There are only three non-giant planets we know of that have thick atmospheres. One is Earth (just right). One is Venus (just so wrong). And one is a moon where the rain is made of methane, the lava is made of water, and waves serenely roll over oceans of LNG. This is Titan – the world that no-one saw coming.
Here on Build Me a Planet, we’re all about fictional worlds and where to find them. But some real-life planets truly are stranger than fiction.
Titan is a moon of Saturn and the second largest moon in our solar system. First spotted by Christiaan Huygens in the 17th century, its thick yellow atmosphere mystefied and tantalised generations of scientists until one brave little robot pierced the hazy veil in 2005 – and revealed a world far stranger than anyone had anticipated.
Let’s delve into our first Planet Profile.
Knowing your neighbours: Titan
Here are the fundamentals:
- Titan is half the width, a tenth of the volume, and 2% the mass of Earth. A cubic metre of Titan, on average, weighs about the same as a typical car (unless it’s an American car).
- It has only 15% of Earth’s surface gravity. An Olympic pole vaulter on Titan could clear a mature oak tree without breaking a sweat.
- Titan has as an atmosphere as massive as Earth’s but squeezed over less than a fifth of the space. The combination of thick air and low gravity means an ordinary person with a couple of cardboard wings taped to their arms could fly on Titan. It’s the new, healthier way to get around.
- Titan receives only 1% of the sunlight per area that Earth does, and only a tenth of that makes it to the ground. The atmosphere is transparent to infrared but virtually opaque to visible light. This creates a reverse greenhouse effect, and as a result…
- Titan is cold. Titan is really, really cold. Let me tell you how cold it is. If you apparated to Titan right now, all your bodily fluids would immediately freeze, and all your bodily gasses would sublimate. On a good day, Titan might hit minus 175 degrees. That’s closer to absolute zero than it is to any temperature you’ve ever experienced. Bring a coat.
- Mountains on Titan are named after mountains from Middle-Earth, and hills are named after characters from Lord of the Rings. When you work at JPL you can just do that, apparently.
Clearly, Titan is not your average moon. Let’s peer under the clouds and see what makes it tick.
Show us what you’re made of
A planet’s chemical composition is its first, most fundamental fact.
Our own Planet Earth is a third iron, a third oxygen, and about a third silicon and magnesium. Planetologists call this mix ‘rocky’ because most rocks you ever saw were made of these ingredients. Earth is one of five ‘rocky’ planets in our solar system, the others being Mars, Venus, Mercury, and the Moon.
But Titan is a bit different. Its density tells us it must be half ‘rocky’ material and half ‘icy’ material – water, methane, and ammonia.
A planet’s composition determines its structure. Rocky old Earth, for example, has a ‘core’ of mostly iron, surrounded by a ‘mantle’ of rocky stuff, topped off with a ‘crust’ made of a mixture of rock and lots of scungy mixed bits that don’t fit in anywhere else. Sometimes these outer bits melt and cause eruptions of what we call ‘lava’.
Titan is mostly the same, really. It’s just that the ‘core’ is made of wet rocks instead of iron, the ‘mantle’ is made of weird high-pressure water ice instead of rocks, and the crust is an enormous iceberg floating on a subterranean ocean. Sometimes these outer bits melt and cause eruptions of what we call ‘water’.
So, I guess it’s a little different from Earth.
Just like home
After reading the above, one might be surprised to learn that Titan it is often described as one of the most Earth-like worlds yet discovered. It has a thick atmosphere, winds, clouds, rainfall, rivers, and seas. Satellite images reveal a world scoured by fluid, just like Earth.
It’s just that the fluid in question happens to be petrol.
Petrol, petrol everywhere
Right, petrol: a blend of ‘hydrocarbons’, which are molecules of carbon and hydrogen. You may be familiar with some of them – for example, methane (an odourless flammable gas found in LNG and a common byproduct of digestion), propane (used in camping stoves and massive industrial accidents), and ethane (related to the active ingredient in certain popular beverages).
On the surface of the Earth we usually encounter these molecules as gases. On frigid Titan, however, hydrocarbons are like water on Earth: they can get around as gases, liquids, or solids. That allows them to do all the tricks water can do, and then some.
On Titan, it rains petrol, snows petrol, flows petrol – everything is petrol. The icy bedrock is overlain by a thick sand dunes made of soot which rains out of the sky, and low areas of the planet are covered in hydrocarbon seas, which stir with the tides and winds just like Earth lakes. The lakes are fed by hydrocarbon rivers hundreds of kilometres long, scouring the ice-block mountains into Tour de France-eque vistas.
Mountains, rivers, lakes… if you ignore the colour, the bizarre chemistry, and the fact that the whole planet is basically a big flammable iceberg wrapped around a greasy mudcake, Titan really is a lot like Earth.
A Titanic conundrum
Scientists are pretty mystified about where all these hydrocarbons come from. Most are likely produced by the breakdown of methane by UV light from the Sun, but that just raises the question of what’s making all that methane in the first place. On Earth, life is responsible for almost all of it – bovine flatulence being the most infamous contributor.
So, is there life on Titan?
Let me put it this way. If we don’t find life on Titan, I’ll start believing in God. How can you put that many organic compounds in a bowl for five billion years and not start growing some mold?
The real question is what will that life be like? If it lives on the surface, it won’t be able to use water like we do. Liquid methane could perhaps fill the same role in living organisms, but the cold would ensure that any chemical reactions would happen extremely slowly. Imagine a lake-dwelling squid with ice for bones, plastic for flesh, petrol for blood, and a metabolism slower than Anna Karenina. Don’t imagine too hard because it sounds terrifying.
Even if there’s no life on the surface, the subsurface ocean could host oodles of it, clustered around hydrothermal vents just like on Earth. Perhaps life could have been delivered to Titan from its fellow Saturnian, Enceladus, whose life-scented water plumes have excited many an exobiologist of late.
UPDATE – 29th July: NASA today announced the discovery of membrane-forming vinyl molecules in the stratosphere of Titan. Scientists predict that Titan’s largest lakes could host ten million of these cell-like structures per millilitre – comparable to the one million per millilitre count of microbial cells in Earth’s oceans. Life on Titan just got a major hand up.
A shack on Titan
We’ve talked about what makes Titan familiar, what makes it unfamiliar, and what critters might live there. That only leaves the one question everyone always asks.
Can we go there?
Why not? Let me put it this way. If Titan was a proven source of 100% effective slimming pills, we’d have a colony there already. Let’s run down the essentials:
- The trip
It would take a few years with current technology. You’d get a lot of reading done.
- The environment
Pretty chilly. No shortage of fuel, though, if you can find (or make) some free oxygen to burn it with.
Ample. There’s not much sunlight for energy, but tidal might work.
Ever heard of plastic? How about fertiliser? Petrol is the goop with a million uses.
It’s a pretty gloomy place. You’d want to bring plenty of Marvin Gaye records.
I wouldn’t recommend it.
- The bottom line
Humans can fly on Titan. End of story.
Titan – or, what are we waiting for?
The discovery of Titan’s true weirdness should be ambrosia for the imagination. Nothing you’ve ever seen in fiction compares to this unlikely and astonishing hydrocarbon world. This article barely scratches the surface of what we’ve learned so far, and what we’ve learned so far is only the tip of a very big, grimy iceberg.
The Cassini mission is nearing its end. But our business on Titan is far from finished.
Science is boring! Stabbing is awesome! If this sounds like you, check out Qo’noS, the Klingon homeworld. It’s just as dirty as Titan, but populated entirely by bone-headed murderers. Oh, and it rains acid. You’re welcome.
Or perhaps a forest retreat is more your style? I recommend Endor, the Forest Moon, and so does your couples therapist. Trees, treehouses, dwarfs dressed as teddy bears – it’s got everything.