In our solar system, Vesta and Ceres are the two largest of which kind of celestial body?
And the answer: asteroids.
Located between Mars and Jupiter, the asteroid belt is where millions of asteroids orbit the sun. The largest asteroid is named Ceres and is about 1,000 km wide, while Vesta is about half that size. Both are still much smaller than the Earth's moon.
Early in the life of the solar system, dust and rock circling the sun were pulled together by gravity into planets. But not all of the ingredients created new worlds. Many of the byproducts of the dawn of the solar system continue to be just that – wayward dust and rock banded together by gravity. The asteroid belt formed initially when the gravity of newly-formed Jupiter brought an end to the formation of planetary bodies in that region. Consequently, the small, leftover bodies of rock began to collide with one another, fragmenting them into the asteroids we observe today.
While asteroids are not usually caught in Earth's gravity or stray too close to our surface, there are a few moments in Earth's history to which we can attribute an asteroid impact event. The most significant of which is known as the Cretaceous-Paleogene extinction event, over 66 million years ago. This event is described as a sudden mass extinction of 3/4 of life on this planet. Scientists believe an asteroid may have been the cause as due to the fact that the metal iridium is present in a thin layer of sediment called the K–Pg boundary, which can be found throughout the world in marine and terrestrial rocks. This metal is rare in the Earth's crust but abundant in asteroids.
Did you know?
The total mass of all the asteroids in the main asteroid belt (between 1.1 and 1.9 million asteroids larger than 1 km in diameter, and millions of smaller ones) combined is less than that of Earth's Moon.
Check out NASA's exploration of these ancient rocks here.