Asteroids are rocky worlds revolving around the Sun, also known as planetesimals; they are the remnants left over from the early formation of our solar system about 4.6 billion years ago, that are too small to be called planets.

Most of this ancient space rubble can be found orbiting between Mars and Jupiter within the main asteroid belt. Some asteroids, called Jupiter Trojans, are outside the main belt and circle the Sun in Jupiter’s orbit, at two special places known as the Lagrange points, where the gravitational pull of the Sun and planets are balanced. Neptune, Mars and Earth also have Trojan asteroids. Others like the Near-Earth asteroids (NEAs) circle closer to Earth than the Sun. The Amor asteroids for example have close orbits that approach but don’t cross Earth’s path. Apollo asteroids have Earth-crossing orbits and for obvious reasons attract close attention, but spend most of their time outside the planet’s path. Roughly 10,000 of the known asteroids are NEAs, and the current known asteroid count is approximately 992,230, and thousands more are plotted every year.

A few of them are big, Ceres for instance is 933kms in diameter and has been re-classified as a Dwarf Planet. Twenty or more are over 200kms across, and astronomers are fairly confident they have found 99% of those larger than 100kms. 

While it is clear that monitoring hazardous asteroids that pose a potential danger to Earth is essential for our future safety, the interest in the study and composition of asteroids is also due to the fact that, in the future, as resources on Earth become scarcer and extracting them ever more environmentally damaging, asteroids could provide a solution. There are potentially thousands of asteroids ranging from a few meters to a kilometre or more that could provide both valuable resources for further space exploration, especially for the colonization of Mars, and also essential minerals such as rare-earth elements, in short supply here and damaging to extract.

So, what are they mainly composed of? There are three main types of asteroids: the C-type are carbonaceous, they are the most common and inhabit the main belt’s outer regions, closer to Jupiter and colder, retaining their water, locked up as ice. The S-type asteroids are silicaceous, rich in silicates such as quartz and granite and also containing nickel, iron and precious metals. The M-types are metal-rich and only make up 5% of asteroids.


One of these, 16 Psyche, is thought to be the exposed iron core of a protoplanet. It is 200kms in diameter and contains an abundance of platinum, gold, titanium and other highly desirable metals. 

NASA has approved a mission that will orbit Psyche for 20 months (launching in 2022) and will study the topography, surface features, gravity, magnetism and other characteristics. A number of probes have already visited and collected data from other asteroids: Ida, Gaspra, and Mathilde, while NASA’s NEAR probe landed on Eros, ESA’s Rosetta probe studied a comet, and its lander module Philae successfully landed but sadly bounced a few times and ended up in a crevice (no-one said it was easy)!

The scientific benefits alone in the course of the 21st century will be immense, as we strive to advance our knowledge, and extend our plans for the manned exploration of the solar system. 

It is of course a timely reminder that all the metals we already mine in the Earth’s crust were delivered to us by asteroids and comets billions of years ago, though much of it is now inaccessible, as gravity pulled these heavy metals down into its molten core. Nonetheless, with a huge reservoir of asteroids out there and with advanced technology it should be possible to process asteroid material into fuel, oxygen and water that would make long-duration missions self-sustaining.

Learning how to move asteroids into more convenient orbits for commercial purposes will give us a great advantage in dealing with the obvious dangers of some of those NEAs that could pose a future threat to our planet itself.

All this of course with the caveat that we haven’t already wrecked the place ourselves. Oh, but wait there is an asteroid, a celestial object known as 2018VP1, projected to come close to Earth the day before the US presidential election vote, on November 2nd. Maybe it could just skim low over the White House, do us a favour, remove a dinosaur, and go back into space.

Ah well, dream on. Back to reality, and that is that the best defence against “asteroid attack” is to simply learn more about them; this knowledge will protect the Earth, inform us better on the birth of the early solar system and in the future offer rich commercial opportunities, hopefully for the benefit of mankind and our planet.


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