Although asteroids are some of the oldest objects in our Solar System, they were only first discovered in the early 19th century. Since then, millions have been found in various places throughout our celestial neighborhood. Of all these, what is the largest asteroid in the Solar System?
What Is an Asteroid?
An asteroid is commonly thought of as “space rubble” left behind when our Solar System first formed. These small, rocky objects orbit the Sun just as the planets do but are much smaller in size. Most of the time, these cosmic leftovers are not round but rather jagged and irregular in shape. Although having no starry qualities, the term asteroid actually means “starlike.”
Scientists break down asteroids into one of three classes:
- C-Types, known as carbonaceous asteroids, are typically made of clay, carbons, and silicates. C-types are the most numerous asteroids in our Solar System, accounting for some 75% of the total population. They are also some of the oldest rocks out there.
- S-Types, or silicate asteroids, are a combination of silicates and nickel-iron. These account for about 17% of the total asteroids in the Solar System.
- M-Types are mostly metallic nickel-iron in nature. At 8% of all asteroids, we know less about M-types than the other types. Some metallic asteroids that venture too close to the Sun melt into pools of lava.
These asteroids can range from a few feet across to hundreds of miles in diameter. A few of the larger asteroids have even collected smaller ones as moons. There are over a million of these rocky objects cataloged, but scientists are confident there are millions more left to document.
Where Are Asteroids Located?
While there are stragglers throughout the Solar System, most asteroids are located in just a handful of places.
The Asteroid Belt
The Asteroid Belt sits in the gap between Mars and Jupiter and contains the vast majority of the asteroids in the Solar System. It is over twice the distance from the Earth as our planet is from the Sun. The very first object in this belt was discovered in just 1801 and sparked a search that would lead to the discovery of roughly a million more.
Scientists once believed that this belt is the remains of an exploded planet, but more recent discoveries seem to rule out this being the case. All of these individual asteroids together wouldn’t even make up the mass of our Moon, let alone a planet. Thanks to Jupiter’s influence, these pieces of rock are simply kept in the limbo of space.
Much of the information we currently have from this region comes from the Dawn Spacecraft that explored the area from 2011 to 2018.
Trans-Neptunian Objects
On the outer reaches of the Solar System exists the Kuiper Belt. It is a massive ring of ice and debris that starts on the far side of Neptune’s orbit and extends some 25 astronomical units out into space. Pluto is undoubtedly the most well-known object that spends at least a majority of its time in this region.
Pluto is one of three dwarf planets that dot the Kuiper Belt, but there is so much more out there. Being so far from Earth, we’ve barely even scratched the surface of what’s located within. That being said, there are plenty of rocky objects out there that fit the description of asteroids.
NASA’s New Horizons spacecraft is currently out in the region after launching from Earth some 15 years ago.
Beyond even the Kuiper Belt exists the Scattered Disc and finally the Oort Cloud, representing the edge of the Solar System as we know it. One confirmed dwarf planet exists in the Scattered Disc region, and there’s little doubt we will someday count how many asteroids orbit this far from the Sun.
Trojan Asteroids
Trojan asteroids are pieces of cosmic rock that share an orbit with one of our planets. Although they share an orbit, Trojan asteroids are far enough ahead of behind a planet to not get caught in its gravity. With its proximity to the Asteroid Belt, Jupiter has by far the most Trojans with an estimated number of over one million. Only 7000 have been recorded to date.
Neptune has 28 known Trojan asteroids, likely those that floated free of the Kuiper belt. Mars manages nine in its orbit, and a solitary asteroid was discovered traveling in Earth’s orbit just ten years ago.
Repurposed As Moons
While a bit speculatory, it’s likely that at least a few moons floating around our planets were once asteroids. Phobos and Deimos, the two moons of Mars, are very irregular in shape and are some of the smallest in the Solar System. They definitely fit the description of former asteroids.
With the number of moons Jupiter has, it’s probable that the gas giant has stolen at least a few from the Asteroid Belt not too terribly far away. It’s interesting to note that many of Jupiter’s outer moons orbit in the opposite direction that the planet spins, indicating that they were not formed with the planet.
Near-Earth Asteroids
There’s an entire classification of space debris that likes to hang out in space near our planet called near-Earth asteroids. While some don’t ever touch Earth’s orbit, some asteroids cross that imaginary line as they travel around the Sun.
What Is the Largest Asteroid in the Solar System?
A straightforward question, the answer is a little more complicated than you may think.
Ceres
We actually alluded to it earlier, but Ceres is the first object discovered in what’s now known as the Asteroid Belt. It is also the largest at 583 miles (950 kilometers) across. This is nearly double the size of the next largest rock in the belt.
Naturally, it would make sense to classify Ceres as an asteroid. It certainly meets the requirements and would be a C-type. However, things got a little fuzzy with the introduction of dwarf planets in 2006.
Due to its large size, Ceres was included in this list of dwarf planets. It has enough gravity to maintain a nearly spherical shape, something none of the other asteroids in the belt can claim.
To call Ceres an asteroid at this point just doesn’t seem fair. Plus, there are other dwarf planets in the Kuiper Belt bigger than Ceres. If these dwarf planets meet the criteria for one of the asteroid classes, would it then be considered the largest? The best solution should be to let dwarf planets be and look instead at something that can only be called an asteroid.
Vesta
Vesta is the second-largest object in the Asteroid Belt at 336 miles (525 kilometers) in diameter. It is somewhat spherical in shape but lacks some of the smoothness that Ceres has. It is possible that some of these rough edges were formed from the countless collisions the asteroid has experienced over the years.
Vesta has been hit so many times that the asteroid likely came close to shattering at one point in history. Being just over the distance from the Earth as the Earth is from the Sun, a few pieces of Vesta have made their way to the Earth’s surface even within the last 50 years.
Due to its size, Vesta has a definitive set of layers. Cooled lava covers a rocky mantle that houses a core consisting of iron and nickel. It is large enough to occasionally be visible from Earth with the naked eye.
Final Thoughts
Even though there are millions in our Solar System alone, each asteroid has a unique shape and composition. Of these, the largest known asteroids fly through space between Mars and Jupiter. Vesta wins out as the largest asteroid in the Solar System because it simply can’t hold itself together well enough to be considered a dwarf planet.