year 2000. Unlike other hydrothermal vents on Earth, this unique environment has basic, non-acidic waters that clock in at comfortable temperatures between 100 and 200 degrees Fahrenheit. Other vents can reach up to a scorching 860 degrees Fahrenheit.
Moreover, the life that thrives in the Lost City is mostly simple microorganisms — nothing like the larger, more complex life-forms hanging around other vents on Earth's ocean floor. Some scientists think these super-simple life-forms could be close-descendants of the first single-celled life on Earth.
The team's latest discovery makes Enceladus one of the most likely places in the solar system where alien life could exist, Linda Spilker, a project scientist with Cassini at NASA's Jet Propulsion Laboratory who was not involved with the study, told Business Insider.
"You have energy, nutrients, and liquid water, which create a potential habit that could support life," Spilker said.
In another recent paper published online in the journal Geophysical Research Letters, a different team of researchers reports additional evidence supporting the presence of hydrothermal vents. The researchers used Cassini to measure the amount of methane inside of the plumes of Enceladus as Cassini flew through them, and they found more methane than what was expected.
Methane is one of the main products generated by the Lost City's hydrothermal vents. This excess methane is most likely coming from hydrothermal vents, Spilker said.
"The methane story helps verify what we found with the tiny sillica particles," Spilker said.
These vents may be powered by tidal energy generated by Saturn's powerful gravitational tug on the tiny moon.
A recipe for success
(NASA/JPL-Caltech/Space Science Institute) Enceladus floating in space beneath Saturn's rings with a larger moon, Titan, in the background. Scientists first discovered that Enceladus was spewing jets of water vapor and ice back in 2005. This discovery rocked the scientific community because it indicated that Enceladus hosted liquid water underneath its surface. That was the first time astrobiologists began looking at Enceladus as a possible place to harbor alien life.
Then, in 2009, scientists discovered that not only was there an ocean, but it was salty, like the oceans on Earth.
Now there is compelling evidence that deep beneath the moon's icy surface, these salty oceans contain active hydrothermal vents like the vents of the Lost City.
About the only difference between Earth's oceans and those on Enceladus is evidence of life.
Although Spilker said the most likely source for both teams' measurements is hydrothermal vents, the authors of the Nature paper caution that further investigations are needed to confirm the presence of active vents on Enceladus. It's not as if we can see them under all that ice and ocean.
That we now have two very different measurements pointing to the same hydrothermal source, however, is encouraging.
The ultimate question
Cassini has made game-changing discoveries of Enceladus since it first began flying by the tiny moon in 2005, but it is not equipped with the right instruments to answer the ultimate question: Is there life on Enceladus?
And right now, NASA has no official plans to dispatch another spacecraft to Saturn anytime soon, Spilker told Business Insider. Moreover, it takes at least three years to reach Saturn, so it's going to be a while before we gain a better idea of what might be lurking beneath Enceladus' surface.
Cassini is scheduled to make its last three visits to Enceladus this year: two in October and the final flyby on December 19.
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