Updated: Jul 6
Asteroids are referred to as minor planets, and larger asteroids are called planetoids. They are smaller rocky bodies that orbit the sun. There are millions of these asteroids in our solar system.
Most asteroids are found at an orbital range between Mars and Jupiter, this is where the asteroid belt is located (a collection of asteroids). A large number of asteroids are co-orbital with Jupiter and others are in other orbital families such as that of near-Earth asteroids (NEAs).
Asteroid 2015 TB145. Image credit: NASA images
Asteroids are leftover loose piles/rubble from the formation of our solar system approximately 4.5 billion years ago. The formation of the larger planet Jupiter, which has a lot of gravity, made it almost impossible for the asteroids to collect to form a bigger planet, leaving an area housing these minor planets and planetoids. Asteroids are composed of rock, metals, and other elements. Some also include water, and it is believed that much of Earth's water that facilitates life originated from asteroids impacting Earth during its beginnings. They are classified by their emission spectra with most being in three groups: C-type (carbon-rich), M-type (metallic), and S-type (silicate).
Asteroid Lutetia. Image credit: NASA images
Asteroids differ from comets, because of composition. Comets, in comparison to asteroids which are a mixture of mineral and rock, are composed of dust and ice. This is because asteroids form closer to the sun and therefore are unable to accumulate substantial amounts of ice.
Asteroids differ from meteoroids because they are bigger. Meteoroids must have a diameter of 1 meter or less, whereas an asteroid must be over a meter. Meteoroids are also composed of either asteroidal or cometary materials.
A comparison of Asteroids sizes
The asteroid 4 Vesta has a seemingly “shiny” (reflective) surface, and therefore we are able to see it with the naked eye from Earth. Asteroid’s range in size, the largest asteroid was Ceres which is located in the asteroid belt and has a diameter of 946km. Although recently, Ceres was classified as a dwarf planet in 2006. However, we must bear in mind that it is still only 14 times smaller than Pluto and that it comprises 25 percent of the asteroid belt’s total mass.
Full image of asteroid Vesta. Image credit: NASA images
Kepler in 1596 noticed a gap between Mars and Jupiter. There was a regular pattern between all the planets that orbited the Sun, although Mars and Jupiter didn’t follow this rule. In 1772, Johann Elert Bode suggested the existence of a planet in between this gap. This predicted planet would have had an orbit of approximately 28 Astronomical Units (AU). In 1781, William Herschel discovered Uranus, in the predicted area before Saturn, which increased the belief that there could be a planet between Mars and Jupiter. Xavier Von Zach grouped together 25 astronomers with the hopes of finding this planet. However, Giuseppe Piazzi who was not a member of the team at the time found Ceres in January of 1801. He first observed a uniformly slow-moving star-like object, that he thought was a comet. He observed this object around 24 times before eventually sending his findings to the rest of the team who tracked it from there. Ceres was classified as an asteroid and its status as a dwarf planet came much later.
Ceres in Colour. Image credit: NASA images
There are plenty of asteroids in our solar system, however, due to a lack of magnetic field and atmosphere, it would be incredibly difficult for us to live on one. Scientists have claimed that in order to protect ourselves from radiation, we would have to burrow at least 100m into the depths of an asteroid. With a lack of natural sunlight and gravity, we would face even graver dangers at these depths. Unless we would want to evolve into the people that they feature in the tv show “The Expanse”, it is very unlikely that we would call asteroids home.
Asteroid Redirect Mission Planetary Defense Demonstration. Image credit: NASA images
We now use cameras on telescopes to detect asteroids. Numerous images of the night sky are taken and compared, to see if any objects become brighter, move, or appear. If an asteroid were to approach us, the idea would be to detonate a nuclear explosive device approximately 20m above an asteroid, to change its direction but to not fracture it. We are currently tracking over 20,000 NEAs, over 100 short-period near-Earth comets (NECs), solar-orbiting spacecraft, and meteoroids that are big enough to track before they land. Asteroids with 1km diameter only strike Earth every 50,000 years and larger collisions (5km in diameter) only happen every 20 million years, but are very catastrophic (hence the current lack of dinosaurs). For the time being, it is believed that we know enough about asteroids, for us to remain relatively safe. Nevertheless, our amazing space agencies are doing their best to mitigate any serious damage from any dangerous asteroids.
Top 7 asteroids, according to their impact probability in ESA's asteroid risk list. Image credit: ESA Operations twitter account
Join the world in appreciating these incredible celestial objects this World Asteroid Day on 30th June 2020 by watching the AstroidDay LIVE at: https://www.twitch.tv/asteroidday
“The Asteroid Foundation will launch Asteroid Day TV 2020 with digital video content from Discovery Science, TED, IMAX, BBC, CNN, The European Space Agency (ESA), European Southern Observatory (ESO) and other top content producers.”