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Rocky Asteroids

Its a cold and empty universe for a single asteroid orbiting the Sun. Asteroids are different from comets. They are like small pieces of planets. Some asteroids that orbit planets are even considered moons. One of the moons of Mars (Deimos) is only four miles across. In our Solar System, you will find asteroids orbiting the Sun in a regular orbit (not like comets, which have stretched elliptical orbits). There is also an Asteroid Belt between the orbits of Mars and Jupiter. The belt holds small pieces of rock that spin around the Sun in a specific orbit. It is almost like a planet that never formed.

Asteroid Structure

Asteroids are made of rocks and metals. Some astronomers consider them to be minor planets (like the moons of Mars and Saturn). Most asteroids are very small but they do have gravity and can affect any objects that come too close. The more iron (Fe) and nickel (Ni) in the makeup of an asteroid, the greater its mass (and gravity). Scientists also use the amount of metal in asteroid classification. Using an infrared sensor, asteroids are classified as light or dark. The lighter ones have more metal than the darker ones.

Traveling Asteroids

Beyond our Solar System, asteroids travel through the galaxy from system to system. These asteroids do not necessarily orbit a star but stars influence their direction and speed. Many astronomers believe that asteroids are pieces from the origins of the universe. Some asteroids were large enough and lucky enough to combine with others and form planets. Some asteroids just continued their existence floating through the universe.

Hitting The Earth

Chances are the Earth doesn't have to worry about a collision with a comet. Asteroids are another matter. Scientists already think that a large asteroid may have hit the Earth when the dinosaurs were alive. That collision may have changed our atmosphere and led to the extinction of the dinosaurs.

We just told you about that asteroid belt just outside Mars' orbit. There may come a day when one of those asteroids drops out of orbit (maybe from a collision with another asteroid) and heads toward Earth. If it is small enough, it will burn up in the atmosphere. Larger ones will hit the surface of the planet. Hundreds of millions of years ago, collisions with asteroids happened more often. Over time, the number of asteroids in the path of the Earth decreased and collisions became less frequent.

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Playing Tag with an Asteroid (NASA/Goddard Video)
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Keywords for Review

Kinetic Energy: The energy of an object related to the motion of the object. On a simple level, an object that is not moving has no kinetic energy. An object that is moving has some amount of kinetic energy. The more an object moves, the more kinetic energy it has. An object increases its kinetic energy if it accelerates and increases its velocity. For example, as you increase the temperature of a gas, the molecules become more energetic and the system has an overall increase in kinetic energy. Kinetic Energy=(0.5)* mass * (velocity)2

Exothermic: A chemical reaction that releases energy after the reaction is complete. The energy is usually released as heat, but it can also be released as light or sound. On a small scale, a burning candle releases light and heat because of exothermic reactions as the wax burns. On a large scale, an explosion might occur when blasting with sticks of dynamite (TNT).

Activation Energy: The least amount of energy needed for a chemical reaction to occur. Reactions often require some amount of energy to get moving. For example, placing hydrogen and oxygen gases in a container will not give you water. There is a certain amount of energy required to get the first reaction going. Catalysts are substances that help to lower activation energies so that reactions can proceed.

Viscosity: A term used to measure the fluidity of a liquid. As the attractions between the molecules increase, viscosity increases. Fluids with high viscosities don’t flow easily. Some substances such as honey or sap are very slow moving and have high viscosities. Other fluids such as water or mercury (Hg) have very low viscosities.

Volatile: Volatility is the likelihood that a substance will vaporize (become a gas). Volatility measurements are all about comparing two substances. Substances with a higher vapor pressure are more volatile. Alcohol is more volatile than water because it evaporates at a lower temperature.

Reference Materials

Encyclopædia Britannica: http://www.britannica.com/EBchecked/topic/369668/matter
NYU.edu: http://www.nyu.edu/pages/mathmol/textbook/whatismatter.html
NASA: http://www.grc.nasa.gov/WWW/k-12/airplane/state.html
NASA: http://astroventure.arc.nasa.gov/teachers/pdf/AV-Astronolesson-Part2.pdf
Wikipedia: http://en.wikipedia.org/wiki/States_of_matter


 
RELATED LINKS
- Cosmos4Kids: Kuiper Belt
- Chem4Kids: Matter
- Chem4Kids: Astrochemistry
- Chem4Kids: Elements
- Geography4Kids: Earth Energy
- Geography4Kids: Earth Structure
- Geography4Kids: Solar Radiation
- Physics4Kids: Gravity
- Physics4Kids: Acceleration
- Physics4Kids: Magnetic Fields
- Physics4Kids: Light

- NASA: Home Page
- NASA: Kids Home Page
- ESA: Home Page
- ESA: Kids Home Page

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