Washington, October 14 Scientists have come up with a new index to measure a world's fitness for life, and have decided upon three names that are most likely to harbor life.

According to a report in National Geographic News, known as the Standard Microbial Habitability index, the system rates worlds on a scale of 0 to 1 as to how suitable they are for microscopic life-forms like those on Earth.

"What's good for microorganisms is good for life in general," said research leader Abel Mendez, of the University of Puerto Rico at Arecibo.

The index suggests that Saturn's icy moon Enceladus may be the extraterrestrial body most likely to support life as we know it in our solar system.

Enceladus scored 0.4, which is the same as Earth.

Scientists think Enceladus's icy shell hides a vast under-ice ocean, and the moon's relatively small size means its internal pressure is not too great.

The second world that scores high on the index is Mars.

Previous tests for life on Mars have turned up negative or inconclusive. But, the red planet received a promising score of 0.3 on the new Standard Microbial Habitability index, announced in October 2009.

Researchers think that the answer is to dig deeper. The sweet spot for Mars's life may be about 4 miles (6 kilometers) underground, according to Mendez.

"You have an envelope where the temperature and pressure are ideal for microbial communities," he said.

According to the new Standard Microbial Habitability index, like Saturn's moon Enceladus, Jupiter's moon Europa has a subsurface ocean that might support earthly life.

"The purported habitable zone on Europa, which earned a 0.3 on the index, is not as large as that of Saturn's Enceladus, but the ocean is shallower and perhaps easier to explore than that of Enceladus," said Mendez. (ANI)