Above: The asteroid 243 Ida. The tiny dot on the right is Ida's moon, Dactyl (NASA)
Fast Fact: One of the most distant objects in the solar system is actually man-made! Launched in 1977, the Voyager 1 spacecraft has travelled 122 times the Earth-Sun distance!Ever take a look at the night sky? Other than the moon, it just looks like a bunch of stars and empty space. You’d never guess there was a liquid ocean out there. Or weather. Or a Death Star.
Most of the objects in the solar system aren’t visible to the naked eye; you can really only see the largest objects. The sun–the star of the solar system–is the largest of all. There are also eight planets. Four of them make up the inner solar system: Mercury, Venus, Earth, and Mars. These are all rocky planets, with solid outer crusts, iron cores, and many other things in common. The outer solar system is made up of Jupiter, Saturn, Uranus, and Neptune. These planets are all gas giants, many times the size of the rocky planets, but with no solid surface to walk on. All eight planets are large round objects orbiting the sun. But aside from that, the gas giants and the rocky planets really don’t have much in common.
|Mimas, one of Saturn's moons, bears an uncanny resemblance to the Death Star from Star Wars. Click to enlarge (NASA) |
There are also many moons in the solar system. Every planet except Mercury and Venus have at least one. In fact, except for Earth, all the remaining planets have multiple moons. The gas giants have dozens! But of all the moons in the solar system, Earth’s is actually the largest in relation to the planet it orbits. Mimas, one of Saturn’s moons, actually looks like the Death Star from Star Wars!
Fast Fact: A dwarf planet is a round object orbiting the sun. However, unlike a planet, it shares its orbit with many other objects.
But there’s still more to our solar system than the sun, the planets, and their moons. Large numbers of asteroids, which are chunks of rock left over from the solar system’s formation, orbit the sun in a belt located between Mars and Jupiter. Some of these objects are as small as a house, but the largest is almost 1000 km across! In fact, one of them, Ceres, is classified as a “dwarf planet.” Not all asteroids are confined to the region between Mars and Jupiter. Thousands more fly throughout the inner solar system. Some of them even cross Earth’s orbit!
Like asteroids, comets are made up of leftover material from the early solar system. But comets are made of ice, or a combination of ice and rock, rather than just rock. When they get too close to the Sun, they grow a tail, as some of their ice boils away!
In 1992, another ring of objects was discovered orbiting the sun out beyond Neptune. Similar to the asteroid belt located between Mars and Jupiter, this ring is called the Kuiper belt. It is full of comets and icy objects, including Pluto, another dwarf planet. The Kuiper belt is also where most comets originate.
Fast Fact: In ancient and medieval times, comets were often seen as bad omens for rulers and their kingdoms.At the very edge of the solar system, there is a spherical cloud called the Oort cloud. Full of bits of ice and rock scattered out into space early in the solar system's evolution, the Oort cloud orbits the sun at a distance 50,000 times the Earth-sun distance. In other words, if the sun were a ball 7.5 kilometres away from you, the Oort could would be as far away as the moon!
So next time you look up at the night sky, remember: you’re looking at the playground of planets, comets, asteroids, and everything in between.
Where are the Voyagers? (NASA)
http://voyager.jpl.nasa.gov/where/index.html Comets (Journey Through the Galaxy)
http://burro.astr.cwru.edu/stu/comets.html A 'Smoking Gun' for Dinosaur Extinction (NASA)
http://www.jpl.nasa.gov/news/news.php?feature=8 "Astronomical Unit," or Earth-Sun Distance, Gets an Overhaul (Scientific American)