During the early stages of our solar system, dust and rock that circled the Sun consolidated into planets due to gravity’s pull. However, not all materials formed new worlds. A swath of space between Mars and Jupiter became known as the asteroid belt.
In the 18th century, German astronomer Johann Titius observed a unique pattern in the arrangement of the planets. Using this pattern, he anticipated the presence of a planet between Mars and Jupiter. Eager to find this missing world, 24 astronomers united in 1800, calling themselves the Celestial Police. Despite their efforts, the first celestial body in that region was identified by someone outside the group: Italian astronomer Giuseppe Piazzi, who named it Ceres. Just over a year later, another body, Pallas, was discovered.
Initially, Ceres and Pallas were labeled as planets. However, as more objects were uncovered in the same region, numbering over 100 by the 19th century’s onset, it became evident that they were too diminutive to be planets. These celestial bodies earned a new name: asteroids.
The asteroid belt between Mars and Jupiter, and the trojans. Credit: ESA/Hubble, M. Kornmesser
Some have speculated that the asteroid belt was once a planet that either got destroyed or failed to form. Yet, NASA states that the belt’s total mass is less than our Moon’s, making it too light to have been a planet.
Contrary to popular belief, the asteroid belt consists mainly of empty space. The average distance separating these asteroids is about 600,000 miles (around 1 million km). Hence, spacecraft can journey through the belt without crashing into any asteroids.
The asteroid belt is home to a vast range of sizes. It holds between 1 to 2 million asteroids more than half a mile (around a km) in diameter. Beyond these, there are likely billions of smaller asteroids, with some as tiny as pebbles. Piazzi’s discovery, Ceres, is the biggest body in the belt, spanning about 587 miles (945 km). Later on, the International Astronomical Union redefined Ceres as a dwarf planet. This means Vesta, with a diameter of approximately 329 miles (530 km), is now considered the largest asteroid in the belt.
Dwarf planet Ceres. Credit: NASA/JPL-Caltech
Located between Mars and Jupiter, the main belt stretches about two to four times the distance from Earth to the Sun. While the majority of asteroids in this belt consist of rock and stone, a minor fraction has iron and nickel metals. The rest comprise a combination of these materials and carbon-rich substances. Some distant asteroids even possess ice. While they can’t sustain an atmosphere, evidence suggests some asteroids hold water.
In addition to these, there are the trojans. These asteroids coexist in the same orbit as a bigger planet, yet they avoid collisions. They achieve this by clustering at two specific points in the orbit. Here, the planet and Sun’s gravitational forces counterbalance the trojan’s natural drift. Among these, the Jupiter trojans are the most prevalent, believed to rival the asteroid belt in number. Trojans are also associated with Mars and Neptune. In 2011, NASA reported the discovery of a trojan accompanying Earth.
Overview of the Inner Solar System asteroids
Interestingly, the orbits of asteroids can be influenced by Jupiter’s potent gravitational force and sporadic close brushes with Mars or other celestial bodies. Such interactions can eject asteroids from the main belt, sending them scattering through space and across other planets’ orbits. In the past, these wandering asteroids have impacted Earth and other planets, reshaping geological histories and influencing the course of life on Earth. Scientists constantly track asteroids nearing Earth to safeguard our planet.
Looking ahead, there’s potential for humans to mine the asteroid belt. It’s abundant with resources like precious metals, minerals, and volatiles. These could be used for construction and fuel in space or transported back to Earth.
Words of wisdom
“You can, you should, and if you’re brave enough to start, you will.” ―Stephen King
“If you wish to make an apple pie from scratch, you must first invent the universe.” ―Carl Sagan, Cosmos
“To summarize the summary of the summary: people are a problem.” ―Douglas Adams, The Restaurant at the End of the Universe
“The question is not what you look at, but what you see.” ―Henry David Thoreau