Oh no, it’s coming towards us! We’re all going to die! Lots of people fear something of this nature could happen in the future, and they’re not wrong. An asteroid could strike the Earth at any time and cause a nuclear-type winter effect creating food shortages and eventually seeing the end of life as we know it. It is believed that an asteroid impact contributed to the extinction of the dinosaurs 65 million years ago and it was one of several factors that affected all life on Earth at the time. But the likelihood of this happening again? Slim. Get comfortable and we’ll explain more and give you some interesting asteroid facts along the way.
Asteroids are small airless rocky worlds that revolve around our sun but are too small to be called planets. They populate interplanetary space out as far as the orbit of the planet Jupiter. There are literally thousands of them in many different sizes. Smaller ones are known as asteroids, while larger ones are sometimes called planetoids, or small planets. Where did they come from? I’m glad you asked!
The most popular theory about the creation of our solar system and how it came to be is this: The sun blended from a grouping of compressed gas that then eventually began to fuse atoms to create the star. Meanwhile, the surrounding dust and particles near the sun began to crash together and combine as well. Tiny grains started to become small rocks, which then became bigger ones. These continued to crash into each other and eventually formed the planets and moons we see today. The process of collision and impact still continues to this day, although with smaller objects, since the larger ones all became the planets we see today.
The asteroids are the leftover bits of rock that didn’t quite make it to planet size 4.6 billion years ago. Some are as small as six metres across, but they also can be as big as Ceres, which is 940 kilometres (583 miles) across. Ceres is the most famous asteroid in the solar system, and was the first discovered. Two other well-known asteroids are Pallas, which is 544 kilometres (338 miles) in diameter, and Vesta, which is about 580 kilometres (360 miles) across. Pallas has a very irregular shape and may be what’s left of an early proto-planet. Vesta is very bright and is also likely the leftover of a rocky proto-planet.
Ceres is called a differentiated asteroid because it has a rocky core but an icy outer crust. It might have an internal ocean. It was discovered by accident in 1801 by Giuseppe Piazzi, an Italian priest and astronomer who was making a star map at the time he discovered it. Although it is now known as a dwarf planet, Ceres is actually a large asteroid, and it accounts for a quarter of all the mass of all the thousands of known asteroids in or near the main asteroid belt.
While there are asteroids across the solar system, the largest collection of them lies in a belt between the orbits of Jupier and Mars. Many scientists think these would have formed another planet if Jupiter had not been nearby. And though it looks like you need to be Luke Skywalker to fly around them all, in fact there is usually hundreds or thousands of miles between asteroids in this belt. This gives you an idea of how big the solar system really is.
An asteroid’s composition is determined by how far it was from the sun when it was formed. There are many types of asteroid, but there are three main classifications:
- C-Types (also called Dark C or chondrite types): These are carbonaceous asteroids. They are the most numerous type (more than 75% of asteroids are carbonaceous) and reside in the outer parts of the asteroid belt. They’re believed to be close to the sun’s composition, without the hydrogen, helium or other “volatile” elements. They are made of clay and silicate rocks.
- S-Types (also called Bright S): These are silicaceous asteroids, and represent about 17% of all asteroids in the belt. These reside in the inner ring of the asteroid belt, and are known as “stony” asteroids. They are made of silicate rocks and nickel-iron mixtures.
- M-Types (also called Bright M): These are metallic asteroids, residing in the middle of the asteroid belt and mostly made up of metallic iron or nickel-iron. These are the least common type, making up the balance of asteroids in the belt, or about 8% of them.
There are other rare types of asteroids. For example, Vesta is a V-Type, typified by a basaltic volcanic type crust. Nearly all asteroids are irregularly shaped, but some, like Ceres, are nearly spherical. They are usually pitted or covered in craters. For example, Vesta has a giant crater on its surface that is 460 km in diameter (285 miles). Some are solid bodies, while others are small piles of rubble bound together by a small gravitational field. Most asteroids are believed to be covered in surface dust. One asteroid that lies between the planets Neptune and Uranus comes complete with its own set of rings, while another has not one, but six tails. The ringed asteroid is called Chariklo, and it was discovered to have two rings when scientists watch it pass in front of a star in 2013 and it made the star “blink” a few times.
Scientists estimate that the asteroid belt alone contains over 200 asteroids that are larger than 100 kilometres (62 miles) in diameter. They have also identified more than 750,000 asteroids that are greater than one kilometre (three-fifths of a mile) in diameter. There are also millions of smaller ones. And any numbers of asteroids lie outside the main asteroid belt. A group of asteroids that are called Trojans lay along Jupiter’s orbital path, and three other groups (Atens, Amors and Apollos) orbit the sun in the inner solar system and sometimes cross the path of both Mars and the Earth. Trojans are asteroids that stay in the same orbit as a planet but they “hover”in their own little spot known as a Lagrangian point, where the balance between the gravitational pull of the planet and the Sun is about equal. Trojans have been discovered near Mars and Jupiter, as well as at least one near Earth that was discovered in 2011.
Some asteroids have smaller bodies that orbit them, or their own little moons. The first such one discovered is known as Dactyl, found to be orbiting a larger asteroid called Ida. More than 150 asteroids are known to have their own moons, and more are being discovered occasionally. Asteroids are similar to comets, but do not have the “tails” that typically trail behind comets. The average temperature on an asteroid is about minus 73°C (minus 100°F).
Asteroids are too small to support life as we know it. This is because they are too small to hold onto an atmosphere. Many of them have gravitational fields that are even too weak to pull them into a regular spherical shape. Despite their small size, some may have water on their surface. Observations of Vesta released this year (2015) show the existence of gullies that look like they may have been created by water flow. If a smaller asteroid had crashed into a bigger one, the smaller one may release a layer of ice that may surround it. The heat of the collision briefly turns the ice to water and it creates the gullies as it flows off the surface. Scientists are still investigating how the ice could get there in the first place, but theories continue.
Asteroids that come close to the Earth are called Near-Earth Objects, or NEO’s or Potentially Hazardous Asteroids (PHO’s). If conditions are right, it’s possible that a PHA or NEO could crash to the Earth’s surface. Depending on the size of the asteroid, the damage to the planet could range from very little to catastrophic. But every day than 100 tons of material from comets and asteroids falls towards Earth. Most of it is destroyed by friction as it attempts to pass through our atmosphere. If one of them does hit the ground, then it is called a meteorite.
There are two types of meteorites: Iron meteorites and Stony meteorites. Their typical composition is:
Iron meteorites:
- Iron: 91%
- Nickel: 8.5%
- Cobalt: 0.6%
Stony meteorites:
- Oxygen: 36%
- Iron: 26%
- Silicon: 18%
- Magnesium: 14%
- Aluminum: 1.5%
- Nickel: 1.4%
- Calcium: 1.3%
About once a year, a car-sized object enters the Earth’s atmosphere, creates an impressive fireball as it burns up, and fails to reach the planet’s surface. An asteroid that could cause catastrophe on earth would have to be more than 400 metres (a quarter of a mile) in diameter. Researchers say it would have to be able to pass through the atmosphere without burning up, and upon colliding with the Earth, it would have to raise enough dust into the atmosphere to effectively cause a “nuclear winter” and hence severely disrupt the production of food through agriculture around the world. This means it would also have to land on part of the only 30% of the planet that is not covered in water (the oceans). Should one land in the oceans, it may cause severe tidal waves in various areas of the Earth, which could lead to numerous deaths depending on where they hit, but is unlikely to have as severe an impact globally. NASA officials say that asteroids this size strikes the Earth only about once every 1,000 centuries, on average.
As an example, on February 15, 2013, an asteroid hit the Earth’s atmosphere over the Russian city of Chelyabinsk. This asteroid is thought to have measured about 20 metres in diameter (65 feet) when it entered the atmosphere, before it burned up. Even so, it caused a shock wave that injured 1,200 people in the city. There is a crater called Chicxulub in Mexico’s Yucatan Peninsula that is about 65 million years old and is covered with a layer of iridium, which is extremely rare on the Earth’s surface. This is the asteroid that is thought to have killed the dinosaurs.
There are many groups and organisations that work to track asteroids and identify the ones which may collide with the Earth. Using mostly automated systems, they continue to discover new ones, and to suggest ideas for preventing a potentially life-ending collision. One company called Planetary Resources Inc. plans to one day send a mission to an asteroid so they can mine it for its rich metals and (possibly) water.
The first spacecraft to take pictures of an asteroid close-up was the NASA craft Galileo in 1991. This same craft also first discovered a moon around an asteroid in 1994. NASA sent it’s NEAR (Near Earth Asteroid Rendezvous) spacecraft out to study the asteroid Eros. In 2001 they monitored Eros for over a year and eventually even landed the craft onto the asteroid (even though it wasn’t designed for landing). In 2006, Japan sent its own craft Hayabusa to space to land and take off from an asteroid. In June 2010 it returned to Earth, bring samples which are still being studied today. In 2007 NASA sent a second craft, it’s Dawn Mission, to begin exploring Vesta in 2011. After a year it left Vesta to visit Ceres, and is expected to arrive near that asteroid this year.
The International Astronomical union is not very strict about naming of asteroids, so there are asteroids named after Mr Spock (from the Star Trek series), and rock musician Frank Zappa as well as other more solemn tributes, such as the seven named for the astronauts killed when the Space Shuttle Columbia exploded in 2003. However, you are no longer allowed to name an asteroid after your pets. Asteroids are also given numbers for names, for example 99942, also known as Apophis.