Planets, exoplanets

Universe > Earth's place in the universe, Celestial objects > Planets, Exoplanets 

Planets are celestial objects much smaller than stars that orbit around a star. Their shape is nearly round due to their own gravity but their mass is not high enough to produce their own light (as the stars do). Around our star, the Sun, there are 8 orbiting planets, among them is Earth. Recently several thousand planets have been discovered orbiting around other stars. These planets are called exoplanets and some of them have been found to be residing in the habitable zone of their star, something that means that its possible that liquid water exists in the surface of a terrestrial type planet, and liquid water is a prerequisite for life has we know it.

Connection to Big Idea about energy: Exoplanets emit energy, just like Earth. However, the energy radiated from their central star much higher Thus, is impossible to see exoplanets directly and special techniques should be applied in order to observed and identify exoplanets.   

Connection to Big Idea about forces: All objects in the Universe are attracted to each other via the gravitational force. In our solar system, this force acts to hold the Earth and other planets in orbital motion around our central star, the Sun. Exoplanets are held in orbit around their parent star via the same force.

Connection to Big Idea about evolution: Life has evolved on Earth due to a number of factors including proximity to the Sun, location in the solar system, and the ‘bodyguard’ effect of Jupiter, whose large mass attracts asteroids and comets which might otherwise be in a collision course with the Earth. Life may exist on other exoplanets in the Universe, but special conditions are required for life to develop in the first place. 

Subjects related: Physics, Biology

Age ranges: 17-18