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Published on May 17th, 2011 | by Yellow Magpie


The Asteroid Belt: Striding Betwixt The Terrestrial And The Jovian


The Asteroid Belt

Sitting in a strange world, lit by our Sun, it is a boundary. A safe-zone between the terrestrial inner planets and the massive gas giants, the Jovian planets. The Asteroid Belt marks the end of the Inner Solar System and the beginning of a strange world, that gets more incredible the farther, and indeed further, one travels.

A World Of Multitudes

The Asteroid belt is a vast place. There are thought to be between 700,000 to 1,700,000 asteroids that are at least one kilometre in width (over half a mile). 200 hundred asteroids are estimated to be a least 100 km in width (62 miles). Unlike in the films where the Asteroid Belt is portrayed as being densely packed with asteroids.

In reality, the distances between individual asteroids is great and objects travelling through Space are very unlikely to collide with an asteroid.

This bewilderingly large place inhabits the area between Mars and Jupiter. Much of the belt is thought to consist of comets. Comets are known to have played a critical role in the development of life on Earth providing both water and some of the complex molecules needed for life.

Here are some of the most interesting objects in the Asteroid Belt. The dwarf planet Ceres will be looked at in more detail next week.

The Asteroid Belt's Near Earth Asteroid Eros

433 Eros

One of the most famous asteroids orbiting the Sun is Eros. At it’s farthest orbit, Eros is 1.78 astronomical units (AU) from the Sun (the Earth is one AU from the Sun).

There are two reasons why this potato-shaped asteroid is relatively famous. The first is because in 2000 and 2001 it was extensively mapped and photographed by the Shoemaker Space probe.

The second reason was because it was the subject of a law-suit over its ownership, which was later dismissed. Gregory Nemitz unsuccessfully argued in court that he had an ownership right over Eros under the homestead principle. Nemitz designated it a spacecraft parking port and wanted to charge NASA rent for parking Shoemaker on it. The court dismissed the claim and refused Nemitz the right to appeal.

Eros is roughly 34 km (21 miles) in length and 11 km (under 7 miles) in width. Because of its non-spherical shape the gravitational pull on Eros is highly varied. It takes the asteroid 1.76 years to make a complete orbit around the Sun.

4 Vesta

Vesta is the largest non-planetary object in the Asteroid Belt. It is considered by some scientists to be the remains of a protoplanet but many others consider it to be an asteroid. Vesta is almost 580 kilometres in diameter (360 miles) however an enormous impact crater in its southern pole means a huge chunk of the asteroid is missing.

Asteroid Vesta

It is believed that Vesta originally had a molten mantle which made its way towards its crust when convection stopped. This reshaped its surface, the only known asteroid which has been reshaped in this manner. Because of its unique reshaping this has led some scientists to classify Vesta as a protoplanet but most agree that it is an asteroid.

Vesta orbits the Sun at 2.57 AU at its farthest, taking 3.63 years to complete one revolution. It’s relatively large size means that Vesta is sometimes visible in the dark night skies in places free of light pollution.

253 Mathilde

Mathilde is a very large asteroid with a dimater of 53 km (33 miles). It orbits the Sun at a distance of 2.65 AU. Mathilde takes 4.31 Earth-years to orbit the Sun.

Like Eros, Mathilde is a C-Type asteroid which means that it is largely composed of carbon. This also has the eerie effect of making it very dark and very little light is reflected back off its surface. It is also the same with Eros. It is thought that the interior of Mathilde is porous due to its low-mass.

Asteroid Mathilde

243 Ida

Ida occupies a special place in the asteroid belt with its satellite moon, Dactyl. This was the first asteroid to be discovered to have a moon. Now we known that asteroids orbiting other asteroids are relatively common.

Ida, like Vesta, is an S-Type asteroid. This means that it is rich in Silica materials. S-Types are composed mainly of magnesium- and iron-silicates. S-Types are the second most common of asteroid after C-Types.

The Asteroid Belt's Ida And Dactyl

The Asteroid belt and comets in particular played, and continue to play, a crucial role in the Solar System. As we learn more and more about this strange world our understanding of the planet we live in, and indeed the evolution of our own lives, deepens. Missions such as Dawn will greatly help us achieve these goals.

Highly Recommended Reading

Check out Yellow Magpie’s The Dwarf Planet Ceres: A Watery Life-Filled World? and The Solar Maximum: The Years The Earth Is Left Defenceless.

You may also like to a gander at The Solar System And Beyond: A Guide To The Cosmos.

Cosmos is a highly recommended book. It contains large, full-page pictures of the asteroids and writing on the subject by the highly competent author, Giles Sparrow.
For people living in Ireland or the United Kingdom, you can access: Cosmos from here.
For those who live in Canada, you can obtain: Cosmos here.
For Germany: Cosmos.
For France: Cosmos.

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