An Introduction to the Solar System (Part 4)

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or indeed how conservative your school is on updating their textbooks, your picture of our solar system may be a little out of date or even incomplete.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

Saturn & The Saturnian Moons

One of the most visibly spectacular objects in the solar system also happens to be the sixth planet from the Sun, the second largest planet in the solar system and is the next stop on this whirlwind tour of our backyard – Saturn. The gas giant exhibits a series of rings which are visible from here on Earth and which are even more awe inspiring close up.

Like Jupiter, Saturn is a gas giant with a series of bands which reach around the entire planet. Although fainter than the bands seen on Jupiter, the conditions on Saturn can be even more extreme. Composed mainly of molecular hydrogen, Saturn’s atmosphere is surprisingly dynamic with storms, lightening, aurora and the only known instance of a planetary vortex at its southern pole which was discovered by Voyager 1 and confirmed by the Cassini mission in 2006.

Credit: NASA/JPL/STSI

Saturn’s ring system is without a doubt one of the most beautiful sights in the solar system, and one of the few you can see with a small telescope in your own back garden. Comprised of small particles of mostly water ice ranging in sizes from millimetres to metres, the rings range from 7,000km to 80,000km above Saturn’s equator with an intricate series of gaps, ringlets and changes in brightness which give the appearance of gaps. Some gaps within the rings are caused by some of Saturn’s moons, of which is has at least 62. These moonlets clear the material around their orbit which create some of the gaps seen in the rings.

Like Jupiter, Saturn has a wide variety of moons that come in all shapes, sizes and colours. The three most well known provide some striking imagery and have astounded astronomers ever since they were first discovered. The first of those three is Mimas, the smallest body in the solar system able to become rounded in shape due to its own gravitational force. Composed mostly of water ice, with a small amount of rock thrown in, Mimas has a surface feature that has made the moon famous. A massive impact crater, from an event that is thought to have nearly fractured the small moon, dominates one of its sides and gives the moon the appearance of the fictional Death Star from the Star Wars universe. Interestingly, due to the proximity to Saturn, Mimas is not perfectly spherical but elliptical due to the tidal forces acting on it.

Credit: NASA/JPL/Space Science Institute

Moving onto the second celebrity, we arrive at Enceladus. A mysteriously icy world, it is thought that material ejected from this moon is solely responsible for the creations of the outermost ring, or the E ring, around Saturn. Plumes of water ice jet out from along the ‘tiger stripes’ that scar the surface of the moon. Along with Jupiter’s moon Io and Neptune’s moon Triton, Enceladus is one of only three bodies in the outer solar system where active eruptions have actually been observed. Observations of the material being ejected in such eruptions on Enceladus has suggested that an ocean of liquid water exists beneath the surface, fuelling speculation that the icy moon has the potential to harbour life.

If the Saturnian system were a magic act, Saturn’s glamorous assistant would be this moon. The second largest moon in the entire solar system and larger than the planet Mercury, Saturn’s moon Titan remained literally shrouded in mystery until only recently. At first glance, Titan is a hazy orange ball orbiting the ringed planet but on closer inspection it is realised that Titan is much, much more than just an orange ball of rock. Titan is the only moon in the solar system with a thick atmosphere, which is comprised almost entirely of molecular nitrogen; similar to the atmosphere found on the early Earth. Lakes of hydrocarbons are the first stable bodies of water to be found beyond the Earth in the solar system and litter the moon’s surface. Observations have also revealed clouds within Titan’s atmosphere, dunes on its surface much like those seen in Earth’s deserts and evidence for volcanoes whose ‘lava’ would be a mixture of water and ammonia.

Credit: NASA/JPL/Space Science Institute

In early 2005, the Huygens probe landed on Titan and is still holds the title of most distant landing of any spacecraft sent from Earth. The probe sent back images of drainage channels, lakes, oceans and other surface features as it descended through the thick atmosphere and eventually landed on the ‘muddy’ surface. Once settled, the probe sent back the first ever images from the surface of another planet’s moon. Being comparable to the early Earth, Titan is a prime candidate for future missions that will be searching for life, or the building blocks of, in our solar system.

Uranus

The seventh planet from the Sun is also the planet that has been the punchline of many a joke since its discovery in 1781. Uranus was the first planet to be discovered using a telescope and was confused with being a star and then a comet before being accepted as the then newest member of the solar system – and even after it was confirmed as a planet, astronomers couldn’t come to a collective decision on its name until 1850!

Unlike the other major planets in the solar system, Uranus is tilted so that it rotates more like a spinning ball on its side, rather than a spinning ball in the plane of the solar system. Also unlike the other giant planets, Uranus’ internal structure is believed to consist of small metallic core, an outer ‘icy’ mantle (water and ammonia ices) and an outer gaseous atmosphere composed mostly of hydrogen and helium. This gives the planet its blue glow that can be seen from Earth on a clear night. Uranus, like Saturn, Jupiter and Neptune, has a ring system that is slightly less complex than Saturn’s. With at least 13 rings at increasing distances from the planet as well as moons in and between those rings, they are an interesting sight to view and understand – the latter of which astronomers are still not that close to doing!

Credit: NASA/JPL/Voyager mission

So far our only view of Uranus up close has been from NASA’s Voyager 2 spacecraft which visited the blue planet in 1986 when it discovered ten new moons and studied the rings that were known at the time. Although we know differently now, Uranus appeared as an almost featureless blue ball to the now infamous visiting spacecraft. Since Voyager 2, no other craft has visited Uranus and all we know has come from Earth based observations as well as the Hubble Space Telescope.

No future missions to this seemingly plain planet are currently planned, although many have been suggested. Until that time, Uranus will continue to orbit the Sun, sitting happily between Saturn and Neptune minding its own business and, for now, keeping hold of any secrets it may have.