Did Aliens Cause the Tiger Stripes on Enceladus? | Unveiled

Did Aliens Cause the Tiger Stripes on Enceladus?

Introducing the solar system! It’s home to Earth and seven other planets, all cutting their cosmic path through space and zooming around the sun. There’s also the asteroid belt, various dwarf planets, and many, many moons. The gas giant Saturn plays host to a lot of those moons, and some of them rank amongst the most interesting worlds we know about so far.

But this is Unveiled, and today we’re answering the extraordinary question, did aliens cause the tiger stripes on Enceladus?

While not all of them have been officially confirmed, Saturn has 82 moons and counting. As our technology improves, we’re discovering more and more objects orbiting this famously ringed world… but already some stand out as being particularly notable. Titan, for example, usually features at the top of the list whenever humankind is thinking about where it might want to move to next. Titan is Saturn’s largest moon and, significantly, it has a dense atmosphere and surface liquid. Both these things combined mean that it could, one day, be a habitable destination for off-Earth human colonisers. Or, if alien life does exist in the solar system, then here is where it could be thriving.

But, while Titan tends to grab most of the headlines, Enceladus is another Saturnian moon that increasingly demands attention. It was discovered back in 1789, by William Herschel… although so much of the detail we know about Enceladus today comes from the ground-breaking Cassini probe, which performed multiple flybys of this most enigmatic of moons, between the years 2005 and 2015.

With a diameter of just over three hundred miles, Enceladus is about ten times smaller than Titan is. On the surface, it’s ice for as far as the eye can see… resulting in this moon usually being labelled as the most reflective astronomical object in the entire solar system. Out here, we’re about nine hundred million miles away from the sun but, even so, most of the little light that does reach Enceladus is bounced back out again.

However, although it hangs marble-like in space, Enceladus isn’t smooth. There are craters pockmarking its surface, but also deep and wide-reaching trenches, and chasms. The most famous of these are known as the tiger stripes, located near the moon’s south pole. Again, most of what we know about them comes from observations made by the Cassini probe. And, while scientists are still trying to work out exactly what the stripes are, we do know that there are four of them, they’re around eighty miles long and more than one mile wide on average, they’re a third of a mile deep, and they’re active. We know that Enceladus as a whole is a geologically active world, unlike many of the solar system’s other moons… but this region is more so than most. There are streams of gas, vapour and dust shooting out of the tiger stripes, as modern astronomers look to them as one of the best examples that we have of cryovolcanism in action.

The tiger stripe streams are thought to originate from a sub-but-near-surface ocean. And the watery vapours and gas they produce are believed to be vital to the Saturnian system because they contribute to the chemical makeup of Saturn’s E Ring - the widest of all the rings circling it. This moon Enceladus is more than just a satellite orbiting a planet, then. It’s actually crucial to that planet’s iconic look and composition. But, still, regardless of the function they have now, the tiger stripes have been source of much discussion since they were first observed in detail in the mid-2000s. These unusual features get their name mostly thanks to how regular the pattern they create appears to be. These are huge, miles-wide cracks in the surface, but from afar they look almost like deliberate scratch marks. Or the striped pattern of a tiger’s coat. So, what’s going on?

Naturally, as whenever something strange emerges in space, one answer put forward as to why the tiger stripes are there is… aliens. That some kind of extraterrestrial presence could’ve somehow built or caused them. This isn’t the answer that most scientists give, but the seeming symmetry and even spacing between the tiger stripes may have led to some of the more speculative fringe theories. But, really, even without the suggestion of an intelligent alien influence on them, the search for alien life does at least have an interest in the tiger stripes. That’s because these massive, visible cracks could one day provide us with a route to the water just beneath Enceladus’ surface. And alien microbes could, according to some theories, be hiding there.

In reality, though, the stripes’ formation has to do not with alien activity, but with chance physics. A study by researchers Douglas Hemingway, Maxwell Rudolph, and Michael Manga, and published in late 2019, found that these unusual trenches will have most likely opened up in Enceladus’ history thanks to gravity. Two things are happening; 1) as Enceladus moves around Saturn, it’s subject to tidal forces that gradually pull at the moon and heat it up… 2) because the surface ice on Enceladus is thinnest at its poles, here’s where the greatest impact of those tidal forces is felt.

It’s thought that the subsurface waters will have thawed, refrozen, and expanded over time, until one day when they burst out of the icy ground above. This is how it’s believed that the first tiger stripe was formed. From there, material from the subsurface ocean had a direct route to above the surface, which it took, before settling back down on the surface, thereby adding weight, and increasing pressure until… the next crack opened up and the next stripe formed. Then the same thing happened for the third stripe, and for the fourth. This may have taken place quickly or gradually, but it will have amounted to a kind of ripple effect across Enceladus’ surface - the results of which we see today.

Still, the question as to why the tiger stripes appear precisely where they do has continued to bug scientists. In the 2019 Hemingway, Rudolph, and Manga study, one implication was that the cracks could just as easily have formed at the moon’s north pole, rather than the south. However, an August 2020 study, led by the planetary scientist Alyssa Rhoden, suggested that stripes to the south may not have been quite such a chance event. The broad idea put forward by this new approach was that ice to the north may actually be notably thicker - and maybe even two or three times as thick - as the ice in the south is. Meanwhile, computer modelling found that ice in the south may need to have been less than three miles thick, to allow for the first stripe to form. All of which means that Enceladus’ subsurface ocean could, in reality, be extremely close to the surface. And within touching distance, in cosmological terms.

So, why do these strange marks on a moon that’s almost one billion miles away from Earth matter? It boils down to us, human beings, striving to understand the solar system in better ways. We’ve known that Enceladus is there for more than 230 years, but it’s only relatively recently that we’ve been able to explore. And, because of the subsurface ocean that it has, it remains a main site of interest on two fronts - in the search for alien life, and the search for potentially hospitable future human homes. So, now imagine a future time when we do have technology enough to pay Enceladus a visit… when space travel has advanced to the point that one billion miles is a genuinely manageable distance for humans… where’s the first place we’re likely to land? If we can gather enough background knowledge on the tiger stripes, then it could be them that we see outside our spaceship window when we make our first approach!

Between now and that hypothetical time ahead, there’s clearly so much that we need to achieve. The pioneering Cassini mission was ended on September 15th, 2017, when the probe was deliberately driven into Saturn’s atmosphere and destroyed. But the good news is that there are plans for future missions, including the Enceladus Life Finder, a proposed NASA probe that’s waiting to be given the green light. If it is given the go-ahead, this orbiter will specifically target Enceladus, and especially its subsurface ocean… to further improve our knowledge and understanding.

However we get there, though, let’s hope that we do get there soon… because Enceladus is rapidly emerging as one of the solar system’s most intriguing destinations. And the tiger stripes are its main attraction, even if they probably weren’t caused by aliens.