Our Place in Space: Callisto

Hello, friends!  Welcome to Our Place in Space: A to Z!  For this year’s A to Z Challenge, I’ll be taking you on a partly imaginative and highly optimistic tour of humanity’s future in outer space.  If you don’t know what the A to Z Challenge is, click here to learn more.  In today’s post, C is for…


The major moons of Jupiter are Io, Europa, Ganymede, and Callisto.  In science fiction, Europa and Ganymede seem to get the most attention.  Sci-Fi writers often end up putting human colonists (or at least a handful of plucky human scientists) on the surfaces of one or both of these icy moons.  But today, I’m going to argue that Callisto would be a far more suitable home for future humans.

First off, and most importantly, there’s the issue of radiation.  The space around Jupiter is one of the most dangerous radiation environments in the entire Solar System.  As you can see in the highly technical diagram below, the radiation is most intense in the vicinity of Io.  The radiation levels get better in the vicinity of Europa and continue to taper off when you reach Ganymede.  You’re still soaking up a lot of radiation, though!  Callisto’s radiation levels, however, are fairly low.  You might even describe the radiation levels on Callisto as “survivable.”

Furthermore, planetary protection laws in the future may mean that both Europa and Ganymede are off limits to human settlers.  Scientists today are 99.99% sure that Europa has a vast ocean of liquid water beneath her surface, and (as you know) wherever there’s water, there may also be life.  There’s evidence suggesting Ganymede may have a subsurface ocean, too.  Europa is often said to be the #1 most likely place where we might find alien life here in the Solar System.  While the odds of finding life on Ganymede are considerably lower, the possibility of Ganymedean life shouldn’t be ignored.

There are already international agreements in place regarding extraterrestrial life.  Space agencies like NASA, the E.S.A., and others are legally obligated to do everything they can to protect suspected alien biospheres from our Earth germs (and also to protect Earth’s biosphere from any germs we might find in outer space).  For obvious reasons, these international agreements haven’t exactly been tested in court, and it’s a little unclear how they would be enforced.

But in a future where human civilization is spreading out across the Solar System, I’d imagine bio-contamination laws would become stronger, not weaker.  Europa would almost certainly be declared off-limits to humans, unless it is proven beyond a shadow of a doubt that no aliens currently live there.  Ganymede may end up being off-limits, too, for the same reason.

Meanwhile, we have Callisto.  Scientists who want to study possible biospheres on Europa and Ganymede could set up a research station on Callisto.  From there, they could keep a close eye on the other moons of Jupiter.  They could operate remote-controlled probes to explore Europa and Ganymede without risking contamination, or they could go on brief excursions to Europa and Ganymede themselves (taking proper safety precautions, of course).  While they’re at it, these scientist could also explore Io.  Io is the most volcanically active object in the Solar System.  There is virtually no chance that we’ll find life there, but studying Io’s volcanoes would still be interesting.

I’d be remiss if I didn’t mention this: Callisto might have liquid water beneath her surface, too.  Not as much liquid water as Ganymede, and nowhere near as much as Europa, but still… it’s possible.  Which means there’s a slim possibility that there could be life on Callisto.  But in Callisto’s case, it is a very slim possibility.  Based on what we currently know about Jupiter’s moons, Callisto still seems like the best place for humans to live.  The radiation levels are much lower, the risk of bio-contamination is negligible…  Yeah, if I were a science fiction writer, I’d put my human colonists on Callisto.

Want to Learn More?

In 2003, NASA published a plan to send astronauts to Callisto, with the intention of using Callisto as a base of operations to explore the other Jovian moons.  Click here to read that plan.  Some of the information is out of date, of course, but it’s still got some interesting ideas.  Maybe someday, something like this plan could work!

I’d also recommend this article on Planetary Protection Policy, covering some of the rules that are already in place to protect planets and moons where we might find alien life.

P.S.: If I were a science fiction writer…?  Wait a minute, I am a science fiction writer!  Click here if you want to buy my first book.  It’s not set on Callisto, unfortunately, but it’s still a fun story.

The Office of Planetary Protection

I have said before that one day science fiction won’t be science fiction anymore; it will just be fiction.  To some degree, we already live in a sci-fi world.  Look at all the diseases we can now cure, or look at the International Space Station, or just look at everything our cell phones can do.  Today, we’re going to take a look at something else that may sound like science fiction but is in fact 100% real: the Office of Planetary Protection.

The Office of Planetary Protection is sort of like the Environmental Protection Agency for the Solar System.  Its job is to ensure that NASA doesn’t violate the Outer Space Treaty of 1967, which stipulates among other things that any probe sent to another planet must not contaminate that planet with Earth-born bacteria.  The point of this is not only to protect alien ecosystems (if they exist) but also to ensure that if we do discover life on another planet, we can be certain it’s genuine alien life and not something that stowed away on one of our own space vehicles.

Take Mars as an example.  While it’s clear there isn’t anything like deer or grizzly bears on Mars, or even anything as small as a mouse or insect, there could be native Martian bacteria.  These microscopic organisms might live in areas like Newton Crater, where scientists have observed what appears to be liquid water seeping through the soil.  This water might be enough to support an entire ecosystem of microorganisms.

The Planetary Protection Office has another job as well: protecting us from any life forms that might threaten our own ecosystem.  Many nations, including the United States, are planning “sample return missions,” meaning they want to send a spacecraft to another world, have it collect samples, and send those samples back to Earth for further analysis in a laboratory.  Obviously we want to avoid an outbreak of alien bacteria similar to what happened in Michael Crichton’s The Andromeda Strain.  The Planetary Protection Office will make sure that doesn’t happen.

But just as the EPA is the source of a lot of controversy, so too is the Office of Planetary Protection.  Some scientists complain that planetary protection rules are making space exploration prohibitively expensive.  Sending a probe to Mars is costly enough without having to pay so much extra to sterilize every single delicate, mechanical component.  Given the current state of the economy and the current state of NASA’s budget, some say we shouldn’t waste money protecting alien ecosystems that might not even exist.  There are also questions about how effective the Planetary Protection Office really is given the fact that some of the Curiosity rover’s tools may have been contaminated before its launch in 2011.

Dr. Catharine Conley, the person currently in charge of NASA’s Planetary Protection Office, at least has a sense of humor about her work.  She owns a pair of Ray-Ban sunglasses, just like Will Smith from Men in Black.  She got them as a gift her first day on the job.  Despite the controversies, I feel safer knowing she’s there, keeping planet Earth safe from alien bacteria and keeping the alien bacteria safe from us.