This is about the biggest planet of them all and one very special moon, Europa, one of the places in our Solar Syatem where life may have developed independantly of Earth, a second Genesis. We’re going to look at Jupiter and then Europa but, like us humans, it is their relationship that makes Europa special so we also have to look at that.
So first some cold facts about Jupiter. The fifth planet from the Sun, the largest in the Solar System, largely hydrogen with about 25% helium, 67 moons so far discovered and a magnetic field so big that if our eyes could see magnetism it would be one of the biggest objects in the sky. Jupiter is about 1000th the mass of the Sun but it still contains about 2.5 times the mass of all the other planets together. You could fit over 1300 Earths into Jupiter but its mass is only 318 times that of Earth, (rock is a lot heavier than gas) and it is so massive that Jupiter and the Suns barycentre, their common centre of gravity, is actually a bit above the surface of the Sun. Through the process of gravitational contraction Jupiter actually creates more energy than it recieves from the Sun and since it formed Jupiter has shrunk to about half its original size and continues to shrink by about 2 cm per year.
We are not yet absolutely certain what the inside of Jupiter consists of, but it seems likely to be a solid core, possibly rocky, with a shell of metalic hydrogen around that including some helium and outside that molecular hydrogen but we can’t realy be sure how stuff reacts at the extreme pressures of Jupiters interior. At this point I was going to post a very scientific drawing here, but I like this one better!
Jupiter is perhaps best known for its clouds and of course the Great Red Spot, a huge storm that has raged for at least the last few hundred years and could easily swallow the Earth and still come back for more. For all the horror and tragedy that they bring us humans, Earth storms are puny by comparison. The winds in Jupiters storms would flatten any Earth building completely in a matter of seconds! The stripes are created by high level winds moving at up to 100 m/s but despite the vast size of Jupiter, they are only 50 kilometers thick.
We have sent a number of probes to explore Jupiter and its moons, from Pioneer 10 in 1973 to New Horizons which passed by i 2007 on its way to Pluto and the Kuiper Belt. These probes have revealed wonders undreamed of including a ringside view of the impact of comet Levy-Shoemaker 9 in 1994. The aftermath can be seen here in an image taken with University of Hawaii”s 2.2 meter telescope.
Jupiter is on average 778 million kilometers from the Sun and takes 11.86 years to complete one orbit. Interesting enough but nothing compared to Jupiter’s day which is the shortest day in the Solar System, only 10 hours long, so if you complain about not having enough hours in the day to get everything done, don’t move to Jupiter! This, combined with its large size means that its equator is flying round at an alarming rate. It spins so fast in fact that Jupiter bulges out at the equator, enough to make the bulge visible even to amateur telescopes on Earth. So that’s a very quick look at Jupiter. There is so much to tell about this incredible planet that I haven’t even begun to scratch the surface but now we turn our attention to one of Jupiter’s many moons, Europa.
In the old days, before our probes got a proper look, it was assumed that Europa was just a dead ball of rock with some ice on top. Wrong! Look at those lines, cracks in the icy crust showing that the surface ice is made up of huge plates that shift and move relative to each other and that the surface ice creaks and cracks as water, liquid water, moves beneath it, just like the ice sheets of the Arctic Ocean on Earth. the surface is also remarkably free of impact craters, indicating that it is a young surface, being constantly reformed by slushy water ice welling up from below.
We’ll get back to that in a bit because it is important but first a few basic facts. Europa and the three other largest moons of Jupiter were discovered by Gallileo Gallilei in 1610 and this discovery was to rock the very foundations of our understanding of the Universe and our place in it. Not bad for a little moon really. Although Europa is the smallest of Jupiters Gallilean moons, it is the 6th largest moon in the Solar System and is just a little smaller than our own Moon. Here we see Io, Europa and Ganymede in their orbits around Jupiter and it is the details of Europa’s orbit that make it so special.
The orbits of the Gallilean moons don’t just do strange things to Europa, in fact they do something equally amazing to Io creating the most volacanic body in the entire Solar System, with gigantic sulpher volcanoes shooting plumes all the way into space. Europa’s orbit is just over 670,000 kilometers from Jupiter and is almost, but not quite, circular and it is the “not quite” that has a remarkable effect on Europa. When Europa is at its closest to Jupiter, it is stretched towards and away from Jupiter and as it receedes it retracts again, just like the ocean tides on Earth but with Jupiter’s gravity being so much more powerful than our Moon’s, it is the body of Europa itself that gets stretched.This creates friction which in turn creates heat. This heat is enough to maintain a vast ocean of water liquid under the surface of the ice. OK, big deal you say and until 1976 you would have been right. Until then we thought that the deepest parts of Earth’s oceans were cold and dead and we would have said the same of Europa’s ocean. Then we discovered the Hydrothermal vents in the deep ocean. These are places where water seeps down deep underground where it is warmed to extreme temperatures and rises up again through the ocean floor. Scientists were amazed when they saw this-
-entire communities of creatures thriving in these extreme conditions, a whole biosphere existing independant of the Sun’s energy, something that was previosly thought to be impossible. Overnight our ideas about where life could be found elsewhere in the Universe were radically altered. We now knew that life did not need energy from a star and that the outer reaches of our Solar System were not necessarily barren.
More recently, the Gallileo probe has measured the magnetic field surrounding Jupiter and has discovered that Europa also has a magnetic field due to its interaction with that of Jupiter. This points to its ocean being salty, thus increasing its habitabilty. So it seems that Europa is one of the most likely places to go looking for life in the Solar System, but just because a planet or moon has all the requirements necessay for life, doesn’t mean that there is life. My Lottery ticket has all the necessary requirements to make me extremely rich. Unfortunately this hasn’t happened yet and the same may be true of habitable planets and moons.
I think this has ended up being a bit longer than my previous blogs but it is still very superficial. I’ve hardly scratched the surface of Jupiter and Europa, sorry, no joke intented, and barely mentioned the other moons but I hope it has been a little bit informative and given you the desire to do your own research into this amazing planet and its family of moons. Plans are being made for missions to Europa to dig or melt a hole in the ice and drop a probe into the icy depths of Europa’s ocean and who knows, maybe these probes will witness a scene similar to the hydrothermal vents at the bottom of Earth’s oceans, and that discovery would be one of the most profound in all of human history. Not bad for a little moon!
Pictures: 1. picture- http://www.johnstonsarchive.net/spaceart/art-r.html