Water: what is a habitable planet?

Subject:

Numerous planets orbiting stars other than our Sun have now been detected in our galaxy ^? , the Milky
Way. These are known as exoplanets. These exoplanets include gas giants similar to Jupiter, Saturn, Neptune and Uranus in our Solar System, as well as much smaller rocky planets (known as telluric planets) like Earth, Mercury, Venus and Mars in our Solar System. This raises the question of whether these small planets, some of which being more or less similar to Earth, can harbour life. What makes a planet habitable? This question is the subject of much debate within the scientific community, since the only example we know of is the planet Earth... Nevertheless, we can legitimately assume that for life – as we know it – to develop, water in its liquid form is an important element. But what are the necessary conditions for liquid water to be present on the surface of a planet?

Level: Primary school
Time: approximately 1 hour

Prerequisites:

• Exobiology
• Habitability

Objectives:

• Learn about the different states of water.
• Learn that the surface temperature of a star determines its colour.
• Position a planet at the right distance from its star so that liquid water can exist on its surface.

Equipment required:

Activity to be carried out in class in groups (ideally groups of 2 students).

For each group of students:

• 1 pair of scissors per student
• 1 pencil or mechanical pencil per student
• 1 pencil sharpener per student
• 1 eraser per student
• 1 glue stick
• 1 A3 sheet of paper
• 1 ruler
• 1 slate
• 1 felt-tip pen for the slate
• 1 eraser for the slate

Subject, Appendices and correction:

• Subject
• Appendices
• Correction

Author : Caroline Barban, LIRA/UFE, Observatoire de Paris