Asteroids

Comets
Asteroids 2020
Asteroids

By Aparna Kher

Asteroids are small, atmosphere-less rocky objects orbiting the Sun. Here are 10 things that you might not know about these planet-like celestial bodies that can crash into the Earth and create havoc.

Jul 15, 2014 Asteroids are rocky objects primarily found in the asteroid belt, a region of the solar system that lies more than 2 ½ times as far from the Sun as Earth does, between the orbits of Mars and Jupiter. These objects are sometimes called minor planets or planetoids. Play the classic Asteroids game online. NASA.gov brings you the latest images, videos and news from America's space agency. Get the latest updates on NASA missions, watch NASA TV live, and learn about our quest to reveal the unknown and benefit all humankind.

Asteroid, any of a host of small bodies, about 1,000 km (600 miles) or less in diameter, that orbit the Sun primarily between the orbits of Mars and Jupiter in a nearly flat ring called the asteroid belt. Hundreds of thousands of asteroids are known.

1. They were Created at the Same Time as the Earth

Many astronomers believe that asteroids are rocky leftovers from the formation of the Solar System 4.6 billion years ago. One theory is that after the Big Bang, dust particles came together to form celestial objects through a process called accretion – smaller objects came together with other small objects, creating larger space rocks. Some of these celestial rocks were able to grow large enough to develop their own gravity and became planets. Many others were held back from getting together by Jupiter's gravitation force. These became asteroids.

Because they revolve around the Sun like planets do, asteroids are also sometimes called planetoids or minor planets.

2. Most are Found in One Area

Of the millions of asteroids that inhabit our solar system, a majority can be found in a region between the orbits of Mars and Jupiter. This region is called the Asteroid Belt.

3. ...A Very Lonely Area

Imagining the Asteroid Belt as in the movies – a small strip of space littered with huge rocks intent on mowing down your space ship?

Well, imagine again because the Asteroid Belt is nothing like that. In fact it is a very lonely place for an asteroid. Astronomers estimate that the average distance between two asteroids in the asteroid belt is about 600,000 miles (966,000 km). This is about 2.5 times the distance between the Earth and the Moon. That is a lot of space between two neighboring asteroids!

4. Not all of Them Reside in the Belt

While most of the known asteroids live in the Asteroid Belt, there are many that orbit the Sun outside this belt. For example, Trojan Asteroids, named after the Trojan Wars in Greek Mythology, follow the orbits of a planet. Jupiter has two clusters of Trojans following its orbit around the Sun – the one ahead of the planet is called the Greek Camp and the one behind is known as the Trojan Camp.

In 2010, scientists discovered the first Trojan Asteroid, 2010 TK7, that follows the Earth's orbit.

Asteroids that are pushed close to the Earth’s orbit are known as Near Earth Asteroids.

5. They Come in Different Sizes

Asteroids can measure anywhere between a few feet to several hundred miles in diameter. The largest asteroid known to man, Ceres, is about 590 miles (950 km) in diameter.

Astronomers estimate that if all the asteroids in the Solar System were put together, the size of the resulting rock will be much smaller than our Moon!

6. And Yet, some Asteroids have Moons

About 150 Asteroids are known today to have one or more moons orbiting them. The most famous of these is Dactyl, a small moon orbiting Ida, an Asteroid Belt asteroid.

7.They can be Classified According to their Composition

Most Asteroids fall into one of three groups based on their composition: C, S and M types. The composition is determined by how far the asteroid was from the Sun during the time of its formation.

About two-thirds of all asteroids are thought to be C type asteroids. These asteroids are very dark, with an average albedo of about 0.06 and are thought to have a similar composition as the Sun. They can be found in the outer regions of the Asteroid Belt

S type asteroids are considerably brighter with an average albedo of 0.16. These asteroids are usually found in the inner regions of the Asteroid Belt and are composed of iron and magnesuim silicates.

M type asteroids can be found in the middle of the Asteroid Belt and are much brighter than an average albedo of 0.19. These are mostly composed of Iron.

8. ...This makes Asteroids Attractive to Miners

Asteroid mining? That is no longer in the realm of science fiction. Asteroids are rich sources of metals like Iron, Platinum and Titanium, metals that humans use daily to build and create things. In addition, scientists believe that water present on the surface of these asteroids could be broken down and used as fuel for space vehicles.

While asteroid mining hasn't started yet, many companies around the world have started exploring the idea seriously.

9.Close Encounters of the Asteroid Kind

The Earth's atmosphere acts as a shield protecting us from meteoroids and other objects that populate space. When a meteoroid enters the atmosphere, it usually burns up before hitting the surface of the Earth. If any part of the meteoroid survives and hits the surface of the Earth, it is called a meteorite.

Sometimes however larger space objects collide with the Earth's atmopshere and impact the surface of the Earth. Scientists have identified about 100 sites on Earth that may have been impacted by a large asteroid or comet.

While no humans have been killed due to a meteorite in recent history, there is some worry among the scientific community about the possiblity of a large asteroid impact and the effect it may have on human life.

10. An Asteroid may have Killed the Dinosaurs

In fact, there is a theory prevalent among the scientific community that it was an asteroid that wiped out the dinosaurs. Many scientists believe that the epicenter of the mass extinction of the dinosaurs lies in the Chicxulub Crater, an impact crater that was discovered under the Yucatán Peninsula in Mexico.

Browse and discover detailed information about 79 of the most interesting asteroids and dwarf planets. Objects are listed in order of decreasing brightness.

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