The sky is the ultimate art gallery just above us.
— Ralph Waldo Emerson
The Art of the Universe
We should do astronomy because it is beautiful and because it is fun. We should do it because people want to know. We want to know our place in the universe and how things happen.
— John N. Bahcall
There are many other things in the Solar System beyond the planets, their moons, and the Sun. These miscellaneous objects tend to group together, creating belts and clouds. We have recently begun paying more attention to these other objects, and missions such as Philae, which is the first probe to land on a comet, aid us in learning much more about our Solar System.
Meteors
Meteors are space rocks. While floating about in space, the rocks are called meteoroids, and only
become meteors when they interact with the Earth's atmosphere. They appear as a bright streak of light
in the sky. When they land – if they make it to the ground before burning up in the atmosphere, that is –
they are called meteorites. Meteorites can be anywhere from the size of a granule of sand to a rather
large boulder. They are made of iron, stone, or a mix of the two. These rocks are unable to support life,
but it is thought that they may have brought amino acids, the building blocks of life, to Earth. Meteor
showers are what occur when there are several visible meteors falling per hour. These are a result of
the Earth passing through the debris field left behind by a comet. Showers tend to be named after the
constellation in which the meteors appear to originate from. It is estimated that about 44,000 kilograms
of space debris falls to Earth on a daily basis.
Source: solarsystem.nasa.gov
Asteroids
Asteroids are also space rocks. Most orbit the Sun in a region between Mars and Jupiter known as the Asteroid Belt. If all of the asteroids of the Asteroid Belt were to gather together in the shape of a sphere, they would still be smaller than the Moon.
While some of these rocky bodies have moons or even rings, none of them have atmospheres,
and thus cannot support life as we know it. Over 10 spacecraft have been sent to study asteroids
with the spacecraft NEAR Shoemaker even landing on Eros.
Asteroids are sorted into three classes based on their composition. C-type asteroids (chrondite
type) are dark and made up of clay and silicate rock. S-types (stony types) are comprised of
silicate materials and nickel-iron. The third type, M-type (metallic type), are made of nickel-iron
metal. They are also classified based on their orbits. While most orbit in the Asteroid Belt, there
are some which share orbits with planets, called Trojan asteroids. Near-Earth asteroids are
objects that orbit near to Earth's orbit. If they actually cross Earth's orbit, they are called Earth-crossers.
The naming of asteroids is very arbitrary when compared to the naming of other objects such as moons. One is named Mr. Spock, after a cat that got its name from the Star-Trek character, while another is named after Frank Zappa. Seven are named in tribute of the crew of the Space Shuttle Colombia.
The Itokawa asteroid Source: solarsystem.nasa.gov
Comets
If meteors and asteroids are space rocks, then comets can be called space snowballs. They are composed
of frozen gas, rock, and dust. There are two types of comets: long period and short period. Short period
comets have predictable orbits that orbit the Sun at least once every 200 years and originate from the
Kuiper Belt. Long period comets, however, have unpredictable orbits and usually originate from the Oort
Cloud. Comets (and asteroids) are most likely the remains of the building blocks of the planets during the
formation of the Solar System.
The main body of a comet is the nucleus, a chunk of frozen gases embedded with dust. As it gets closer to
the Sun, some of the gases melt, creating an atmosphere known as a coma. There are two parts to the
coma: the dust tail and the ion tail. Radiation and solar winds push the particles of the coma away from the Sun, so the tail is always trailing away from the Sun, regardless of which way the comet is travelling.
The Hale-Bopp comet Source: solarsystem.nasa.com
Kuiper Belt
The Kuiper Belt is a region of the Solar System beyond the orbit of Neptune. This region is approximately 25 AU in width, and begins about 30 AU from the Sun. It is where most short-period comets originate, and is shaped like a donut. There are estimated to be over a trillion comets in the Kuiper Belt. Pluto, Eris, and two of the other 5 known dwarf planets (Makemake and Haumea) orbit the Sun in this region. The objects in this region are presumed to be remains from the formation of the Solar System.
Oort Cloud
The Oort Cloud is a spherical region even farther from the Sun than the Kuiper Belt. It is where long-period comets originate. Possibly 2 trillion icy bodies orbit in this region. These bodies sometimes interact with passing molecular gas clouds, stars, or tidal pulls from the disc of the Milky Way, sending comets falling toward the Sun. These long-period comets have long, eccentric orbits, and are usually only observed once in recorded history. Like the Kuiper Belt, the objects in this region are most likely leftover materials from the formation of the Solar System.