here comes the post about another moon of our Solar System. This time it is Europa. Europa the awesome moon with so white surface and those red streaks across but still the smoothest crust, Europa another Galilean moon!
Europa is very famous moon. It is also very large, sixth moon in whole Solar System and 15th object in size in whole System.
Like all other Galilean moons this one was also discovered by Galileo Galilei who named it Jupiter II and independently by Simon Marius who called it Europa after Zeus’s lover.
I think that Europa is very well known do to popularization of high chance of extraterrestrial life there. Probably also because of that enormous water ocean under its surface.
First of all lets look at its enormous size.
On the right you can see for comparison the size of Europa, Moon and Earth.
Mean radius of Moon is 1,737 km while for Europa it is 1,560 km. Mass of course is lower. This corresponds with density. There is 0.3 g/cm3 difference, which is not much.
Moon orbits at 380,000 km while Europa at 670,000 km. As I said in previous posts Ganymede, Io and Europa are in orbital resonance.
This means that Europa’s interior is heated by friction.
Surface of this moon is the smoothest in whole Solar System. This seems to be from the process of water running from under the crust of ice and smoothing everything out. While there are no high features, you can find there things called penitentes. Those can appear on Earth in high altitudes when snow sublimates in temperatures below zero. It creates those snowy spikes.
If you look on the first picture of whole satellite you can see that there are those red stripes.
It seems that they are created by “hot” ice flowing sometimes from under the surface. This also hints to plate tectonics on other object than Earth.
There is extreme radiation on Europa, about 5,400 mSv which is a lot and it would kill you in about a day.
Under the surface which is made of silicate rock and ice is gigantic ocean of liquid water. It is liquid because of pressure and the friction which causes its temperature to rise.
This is why astronomers think that there could be life.
There are some missions planned, one of them is very interesting and it requires some robot to land on Europa and by heating to melt down through the ice crust towards the ocean. The heat would be made by radioactive fuel.
This thing would have to be very well sterilized so it wont find its own bacteria in the ocean. Hydrobot (on the right) would be dropped there and then it would collect samples and analyze them right in the ocean.
The volume of the ocean is more than twice as much as on Earth and it may be 100 km deep.
Because of enormous tides made by Jupiter, there are water plumes of water vapor which are 200 km high. Those plumes may carry about 7,000 kg/s of material.
Europa has atmosphere but it is not very thick with pressure of 0.1 micro pascal. This atmosphere is made by ionizing radiation hitting the ground and leaving some free atoms which than become the part of atmosphere. Part of the oxygen in atmosphere is made by process called radiolysis.
To date there were already couple of missions which saw Europa from close distance, while yes, we can see Europa even from Earth because when its whole surface turned to us is lighted its apparent magnitude is 5.27 which is pretty good.
First picture taken from close distance was this one on the left. It’s Pioneer 10s picture.
Also Pioneer 11 saw him year later (1974) and after this Voyager 1 and 2 took much better pictures. First satellite to orbit Jupiter was Galileo which was working for 8 years and then it’s course was changed towards Jupiter’s atmosphere.
For now there are planned some missions that would again orbit Jupiter and collect data about its moons especially Europa because of the ocean.
For direct studying of Europa there is planned mission called Europa clipper, which would investigate its habitability and also planned is JUICE – Jupiter Icy Moon Explorer, but this one would be mostly observing Ganymede.
All pictures are from here.