London: Earth is worth 3,000 trillion pounds, according to an astrophysicist who claims to have created a formula to calculate the value of a planet.

In fact, the astrophysicist, Greg Laughlin, came up with the figure by calculating the sum of the planet's age, size, temperature, mass and other vital statistics - and Earth came out as the most expensive.

"The formula makes you realise how precious Earth is and I hope it will help us as a society safeguard what we have," a daily quoted him as saying.

Mars was only valued at 10,000 pounds, while Venus is said to be worth less than a penny. There are about 1,235 other planets in the universe, most of which weren't given a high price tag because of their inhospitable climates.

Professor Laughlin from the University of California invented the equation, which he used to evaluate the discoveries made by US space agency NASA's 600 million pounds Kepler spacecraft.

The planet-hunting spacecraft went into orbit two years ago and a year later Laughlin decided to create price tags for the terrestrial planets that Keplar was to discover.

At the time, the exoplanet Gilese 581 c was considered the most Earth-like world known to scientists, but the equation only valued it at 100 pounds, while KOI 326.01 is said to be worth 150,000 pounds.

"I've just always thought that the concept of an 'Earth-like planet in the habitable zone' was pretty vaguely defined, and I wanted a metric that I could plug a planet into to see whether its value was high enough to warrant mediahype.

"This is just a way for me to be able to quantify how excited I should be about any particular planet," Laughlin was quoted as saying.

The older the star, the more value it has because it has had the chance to mature, the mass is then taken into account and generally if it's around the same size as Earth it is thought of as a good size for supporting life.

Laughlin also took into account the amount of energy the star creates and whether its temperatures could also support life.