Astronomers using a powerful space telescope said they have spotted the ideal conditions for the formation of an Earth-like planet in a star system located some 424 light years away.

The sun-like star found in the system HD 113766 has enough warm dust swirling around it to build a Mars-like planet or larger, said astronomers at Johns Hopkins University.

The belt of interstellar stuff is also in the right place and at the right time to form a planet, said astronomer Carey Lisse, the lead author of a paper to be published in an upcoming issue of Astrophysical Journal.

"The timing for this system to be building an Earth is very good," said Lisse in a statement.

"If the system was too young, its planet-forming disk would be full of gas, and it would be making gas-giant planets like Jupiter instead. If the system was too old, then dust aggregation or clumping would have already occurred and all the system's rocky planets would have already formed."

The star is about 10 million years old, an age similar to the age of the sun when our solar system began taking shape. Our sun is now approximately 4.6 billion years old.

The astronomers found the star using NASA's Spitzer Space Telescope, which provided details not only on the location of the belt of space dust but also its chemical composition.

Using the telescope's infrared spectrometer, Lisse and his colleagues found the material surrounding the star was more complex than comets and other early-solar system material, but not as processed as the mix found on mature planets like Earth.

"The material mix in this belt is most reminiscent of the stuff found in lava flows on Earth," said Lisse.

Studying the process of planet forming could provide new insights into the origins of our own planet, said Lisse.

Astronomers have so far discovered over 250 extrasolar planets, or "exoplanets."

The bulk of these have been gas-giant planets similar in size to Jupiter, which are easier to spot because their large mass has a greater gravitational influence on the stars they orbit, thus allowing astronomers to infer their existence even when they cannot directly "see" them.

Earth-size planets have proved more difficult to find, though earlier this year scientists made headlines when theyfound evidence of an already-formed Earth-like planet around the star Gliese 581, a star 20.5 light years away, or 1.93 hundred million million kilometres distant.