'Red giants' are evolved giant stars of 1000 times the volume of the Sun and with a surface temperature of 2,500 to 3,500 °C. In about five billion years, the sun will become a red giant and the planets that are the closest to the Sun (including Earth) will be burnt away.

A recent survey of red giant stars that host planets showed that giant alien worlds may form far more readily than previously suspected. It is a well known fact that planets are found much more commonly around stars like our sun that are rich in iron and other metals which conduct to the idea that such elements played an important role in planet formation. The new study found but little traces of metals in the red giants, fact which suggests that large amounts of metals aren't necessary for the planet formation.

Alan Boss, a planetary scientist at the Carnegie Institution of Washington and a champion of an alternative, low-metal theory of planet formation explained that "For all we know now, habitable Earths can form around almost every single type of star".

"Actually - he continued - the minimum amount of metal needed for planets to be born might be far lower than commonly believed." Red giants occur when certain stars exhaust their principal source of fuel, namely hydrogen. These dying stars will gulp at least some of their planets during expansion.

Why is it so interesting for us to know if giant planets such as Jupiter, Saturn, Uranus, and Neptune can form around a star with little metal? There's a clear answer to this question: in the next billion years our own sun will also run out of hydrogen and become a red giant.

Alex Wolszczan, an astronomer at Pennsylvania State University explained that "for me, the main motivation is to actually see what happens to planetary systems when the star evolves,"

Beside discovering planets around these stars, Wolszczan believes that his survey will help us understand what happens to the solar systems when red giants expand. "Orbits may cross and there may be collisions, but the habitable zone will expand as the star expands. So does life have a chance in a somewhat wild environment like that?". His answer would be that "planets that could have been dead for billions of years will all of a sudden find themselves suitable for life," and "an example would be Jupiter's moon of Europa. That's just water ice, so if that melts you will have an ocean planet."