Last week, Elon Musk caused a bit of a stir when he suggested that his upcoming plan to colonize Mars – which we should be hearing more about next week – might not just stop at the Red Planet.
Musk has long been working on something called the Mars Colonial Transporter (MCT), a mysterious proposal to take 100 people on a journey to colonize the planet. But on Twitter last Friday, he revealed that the MCT could go “well beyond Mars”, so he’d instead be calling it the Interplanetary Transport System (ITS).
Now, there’s still a lot we don’t know about Musk’s plan. But, assuming he’s talking about sending humans to destinations elsewhere in the Solar System, where might be on the agenda? Let’s take a look at some of the candidates.
Mars, of course, is the obvious port of call for colonization. It’s an attractive proposition for being fairly similar to Earth. It’s a rocky world with an average surface temperature of -55°C (-67°F), it once had liquid water on the surface, and it has got resources that might be useful to a human colony.
It’s the latter point that often gets people talking. Mars has a huge amount of frozen carbon dioxide at its poles, and possibly vast reservoirs of water under the surface. If we are to set up a colony somewhere, it must be self-sustaining. These resources offer a tantalizing source of fuel and energy.
Is Mars our best bet for a colony on another world? NASA
Mars also appears to have a replenishing source of methane, fed by unknown processes (the first part of the ExoMars mission, the Trace Gas Orbiter, is due to arrive in October and tell us more about this). Some have suggested this methane could be used to create fuel on the surface – and there have even been tentative tests to prove this is possible.
Another benefit of Mars is that, relatively speaking, it’s quite close. Every 26 months, Mars and Earth align in such a way that we can make the trip to the Red Planet in about seven or eight months with current technology. At their closest, they are less than 60 million kilometers (37 million miles) apart, close enough for us to send resupply missions or support for a colony on Mars.
What a colony on Mars might look like is anyone’s guess, though. The base itself might be partially buried underneath Martian soil in order to protect it from solar radiation, and it will likely be heavily reliant on solar power. You’d also need a spacesuit to explore the surface – although some suggest that we could melt the frozen carbon dioxide at the poles of Mars to try and trigger global warming, producing breathable oxygen and warming the planet up, too.
Aside from Earth, Titan is the only place in the Solar System that we know to have bodies of liquids on its surface. Admittedly, on Titan these are lakes of liquid hydrocarbons like methane and ethane, rather than water. But it does still give Titan some Earth-like characteristics, such as a weather and climate system not wholly dissimilar to our own.
Interestingly, Titan has just 1.5 times the air pressure of Earth. This means, in theory, you could walk around on the surface with a thin protective suit and a breathing mask, rather than a fully-fledged spacesuit.
It’s pretty chilly though, at about -180°C (-290°F) on average, so the temperature would certainly be a factor. But those lakes of liquid methane are enticing – they could essentially be vast reservoirs of fuel, if we could learn how to harness methane such as on Mars.
"Titan's probably the one after Mars," Jonathan McDowell, an astronomer at the Harvard-Smithsonian Center for Astrophysics, told IFLScience. "It has an atmosphere (unbreathable of course), and frozen water and methane for fuel."
NASA's Cassini spacecraft has revealed much of what we know about Titan so far. NASA/JPL-Caltech/Cassini
Titan also has an extremely thick atmosphere, which does a good job of blocking radiation from the Sun and Saturn. It’s possible, too, that there may even be water hiding beneath the surface of Titan.
Getting there would be a bit of an issue, though, with a one-way journey time bordering on about half a decade with current propulsion systems. But if we can utilize everything available to us at Titan, would we even need to come back?
A bit closer to home, we’ve got the Moon. Aside from Earth, it’s the only place in the Solar System humans have set foot on. And it could be a great staging outpost to explore other worlds.
The Moon has essentially no atmosphere, leaving any explorers fully exposed on the surface. It’s also fairly barren, with no noticeable resources obviously apparent.
But recent evidence suggests that in some craters on the Moon that are in permanent shadow, water-ice may exist. One proposal is to build a base at the southern pole of the Moon, which experiences endless sunlight, and use the solar power generated here to supply a nearby base, perhaps one with access to a permanently shadowed crater.
Europe and Russia have been in talks about building a Moon base. ESA/Foster + Partners
Having about 17 percent of Earth’s gravity, landing on and leaving the Moon is also relatively easy compared to, say, landing and launching on Earth. If we could set up a base there, it could be a good place from which to launch elsewhere, using the Moon’s water-ice to make rocket fuel.
Many often also highlight the existence of helium-3 on the Moon, an isotope that could supposedly be used in nuclear fusion machines. That’s very hypothetical at the moment, but it could be another reason why we should return to the Moon – and never leave.
Life on the surface of Venus might not be too fun. Temperatures are hot enough to melt lead, and the atmospheric pressure is 90 times that on Earth.
But, about 50 kilometers (30 miles) above the surface, there’s a rather intriguing region. Here, the atmospheric temperature and pressure mimic Earth.
And how would we make use of this? Why, with floating cities of course. Yes, it has been touted that we could create essentially giant floating blimps that drift around this region. From these, you could either try to repurpose the atmosphere into something more terrestrial, or use these floating cities to shade the ground, lowering its temperature.
It’s unlikely Musk has developed a way to colonize Venus. But perhaps he could inspire our descendants to do so far in the future.
Animated view of Venus. M. Perez-Ayœcar & C. Wilson,IDA/DLR/MPS/ESA
Perhaps even more fanciful than Venus is the prospect of colonizing Jupiter’s moon Europa. The intense radiation from the gas giant makes the surface of Europa pretty much off limits, but what about underground?
Europa has a thick icy shell, beneath which we think there is a vast ocean. This ocean may in turn be fed heat by hydrothermal vents at the sea floor. This has led some to speculate whether there may be life under Europa’s surface.
Water, obviously, is also a pretty handy resource. If we could access it, we could use it to sustain some sort of colony.
Life on Europa would be tough, but not impossible. NASA/JPL-Caltech
The only problem is, we don’t know how to drill beneath the several kilometers thick ice crust yet. One novel proposition suggests that we could wait for cracks on Europa to open, and drop a probe down them to sample the subsurface layer. Harnessing the water, though, would not exactly be easy.
Europa might not be the best destination for Musk to consider at the moment, then. But there are plenty of other fascinating worlds the ITS could – and perhaps will – set its sights on.