What in the solar system?!
Stars (Sun) – Planets – Dwarf Planets – Small Solar System Bodies (Minor Planets) – Asteroids – Meteoroids – Meteors – Meteorites – Ccomets.
There’s a lot of stuff flying around the solar system, big, small, round, irregular etc. What’s the difference between some of the most basic objects orbiting our Sun? Well, honestly that’s not an easy question to answer but let’s scratch the surface.
Ok, ok, I put this in here half as a joke but truth be told most don’t remind themselves enough that the Sun is a medium to small, 4.6 billion year old, second generation G-Type Main Sequence Star (G2V). A star is a massive fusion reactor fusing hydrogen atoms into helium atoms and our Sun comprises 99.86% of the entire mass of the solar system. It has a diameter of 865,000 miles (1,392,000 km) and you can squeeze 1.3 million Earths into it.
Well to start, the word “planet’ is Greek for “wanderer”. The then 5 planets; Mercury, Venus, Mars, Jupiter and Saturn in conjunction with the Sun and Moon help to make up the names of our 7 days of the week today (Earth did not count because, of course they lived by the Geocentric solar system model). To be a planet you must meet three stringent criteria.
1: You must orbit the Sun (Fair enough).
2: It must be large and massive enough for gravity to have shaped you into a spherical shape.
3: It must be dominant enough to have cleared its orbital path of all other orbital debris either by pulling it into itself gravitationally or to sling-shot them out of the way out into space.
According to these specs, we have 8 such objects: The 4 terrestrial planets of Mercury, Venus, Earth and Mars. The 4 jovian planets of the outer solar system; the gas giants of Jupiter and Saturn as well as the ice giants of Uranus and Neptune.
Somewhere between minor planets and planets lie an odd class of solar system objects; the dwarf planets. The term dwarf planet was adopted in 2006 as part of a three tier approach to classifying solar system bodies in orbit around the Sun.
The International Astronomical Union (IAU) defines dwarf planets as solar system bodies in orbit around the Sun that are massive enough to have been pulled into a spherical shape by gravity but have not cleared their paths of planetismals or debris.
There are currently 5 dwarf planets recognized in the solar system. Four are found in the Kuiper Belt and they are Pluto, Eris, MakeMake, Haumea, as well as one in the Main Asteroid Belt; Ceres.
It was decided by the IAU that future entries of Trans Neptunian Objects (TNOs) into this classification must have an absolute magnitude brighter than 1 (or +1) and a mathematically delimited minimum diameter of 838km are to be included.
***Small Solar System Bodies (Minor Planets)***
Anything that is in orbit around the Sun and is not a planet, dwarf planet, moon and isn’t massive enough for gravity to have formed it into a spherical shape is a small solar system body (formerly known as minor planets). The term small solar system body was adopted in 2006 by the International Astronomical Union (IAU) as part of a three tier approach to classifying solar system bodies in orbit around the Sun.
The list of SSSB’s are in the hundreds of thousands, possibly millions but they fall into a large handful of categories and sub-categories as follows (Don’t be freaked out, it’s just a list). Planetoids, Asteroids, Main Belt Asteroids, Near Earth Asteroids, Aten Asteroids, Apohele Asteroids, Amor Asteroids, Apollo Asteroids, Earth Trojans, Mars Trojans, Jupiter Trojans, Distant Minor Planets, Centaurs, Neptune Trojans, trans-Neptunian Objects, Kuiper Belt Objects, Cubewanos, Plutinos, Resonant Trans-Neptunian Objects, Scattered Disk Objects, Detached Objects (such as Sedna), Oort Cloud Objects, Damocloids, all comet classifications (Extinct, Great, Lost Main-Belt, Periodic, Non-Periodic, Long Period, Sungrazing) and all Meteoroid classifications (Bolide, Dust, Fireball, Meteor, Meteorite, Tektite).
Objects left over from the formation of the solar system comprised primarily of rock and metal and ranging in sizes anywhere from dust particles to hundreds of miles wide. Classified as small solar system bodies and often referred to as planetoids, really anything that’s not a planet, dwarf planet, moon or human built is an asteroid. Most reside in the Main Asteroid Belt and Kuiper Belt and most but not all orbit the Sun. Small asteroids or fragments of space debris are also known as meteoroids.
A meteoroid is a small body as they travel through space and they range from a grain of dust to meters wide. They are mostly rocky, icy or metallic and typically come from broken fragments of comets (meteor showers) and debris from collisions that have taken place throughout the solar system to include the Moon and even Mars. You may even hear the term micro meteoroids which are still meteoroids, just tiny ones being referred to in a different name.
*** Meteors (Shooting Stars)***
Meteors are Meteoroids as they encounter Earth’s atmosphere, heat up in a process called ablation and streak across the night sky in an instant. If you are lucky you may get to see a fireball (bolide) and or an associated smoke trail. If you are unlucky (depends on youroutlook I suppose), you will get to see a massive air burst that packs a shockwave and possible impact debris. Meteor dust is believed to be the single largest cause of Noctilucent Clouds.
Meteorites are the final product. After the Meteoroid encounters the Earth’s atmosphere and becomes a meteor, it must then survive the ablation process. If it’s lucky enough to reach the ground we then call them meteorites.
Meteorites fall into 3 main groups.
Stony: The name tells you the story here and they fall into 2 sub-categories; chondrites, which contain small minerals that formed spheres while in space and achondrites which mean they have no chondrites.
Stony-Iron: These meteorites contain pretty much equal portions of nickel/iron and stone in their composition.
Iron: These meteors contain primarily nickel/iron in their composition.
A comet is a small solar system body that orbits the Sun but unlike most objects in the solar system they swing very far out from the Sun in their orbit (parabolic orbit). Comets typically have a solid nucleus upwards of 10 km in diameter and are comprised of mostly ice, dust and rock left over from the formation of the solar system which lends them to be referred to as “dirty snowballs”. When the comet approaches the Sun it begins to heat up and begins to out gas or sublimate (transform directly from ice into steam). When this occurs it creates the coma which shrouds the nucleus from view and also creates the stream of material in the form of a tail that typically stretches millions of miles long and always points away from the sun even when leaving the inner solar system.