Jawaban:

1. Earth is the third planet from the Sun and the only one in the outer solar system to be in the habitable zone. It is by far the most Earth-like of all the terrestrial planets. Earth-like can be a difficult term to define. According to NASA, "the term planet Earth is used to describe a planetary body that is in many ways similar to Earth. Some scientists refer to the planet Earth, the Earth, or more specifically to the Earth-Moon system." The definition can vary from one to an infinite number of Earths. Earths are usually planets, but an astronomical body may also be referred to as an Earth-like planet if it can, in some way, be similar to the Earth.  

The term "Earth-like" is often used to describe planets, moons, and asteroids that are in the habitable zone of a star. It is a term also used to describe planets, moons, and asteroids that are orbiting in the same plane as the Earth orbits the Sun.

2. Comet is rocky material ejected from the Sun, made up of mainly silicon and oxygen with a little carbon and other elements. When it is in our outer Solar System it is a loose, dirty, grainy object with a strong electric current flowing through it. Comet is a leftover from when the Solar System formed 4.5 billion years ago. Comet consists of material that formed a disk around the young Sun. As Comet heated up and grew older it pushed against the other objects in the disk until it exploded away. Some astronomers classify comets as planets. The orbits of the planets are inclined to the Earth's equatorial plane, so a comet in an inclined orbit comes closer to the Earth than a comet in a nearly-equatorial orbit.

3. Solar system is a unique planetary system that has two suns (planets) that revolve around each other (tidally locked) and the planets that revolve around one of the suns (the other sun being a white dwarf, a stellar corpse). Due to this unique circumstance and in order to prevent a gravitational tidal lock, the planets (or moons) have to keep moving around the two suns. Also to prevent the planet (or moon) from getting too close to one of the suns (or moons), they have to move away from the sun (or moon) (and sometimes even the other planet) with very high speeds, like in the case of Uranus. This is how Pluto got to move away from the sun (the other sun being the Sun). However, there is a caveat in the entire process. The Earth has to orbit the Sun. But in the case of the Solar System, both the Sun and the Earth have to move along with the planets (and the moon, if there is a moon), which seems impossible.