Jumat, 26 Juni 2015

Ancient exoplanets raise prospects of intelligent alien life

Can life survive for billions of years longer than the expected timeline on Earth? 
As scientists discover older and older solar systems, it's likely that before long we'll find an ancient planet in the habitable zone. Knowing if life is possible on this exoplanet would have immense implications for habitability and the development of ancient life, one researcher says.
In January, a group led by Tiago Campante — an astroseismology or "starquake" researcher at the University of Birmingham in the United Kingdom — announced the discovery of five tiny, likely rocky worlds close to an ancient star. The star is named Kepler-444 after NASA's planet-hunting Kepler mission, which first made a tentative discovery. [10 Exoplanets That Could Host Alien Life ]
Campante's contribution was narrowing down the age of Kepler-444 and its planets to an astounding 11.2 billion years old. That's nearly 2.5 times as old as our solar system. None of Kepler-444's planets are thought to be habitable, as they circle the star at a scorchingly close distance. However, Campante said that finding those planets is a great stride forward in the search for older, habitable worlds, and the best may be yet to come.
"This system gives us hope that there are other habitable worlds that we can’t detect because we don’t have enough observing timespan yet," Campante said. 
Upcoming observatories could change that, he added. Whether life can live for billions of years, however, is pure speculation. 
"If intelligent life develops in a system as old as this one, would it still exist or would they extinguish themselves?" Campante asked. 
Results from Campante's paper were published in January in The Astrophysical Journal, in a paper entitled, "An Ancient Extrasolar System with Five Sub-Earth-Size Planets."
 Surprise composition
The researchers observed Kepler-444 with the W.M. Keck telescope near the summit of Mauna Kea, Hawaii to learn more about its chemical composition.
The star is deficient in iron but is rich in what are called "alpha elements," such as silicon, carbon, nitrogen and oxygen. These elements were all formed in the first stellar explosions of our universe, when older stars ran out of fuel to burn and spread these elements far and wide. These elements make the composition of the star's orbiting planets a bit of a surprise, Campante said. 
Normally, scientists expect that "terrestrial" planets — rocky ones such as Mercury, Venus or Earth —  have lots of iron in their interiors. This discovery shows it's also possible to create planets that are primarily made of alpha elements, he said. This means that rocky planets may be able to form in multiple ways, making them more common across the universe.
The Kepler-444 system is not much like ours, though. Kepler-444 is slightly smaller than our sun, and its planets orbit extremely close in. The habitable zone in this system starts around 0.4 astronomical units (AU), or Earth-sun distances. Yet the outermost planet huddles at only 0.08 AU. That's roughly five times closer than Mercury is to our own sun.

Widening the search

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