The Outer Planets

[title type=”modern-h2″ align=”center”]The Outer Planets[/title]

Mars is probably the closest planet we have that resembles Earth however its about half the size. Over the decades that astronomers have been observing the red planet there have often been rumors that life exists but more often this has its roots in mankind’s active imagination. To date, we know of no firm evidence of life on Mars. When you look at Mars telescopically, its red colour becomes more apparent although it actually looks a little more pink than red. The red colour is caused by the presence of iron oxide, a fine dusty material that covers the Martian surface. Closer study will reveal polar ice caps which are made of carbon dioxide ice, a colossal volcano called Olympus Mons that dwarfs any here on Earth and a valley system called Valles Marineris that makes the Grand Canyon on Earth look like a tiny crack!

Beyond Mars, is a belt of asteroids that separate the small rocky planets from the large gaseous ones. The first we come across on our journey out of the Solar System is the largest of all the planets, Jupiter, at an average distance of 700 million km from the Sun. Like the rest of the planets we cover here, Jupiter is a big ball of gas and all we can see from Earth is the top of its atmosphere. It may have a liquid metal core but there is no solid surface like the small rocky planets of the inner Solar System. One of the most prominent features in Jupiter’s atmosphere is its great red spot which is a hurricane system that has been raging for hundreds of years. This can easily be seen in amateur telescopes due to it’s colossal size, almost three Earth’s would fit inside! Its also possible to see banding in the upper layers too which are the result of different gasses and the wind systems found in the upper atmosphere. Telescopic observations will also show up some of Jupiter’s moons, four of which were discovered by Galileo when he first turned a telescope to the sky.

Saturn is the next planet from the Sun and is famous for its incredible ring system. Whilst the rings look like a solid structure from Earth, gaps can be detected. In fact the rings are made up of billions upon billions of tiny pieces of rock and ice all in orbit around the planet, in just the same way our Moon orbits around us. The rocks making up the ring system are kept in place by bigger moons called shepherd moons. Saturn, like Jupiter has well over 60 moons of appreciable size, some can be seen with amateur telescopes.

Uranus and Neptune are the final two outer planets in our Solar System and can just be seen through modest telescopes. Both are gas giants and blue in colour due to the gas present in their atmosphere. Uranus is a little unique in the way it orbits the Sun. The planets all orbit the Sun, more or less along a plane that we call the ecliptic. With respect to this ecliptic, the planets spin on an axis that is near enough upright (although even Earth is tilted a little by about 23 degrees) Uranus though is tilted over on its axis by about 91 degrees so is almost rolling around the Solar System.

Mark’s Observing Tip

The best time to observe the planets is when they are at opposition. That means they are opposite the Sun in the sky so are at their closest and biggest. Features should be easiest to pick out when they are at this point in their orbit.

Leave a Reply

Your email address will not be published. Required fields are marked *