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Goldilocks and ET

feast or famine
Sydney - March 19, 2001
So far, searches for ET have come up empty-handed. No signals have been detected. But an Australian astronomer Dr Charles Lineweaver has come up with a new way to tell us something about extra-terrestrials. By cleverly combining observations of extra-solar planets and the rate of star formation in the Universe, he has found that our Earth is much younger than other Earth-like planets in the Universe.

In a paper recently submitted to Icarus, the leading journal of planetary science, Dr Lineweaver reported that "three quarters of the Earth-like planets in the Universe are older than the Earth and their average age is 1.8 (plus or minus 0.9) billion years older than the Earth".

Dr Lineweaver outlined his argument as follows:

"Immediately after the Big Bang, 13 billion years ago, the Universe was made of hydrogen and helium. There was no carbon, oxygen, iron or silicon. Therefore no Earth-like planets could form around the first stars.

"Then, in a strong burst of star formation that lasted a few billion years, these ingredients were produced in abundance by stars. This meant the formation of Earth-like planets became possible.

"But there is a catch. Too much of these ingredients seems to be a bad thing for Earth formation. The 50 or so huge extra-solar planets detected so far are found preferentially around stars rich in these ingredients. And these huge planets are in orbits that would destroy any Earth-like planets.

"You can think of this as a 'Goldilocks effect': with a shortage of ingredients Earths were unable to form, with too much, giant planets would destroy any Earths trying to form. As Goldilocks insisted, the porridge had to be 'just right' or there was no deal."

Although his analysis is about terrestrial planets, not life on them, Dr Lineweaver concluded that if life formed as readily on other Earth-like planets as it did on Earth some 3.5 billion years ago -- then this gives us an age distribution for life on such planets and a rare clue about how we compare with other life that might inhabit the Universe.

"The 'rare clue' is this: most of the life forms in the Universe have had two billion years longer to evolve than we have. To put this time span in perspective, two billion years ago our ancestors were microscopic single-celled amoebas," he said.

Related Links
An Estimate of the Age Distribution of Terrestrial Planets
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Are Life's Diamonds That Rare
Cameron Park - July 27, 1999
Belief in the rarity of the Earth as an abode for life keeps swinging back and forth. After the triumph of Copernicus' belief that the Earth was not the center of the universe, the general feeling among scientists was that inhabited worlds were common.

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