Asteroids are celestial bodies that are too small to be considered planets. An asteroid is mostly made up of carbon, rock, or metal. Asteroids are also known as planetoids or minor planets. Most of us recognize asteroids from the phenomenon called asteroid crash. A number of asteroids have hit earth in the past and there is a possibility of suffering the same consequences in the future. The reason why the study of asteroids is important to us is that it allows us to predict this collision. Asteroids were formed 4.5 billion years ago during the formation of our solar system. According to NASA, currently, 1,041,080 asteroids known to us. The total mass of all the asteroids combined is less than the earth’s moon. Most of the asteroids are found in the main asteroid belt that is located between the orbit of Mars and Jupiter. Some asteroids are able to escape and overcome the main asteroid belt and enter the earth’s orbit. They are known as Near-Earth asteroids (NEAs).
Types of Asteroid
C-group, carbonaceous, or the chondrite asteroids, are the most common asteroids. About 75 percent of the total known asteroids fall into this category. These types of asteroids are dark-colored and rich in carbon. Most of them contain clay and silica. C-group asteroids are considered to be the oldest celestial objects.
The asteroids belonging to the s-group are most commonly known as stony or silicaceous asteroids. Approximately 15 percent of the total asteroids lie in this group. They are stony and bright in color. The s-group asteroids consist of silicate material and nickel-iron.
This group of asteroids consists of the rare asteroids that are mainly composed of metallic elements. About 8-10 percent of total asteroids fall into this category. The m-group asteroids are brighter than the c-type. They are mostly found in the middle region of the asteroid belt. They are made up of nickel and iron.
Ceres is the only dwarf planet in the inner solar system. It was discovered in 1801 by Italian astronomer Giuseppe Piazzi. It was first identified as a planet but was later downgraded to the category of dwarf planets. Ceres is the largest celestial body present in the main asteroid belt. Ceres is round in shape.
2. Earth-crossing asteroids
The asteroids that cross the earth’s orbit during their revolution around the sun are known as Earth-crossing asteroids. The Aten and Apollo are the subcategories of Earth-crossing asteroids. Most of the asteroids crossing the earth’s orbit are about 1 km in diameter. These asteroids sometimes encounter collisions with the earth causing massive environmental losses and climatic imbalance. For example, the end of the Cretaceous period, and the eradication of all the species of dinosaurs.
Eros was discovered in the year 1898 by German astronomer Carl Gustav Witt. It is the first-ever known Near-Earth asteroid. It is an s-type asteroid that is mainly found to travel inside the orbit of Mars. Eros is the first asteroid to be orbited and landed on by a spacecraft. A spacecraft called NEAR Shoemaker prepared by NASA was made to enter the orbit around Eros in the year 2000. It landed on Eros in the year 2001.
It is one of the Earth-crossing Apollo asteroids. Geographos was discovered on September 14, 1951, by American astronomers Albert Wilson and Rudolf Minkowski at the Palomar Observatory. The surface of geographos is mainly composed of stony-iron meteorites. The diameter of geographos is approximately 2.56 km, which is larger than 90% of the existing asteroids. It is primarily composed of magnesium silicate and iron silicate.
Hathor belongs to the class of Aten asteroids, which is a subclass of near-Earth asteroids. It was discovered on October 22, 1976, by C. T. Kowal. The albedo, which is the amount of radiation sent back to space by any object, of Hathor is 1. The diameter of Hathor is about 0.3 km. It is classified as one of the potentially hazardous asteroids.
It was discovered on October 28, 1937, by German astronomer Karl Wilhelm Reinmuth. It crosses the earth’s orbit after every 777 days and also suffers frequent encounters with the planet venus. The name Hermes is influenced by a greek olympian god for its fast motion. The discoverer was only able to observe Hermes for 5 days. These many days are highly insufficient to perfectly record the orbit. Hence, due to the fast speed, it got lost and was rediscovered 66 years later.
Icarus is placed under the group of Apollo asteroids. It is also one of the potentially hazardous asteroids. Icarus holds a record of being one of the asteroids to approach the sun closely for a number of decades. It moves in an elliptical orbit. It is around 1 km in diameter and larger than 97% of the existing asteroids.
On March 28, 1802, Wilhelm Olbers, a German astronomer and physician, discovered the Pallas asteroid; almost a year after the successful discovery of the largest asteroid Ceres. It is the third-largest asteroid seen in the main asteroid belt. It is ellipsoid in shape and has a diameter of about 15% that of the moon, which is equal to 545 km. There are a number of hydrated minerals present on the surface of the Pallas. The detailed image of the Pallas asteroid shows that its structure is similar to a golf ball. The structure of the Pallas comprises of a combination of water, ice, and silicates.
9. Trojan Asteroids
Asteroids that are located on the leading and the trailing edge of Lagrangian points and share their orbit with a planet are known as trojan asteroids. Most of Jupiter’s Trojans are dark in color. The albedos of trojan asteroids, which is the amount of light reflected back, lies in between 0.04 and 0.10. The search for Saturn’s trojan asteroids is currently (as of 2021) going on.
Vesta is one of the largest asteroids with a diameter equal to 525 km. It was discovered by the German astronomer Heinrich Wilhelm Matthias Olbers on 29 March 1807 and is named after Vesta, the virgin goddess of home and hearth from Roman mythology. Vesta is considered to be the brightest asteroid. Sometimes, it is possible to see Vesta from the earth through naked eyes. It has dark and light patches on its surface that are very much similar to the Earth’s moon. The structure of Vesta has an outer rock covering and an iron-nickel core.