Pretty but ordinary: A remarkable close-up shot of the surface of the Sun captured by the Swedish Solar Telescope.

Credit: Swedish Solar Telescope/NASA

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SYDNEY: The Sun has no unique properties that might have caused it to be the only star we know of that hosts a life bearing planet, say a new study.

An Australian team came to that conclusion after conducting the most thorough survey ever of how the Sun compares to other stars.

The research has implications for the possibility of finding life elsewhere, said the researhers led by Jose Robles from the Australian National University in Canberra. They will publish their findings in an upcoming issue of the Astrophysical Journal.

Stellar characteristics

It has been difficult to determine how unique Earth is in the universe since there is no data on other Earth-like planets to compare it against. Instead, astronomers have previously looked at whether there is anything significantly special about our Sun. Their research has yielded a mixed bag, however with astronomers divided on the findings.

To get a better answer, Robles and his co-workers simultaneously compared 11 stellar characteristics that could plausibly influence the evolution of life.

They looked at parameters such as: the Sun's mass; age; metallicity (the amount of elements heavier than helium and hydrogen, such as oxygen, carbon and nitrogen); as well as its rotation rate; its whereabouts within the galaxy; how it 'bobs up and down in the galactic plane'; and the activity of its photosphere. Using statistical methods, these were measured against data available on other stars.

The analysis revealed that the Sun's most anomalous property is its mass, which is greater than 95 per cent of nearby, Sun-like stars. Its orbit is more circular than 93 per cent of these other stars and it is also older and more metal-rich than most Sun-like stars. But none of these figures were significant enough to differentiate the Sun from any other star chosen at random.

Life in other solar systems

"When analysing the 11 properties together, the Sun shows up as a star selected at random, rather than one selected for some life-enhancing property," Robles said. "The upshot is that there doesn't seem to be anything special about the Sun. It seems to be a random star that was blindly pulled out of the bag of all stars."

The implications are that life doesn't require anything special from its host star and supports the idea that life may be common in the universe, the researchers said.

Co-author Charley Lineweaver, also of ANU, said the analysis was a "simple idea with an interesting result". He said this was the most careful comparison yet done with other stars and used a lot of new data. It was also important that the research removed 'selection biases' on data, such as whether the data was taken for just bright stars.

"We were expecting to find something that stood out a bit. I would have loved to have found something particular about these parameters, for example that the Sun has more uranium than other stars, but to our surprise nothing stood out," Lineweaver said.

"Those who are searching for justification for their beliefs that terrestrial life and humanity in particular are special, will probably interpret this result as a humiliating dethronement," he added.