Jupiter- The Solar System’s Jovian Giant
The Solar System has eight planets, three of which are terrestrial, whilst the remaining five are gas giants. The largest of them all, however, is the gas giant Jupiter- a planet dearly beloved of misled astrologers and one that, due to its position in the solar system, can be seen with the naked eye as a very bright star in the night sky; its bands and four of its moons can be seen through a simple refractor telescope. For those just beginning their journey into the joys of astronomy, it is definitely worth checking out.
I have been observing Jupiter a fair bit this month, as it makes its appearance in the southern portion of the British sky. I only have a small refractor telescope, but even with this you can see the faint brown bands of the Northern and Southern Equatorial Belts, and at times, all four of its most prominent moons (Io, Callisto, Europa and Ganymede). When observing over a few nights, you can track the positions of the moons as they orbit the giant, and at one point they line up in a beautiful diagonal running from the planet’s uppermost right corner to the lower most left corner. It is, truly, a breath-taking sight.
This giant is two and a half times the mass of all the other Solar System’s planets combined, and is mostly composed of hydrogen, with a quarter of its mass being helium. Jupiter has rotating cloud layers (which can be seen in the eyepiece of a telescope as lighter bands called zones and darker bands called belts) which give rise to storms, including, interestingly, lightning. We think of lightning as an earthly phenomena, so the fact that it can be seen on other planets shows just how deeply connected we are to the rest of the solar system and the star systems beyond. Another feature of the cloud layers is the Great Red Spot, a huge storm that has been raging across the planet for as long as we have been observing it (around 1831).
This giant also has a faint ring system composed of four segments (a halo ring, a main ring and two gossamer rings) mainly made of dust. The halo ring, the innermost and thickest of the rings, lies close to the main ring. The gossamer rings, the outermost rings, are very faint and although they are particles of fine dust you could be mistaken for thinking they were just rays of light somehow being ejected from the other rings. It gives the rings an almost ethereal appearance. You can read more about these ethereal gossamer rings here (I really love these rings!).
Jupiter also has an incredibly strong magnetic field, which results in a Jovian version of our own aurora borealis; yes indeed, like lightning, this phenomenon is not unique to our planet alone. Jupiter has a magnetic field fourteen times stronger than our own, meaning that the aurora is a very powerful source of energy in its magnetosphere. It is thought that the Jovian aurora is induced by its moon Io, and from particles carried in currents from deep inside Jupiter’s magnetosphere.
Europa, Ganymede, Io and Callisto are Jupiter’s largest moons and are named Galilean satellites as they were the only four moons Galileo could originally see through his telescope many centuries ago. If Ganymede, one of these Galilean satellites, were not bound to Jupiter, it’d be considered a planet in its own right as it is actually larger than Mercury. Not including these Galilean satellites, there are 57 other moons that orbit Jupiter, and not all others are the traditional billiard ball shape we expect. Many of them are so small that they actually take on the appearance of simple space rock, as their mass is so small that gravity has not been able to act on their matter to become strong enough to be “pulled” into the spherical shape we see other planets take up.
Past Explorations of the Jovian system and the JUICE Mission
Since Galileo first studied Jupiter through his telescope centuries ago, humankind have longed to be able to see this giant in further detail, and that is exactly what we went on to do in the late twentieth century. Starting with Pioneer in 1973, and later Pioneer 11, Voyager 1 and Voyager 2, Ulysses, Cassini, New Horizons and the Galileo spacecraft, the data we have on this gas giant has increased in leaps and bounds as we continue to reach for the stars and learn more about the cosmos in which we live. Now, a new mission is to be launched to explore the quirks of the Jovian system, and it’s rather endearingly named JUICE. JUICE stands for Jupiter Icy Moons Explorer and its primary aim is to explore the possible emergence of habitable worlds orbiting around gas giants. For some time, scientists have proposed that icy moons such as Europa may hold vast oceans of liquid water beneath their icy crust, which poses a question: could life exist within such an environment?
There is certainly evidence for enough heat being generated inside the planet to allow liquid water to exist under the ice, as previous flybys of the satellite have shown high thermal readings coming from its famous “tiger stripes”. However, this heat cannot be created by the satellite’s core itself. It is simply too small an astronomical body to have retained any form of molten core like the one that lies within our own planet. No, scientists have come up with a different explanation for the generation of such heat: friction.
As a moon like Europa orbits Jupiter, its volume is pulled and “stretched” as Jupiter’s enormous gravitational influence affects the planet. This slight bulging of the planet generated enough friction to explain these hot tiger stripes. And that heat, combined with the composition of the satellite itself (primarily ice) suggests one thing: liquid water.
It is hoped that, with exploration of this system, we will be able to answer more and more questions about the nature of our own existence: are we alone in this little corner of the universe or are there other (albeit most likely primitive) forms of life out there, somewhere, in the depths of some icy ocean on a distant satellite orbiting Jupiter?
As I have said, you only need a small refractor telescope in order to see its banding in faint detail and the accompanying specks of light that are the four Galilean satellites. With larger and more powerful telescopes, you can see the Great Red Spot and the cloud layers in finer detail. Failing that, Jupiter can also be seen with the naked eye as it is one of the brightest objects in the night sky, and comes across as a very bright star. Throughout this month, Jupiter has displayed itself as a very bright point of light just below the Moon; Jupiter will remain visible in the sky throughout the coming weeks into March.