EUROPA
Parent planet: Jupiter
Orbital period: 3.551 days
Radius: 0.245 Earth radii
Mass: 0.008 Earth mass
Planetary Habitability Index: 0.49
This was the moon that opened up our eyes to the possibility of
oceans in the outer Solar System. Suspicions first arose in the late
1970s, when NASA’s Voyager 1 and 2 spacecraft passed the moon.
The images showed a mostly smooth icy surface, almost devoid of
craters. Since these impact scars accumulate as time goes by, for
Europa to show hardly any meant that the surface was being
renewed. But how?
Cracks on the surface provided us with an answer. In the
1990s, NASA’s Galileo spacecraft explored the moon and revealed
that dark materials around the cracks were salty, as if they had
come from an ocean. Magnetic readings also hinted at a shifting
body of water inside the moon. The final piece of the puzzle
came in images of the surface, which clearly showed ice f loes.
The heat to keep this ocean liquid was calculated to be
coming from the gravity of Jupiter. A so-called tidal force
squeezed the moon, producing friction to melt the underground
ice and maybe even drive black smokers. But getting down to see
them will be tough. The ice sheet that makes up the surface of
Europa is estimated to be between one and 10 kilometres thick.
“It would be very difficult to go to Europa, drill through the
ice and send a submersible to the black smoker on the ocean f loor,
but you could potentially land at one of the cracks and sample the
slush that’s squeezed up through it,” says Rothery.This would allow equipment to look for biologically important
molecules. The kit would have to be designed to work in high
radiation levels. Every day the surface of Europa is bathed in
thousands of times more harmful radiation than Earth. An
astronaut standing on Europa would receive a fatal dose within
24 hours. Luckily for any life on the ocean f loor, the radiation
will not penetrate beneath the ice sheets.
NASA is developing a mission to study the moon from orbit.
Called the Europa Multiple-Flyby Mission, the space agency is
currently designing the instruments that will allow it to assess
the moon for habitability. Intended for launch in 2022, the
spacecraft could carry a lander built by the European Space
Agency (ESA).
ESA itself has a mission to Jupiter called Juice ( Jupiter Icy
Moons Explorer). Although not designed to concentrate on
Europa, it will be making some f lybys of the moon, during
which it will use its ice-penetrating radar to measure the
PHOTO: GETTYthickness of the ice crust.
SCIENCE