About a million kilometers above the clouds of Saturn hangs the giant moon Titan. The biggest moon of Saturn, Titan would easily be its own planet if it was orbiting the sun directly. This world is probably one of the most interesting objects in the solar system due to it being somewhat similar to Earth.
Titan over Saturn
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Titan is a perfect showcase of the diversity of the worlds of the solar system. This moon contains liquid oceans and rivers, along with an Earth-like atmosphere. Let's see what it has to offer!
Where is Titan?
Any discussion of Titan would be incomplete without first addressing its planet. Titan is locked in orbit around the massive planet Saturn, which orbits the sun at about 9 AU. Earth orbits around 1 AU from the sun - making Saturn around over one billion kilometers from Earth at any given time.
Saturn relative to the other planets
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And yet, its massive size allows anyone to easily see this planet in the night sky, and with decent binonculars one can even see the planet's huge rings. Although Saturn doesn't boast quite the assortment of giant moons that Jupiter does, it holds its own with Titan.
Titan orbits Saturn is a mostly circular orbit just over 1 million kilometers high, completely one revolution around Saturn every 16 days. Like our own Moon, Titan is tidally locked - only one side of Titan can ever face Saturn. The other side never faces Saturn, and if you grew up here you would likely never even know that Saturn exists (without some knowledge of orbits and astronomy).
The circle marks Titan's orbit around Saturn, which is visible in the center of the picture.
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As previously mentioned, as far as solar system objects go, Titan is enormous. Titan is over 5000 kilometers across, making this moon is larger than the planet Mercury and our moon. In fact, Titan is nearly as big as Mars, falling about 1500 kilometers short.
Titan is 40% of the size of Earth itself despite only being a moon
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From right to left: Mars, Ganymede, Titan - to scale.
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The total surface area of Titan adds up to about half of all of the dry land on Earth. In fact, Titan is the second largest moon in the entire solar system, falling short of only the massive moon of Jupiter, Ganymede. Titan is so big that you can see it from Earth with a moderate telescope without too much trouble. It can be viewed as a bright speck in the plane of Saturn's rings - unfortunately no further detail is visible without the Hubble Space Telescope due to its massive distance from us.
The Surface of Titan
But what really makes Titan stand out is not its size, but its unique characteristics. Many articles will claim that Venus is the most similar place in the solar system to Earth due to its similar size. However, I respectfully disagree that this hellhole is anywhere near as close to the environment on Earth as Titan is.
First, let's get the dissimilarities out of the way. Titan, being a billion kilometers from the sun's surface, is very cold. In fact, "very cold" doesn't do it justice. The surface of Titan has an average temperature of just over 90 Kelvin, or -180 degrees Celsius. For comparison, the coldest ever temperature recorded outside on Earth, measured at the Vostok Station in Antarctica, was a nice and warm -89.2 degrees Celsius, or 184 Kelvin. This means that in absolute terms, the surface of Titan on a good day is twice as cold as the coldest ever recorded place on Earth. To say that you'd freeze quickly is an understatement. But, at least lead isn't melting there like on the surface of our friend Venus.
Titan's surface is obscured by thick clouds
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You would also weigh a lot less on Titan due to its reduced mass. The total mass of Titan is about 2.2% of Earth's mass (and almost double the mass of our moon!), and as such the surface gravity is about 14% of Earth's. In other words, if you weighed 100 pounds on Earth, you'd weigh just 14 pounds on Titan, and could jump a lot higher too.
But Titan's most unique feature is its fully-fledged atmosphere. This atmosphere actually has more mass than Earth's despite Titan's small size, helped by the lower temperature preventing as many gas molecules from escaping into space. Like Earth, Titan has an atmosphere composed of mostly Nitrogen gas (N2). Titan's atmosphere is over 98% Nitrogen gas, with the remainder being mostly methane. The amazing thing is the surface pressure - Titan's surface atmospheric pressure is just 1.4 atmospheres, only a little bit more than sea level on Earth! This means that you technically wouldn't need a spacesuit to walk on Titan. Now you'd need the world's best jacket to survive the almost negative 200 Celsius weather and an oxygen mask to breath, but you certainly wouldn't have any issues with the pressure itself, unlike being crushed on Venus or depressurized on the Moon.
What makes Titan even more like Earth is that its surface has lakes and rivers. Thanks to the large atmosphere, liquid methane (yes, the same methane in cow farts) can and does exist on Titan's surface. These aren't even subsurface oceans, they're surface lakes just like lakes on Earth ... just not made of water.
One example is Ontario Lacus, a large methane lake near Titan's south pole. This lake is about the size of California's Salton Sea. This body of methane liquid has things like river deltas along the shoreline - things we would only expect to see on Earth. This makes Titan even more like a strange, bitterly cold ice Earth.
Ontario Lacus, imaged by the Cassini mission
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One of Titan's poles. Ontario Lake is visible here.
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Personally, looking at these images reminds me of places I've been to on our own planet. It's somewhat mind-blowing that things like lakes and rivers exist right now, on another world a billion kilometers above our heads.
Titan also has its own sea. Kraken Mare, the largest body of methane liquid (mixed with liquid ethane) on Titan, has over 400000 square kilometers of liquid surface. Take a look at the pictures of it below. In false color, these pictures easily look like they could have come from Earth:
Heavily-modified picture of Kraken Mare
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An island in Kraken Mare
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Lakes on Titan, imaged in non-visible light and false-color
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Rivers, creek beds, and river canyons have been found on Titan. Over a decade ago, the Huygens lander vehicle descended to the surface of Titan, sending back images of its surface. On the way down, Huygens returned this image of obvious liquid-formed landscape on the surface:
Riverbeds on Titan from Huygens
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This is the Morro Bay estuary tidal flat in western California, a place I just visited last weekend. It stood out to me as a place that looked very similar to the above image of Titan's riverbeds.
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Of course, Huygens also returned a picture of the surface, from the surface. Here you can see the surface of Titan for yourself:
How Titan would look if you were standing there
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The rocks visible in the picture lying on the surface are actually made of ordinary water ice!
Wrap-Up
Titan is easily one of my favorite solar system objects, and if I could choose places to land humans, this would be very high on the list. That task isn't currently possible, but one day it will be, and hopefully some day people can set foot here and explore it for themselves.
There have been many proposals for return missions to Titan, including undersea submarines to travel through Titan's lakes and oceans. Titan's distance from us makes these missions difficult and expensive, but they are absolutely possible if necessary funding is approved by Congress. The existence of large quantities of liquid on Titan makes it, in my opinion, one of the most interesting worlds for spacecraft to explore in the future.
I hope you learned something new about Titan, or at least were able to appreciate the pictures. If you have any questions, or if I got something wrong, please let me know in the comments.
As always, thanks for reading!
Rendering of a lake on Titan
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Rendering of proposed NASA Titan submarine vehicle. To be honest, this would probably be one of the most incredible robotic missions possible in the near future.
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Sources Used:
JPL Cassini Legacy
Titan Wikipedia Entry
Ontario Lacus Wikipedia Entry
NASA Kraken Mare Submarine Concept