Yahoo – AFP,
27 Jan 2015
 |
This NASA
artist concept shows NASA's planet-hunting Kepler spacecraft
operating in a new
mission profile called K2 on December 19, 2014 (AFP Photo)
|
Miami (AFP)
- International astronomers said Tuesday they have discovered the oldest known
star encircled by five Earth-sized planets, signaling that planets formed
throughout the history of the universe.
The system
is 11.2 billion years old and was born near the dawn of the galaxy, said the
report in the Astrophysical Journal.
The star
has been named Kepler-444, since it was found with the help of NASA's
planet-hunting Kepler spacecraft which launched in 2009.
Its five
planets are a bit smaller than the Earth, ranging in size from Venus to
Mercury.
They circle
their Sun-like star in less than 10 days, at a distance smaller than one-tenth
the distance between the Earth and Sun -- making them too hot to be habitable.
But the
sheer age of the star has stunned astronomers.
At a
distance of 117 light-years from Earth, Kepler-444 is two and a half times
older than our solar system, which is 4.5 billion years old.
"We've
never seen anything like this -- it is such an old star and the large number of
small planets make it very special," said co-author Daniel Huber from the
University of Sydney's School of Physics.
"It is
extraordinary that such an ancient system of terrestrial-sized planets formed
when the universe was just starting out, at a fifth its current age," he
added.
Astronomers
can measure a distant planet's age using a technique called asteroseismology,
which measures the oscillations of the host star caused by sound waves trapped
within it.
These waves
lead to small pulses in the star's brightness, which can be analyzed to measure
its diameter, mass and age.
Co-author
Steve Kawaler, an Iowa State University professor of physics and astronomy,
said Kepler-444 is very bright and can be easily seen with binoculars.
"We
now know that Earth-size planets have formed throughout most of the universe's
13.8-billion-year history," said lead author Tiago Campante from the
University of Birmingham.
"Which
could provide scope for the existence of ancient life in the galaxy."
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