1. Other Objects in the Solar System

2. Comets: Structure

3. Comets: Structure
As a comet approaches the Sun ices of water, methane, and ammonia vaporize because of the heat from the sun.
This releases dust and jets of gas.
The gases and released dust for a bright cloud called a coma around the nucleus of the comet.
Solar wind pushes on the gases and dust in the coma, causing the particles to form separate tails that always point away from the sun.

4. Comets: Where do they come from?
Astronomer Jan Oort proposed the idea that billions of comets surround the solar system.
This cloud of comets, called the Oort Cloud, is located beyond the orbit of Pluto.

6. Meteoroids, Meteors, and Meteorites
After comets vaporize and break up after they have passed close to the Sun many times the small pieces from the comet’s nucleus spread out into a loose group within the orbit of the comet.
These pieces of dust and rock , along with others from other sources are called meteoroids.

7. Meteoroids, Meteors, and Meteorites
When the path of a meteoroid crosses the position of Earth they can enter Earth’s atmosphere at speeds of km/s.
Most meteoroids are so small that they completely burn up in Earth’s atmosphere.
A meteoroid that burns up in Earth’s atmosphere is called a meteor.

8. Meteoroids, Meteors, and Meteorites
When a meteoroid is large enough it might not burn up completely in the atmosphere.
If it strikes Earth, it is called a meteorite.
Most meteorites are debris from asteroid collision or broken-up comets.
Barringer Crater
1.2 km in diameter
200 m deep

9. Asteroids
Most asteroids are located in an area between the orbits of Mars and Jupiter called the asteroid belt.
The sizes of the asteroids in the asteroid belt range from tiny particles to objects 940 km in diameter.
Ceres (940 km in diameter) is the largest and the first one discovered.
Vesta (530 km in diameter)
Pallas (522 km in diameter)
10 Hygiea (430 km in diameter)

10. Asteroids

11. Asteroids
Comets, asteroids, and most meteorites formed early in the history of the solar system.
Scientists study these space objects to learn what the solar system might have been like long ago.

12. Dwarf Planets

13. What is a dwarf planet?
The definition of a planet was revised again in According to NASA, the International Astronomical Union (IAU) most recently defines a planet as a celestial body that:
Is in orbit around a star, but is not itself a satellite*
Has sufficient mass so it is nearly spherical in shape*
Has cleared the neighborhood around its orbit*