Arizona State University (ASU) researchers have reported that a star Tau Ceti is considered to have five exoplanets and two of which have been posited to lie in the habitable zone.

The star lies just 11.9 light-years from Earth. Out of five, two of them named Tau Ceti e and Tau Ceti f are at the right-range of distances that could support existence of liquid water.

ASU's Michael Pagano, lead author of the study said, "Planet f initially looks more promising, but modeling the evolution of the star makes it seem probable that it has only moved into the habitable zone recently, as Tau Ceti has gotten more luminous over the course of its life".

According to the researchers, Tau Ceti f has likely resided in the habitable zone for much less than 1 billion years.

The researchers used chemical composition of Tau Ceti and modeled the star's evolution to calculate its habitable zone.

Although planets (e and f) may be in the habitable zone, it doesn't mean life flourishes or even exist there. The study team members said that it took about 2 billion years for detectable 'biosignatures' to build up in Earth's air after the first organisms evolved.

The remaining three exoplanets of the star Tau Ceti (b, c and d) orbit considerably closer to the star than do e and f, which makes them too hot to harbor life.

All the five worlds are likely larger than Earth and planets e and f are estimated to be 4.3 and 6.6 times more massive than Earth, respectively. The other three worlds appear to harbor between 2 and 4 Earth masses.

The new study also noted that Tau Ceti has much more magnesium compared to silicon than the sun does. This led the researchers to conclude that the exponents' worlds could be quite different from Earth in key ways.

The study was published in The Astrophysical Journal.