Asteroids are celestial bodies that are present in millions in our solar system, and surprisingly, there are many different types of them. Not only are they found in the asteroid belt, but they also move around in our solar system. In this article, we'll explore some of the most interesting asteroids discovered so far and maybe you can find some with the help of a telescope that is perfect for beginners.
So, what exactly is an asteroid, and how is it different from a comet? An asteroid is a minor planet or a small solar system body. A minor planet is an astronomical term for a small solar system body that is not outgassing, and they are generally rocky or metallic but may contain volatile compounds underneath the surface protected from sunlight. Comets, on the other hand, have volatile materials near the surface, and when they are heated by solar radiation, they produce coma and tails. This distinction between asteroids and comets has existed for over a century. However, the lines between the two are a lot more blurred than previously thought.
The level of activity of a body depends on its distance from the sun. Objects that exist far beyond the orbits of Neptune are inert all year round, but if they were brought close to the sun, they would turn into comets. In this article, we'll only talk about asteroids that have orbits in the inner solar system, between the Sun and Jupiter.
Not all asteroids are the same. There is a difference in size, from dust particles to the biggest known asteroid, which is almost 1000 kilometres in diameter. Asteroids are also classified based on their spectrum or colour, which often indicates what the asteroid is made of. There are three main spectral categories that most asteroids fall into: the C group, which are dark carbonaceous asteroids; the S-type, which are stony or silicate asteroids, and the M-types, which are metallic asteroids.
Now, let's take a look at ten of the most interesting asteroids you will ever read about...
2005 VX3
It is the minor planet with the largest aphelion that we know of. At its closest approach to the Sun, it's only 4.1 AUs, which is inside the orbit of Jupiter. But when it's furthest away, it has a massive estimated heliocentric distance of 3000 AUs from the Sun. Because of this, it is estimated to have the largest orbital eccentricity of any known minor planet. It could well be a dormant comet that has not seen outgassing. It is estimated to be about seven kilometres in diameter.
433 Eros
433 Eros is an asteroid that was discovered in 1898 by Gustav Witt and Auguste Charlois. It is an S-type asteroid, which means that it has a composition that is similar to that of stony meteorites. Eros is known for being the first asteroid to be orbited and landed on by a spacecraft, the NEAR Shoemaker, which arrived at the asteroid in 2000. The NEAR Shoemaker orbited Eros for a year, during which time it took detailed measurements and images of the asteroid's surface. The spacecraft also made a soft landing on Eros in 2001, becoming the first spacecraft to land on an asteroid. Eros is relatively small, measuring only 34.4 kilometres long and 11.2 kilometres wide, and it has an irregular shape.
99942 Apophis
This is a near-Earth asteroid that caused a bit of a stir in December 2004 because the initial observations indicated a probability of about 2.7 that it would hit Earth on April 13th, 2029. However, additional observations improved the asteroid's predicted orbit, which eliminated the chance of a collision in 2029. Apophis did, however, set the record for the highest rating on the Torino scale, reaching a level four at one point. Had it hit Earth, the estimated kinetic energy would have been about 750 megatons, 13 times more powerful than the largest hydrogen bomb ever exploded. The most recent observation of it in 2013 estimated the asteroid to be about 325 meters across.
25143 Itokawa
This is a Mars-crossing asteroid. It was the first asteroid to be the target of a sample return mission accomplished by the Japanese space probe Hayabusa. It is the smallest asteroid ever to be photographed by a spacecraft, being only 500 meters across at its longest point. It is an S-type asteroid, but it may be a contact binary, which means it would effectively be two separate asteroids that have merged over time.
162173 Ryugu
162173 Ryugu is a near-Earth asteroid that has garnered significant attention due to its close proximity to our planet and its potential as a research target. It was discovered in 1999 and has since been studied by various spacecraft missions, including Japan's Hayabusa2 mission, which successfully collected samples from Ryugu's surface in 2019. Ryugu is approximately one kilometre in diameter and has a unique diamond-shaped appearance, with a flattened top and bottom. Its surface is rocky and contains a variety of minerals, including water and organic matter, which make it an important target for scientific exploration.
16 Psyche
This massive metallic asteroid is located in the asteroid belt between Mars and Jupiter. It's about 226 kilometres in diameter, making it one of the largest asteroids in the belt. But what makes 16 Psyche truly unique is its composition. It's composed mostly of metal, specifically iron and nickel, making it a potentially valuable target for future asteroid mining missions. Some estimates suggest that the asteroid's metal content alone could be worth over $10,000 quadrillion. NASA is planning to launch a mission to 16 Psyche in 2025, which will study the asteroid's composition, history, and geology. The mission will also provide valuable insights into the formation and evolution of our solar system.
Bennu
Bennu is a near-Earth asteroid and the target of NASA's OSIRIS-REx mission, which launched in 2016. The mission's objective is to study Bennu's composition and return a sample to Earth. The asteroid is about 500 meters in diameter and is classified as a B-type asteroid, which means it's rich in carbon and likely contains organic molecules. Bennu is also considered a potentially hazardous asteroid, meaning it has a non-negligible chance of colliding with Earth in the future. However, the OSIRIS-REx mission will provide valuable information about the asteroid's orbit and composition, which will help scientists better understand how to mitigate the threat of asteroid impacts.
243 Ida
243 Ida is a small asteroid in the inner solar system that was discovered in 1884. It is about 2.4 kilometres in diameter and is a member of the Koronis family of asteroids. In 1993, the Galileo spacecraft flew by Ida and discovered a small moon orbiting it, which was named Dactyl. This was the first time a moon had been discovered orbiting an asteroid. Ida is also notable for its irregular shape and the presence of a large impact crater on its surface, which is thought to have been formed by a collision with another asteroid. The study of asteroids like Ida is important because they can provide valuable information about the early solar system and the formation of the planets.
Ceres
Ceres is the largest object in the asteroid belt, with a diameter of about 940 kilometres. However, it's not classified as an asteroid but rather a dwarf planet. It's also the only dwarf planet in the inner solar system. Ceres is unique because it's believed to contain a significant amount of water ice, possibly even a subsurface ocean. It's also rich in minerals such as clay, carbonate, and ammonium salts. In 2015, NASA's Dawn mission became the first spacecraft to orbit and study Ceres, providing valuable insights into its composition and geology.
Oumuamua
Finally, we have Oumuamua, the first interstellar object detected passing through our solar system. Oumuamua was first discovered in 2017 and caused quite a stir among astronomers and the public alike. Its unusual shape and trajectory sparked speculation that it could be an alien spacecraft, but subsequent observations revealed that it was likely a natural object. Oumuamua's exact nature is still somewhat of a mystery, but it's believed to be a rocky or icy body with a highly elongated shape. Its origins are also uncertain, but it's thought to have been ejected from its home star system and travelled through interstellar space for millions of years before passing through our solar system. Oumuamua's visit provided a rare opportunity for scientists to study an object from another star system and learn more about the nature of interstellar objects.
Asteroids are fascinating objects with a wide variety of sizes and compositions. From potentially valuable metal-rich asteroids to potentially hazardous near-Earth asteroids, these objects provide valuable insights into the formation and evolution of our solar system. And with ongoing and planned missions to study these objects up close, we can expect to learn even more about them in the years to come. I've only mentioned 10 today but there are so many more to discover for yourself and we have only just scratched the surface of them in this article, so I would love to hear your thoughts and knowledge in the comments below.
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