How Big Are the Largest Known Asteroids?

Ceres (bottom left), the Moon and Earth, shown to scale.
Ceres (bottom left), the Moon and Earth, shown to scale.

Asteroids are bodies of rock of varying sizes that orbit around the sun. Large numbers are found in the appropriately named asteroid belt, which is a circle shaped ring located between Mars and Jupiter. Asteroids are thought to be fragments of celestial objects produced during the formation of the solar system. The sizes of asteroids are measured by using infrared light as that gives a better estimate of the real size of an asteroid as opposed to visible light. When an asteroid is hit by sunlight, it radiates back some of that as infrared light. Scientists observing the asteroid can then use the amount of infrared light reflecting back as a way to determine the size of its surface area. Asteroids can range in size from tiny pebble sized particles to massive chunks of rock.

The Five Biggest Asteroids

5. 31 Euphrosyne

31 Euphrosyne is the fifth most massive asteroid found so far in the asteroid belt and has the twelfth largest diameter. It has a primitive surface and a C-type (carbonaceous) asteroid, which is the most common type. Being a C-type means it is very dark and is depleted on hydrogen, helium, and other volatiles. Its orbit is tilted, which is unusual. Its orbit also has a high inclination and eccentricity to it. It was discovered in 1854 by Scottish-born American James Ferguson and was the first asteroid found from North America.

4. 10 Hygiea

10 Hygiea is the fourth most massive asteroid found so far in the asteroid belt and also has the fourth largest diameter. It is also a C-type asteroid, like 31 Euphrosyne, and is the largest class C-type asteroid found. Evidence indicating that the asteroid had ice water in the past has been found on the celestial body. It has a oblate spheroid shape and a relatively low density. It was discovered in 1854 by Italian Annibale de Gasparis.

3. 2 Pallas

2 Pallas is the third most massive asteroid found so far in the asteroid belt. It also has the third largest diameter and is the third brightest asteroid as seen from Earth. Based on observations its surface is likely composed of silicate materials containing little water or iron. Its orbit is unusually highly inclined, and its orbital is eccentrically great. It is thought to have been a protoplanet due to the fact that it seems to have undergone some thermal alteration and partial differentiation (forming layers). It was discovered in 1802 by German scientist Heinrich Wilhelm Matthias Olbers and was the second asteroid to be discovered.

2. 4 Vesta

4 Vesta is the second most massive asteroid found so far in the asteroid belt. It also has the second largest diameter and is the second brightest asteroid as seen from Earth. Its orbit is moderately inclined and eccentric, and it has a relatively fast rotation for an asteroid. Its density is lower that of Mercury, Venus, Earth, and Mars but higher than most asteroids and all moons, except Io. It is thought to have a metallic iron-nickel core, with a rocky olivine mantle and a rocky crust. It is also a considered a protoplanet by many scientists. It was also discovered by Heinrich Wilhelm Matthias Olbers in the year 1807.

1. 1 Ceres

1 Ceres is the heaviest asteroid ever found in the asteroid belt. It has the largest diameter and is the fourth brightest asteroid as seen from Earth. Ceres is also a possible protoplanet and is so large that it is considered a dwarf planet, like Pluto. It is the largest minor planet in Neptune's orbit and the 33rd largest known object in the solar system. It is also the only object in the asteroid belt to be rounded by its own gravity. Its core is rocky, and its mantle is icy. It is speculated that Ceres may have an internal ocean of liquid water under its icy mantle and emissions of water vapor have been detected for it, which is very unusual for a large asteroid. Its surface is broadly considered to be similar to that of a C-type asteroid, but it has spectral features of carbonates and clay are absent in other C-types. This fact leads some to classify it as a G-type asteroid instead. It was discovered in 1801 by Italian scientist Giuseppe Piazzi and was the first asteroid to be discovered.

The Dangers Of Asteroids To Earth

Since the early days of the Earth, asteroids have been hitting our planet, and they continue to be a major threat to life on Earth. A section of scientists claims that asteroids wiped out the dinosaurs around 66 million years ago and are a constant yet distant threat to humans. Most asteroids are too small to do any damage to the planet or do not have an orbit that crosses paths with Earth. However, the asteroids that are big enough could be able to do damage that ranges from wiping out a city to causing a global mass extinction events. Scientists and government programs have been set up around the world that are dedicated to detecting and tracking near-Earth asteroids that would be large enough to cause major damage to the planet. While the odds of a major asteroid impacting Earth are low, we must be vigilant in finding them because if a major asteroid did hit Earth is would be devastating for humanity and the planet.

The Most Massive Asteroids Known To Man

RankName of asteroidMass (×1018 kg)Approx. prop’n all asteroids
11 Ceres939.331%
24 Vesta259.08.6%
32 Pallas201.06.7%
410 Hygiea86.72.9%
531 Euphrosyne58.11.9%
6704 Interamnia38.81.3%
7511 Davida37.71.3%
8532 Herculina33.01.1%
915 Eunomia31.81.1%
103 Juno28.60.95%

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