Could We Colonize Europa?
A dot of light. This is what Europa has been for almost four centuries: a tiny source of light,
as weak as a sixth magnitude star. Nothing but the second moon in order of distance from Jupiter,
and the smallest of the four discovered by Galileo in January 1610.
At the end of the 19th century it was possible to estimate for Europa a diameter of about 3100 km,
comparable to that of our Moon. It was therefore legitimate to think
that it was a very similar body, arid and very craterized. It was only in the '60s,
thanks to the first spectroscopic studies, that it was suspected that
its surface was instead covered with ice. Then the final word went to interplanetary
probes and the first missions to the outer planets of the Solar System.
It was Voyager 1, in March 1979, to photograph for the first time closely the Galilean satellites,
in particular Io, Ganymede and Callisto; while Europa (which was more out of sight during the
overflight of the probe) had to wait for the arrival of Voyager 2 in July 1979.
And the first high-resolution images of Europa showed ice plains furrowed by thousands of dark
streaks that overlapped like a giant reddish net spread over the entire surface. But from the very
beginning something even more extraordinary was noticed, namely the almost complete absence of
impact craters. Some were detected, but not in the number that one would expect from a
planet without or almost without atmosphere. In their place, instead, only those long scars,
which sometimes stopped abruptly, indicating that at that point the surface was somehow torn,
making the darker material rise from the inside. At this point, the crucial questions had become
(at least) three: 1- why were so few impact craters visible?, 2- why did the surface crack
like that?, 3- what was coming out from inside the planet? Needless to say, all
three issues should have been resolved together. Since it is completely unreasonable to believe
that Europa has few impact craters only by chance, there was only one other hypothesis that could be
put forward to explain the phenomenon. That is that the planetary surface had been "remodeled"
over time by particular geological events. In other words, the satellite had to be still
geologically active, which meant that there must have been a permanent heat source inside Europa.
The first clues in favor of this hypothesis came from considering the so-called
"Laplace resonance", a particular phenomenon of gravitational interaction between Jupiter,
Io, Europa and Ganymede. In practice, the periods of revolution of these satellites are integer
multiples. This means that every time Ganymede makes an orbit around Jupiter (7.2 Earth days),
Europa makes two (3.6 Earth days) and Io four (1.8 Earth days). This particular way of orbiting
around Jupiter causes gravitational perturbations that, by periodically "stretching" the satellite
in all directions, result in tidal effects that produce heat and mechanical effects of
high proportions. This, for example, is the same cause of the very intense volcanic activity of Io,
but it has been calculated that even the interior of Europa could be so hot that the ice melts
below the surface already over 10 km deep. And so it was that, although it may have
seemed like a crazy idea, the astronomers began to seriously think that under the frozen crust of
Europa could really hide a large liquid ocean... This was confirmed by the Galileo probe, which had
flown over Europa a dozen times since December 1995, taking thousands of extraordinary photos,
and had mainly measured in the layers immediately below the ice blanket
the gravimetric values compatible with a density similar to that of water.
Salt water, more precisely... A real ocean, a hundred kilometers deep and
with a volume at least double that of all the terrestrial oceans put together...
Later, what at the time appeared as a peculiarity of Europa, the presence of an ocean of water below
the surface, was also found on Ganymede, the largest moon in the Solar System, and Enceladus,
Saturn's satellite, but at the time of discovery the exceptionality of the thing prompted NASA and
ESA to design exploration missions to reach the surface of the satellite, which at that
point was becoming one of the "hottest" targets in the exploration program of the Solar System.
This interest was dictated not only by the concrete hypothesis of the ocean of water,
but also by the possibility that on Europa there could be an environment similar to that
of the hydrothermal springs present on Earth in the depths of the ocean.
More accurate observations conducted in 2013 by the Hubble Space Telescope,
had in fact allowed to identify steam geysers very similar to those previously found on Enceladus,
which had reinforced the hypothesis of the hot ocean and especially the possibility
of hydrothermal microbial life. On the surface, moreover, spectroscopic analysis
suggested that the long reddish streaks could be interpreted as deposits of magnesium sulfate,
in practice the saline residue of water brought to the surface by the geysers, the ideal
substrate for the growth of organic molecules. These characteristics made Europa one of the most
interesting places in the search for microbial chemosynthetic life (the synthesis of organic
compounds carried out by bacteria in the absence of light), but over the years, partly due to the
discovery of other worlds with similar oceans, and partly due to the economic crisis that has
reduced the budget of space agencies, interest in Europa has been declining and exploration projects
using probes have almost all been abandoned. The only one left, and recently confirmed,
is the one that foresees the launch by 2025 of a NASA mission called Europa Clipper, consisting
of a spacecraft that orbiting Jupiter will be able to make 44 close flyovers of the moon.
Europa Clipper should arrive on Jupiter by the end of this decade,
and then eventually be reached and assisted by the ESA mission Jupiter Icy Moons Explorer, which
will fly over Europa twice and Callisto several times before entering into orbit around Ganymede.
From this joint mission we expect confirmations and assessments
on habitability and the possibility that the surface may allow a future human settlement.
But designing a mission for the colonization of a remote celestial body is obviously something
much more complex than simply sending an interplanetary probe. If for the Moon and
Mars we can reasonably assume that permanent bases will be implanted within the next decade,
for the colonization of Europa the expected time frame is at least a hundred years.
Unless ... one of the probes that are about to leave can not confirm the presence of life,
albeit at the microbial level. In that case, you can bet, sending a manned mission to Europa
would immediately become a priority and the time would probably be halved. In short,
everything will also depend on the motivations of that particular historical moment.
But what could be the way to bring a team of five or six technicians and scientists to the orbit of
Jupiter (which on average is two million times more distant from the Earth than the Moon...
the only celestial body on which we have set foot so far), bring them down to Europa, give them the
opportunity to build a base with accommodation and laboratories, provide them with sufficient
food supplies for years and equip them with machines to generate energy and research tools?
To think of being able to do all this starting from Earth with a direct trip, without using
intermediate colonization stages (Moon, Mars, asteroids), presupposes that we have a capsule
powered by nuclear propulsion engines and not chemical or ionic engines like those of today,
able to bring the astronauts to their destination in six months at most.
Not to mention that the manned mission should be preceded by
an automatic mission capable of bringing a rover to the surface to make sure that the
minimum conditions for survival actually exist. But the colonization of Europa would present
other numerous difficulties. A human being on its surface, for example,
could not survive the lethal radiation emitted by Jupiter's magnetosphere,
a dozen times more intense than on Earth. To overcome this problem,
settlers would have to settle permanently at least three meters below the frozen surface.
Apart from the inconvenience, this could also be convenient to have easier access to water and to
isolate themselves from the low temperatures reached on the surface of the moon, on average
around -160 °C at the equator. However, the magnetic field of Jupiter could also be a problem
for the proper functioning of electronic equipment and solar panels, as well as the low solar energy
supply (30 times less than that arriving on Earth) due to the great distance of the Sun.
Having the foresight to settle near a geyser, however, settlers would have a continuous
source of water (which could also be used to obtain oxygen breathable by the process of
electrolysis), heat and energy. In addition, to ascertain the presence or absence of life,
researchers would have the opportunity to analyze the water brought to the surface by the geyser,
without having to drill the ice to get to the salt ocean. But all this, we repeat, would be addressed
in a "short" time only if the motivational drive was reinforced by the certainty of going to
study - for the first time - an alien life form. We do not believe it is possible that such an
expedition could be organized before 100 or 200 years from now if the goals were generally
exploratory or directed to the search for raw materials unobtainable on Earth, such as Helium-3.
It is estimated that 25 tons of this isotope, used in nuclear fusion reactors, could meet the annual
energy needs of the United States, but picking it up in Europa would not make much sense since it
is also found in quantity on the Moon. In fact, the costs would be absolutely prohibitive since
simply sending the automatic probe Europa Clipper will eventually cost about four billion dollars!
To make a long story short... Compared to other potential places of colonization,
the Jovian system is very far from Earth. As such, the transport of the
crews and all the heavy equipment needed to build a colony would take a long time,
as well as the missions where resources are transported to and from the Jovian moons.
As a result, colonial ships would have to be much larger and heavier and would require
advanced propulsion systems to ensure that they make the journey in a reasonable amount of time.
The missions to and from the Jovian moons would also require bases between Earth and Jupiter to
provide supplies and reduce the costs of individual missions. This would mean that
permanent outposts would have to be established on the Moon, Mars and most likely in the asteroid
belt before any mission to Jupiter's moons could be considered feasible or convenient.
This will of course be done, and the day will come when we will also establish ourselves on Europa,
but this will not happen, according to our forecasts, before the year 2150.
As long as, as we have explained and as we hope,
the "discovery of life" factor does not intervene to speed things up!