Despite writing all about the amazing planets, the Sun, the dwarf planets, the Kuiper Belt and Oort Cloud, I completely skipped the awesome Asteroid Belt!
What is the Asteroid Belt?
Similar to the Kuiper Belt, the Asteroid Belt is a ring of rocky debris between Mars and Jupiter. Contrary to popular belief, the Asteroid Belt is really sparse. Almost half of the total mass within the belt comes from Ceres and the three largest asteroids in the belt, Vesta, Pallas, and Hygiea!
In fact, the total mass of the Asteroid Belt may only be 0.04% of the Earth’s mass!
The types of asteroids.
About ¾ of the asteroids in the belt are carbonaceous (carbon-rich), and are called C-type asteroids. Pallas and Hygiea are but two examples of C-type asteroids.
Under 20% of the asteroids are composed mainly of silicate material, a bit like the terrestrial planets. These asteroids are named S-type. Eunomia is the largest of this type, and has been featured in multiple sci-fi novels, films, and video games.
M-type asteroids are far more metallic in composition, and show iron and nickel in their spectra. M-types make up only 10% of the asteroids. 216 Kleopatra is an M-type, and looks like a dog bone!
V-type asteroids are the weirdest of them all, and are mostly composed of either basalt or Olivine. These asteroids have little information on them that I could find. Vesta is a V-type asteroid (hence the V in V-type.)
Comets are also found in the asteroid belt, and have unusual orbits and it is speculated that these non-classical comets may have been a source of Earth’s water.
The Belt’s only dwarf planet, Ceres
Ceres lives in the asteroid belt unlike the other dwarf planets. It is a very small dwarf planet, being only 939 km wide.
Interestingly enough, you can observe Ceres with even just binoculars. I will admit, you’ll probably see just a teeny dot at most.
Observing Ceres is a difficult task, so a tiny dot is an amazing feat! If it makes you feel any better, even Hubble struggles to image Ceres. The image below is one of the clearest images of Ceres taken by Hubble.
Ceres’ structure seems to be most like a terrestrial planet: made of a non-dense core and mantle. This core is most likely solid, but the mantle is composed of layers of water ice and salts.
The surface of Ceres is fairly smooth, unlike its asteroid neighbours. It is believed that the salt in the ice below the surface may have smoothed out larger impacts, leaving only smaller craters.
The Belt has many families
The asteroids within the belt are not all evenly spaced out. Instead some are grouped together in families.
Those that are in a family share almost the same semi-major axis, orbit, and often a very similar composition. There are dozens of families, the main ones being the Flora family, Vesta family, Eos family, and the Themis family. Families are usually named after the largest asteroid in them.
The family with the biggest amount of members is the Nysa/Hertha family, which has over 19’000 members! This family makes up about 5% of the asteroid belt.