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00:00In space, we all share the same home.
00:03But more than just a planet on its own, Earth is also a key point in its surrounding cosmic
00:09neighbourhood.
00:10What's strange, though, is that so much of what is all around us is still unknown.
00:16In this video, we're diving into six intriguing, unusual and crucial topics about the solar
00:22system we live in.
00:23Was there life on Mars before Earth?
00:25What's hiding on Pluto?
00:28Did humans live on Europa?
00:30Have aliens visited Enceladus?
00:33Did life exist on Venus before Earth?
00:36And what and where are the seven wonders of our system?
00:40This is Unveiled, and today we're taking a closer look at some of the biggest questions
00:46and most enduring mysteries about the solar system, its planets and moons, and about life
00:52within it.
00:53Do you need the big questions answered?
00:55Are you constantly curious?
00:56Then why not subscribe to Unveiled for more clips like this one?
00:59And ring the bell for more thought-provoking content!
01:06Around 3.5 billion years ago, the Earth was a very different place.
01:11Oxygen was extremely low, the ozone layer didn't exist yet, and the planet's surface
01:16was constantly blazed with radiation.
01:19Were a human being to be transported back there, they would die within a minute.
01:23But life still emerged.
01:26Many unicellular microbes, forming the basis of everything to come.
01:30Today, we still have much to learn about our own planet's early years, and yet there
01:34are some who say we should be looking elsewhere in the solar system if we want to truly understand.
01:51Mars, like Earth, is roughly 4.5 billion years old.
01:54It formed, along with most of the rest of the solar system, out of an ancient, swirling
01:59cloud of dust and gas… at a time when the universe as a whole was about 9.3 billion
02:04years old.
02:05Mars is also a rocky planet, like Earth, and it's the last of the inner planets closest
02:11to the sun before our particular star system is split in two by the asteroid belt.
02:16In some ways, Earth and Mars aren't so different, but in others, they're poles apart.
02:21Mars is around half of Earth's size, it barely has an atmosphere to speak of, and
02:26it doesn't have a magnetosphere.
02:28Crucially, it isn't within most estimates for the habitable zone around our star, either.
02:33Not that this has stopped us looking for and dreaming of life on Mars in recent years.
02:38The archetypal alien from Mars has been a pop culture science fiction mainstay for years,
02:43but actually science itself has moved on.
02:46Today, rather than scanning the red planet for an alien colony that's alive and well,
02:51our rovers and orbiters are much more likely searching for signs of ancient life… from
02:56a time when Mars, perhaps, wasn't quite so hostile.
03:00We may yet find an environment hosting life today, but if not, then evidence of life that
03:05once was is the next best thing.
03:07The question of whether life on Mars, if it has ever existed, could've predated life
03:13on Earth was arguably first asked in earnest in 2013.
03:17Back then, NASA was busy analysing streams of data from its Opportunity and Curiosity
03:23rovers.
03:24Among many other things, the vehicles found solid evidence whilst digging in rock that
03:28Mars had once hosted large bodies of liquid water… and also that it is, and was, home
03:35to many of the most essential elements needed for life.
03:39This information has led to theories that microbes may have once existed on our neighbouring
03:43world, too, as they do on our own.
03:46Precisely when this period of possible habitability might've been is still up for debate, but
03:51many scientists and researchers place it somewhere between three and four billion years ago…
03:56within the same distant window, then, that the earliest life on Earth is thought to have
04:01spawned.
04:02Before the rovers, though, there was Allan Hills 84001, a piece of Martian meteorite
04:09found in Antarctica in the last week of 1984.
04:12It's thought that the rock, which weighs a little over four pounds, crashed into Earth
04:17some 13,000 years ago.
04:20The leading theory says it was ejected from Mars following another impact event on the
04:24red planet about 17 million years ago.
04:28But significantly, this meteorite can be dated back a little over four billion years in total.
04:34That's long before even the upper estimates of unicellular life on Earth… which is interesting
04:39because Allan Hills 84001 also formed the basis of one of the first major news stories
04:45pertaining to evidence of life on Mars.
04:49Early study found what appeared to be tiny microbial fossils in the rock, and while these
04:54observations were eventually rejected by most astrobiologists, the hubbub was enough for
04:59former US President Bill Clinton to make a televised speech in the mid-1990s, when analysis
05:04from the meteorite was first made public.
05:07So that's now a seemingly dubious rock found in Antarctica and some arguably more
05:12compelling findings from rovers on the surface, both hinting at the potential for life on
05:16Mars up to four billion years ago… possibly at a time before even life on Earth arose.
05:23And there have been other studies pointing to similar conclusions, too.
05:27But of course, it's imperative to keep in mind that so far, we still have no solid proof
05:31of life on Mars at any time.
05:34We only have basis for various theories.
05:37But what would the planet have been like so far back in history?
05:40As much as Earth was a very different place billions of years ago, so, too, it seems,
05:45was Mars.
05:46When we think of it today, we see stark, barren landscapes layered with dust and stripped
05:51of atmosphere.
05:52A merciless world without air to breathe, soil to grow, and with precious little hope
05:57for survival.
05:58But just as we now suspect there to have once been lakes and pools dotted across the Martian
06:03surface, we also believe that it did once host an atmosphere… and that it wasn't
06:08always so bare.
06:11Scientists estimate that up to 66% of the Martian atmosphere has been lost since its
06:15height around four billion years ago.
06:18One co-authored study, appearing in the journal Science in 2017, for example, outlined how
06:23the planet underwent a, quote, transition in climate from an early, warm, wet environment
06:28to today's cold, dry atmosphere.
06:31That study made use of the Mars orbiter, MAVEN, to measure upper atmosphere levels
06:35of argon, in particular.
06:37But those behind it say that the findings can also be applied to carbon dioxide levels
06:42and therefore the presence of greenhouse gases on Mars, as well as oxygen.
06:47At one time, these gases may have been far more abundant on Mars, again leading to speculation
06:53that life, and especially microbial life, could have once thrived there.
06:58Even today, Mars is still losing its atmosphere to space, with more and more particles escaping
07:03with every passing minute… but it's thought that the majority of the loss did take place
07:08around four billion years ago.
07:10And as for the relatively short time between then and when the planet formed, we're currently
07:15not overly confident as to what conditions were like.
07:18Naturally, though, it's this unknown period which most fuels the majority of life on ancient
07:22Mars theories.
07:24So, let's imagine, for the last part of today's video, that life did once exist
07:28there.
07:29What could that mean for us?
07:31In August 2020, a familiar astrobiological theme made headlines once again, panspermia.
07:38Panspermia is the proposed passing of biological material from one planet to another in a number
07:43of ways, the most often cited being by spacecraft or asteroids.
07:48The 2020 story centred on a study conducted by Tokyo University and JAXA, the Japan Aerospace
07:54Exploration Agency, in which scientists put dried bacteria into exposure panels on the
08:00outside of the International Space Station.
08:03Three years after doing so, they checked to see whether any of the bacteria had survived
08:07and, incredibly, most of it had.
08:10The bacteria on the outermost layer did perish, but underneath it was still alive and well.
08:16We know, then, that in at least one case, microbes could survive in space long enough
08:21to make a journey between Mars and Earth.
08:24Lithopanspermia, more specifically, is the preservation of cells and microbes in rock
08:29such as inside an asteroid.
08:31And we do have various examples throughout our history of Martian rock breaking away
08:35from its parent planet and ending up embedded in our own… including Allan Hills 84001.
08:41And so, herein lies the next question.
08:44If we ever proved that there was life on Mars before Earth, then could that life have
08:49been transported here?
08:51If you were to trace us back far enough, could we be the product of one-time Martian biology?
08:58Importantly, again, panspermia is not a proven process.
09:02And a lot of the time, space agencies are actually more concerned with how we could
09:07be the ones facilitating it the other way, by contaminating other planets with bacteria
09:11carried by our probes and rovers sent across the solar system.
09:15But it does prompt us to consider space in a wholly different manner.
09:19To see it as, potentially, a vast ecosystem of its own, where life isn't only confined
09:25to Earth, it just so happens to be here in abundance right now.
09:29Mars certainly has changed over time.
09:31We know this thanks to an increasing number of studies.
09:34But could everything about us really have started on a different planet?
09:39Unfortunately, our interest in Mars is far from slowing down.
09:42In fact, it's gathering pace as we move through the 21st century… which means that
09:46if there ever was life there, then the signs will become clearer and clearer.
09:54The sun's gravitational pull stretches out much further than Neptune, all the way out
09:59to the Kuiper Belt and beyond.
10:01To these dark and mysterious satellites, the sun is just a pinprick in the sky… and one
10:05of the most mysterious of all is Pluto.
10:17Once classified as the ninth planet in the solar system, in 2006 Pluto was downgraded
10:22from planet to dwarf planet.
10:24To count as a planet, the International Astronomical Union decided an object must have cleared
10:29the neighbourhood around its orbit… which Pluto has failed to do due to its relatively
10:33small mass.
10:34Technically, Pluto is a trans-Neptunian object, drifting through the Kuiper Belt.
10:39It was the discovery of another such object, Eris, that led to the definition of a planet
10:43being changed.
10:44Pluto's surface area is only 3.3% the size of Earth's, making it about the same size
10:49as Russia.
10:50On top of being small, Pluto has incredibly low gravity, so little that you'd hardly
10:54even notice it… about 6.3% the strength of gravity on Earth.
10:58Nonetheless, it does have its own moons, Charon, Styx, Hydra, Nix and Kerberos.
11:04The largest, Charon, wasn't discovered until 1978, almost five decades after Pluto itself
11:10was found.
11:11It's large enough that Pluto and Charon were almost classified as double planets.
11:15The two are tidally locked, always presenting the same face to one another.
11:19Charon's pull causes Pluto's football-shaped moons Nix and Hydra, and possibly Styx and
11:24Kerberos as well, to wobble as they rotate, caught in a game of gravitational tug-of-war.
11:29What little data we have about this was gathered by the New Horizons probe in 2015, and we
11:34likely won't know more until we can investigate further.
11:37Considering the fact that we've detected planets and stars and black holes millions
11:41of light-years away from Earth, it's strange to think that there are so many things we
11:44don't know about what's hiding in our solar system.
11:47For thousands of years, we didn't have any way to study celestial objects apart from
11:51the seven classical planets – the sun, the moon, Mercury, Venus, Mars, Jupiter and Saturn.
11:57Obviously, we now know that the sun and moon aren't planets, but this ancient definition
12:01of planet refers to objects visible to the naked eye.
12:05Until the discovery of Uranus in 1781, which was initially thought to be a star, we had
12:09no idea there were even more in the solar system.
12:12It was over sixty years later that Neptune was discovered in 1846, and in 1930 astronomer
12:18Clyde Tombaugh found Pluto.
12:20The existence of an additional planet had been hypothesized before this, thanks to apparent
12:24perturbations in the orbit of Uranus, that was later attributed to an overestimation
12:28of Neptune's mass.
12:30Pluto may not be a planet any longer, but its discovery was still hugely important,
12:34since it was the first trans-Neptunian object we ever found.
12:38It wasn't until 1992 that the second, Albion, was discovered.
12:42Part of what makes studying Pluto and other trans-Neptunian objects so difficult is the
12:46sheer distance between us and them.
12:49The distance between Earth and Pluto ranges between 2.66 billion miles to 4.67 billion.
12:55For contrast, Mars is sometimes just 34 million miles away.
12:59The vast distance makes sending probes to Pluto and potentially going there one day
13:03incredibly difficult.
13:05If you missed the optimal launch window, you could end up almost doubling the distance
13:08you had to travel.
13:10And considering that Pluto takes 248 years to orbit the sun, you'd be waiting a long
13:14time to get a second chance.
13:16In fact, Pluto hasn't completed even half of its journey around the sun since it was
13:20discovered.
13:21The only man-made object to have reached Pluto so far is NASA's New Horizons probe, which
13:26in 2015 conducted a flyby over the surface.
13:29It discovered a surprisingly youthful surface and varied geography.
13:33This included exotic ice flows, mountain ranges, and possible evidence of cryovolcanic processes.
13:38A vast haze hangs around the planet, the result of sunlight breaking up methane gas particles.
13:44Pluto's plains are mostly nitrogen ice, but its mountains are water ice, with methane
13:48frost.
13:49A dark, reddish band named Cthulhu Macula swirls across its surface, possibly the result
13:54of organic compounds called tholins, formed when ultraviolet light strikes methane and
13:59nitrogen.
14:00Perhaps the best adjective to describe Pluto, apart from distant, is cold.
14:04Pluto has an incredibly low surface temperature, going from minus 369 degrees Fahrenheit at
14:09its warmest to minus 387 degrees at its coldest.
14:13While this is still warmer than the average temperature of outer space itself, which is
14:17around minus 454 degrees, it's still significantly colder than the coldest temperature ever recorded
14:23on Earth.
14:24That was minus 128.6 degrees Fahrenheit, recorded in Antarctica in 1983.
14:30So, Pluto is around three times colder than the Antarctic at its chilliest.
14:34For more context, liquid nitrogen is about minus 320 degrees.
14:39Even at its warmest, the surface temperature of Pluto is still cold enough that if you
14:42were exposed to it you'd freeze almost instantly.
14:45Pluto is clearly one of the most inhospitable places in the solar system.
14:49Living there would involve the same problems as living in an Antarctic outpost, or the
14:53International Space Station, only worse.
14:56Astronauts and Antarctic residents, who are mostly scientists and military personnel,
15:00are incredibly isolated and can't remain in their respective bases for long.
15:04The ISS also has radiation to contend with, which, combined with low gravity, is one of
15:09the biggest reasons that the time astronauts spend there is restricted.
15:13Deadlier still, Pluto's atmosphere is made up largely of nitrogen and highly poisonous
15:17carbon monoxide.
15:18Needless to say, our technology would have to improve drastically to get people to Pluto
15:22in the first place, let alone to set up some kind of outpost, or to have any chance of
15:27a return journey.
15:28It's unlikely that Pluto would ever become more than a research base, even in an advanced
15:32future much like Antarctica, though it might see the odd tourist.
15:36It would just be too difficult and risky to build any large-scale settlement with any
15:40purpose except studying the planet, or perhaps refuelling spacecraft if they journey further
15:45out.
15:46But perhaps Pluto isn't as bleak as it seems at first.
15:49There are many icy worlds in the solar system that we think have subsurface oceans, such
15:53as Jupiter's moon Europa and Saturn's moon Titan.
15:56Europa is much closer and is most likely hiding a massive, warm ocean beneath its frosty outer
16:01shell.
16:02Some scientists think that Pluto could be the same.
16:05A large basin of frozen nitrogen and carbon monoxide ices was spotted on the surface,
16:09which shouldn't have been able to form without an ocean underneath.
16:12This evidence confused astronomers for a long time since they couldn't explain how Pluto
16:16could have an ocean, but new theory suggests that Pluto might have a layer of insulating
16:20gases that keep it warm enough to harbour a vast, alien sea.
16:24If this is true, not only could there be alien life on Pluto, but we may be able to send
16:28humans there one day.
16:30Luckily, by the time we develop the technology to get there, we'll probably already have
16:34explored Europa, so we'll have valuable knowledge to draw from when it comes to building
16:38in this kind of environment.
16:39However, Pluto is still incredibly far away from the sun, which could be enough on its
16:44own to prevent life from evolving.
16:46Pluto is so far away that it's hard to know for sure whether it's a desolate, dark
16:50wasteland or a secret haven for aquatic aliens.
16:53But until technology gives us the answer, we can at least dream of the latter.
17:01When it comes to human colonies in the solar system, Mars is usually billed as our best
17:05bet because it offers some favourable conditions and isn't too far away.
17:09But the red planet isn't without its share of problems, either.
17:13There are other solar system places that we could even be better suited to.
17:26The Galilean moons, Io, Europa, Ganymede and Callisto, are the four largest of the many
17:31moons of the gas giant Jupiter, named that way because they were large enough for Galileo
17:35to spot them through his telescope.
17:38Europa is the smallest of the four, but is still only slightly smaller than our own moon,
17:42and about one-quarter the size of Earth.
17:45Significantly, though, this unassuming, far-off world is thought to contain vast oceans of
17:50water around ten to fifteen miles below its icy surface.
17:54Scientists even estimate that it could hold roughly double the total water content of
17:57our own planet, with seas that are forty to a hundred miles deep.
18:01All of which means that Europa has long been considered one of the most likely places to
18:05find extraterrestrial life in the solar system.
18:08So, if it's already a contender to host life, could humans one day live there as well?
18:13If life does exist on Europa, and there's no proof that it does at the moment, it's
18:17thought that it would probably be bacteria or single-celled organisms, which are generally
18:21much more resilient than human beings.
18:23Humans, by contrast, need a number of conditions and criteria to be met before there's even
18:28a chance of survival.
18:30Europa could naturally provide us with water to drink, but we also need air to breathe,
18:34food to eat and reliable shelter.
18:37And that's just the basics.
18:38We also need to think about surface temperatures, air pressure, the strength of gravity, and
18:42the makeup of the atmosphere.
18:44We need to maintain an internal body temperature of thirty-seven degrees Celsius, and we need
18:48to feed our bodies with just the right balance of nutrients.
18:52With all of that considered, there aren't any places in the solar system where we could
18:55just land, disembark and immediately start setting up base… but Europa offers more
19:00potential than most to terraform.
19:02Crucially, Europa does have an atmosphere.
19:05And even better, that atmosphere is solely made up of oxygen.
19:09But unfortunately, it's also much too thin for humans to breathe.
19:12Still, the fact that there is a small amount of oxygen is a very good start… and something
19:17that already sets Europa apart from a lot of other planets and moons, along with the
19:21water.
19:22In theory, were we to terraform, we'd only need to harness and create more oxygen, in
19:26as safe a way as possible.
19:28However, the thin Europa atmosphere in part explains arguably the most dangerous part
19:32of any potential mission there, the radiation.
19:35The surface of Europa is pelted with about 540 rem daily, comfortably enough to kill
19:40a person very quickly.
19:42So much so, the threat of radiation poisoning is pitched as the biggest reason why Europa
19:46perhaps isn't suitable for human habitation, period.
19:49But in a future world where astronauts can't feasibly travel to Jupiter in the first place,
19:54there could be a couple of ways to bypass this obstacle, too.
19:57We could either try building very thick, ultra-advanced protective shields on the surface, or we could
20:02use Europa's own icy shell as a protective barrier by living below it.
20:06The ice would be thick enough to block out the radiation, which is one reason why scientists
20:10think there already could be life in the water below.
20:14True the idea of a far-off human outpost totally submerged in water and buried underneath fifteen
20:19miles of ice isn't perhaps the most welcoming of mental images… but no one said this would
20:23be easy.
20:24Regardless, say we've mastered and enhanced Europa's oxygen and built a home beneath
20:29its radiation-defeating ice shelf.
20:31What then?
20:32Well, the gravity presents another obvious challenge.
20:35Europa's gravity is slightly weaker than our own moon's, and about thirteen percent
20:39that of Earth's.
20:40In the short term, it'd mean having to get used to floating about in low-gravity conditions.
20:44But in the long term, it poses greater problems for us as low gravity has been linked to weakening
20:48immune systems, lessening bone density, and bringing about muscle atrophy, among other
20:53things.
20:54Astronauts counteract these effects by using exercise machines and following strict exercise
20:58routines during stays on the International Space Station, for example… but were humans
21:03ever to permanently live with less gravity, it'd mean whole generations of people battling
21:07major and unprecedented health issues.
21:10So, the water is fantastic, though it is thought to be salt water so would need purifying,
21:15the atmosphere is also promising, the radiation not so much but there are workarounds, and
21:19the gravity is a great but potentially damaging unknown.
21:23The temperatures on Europa are another key hurdle on our prospective mission to live
21:27there.
21:28The surface sees temperatures ranging from minus-160 to minus-220 degrees Celsius, so
21:33even without the constant radiation threat, living on the surface isn't really feasible.
21:38Luckily, though, the water where we'd be headed isn't nearly as cold… all of which
21:42raises all new questions on underwater settlements.
21:44Specifically, can we even build them?
21:47A growing number of architects think that we can, and some have even started to design
21:51underwater cities on Earth, like the pioneering con shelf stations 1 and 2, built in the 1960s.
21:57These types of projects are still in their very early stages even on our own planet,
22:01but by the time we've developed space travel techniques advanced enough to get people to
22:05Europa, perhaps we'd also have perfected underwater living as well.
22:08Let's not get too far ahead of ourselves, though.
22:12Even in a reality where we really could live underwater en masse, the issues on Europa's
22:16surface wouldn't disappear.
22:18Ultimately, in the event that we successfully arrive at the far-off moon in the future,
22:22navigating the surface to get under the ice could still prove very difficult… but staying
22:26there, maybe not so much.
22:29Europa is by no means the perfect candidate for off-Earth living, but it does offer more
22:33than most other places… and there are even a couple of missions already aiming to place
22:36a colony on Europa, although none are past the research and development phase just yet.
22:42Could humans live on Europa?
22:44More and more people are claiming that it's possible.
22:46Right now, it's a matter of first getting there, second surviving the surface, and third
22:51adapting to life underground, underwater, on a Jovian moon.
22:55It's certainly a long shot, but there are still plenty of reasons to regard Europa with
22:58particular interest.
23:05Introducing the solar system!
23:07It's home to Earth and seven other planets, all cutting their cosmic path through space
23:12and zooming around the sun.
23:13There's also the asteroid belt, various dwarf planets, and many, many moons.
23:19The gas giant Saturn plays host to a lot of those moons, and some of them rank amongst
23:23the most interesting worlds we know about, so far.
23:36While not all of them have been officially confirmed, Saturn has 82 moons and counting.
23:40As our technology improves, we're discovering more and more objects orbiting this famously
23:45ringed world.
23:46But already, some stand out as being particularly notable.
23:49Titan, for example, usually features at the top of the list whenever humankind is thinking
23:53about where it might want to move to next.
23:56Titan is Saturn's largest moon, and significantly, it has a dense atmosphere and surface liquid.
24:02Both of these things combined mean that it could one day be a habitable destination for
24:06off-Earth human colonisers.
24:07Or, if alien life does exist in the solar system, then here's where it could be thriving.
24:13But while Titan tends to grab most of the headlines, Enceladus is another satirian moon
24:18that increasingly demands attention.
24:20It was discovered back in 1789 by William Herschel, although so much of the detail we
24:26know about Enceladus today comes from the groundbreaking Cassini probe, which performed
24:30multiple flybys of this most enigmatic of moons between the years 2005 and 2015.
24:36With a diameter of just over 300 miles, Enceladus is about ten times smaller than Titan is.
24:42On the surface, it's ice for as far as the eye can see, resulting in this moon usually
24:47being labelled as the most reflective astronomical object in the entire solar system.
24:53Out here, we're about 900 million miles away from the sun.
24:57But even so, most of the little light that does reach Enceladus is bounced back out again.
25:02However, though it hangs marble-like in space, Enceladus isn't smooth.
25:07There are craters pockmarking its surface, but also deep and wide-reaching trenches and
25:11chasms.
25:13The most famous of these are known as the Tiger Stripes, located near the moon's south
25:17pole.
25:18Again, most of what we know about them comes from observations made by the Cassini probe.
25:23And while scientists are still trying to work out exactly what the stripes are, we do know
25:28that there are four of them, they're around 80 miles long and more than one mile wide
25:33on average, they're a third of a mile deep, and they're active.
25:38We know that Enceladus as a whole is a geologically active world, unlike many of the solar system's
25:43other moons, but this region is more so than most.
25:47There are streams of gas, vapour and dust shooting out of the Tiger Stripes, as modern
25:53astronomers look to them as one of the best examples that we have of cryovolcanism in
25:58action.
25:59The Tiger Stripe streams are thought to originate from a sub-but-near-surface ocean, and the
26:05watery vapours and gas they produce are believed to be vital to the Satorian system because
26:10they contribute to the chemical make-up of Saturn's E-ring, the widest of all the rings
26:15circling it.
26:16This moon, Enceladus, is more than just a satellite orbiting a planet, then.
26:21It's actually crucial to that planet's iconic look and composition.
26:25But still, regardless of the function they have now, the Tiger Stripes have been a source
26:29of much discussion since they were first observed in detail in the mid-2000s.
26:34These unusual features get their name mostly thanks to how regular the pattern they create
26:39appears to be.
26:40These are huge, miles-wide cracks in the surface, but from far away they look almost like deliberate
26:46scratch marks… or the striped pattern of a tiger's coat.
26:50So, what's going on?
26:51Naturally, as whenever something strange emerges in space, one answer put forward as to why
26:56the Tiger Stripes are there is… aliens.
26:59That some kind of extraterrestrial presence could have somehow built or caused them.
27:05This isn't the answer that most scientists give, but the seeming symmetry and even spacing
27:09between the Tiger Stripes may have led to some of the more speculative fringe theories.
27:14But really, even without the suggestion of an intelligent alien influence on them, the
27:18search for alien life does at least have an interest in the Tiger Stripes.
27:22That's because these massive, visible cracks could one day provide us with a route to the
27:27water just beneath Enceladus' surface.
27:31And alien microbes could, according to some theories, be hiding there.
27:36In reality, though, the Stripes' formation has to do not with alien activity, but with
27:41chance physics.
27:42A study by researchers Douglas Hemingway, Maxwell Rudolph, and Michael Manga, and published
27:48in late 2019, found that these unusual trenches will have most likely opened up in Enceladus'
27:54history thanks to gravity.
27:56Two things are happening.
27:58One, as Enceladus moves around Saturn, it's subject to tidal forces that gradually pull
28:03at the moon and heat it up.
28:05Two, because the surface ice on Enceladus is thinnest at its poles, here's where the
28:10greatest impact of those tidal forces is felt.
28:13It's thought that the subsurface waters will have thawed, refrozen, and expanded over
28:18time… until one day, when they burst out of the icy ground above.
28:23This is how it's believed that the first Tiger Stripe was formed.
28:26From there, material from the subsurface ocean had a direct route to above the surface, which
28:32it took before settling back down on the surface, thereby adding weight and increasing pressure
28:38until the next crack opened up and the next Stripe formed.
28:42Then the same thing happened for the third Stripe and for the fourth.
28:46This may have taken place quickly or gradually, but it will have amounted to a kind of ripple
28:51effect across Enceladus' surface, the results of which we see today.
28:55Still, the question as to why the Tiger Stripes appear precisely where they do has continued
29:00to bug scientists.
29:02In the 2019 Hemingway, Rudolph and Manga study, one implication was that the cracks could
29:07just as easily have formed at the moon's north pole, rather than the south.
29:11However, an August 2020 study, led by the planetary scientist Alyssa Rodin, suggested
29:18that the Stripes to the south may not have been quite such a chance event.
29:22The broad idea put forward by this new approach was that the ice to the north may actually
29:27be notably thicker, and maybe even two or three times as thick as the ice in the south
29:32is.
29:33Meanwhile, computer modelling found that the ice in the south may need to have been less
29:37than three miles thick to allow for the first Stripe to form.
29:41All of which means that Enceladus' subsurface ocean could, in reality, be extremely close
29:46to the surface, and within touching distance in cosmological terms.
29:51So, why do these strange marks on a moon that's almost one billion miles away from Earth matter?
29:57It boils down to us human beings striving to understand the solar system in better ways.
30:03We've known that Enceladus is there for more than 230 years, but it's only relatively recently
30:08that we've been able to explore.
30:10And because of the subsurface ocean that it has, it remains a main site of interest on
30:15two fronts… in the search for alien life, and the search for potentially hospitable
30:20future human homes.
30:22So now, imagine a future time when we do have the technology enough to pay Enceladus a visit.
30:27When space travel has advanced to the point that one billion miles is a genuinely manageable
30:31distance for humans, where's the first place we're likely to land?
30:35If we can gather enough background knowledge on the Tiger Stripes, then it could be them
30:39that we see outside our spaceship window when we make our first approach.
30:44Between now and that hypothetical time ahead, there's clearly so much that we need to achieve.
30:49The pioneering Cassini mission was ended on September 15th, 2017, when the probe was deliberately
30:54driven into Saturn's atmosphere and destroyed.
30:58But the good news is that there are plans for future missions, to further improve our
31:02knowledge and understanding.
31:04However we get there, though, let's hope that we do get there soon.
31:08Because Enceladus is rapidly emerging as one of the solar system's most intriguing destinations.
31:14And the Tiger Stripes are its main attraction… even if they probably weren't caused by aliens.
31:23Earth's evil twin is about the same size and mass, but it has an incredibly toxic atmosphere
31:28full of heavy CO2, scorching temperatures and acid rain.
31:32Venus is so inhospitable that we gave up on sending probes out there before the turn of
31:36the century.
31:37However, plenty of evidence suggests that it wasn't always this way.
31:44The surface of Venus is hostile to life as we know it.
31:52Its atmosphere is made up largely of 96.5% carbon dioxide, and is so thick and heavy
31:58that the atmospheric pressure at its surface is 92 times stronger than Earth's.
32:03That means that walking on Venus would be like walking on the seafloor 3,000 feet down,
32:08through an ocean made of sulfuric acid at temperatures exceeding 880 degrees Fahrenheit.
32:13Every other planet in our solar system is inhospitable to us without some significant
32:17tweaking.
32:18However, Venus's rotation also sets it apart.
32:21Like Uranus, it rotates in the opposite direction to the other planets in the solar system.
32:25Its rotation is also extremely slow.
32:28A day-night cycle on Venus takes 116.75 Earth days.
32:33At least Venus's gravity is something we don't have to worry about.
32:36Its gravity is 8.87 meters per second squared, only slightly less than Earth's.
32:41While today its size and gravitational pull are the only things similar to our own planet,
32:46scientists have used these similarities to suggest that once upon a time, Venus was capable
32:50of supporting life.
32:52A NASA study showed that in computer models that assumed various levels of water coverage,
32:56Venus could have sustained liquid oceans for two to three billion years of its 4.5 billion
33:01year lifespan.
33:03Considering Mars only had liquid water for 400 million years, Venus is a much likelier
33:07candidate for hosting alien life.
33:09In these simulations, it was found that temperatures on Venus ranged between a relatively comfortable
33:1468 to 122 degrees Fahrenheit.
33:17That's about the same temperature as parts of Earth close to the equator, where humans
33:21have been living for thousands of years.
33:23So, it's definitely possible for life, including intelligent life, to develop in these conditions.
33:28This revelation has led to a change in our understanding of what kind of planets may
33:32be habitable outside of our solar system.
33:35Previously, the Venus Zone was thought to be a region of space where there was simply
33:39too much solar radiation to maintain liquid water.
33:42But now we have many reasons to believe that this isn't true.
33:45This means that lots of exoplanets we've discovered and written off as being outside
33:49of what we consider to be the Goldilocks Zone might harbour extraterrestrial life, after
33:54all.
33:55This not only increases our chances of discovering alien life, but also of one day finding a
33:59second home for humanity if we need to.
34:02These Venus Zone planets might be a little warmer than we're used to, but if they can
34:06sustain a decent amount of liquid water for billions of years, then they're definitely
34:10worth our time.
34:11But, if Venus might have once been capable of supporting life, what made it the toxic
34:15wasteland it is today?
34:16Scientists… don't have a solid answer for this.
34:19One popular theory is that Venus experienced an outgassing, a volcanic event that led to
34:24a huge outpouring of poisonous gases, like CO2, and a runaway greenhouse effect around
34:29715 million years ago.
34:31Venus has active volcanoes to this day.
34:34The dense atmosphere and high volume of CO2 could be evidence of an apocalyptic period
34:39of Venusian warming.
34:40With climate change one of the most pressing issues facing mankind, understanding how Venus
34:45came to be this way could help us prevent the same thing from happening to Earth.
34:49If they were identical twins once, they could become identical twins again… and not by
34:53way of Venus' clouds dissipating and allowing alien life to thrive.
34:57Then again, other theories say that Venus' liquid ocean may have also been its downfall.
35:02Unlike Earth, Venus doesn't have any moons, but if it once had water, it would still have
35:06a solar tide controlled by the sun's gravity.
35:09Some evidence suggests that tides can actually slow the rotation of a planet down.
35:14In 2019, researchers at Bangor University in Wales argued that this may have occurred
35:18on Venus, causing its incredibly slow rotation and resulting in the planet becoming uninhabitable.
35:24One barrier to further study is the fact that Venus' surface is only 500 million years
35:29old, so it formed after the planet was already hostile to life.
35:33While Venus' clouds might be full of sulfuric acid, the space above the clouds has often
35:37been suggested as the site of a potential human colony.
35:41About 30 miles over the planet's surface, the pressure is similar to Earth's at sea
35:45level and the temperature drops to 140 degrees Fahrenheit.
35:48Besides being friendlier to humans, though, these clouds could be the last refuge of any
35:52life that may have existed on the planet.
35:55Sturdy, microbial creatures could be living in those clouds quite happily.
35:59We know that some organisms can thrive in extreme conditions on Earth.
36:02Tardigrades, for example, can survive in temperatures ranging from minus 328 degrees Fahrenheit
36:08to 300 degrees Fahrenheit.
36:10And our own clouds are home to all kinds of microbial lifeforms.
36:13So, clouds, thin and light as they may be, are ecosystems all of their own, and Venus'
36:19might just be the same.
36:20It's also possible that such organisms could have spread to Venus from Earth.
36:24Lifeforms ejected by Earth, by violent impacts for instance, could have reached Venus before,
36:28just as Venusian materials could have reached our own modest shores.
36:32This means that an interplanetary migration of small organisms could have taken place
36:36in the past, and that humans are naturally Venusian in origin… or that Venusian lifeforms
36:41are descended from Earth.
36:42It's equally possible that both planets had life seeded on them from another body
36:46in the solar system, and that these lifeforms evolved completely separately on neighbouring
36:51planets for billions of years, before Venus was devastated by greenhouse gases.
36:55We won't know for sure until we study Venus further, but it's definitely possible that
36:59our microscopic ancestors came from another world.
37:03In the wake of revelations about Venus' part, interest in our twin planet has grown.
37:07While NASA hasn't sent a probe to Venus since 1994, they and other space agencies
37:12are planning to change this.
37:14The European Space Agency and Indian Space Research Organisation are making plans to
37:18launch orbiters, and Roscosmos is looking into an orbiter, lander and research station
37:23to analyse Venus' surface, volcanoes and weather conditions.
37:26While we don't have plans to try and send humans to Venus anytime soon, we'll definitely
37:30learn more about what makes this strange planet tick across the next few years.
37:34We don't know for sure whether life once existed on Venus, but we do know that it could
37:38well have had liquid oceans and been habitable for billions of years.
37:46If you could travel in space, where would you go first?
37:50The moon?
37:51Mars?
37:52The many moons of Uranus?
37:54Well, in a future reality where spaceflight is possible for all, there's something of
38:00a bucket list of tick-box travel destinations waiting for you to explore.
38:06Which is what we're going to do today.
38:18The original Seven Wonders of Earth date back to a list compiled in the 2nd century BCE,
38:25which included such legendary places as the Hanging Gardens of Babylon and the Colossus
38:31of Rhodes.
38:32Plus the only structure still standing today, the Great Pyramid of Giza.
38:38A new list of wonders was more recently created, featuring amongst others the Great Wall of
38:43China, Petra in Jordan, and Christ the Redeemer in Brazil.
38:48But really, why stick to just this planet?
38:52The wider solar system has plenty to offer.
38:56And while there's no official list just yet, the seven places or things we're about
39:01to explore do almost always feature, whenever the topic is debated, including most famously
39:08as part of a 2010 documentary shown on History.
39:12So, in no particular order, first up we have the Rings of Saturn.
39:18A celestial spectacle that it's almost universally agreed is deserving of the wonder tag.
39:25Saturn isn't the only planet with rings, of course.
39:28Jupiter, Uranus, and Neptune have them too.
39:32But Saturn's are so spectacular that they've become a defining characteristic of the planet.
39:38The rings are formed from pieces of asteroid, disintegrating comets, and debris from moons,
39:45plus general space dust that has gotten stuck in orbit around the gas giant.
39:50There are eight main rings in total, as well as the fainter Phoebe Ring more recently discovered.
39:57Although there are various smaller rings in the gaps between these markers, each ring
40:03also moves independently of each other, with them travelling all around Saturn at different
40:09speeds.
40:10It's a cosmic balancing act around this particular world, and a majestic part of space.
40:17Not far from Saturn is our next wonder, the Saturnian moon Enceladus.
40:23It's covered in thick ice, and because of this, bounces most of the sunlight that reaches
40:29it back out into space, making Enceladus one of the most reflective objects in the solar
40:35system.
40:36After years of speculation, the presence of subsurface liquid water on Enceladus was proven
40:42in 2014 by NASA's Cassini spacecraft.
40:47It was an extremely important discovery, confirming the moon as one of the most likely places
40:53in the solar system, other than Earth, to support life.
40:57Enceladus also has a role in forming the rings of Saturn, specifically the E Ring, thanks
41:04to eruptions from the ice volcanoes or geysers on its surface.
41:09These volcanoes shoot out water vapour and ice particles with such incredible force that
41:14they've essentially fed the E Ring into being, while some of the erupted material falls back
41:21to Enceladus as snow.
41:23Much of what we know about Enceladus so far does come from the Cassini probe, but it's
41:29a sure bet that this moon will continue to be a key solar system location for us in the
41:36future.
41:37Saturn's neighbour, Jupiter, is home to our next wonder, the Great Red Spot.
41:44This is the largest storm in the solar system, with a diameter far larger than even Earth's
41:51The Great Red Spot is visible to us with a sharp enough telescope.
41:55But what makes it truly amazing isn't simply its size, it's also the fact that scientists
42:02have been watching it rage non-stop for close to 200 years now.
42:09And most researchers think it's been a feature on Jupiter for even longer than that.
42:14Massive clouds inside the spot create destructive cyclones and hurricanes, stretching for more
42:20than 10,000 miles across the Jovian surface, and penetrating some 300 miles down into the
42:27atmosphere.
42:28This storm is so strong that its power can be felt from space itself, as its gravitational
42:35pull reportedly affected the flight path of the Juno probe when it passed Jupiter in 2019.
42:42Interestingly, however, the storm does appear to be shrinking, but scientists are unsure
42:49whether it will disappear completely.
42:52The fourth solar system wonder can be found much closer to our home, on a planet we might
42:58reasonably call home in the future, Mars.
43:02The red planet has a number of massive volcanoes scattered across its surface, but the Olympus
43:08Mons, named after the towering Mount Olympus in Greece, is the largest of them all, and
43:14also the most massive volcano and mountain found anywhere in the entire solar system.
43:21This colossal natural structure rises so high from the Martian surface that it's measured
43:27to be two and a half times the size of Mount Everest, the tallest mountain on Earth.
43:33Olympus Mons is surrounded by unique cliffs that are five miles tall in themselves, while
43:39the volcano as a whole covers an area of Mars that's about the size of Italy.
43:46It's just a staggering landmark.
43:49The leading theory as to how it's been able to grow so big is that, because Mars doesn't
43:54have plate tectonics, lava has just continually erupted from the same spot over and over again,
44:02and that lava has been solidified into rock, layering on top of itself, getting taller
44:09and taller.
44:10What's more, some believe that Olympus Mons is still young, and could still be active,
44:16meaning it may grow to an even larger size in the future.
44:21Next up, we head right to the center, to the surface of the Sun, our next wonder of the
44:27solar system, and for plenty of reasons.
44:31For one, the Sun provides all of the light for the solar system, and without it, everything
44:36would just be dark.
44:38It also dictates the gravity that keeps everything in orbit, and it provides the general energy
44:44for life on Earth to exist too.
44:47The Sun is so massive that it takes up 99% of the solar system's total mass, and for
44:54its surface especially, one layer of it, the photosphere, is around 300 miles thick.
45:02It's also so hot, at around 10,000 degrees Fahrenheit, 5,500 degrees Celsius, that according
45:09to NASA, it wouldn't just melt diamond, it would actually boil it.
45:15The Sun's surface is far from stable, however, hosting, as it does, massive temperature fluctuations
45:22in sunspots, all while it casts out blistering flares into space.
45:28The Sun is, then, a unique balance between the heavenly giver of life and a deadly ball
45:34of scorching nuclear fusion that could feasibly end us all at any moment.
45:41But onto our penultimate wonder now, the asteroid belt.
45:45It too could feasibly cause a disaster for us, but scientists are fairly sure we're safe
45:52from harm.
45:53Located just between Mars and Jupiter, the asteroid belt cumulatively accounts for very
45:58little mass, but it's interesting because it works something like a waste bin for solar
46:04system things that might have been.
46:07The belt is thought to contain the remnants of some long-gone moons and possibly planets
46:12that broke apart over a 4.5 billion year history.
46:17The largest asteroid belt object, though, is the dwarf planet Ceres.
46:22One reason why the belt can be considered a wonder is perhaps the specific conditions
46:28needed for it to form at all.
46:30It's really thanks to Jupiter's position and Jupiter's gravity that the asteroids and dust
46:36within the belt have never coalesced into another, bigger, planet-like object.
46:42But what's even more remarkable is how lucky we are that the belt did form, because asteroids
46:49from it are thought to have accelerated evolution and life on Earth by delivering essential
46:55compounds and water to our world.
46:59And that's pretty wonderful, don't you think?
47:02But the last wonder, maybe unsurprisingly, is Earth itself.
47:07And while it might seem a little vain to include our own world, it's not difficult to see why
47:14so many wonders of the solar system lists do.
47:17The sheer odds of Earth seem impossible, a planet that's seemingly fine-tuned for life.
47:25It's just the right distance from the sun, it has an atmosphere, a magnetosphere, the
47:30right chemical makeup, and it has liquid water, among other things.
47:35Earth has given rise to billions of different lifeforms over its history, from beings as
47:41small as single-celled bacteria to large dinosaurs and predators.
47:46Not to mention us, the super-smart humans.
47:50There's rich diversity on Earth, too, from arid deserts to frozen tundra to lush rainforests
47:56and sprawling cities.
47:59And then, of course, we have the oceans.
48:02So far, Earth is the only place in the universe where we know life has developed.
48:08In time, too, that could change.
48:11But for now, it's a truly special place.
48:14It's easy to see why the destinations we've been to are those which most often come up
48:20whenever there's talk of the most magnificent and awe-inspiring solar system places.
48:26They're the most widely credited with wonder status.
48:29But if you could add something else, what would you choose?
48:33What's your favorite thing about our particular part of the universe?
49:03What do you think?
49:25Is there anything we missed?
49:27Let us know in the comments, check out these other clips from Unveiled, and make sure you
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