Cold, airless, lifeless chunks of rock floating through the vast expanse of space. This is the image that most people conjure up in their minds when they think about asteroids. However, there’s far more to these minor planets than might meet the eye. They’ve been instrumental in the formation of our solar system, our planet and even the course of the evolution of life itself. They may also one day become an essential source of resources for future generations.
Asteroids are important to humanity for a multitude of reasons, and the world’s space agencies are very much aware of this. Only last week, on January 4, 2017, NASA announced the selection of two missionsto explore some of the 1.3-million plus known asteroids in the solar systems. Scheduled for launch in October, 2021, robotic spacecraft Lucy will explore six of the Trojan asteroids that share Jupiter’s orbit around the Sun, while Psyche will explore asteroid 16 Psyche in the asteroid belt.
How Asteroids Differ from Planets and Other Bodies
With the exception of Ceres, asteroids are not massive enough for gravity to pull them into spheres, hence the fact they are irregularly shaped like 243 Ida depicted in this photo. Remarkably, however, this particular asteroid has a tiny one-mile-wide moon named Dactyl!
Asteroids form a broad subcategory of minor planets, but they are most often associated with the Asteroid Belt spanning a huge area of space between Mars and Jupiter. By their simplest definition, asteroids refer to celestial bodies that are too small to be described as dwarf planets or planets. With the sole exception of Ceres, none of the asteroids are massive enough to reach hydrostatic equilibrium, meaning that their gravity is too weak to pull them into spherical shapes.
Ceres is by far the largest asteroid to the extent it’s perhaps better described as a dwarf planet. With a diameter of 587 miles (945 km), it accounts for about a third of the entire collective mass of all the millions of objects in the Asteroid Belt. Owing to its relatively enormous size, it was the first asteroid discovered, by Italian astronomy Giuseppe Piazzi in 1801. Since then, countless more have been found, shedding profound insights into the formation of our solar system.
The smallest asteroids are as little as three feet (1 metre) across. Any object smaller than this is typically referred to as a meteoroid or, when it interacts with our atmosphere, as a meteor. Asteroids should not be confused with comets, which are icy bodies that produce a stream of water vapour and other gasses when they are at their closest to the Sun. However, comets, despite being far fewer in number, have also played an important role in the evolution of the solar system.
How Asteroids Help Us Understand the Formation of the Solar System
An artist’s impression of the one of two asteroid belts in the Epsilon Eridani solar system some 10.5 light years from Earth. With the right gravitational conditions, an asteroid belt such as this can form a protoplanetary disk that may eventually lead to the formation of rocky terrestrial planets.
Owing to their incredibly diverse nature, it’s not easy to define asteroids based on composition alone. Some are made largely of iron and nickel, while others, such as Ceres, appear to consist of a rocky core covered by vast amounts of water ice. More precisely what asteroids are made of remains shrouded in mystery, with most of what we know being down to educated guesswork based on observations of the reflectivity (albedo) of their surfaces.
Some 4.6-billion years ago, our solar system consisted of a chaotic primordial soup in the form of a protoplanetary disk rotating around a young star. Heavier elements, such as iron, came together to form the first meteoroids, asteroids and comets. Areas with higher concentrations of these fundamental building blocks saw much larger amounts of material came together, bound by gravity, to form the terrestrial planets such as Earth.
Asteroids represent the left-over building blocks from the formation of the planets. However, since those far-off times, they have diversified enormously, owing to countless collision events over the aeons. Vesta, the second-most massive asteroid, for example, may actually be the left-over core of a failed protoplanet, as indicated by its crust of solidified lava. Ceres, on the other hand, may even have a subsurface ocean, indicating that asteroids, perhaps along with comets, could have brought water to the early Earth.
Asteroids as Givers and Takers of Life
Asteroids have profoundly changed the course of evolution several times throughout the course of Earth’s history, namely with the extinction of the dinosaurs 66-million years ago. However, some impacts, such as that which may have created the Moon, are great enough to completely resurface a planet or even break it up altogether.
How life on Earth ultimately arose from non-living organic matter, perhaps as far back as the Hadean Aeon over 4-billion years ago, remains one of the greatest cosmic mysteries of all. However, it’s a question that the exploration of asteroids might just be able to answer. Many asteroids, such as Hygiea and Pallas, sport similar chemical compositions to those of the early Earth. In other words, the carbon-based organic compounds that gave rise to life may well have come from asteroids hurtling into the young Earth during the Late Heavy Bombardment of the Hadean.
It’s a universal rule in the world of evolution that that which destroys also creates. Impact events caused by asteroids have without a doubt have played a profound role in shaping the course of evolution. No occurrence throughout the history of our world was so perfectly representative of this fact than the impact that wiped out the non-avian dinosaurs 66-million years ago. This event, which ultimately killed off almost everything larger than a breadbox, also opened up a biological niche in that our mammalian ancestors would come to dominate.
How Asteroids Are Important for the Future of Humanity
Asteroids contain many valuable elements and minerals, making them prime targets for future mining expeditions. This painting illustrates how using solar panels to power the exploration and mining equipment of a near-Earth asteroid could make such an industry economically viable.
Exploration of the asteroids remains a top priority for NASA, hence the recent approval of the aforementioned robotic missions in the coming years. However, while it is now beyond a doubt that asteroids have been instrumental in the formation of the Earth and, consequently, life itself, they may also prove important for the future continuation of human civilisation. Asteroid mining, for example, represents a promising solution to our ever-increasing need for resources.
Although asteroid mining has been a hot topic in the world of science fiction for more than a hundred years, we’re closer than ever before to it becoming a reality. Several private companies, such as Planetary Resources and Deep Space Industries, have already arisen in recent years with the sole purpose of exploiting the financial potential offered by asteroids. Two sample return missions, NASA’s OSIRIS-REx and Japan’s Hayabusa 2, are already underway, and although their focus is not on economic issues, their findings may prove essential for the development of asteroid mining as an industry.
Currently at the top of the list of the most valuable asteroids, according to Asterank, is Ryugu, which the Hayabusa 2 probe is due to reach in July, 2018. Despite being only about 3,200 feet (1 km) in diameter, the rock is estimated to be worth $82.76 billion, owing to its composition of nickel, iron and cobalt. Unfortunately, however, we’re still a long way off finding an economical way to extract the ore and return it to Earth, the costs of which currently far outweigh the market value of the materials.
While asteroids will likely prove themselves valuable sources of precious minerals once we figure out how to make mining them cost-effective, they may one day play an even greater role in the lives of future generations. Among the more exotic of predictions concerns the possibility of using larger asteroids as the hulls for space stations, as proposed by science fiction author Isaac Asimov. After all, there is more than enough material in the average asteroid to build a vast floating city in space.
While asteroids are also known to be bringers of destruction, they’ve also played a crucial role in the evolution of our solar system and our species. One day, they will also play an invaluable role in our future prosperity and the sustainability of human civilisation. In fact, back in April, 2010, U.S. President Barack Obama announced a goal to send astronauts to one by 2025, while privately funded companies are also jumping on the bandwagon.