An Introduction to the Solar System (Part 2)

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indeed how conservative your school is on updating their textbooks, your picture of our solar system may be a little out of date or even incomplete.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

Mars

Due to the iron oxide dust (rust) that covers the surface of Mars, the planet appears as a reddish blur in the night sky. The Egyptians knew Mars as the ‘Red One’ and even today we know Mars more commonly as the red planet. Often featured in tall tales of extra-terrestrial life, the fourth planet from the Sun is one of the most well known bodies in our solar system.

Mars, like Earth, has a thin atmosphere but it’s composition is more like Venus’ with 95% of it being carbon dioxide. Also like Earth, the red planet has seasons due to the tilt of its rotational axis as well as features like polar ice caps, impact craters, valleys and volcanoes. The tallest mountain and extinct volcano in the solar system is found on Mars. With a height of over 25km above the surface of Mars, Olympus Mons is nearly three times as tall as Mount Everest here on Earth! It has been known since the late 19th Century to be a tall feature on Mars as it was one of few features still visible during dust storms that sometimes blanketed the entire planet.

In recent years, the long held belief that Mars could potentially play host to life, including humans, has broken down – even with the confirmation of water ice on the Martian surface. With average surface temperatures of around -63 degrees Celsius (-81 degrees Fahrenheit) it would be a chilly walk to the local supermarket. To add to this, the Phoenix lander confirmed a chemical called perchlorate could be found in the Martian soil which has the ability to inhibit life. Combined with Mars’ lack of an ozone layer, which means UV exposure from the Sun is lethal to life on the surface, the red planet seems to be a rather uncomfortable place to say the least.

Credit: NASA / JPL / University of Arizona

Observations of Mars have given us the wonderfully unexpected and even the downright creepy. In 1976, NASA’s Viking 1 spacecraft took a photo of the surface of Mars which appeared to show a human-like face staring back at it (above). This has become known as the ‘Face on Mars‘ and is just a rocky surface feature. We see a face because our brains are hard-wired to search for and detect faces – just like we see faces, or other objects, in clouds and on toast! Another image came from NASA’s Spirit rover in 2008 which photographed what appeared to be a human-like form crouching on some rocks. Obviously it wasn’t a human, or any form of life, but merely a rock formation that just happened to look like that.

Ceres & The Asteroid Belt

In the expanse between the orbits of Mars and Jupiter, material left over from the formation of our solar system orbits the Sun. The size of these objects range from dust particles to bodies we now call dwarf planets, of which Ceres is one. Several space craft have traversed the asteroid belt without running into problems due to the thin distribution of the bodies within the belt.

The asteroid belt is mainly comprised of three types of asteroid: carbonaceous, silicate and metallic. Carbonaceous asteroids, as the name suggests, are mostly made from carbon and make up around three quarters of all the asteroids we can see. More common towards the inner of the belt are the silicate asteroids which are unsurprisingly made mostly from silicates. These account for around 15% of the asteroids we can see. Lastly, and the pattern should be obvious now, the metallic asteroids are thought to be made from iron and nickel and make up about 10% of the asteroids in the belt.

Within this rocky ring that encircles the Sun are a few oddities that stand out from the rest. With diameters larger than around 400km, Vesta, Pallas and Hygiea are the largest asteroids known in the asteroid belt and are massive enough . These objects have become massive enough to be rounded to some degree under their own gravity and Vesta and Pallas at least are thought to be protoplanet remnants – an object that was on its way to become a planet but which was disrupted at some point. Joining these three is the dwarf planet Ceres which by itself accounts for almost a third of the mass of the entire asteroid belt!

Ceres is currently the smallest dwarf planet in our solar system, and the only one in the asteroid belt. Unlike Vesta, Pallas and Hygiea, Ceres is spherical and observations appear to show it has a rocky core with an outer ice mantle. In 2006, when Pluto was demoted to dwarf planet, it was suggested that Ceres be classified as a planet but the definition later adopted by the International Astronomical Union (IAU) meant that Ceres is now considered a dwarf planet, like Pluto. Observations have shown that this diamond in the rough may also have a thin atmosphere as well as water ice on or near its surface – an unexpected but none the less interesting discovery.

Credit: NASA, ESA, J. Parker (Southwest Research Institute), P. Thomas (Cornell University), and L. McFadden (University of Maryland, College Park)

Until 2015 we will have to observe Ceres from instruments here on Earth or with the Hubble Space Telescope (HST) as this is when the Dawn spacecraft is expected to reach this fascinating and blurry world. What will be found once Dawn arrives is anyone’s guess, which much speculation and debate over what secrets it will give up.

Before Dawn visits Ceres, it is also paying a visit to Vesta. It is expected to arrive at the puzzling rock on July 16, 2011 but has already seen Vesta in its sights. This mission is the first to orbit one body (Vesta) and then move on under its own power to investigate another (Ceres). Visiting both Vesta and Ceres will hopefully help us understand the creation and history of our solar system in unprecedented detail as well as open our eyes to the very weird world of the asteroid belt.

Header image credit: NASA