How do you find out if a planet has possibilities of water and other needed requirements for life to thrive?

Question: How do you find out if a planet has possibilities of water and other needed requirements for life to thrive?
- Keywords:
  life,
  planet,
  water
Asked by Kirsty to Tom on 10 Mar 2015.
- Thomas Barrett answered on 10 Mar 2015:
  
  You can look at a lot of things. Firstly you can look at if the planet is in an area around the star where liquid water is possible some of if not all of the time. This is worked out by how hot and big the star is so has nothing to do with the planet.
  
  Next we have begun to be able to detect atmospheres around some exoplanets (exoplanets are planets not in our solar system) so we can look for water there. Other than that it is really hard without going there. We know lots about Mars and other planets and moons because we have sent spacecraft there.

Question: How do you find out if a planet has possibilities of water and other needed requirements for life to thrive?