Top 5 stars that may have habitable plants shortlist

Several of the criteria she used were related to age.

For stars to be considered in the shortlist, they had to be at least three billion years old - long enough for planets to form and for complex life to develop.

"Fully-formed advanced civilisations don't just spring up overnight. On planet Earth, it took billions of years for civilisation to arise."

Candidate stars also had to have at least 50% of the iron content of the Sun.