[ExI] just another star, yawn

[Damien Broderick]

http://www.cosmosmagazine.com/node/2011


Life doesn't need a special star

Friday, 23 May 2008
by Heather Catchpole
Cosmos Online


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.



More information

<http://arxiv.org/abs/0805.2962>The study - upcoming in the 
<http://arxiv.org/abs/0805.2962>Astrophysical Journal