An Introduction to the Solar System (Part 3)

Carl introduces you to the planets, asteroids and dwarf planets that make up our solar system and that have surprised us with their unexpected properties and beauty since we sent eyes to visit them…

Depending on when you went to school, or indeed how conservative your school is on updating their textbooks, your picture of our solar system may be a little out of date or even incomplete. Our solar system is full of wonders and surprises that you probably didn’t even know were there.

If you want to skip to a particular part of our backyard, click on any of the links below and you will be taken directly to the information on that body.

• The Sun
• Mercury
• Venus
• Earth & The Moon
• Mars
• Ceres & The Asteroid Belt
• Jupiter & The Jovian Moons
• Saturn & The Saturnian Moons
• Uranus
• Neptune
• The Trans-Neptunian Dwarf Planets & Beyond

Jupiter & The Jovian Moons

Jupiter is the fifth planet from the Sun, the largest planet in our solar system and also the first gas giant in the tour of our neighbourhood. With a mass nearly 320 times the mass of the Earth, you could fit over 1,300 Earths inside this giant of the solar system. It has the largest atmosphere of any planet in our solar system at over 5,000km thick and its internal structure is believed to consist of a small rocky core as well as layers of metallic hydrogen and molecular hydrogen.

Credit: NASA/JPL/University of Arizona

Observing Jupiter, we see clear zones, belts and vortices that dominate the top of the planet’s atmosphere. A mixture of brown, red, white and blue, these rotate in opposite directions around the planet. The most famous vortex in the entire solar system is Jupiter’s Great Red Spot (GRS), a giant red storm three times the size of planet Earth just south of Jupiter’s equator. It is believed to have been raging since at least the seventeenth century and takes about six Earth days to complete one rotation.

Being such a large planet, it wouldn’t be right if it had only a few moons. In total, 63 moons have been discovered orbiting Jupiter but the four moons discovered by Galileo in 1610 are both the easiest to observe and the most interesting by far. Io, Europa, Ganymede and Callisto contain over 99% of the mass of Jupiter’s 63 moons. Let us explore these strange and exotic moons in further detail…

Io is the closest of the Galilean moons and has been observed to have over four hundred active volcanoes over its surface making it the most geologically active body in the solar system! Its surface is covered in a sulphur frost courtesy of all these erupting volcanoes. A process called tidal heating is believed to power these volcanoes from deep inside the yellow moon. This is when the gravitational pull from Jupiter, as well as other moons near by, cause the moon to stretch and deform due to these immense forces involved. These processes heat the interior of the moon due to the friction caused by the deformation.

The smallest of the four Galilean moons is Europa but what it lacks in size it makes up for in mystery. Like all the Galilean moons, Europa is also tidally locked to Jupiter, like the Moon to Earth – only one side of the moon ever faces Jupiter. In stark contrast to Io, Europa is a cold icy world. It is believed to have a metallic core and rocky interior with a liquid or icy ocean below a hard icy crust as well as a thin atmosphere of Oxygen. This potential for a liquid ocean below the crust has scientists excited with the possibility of harbouring some form of life. Multiple missions are being proposed to visit, explore and unlock the secrets of this icy world but with funding being cut for such missions around the globe, it is anyone’s guess as to when we will finally meet Europa face to face.

Larger than the planet Mercury, the third Galilean moon Ganymede has twice the mass of Earth’s Moon and is believed to be quite similar to Europa in its internal structure. Furrows and ridges litter the surface of this moon which, like Earth and Mars, has polar caps which are believed to be formed from water frost.

Finally, we come to the fourth Galilean moon Callisto. Like Europa, it is believed to have a liquid water layer below its surface which has the possibility of harbouring life, although conditions are thought to be less hospitable than on the other Jovian moon. Callisto has been bombarded since its formation which has created the heavily cratered surface we observe today. Out of all the Galilean moons, Callisto is thought to be the most suited target for a manned mission to the outer solar system due to the low radiation environment there as well as the moons relatively good geological stability. Although a NASA report from 2003 suggested that such a mission would be possible in the 2040s, it remains to be seen whether such activities still remain a priority to space agencies all over the world.

Credit: NASA/JPL/University of Arizona

Most of our information about the Jovian system comes from robotic missions that have flew past the gas giant. These include two Pioneer spacecraft, both Voyager 1 and Voyager 2 as well the Cassini spacecraft and the New Horizons craft currently on its way to visit Pluto in 2015. So far, the only craft to enter orbit around Jupiter has been the Galileo spacecraft which did so from 1995 until 2003 when it was intentionally steered into Jupiter to prevent any future impact with Europa in order to prevent contamination of the moon. Galileo sent back discovery after discovery and with each one it was realised the Jovian system is something rather special.