Astronomers Have Discovered An Ancient Star With Earth-Sized Planets

Kepler-444 hosts five Earth-sized planets in compact orbits. The planets were detected from the dimming that occurs when they transit the disc of their parent star, as shown in this artist’s conception. Image: Tiago Campante/Peter Devine.

A star similar to our own sun with earth-sized orbiting planets, dating back to the dawn of the Galaxy, has been discovered by an international team of astronomers.

At 11.2 billion years old it is the oldest star with earth-sized planets ever found and proves that such planets have formed throughout the history of the Universe.

The discovery, announced in The Astrophysical Journal, used observations made by NASA’s Kepler satellite. The scientific collaboration was led by the University of Birmingham and contributed to by the University of Sydney.

The star, named Kepler-444, hosts five planets smaller than Earth with sizes varying between those of Mercury and Venus.

“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 Daniel Huber from the University of Sydney’s School of Physics and an author on the paper.

“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. Kepler-444 is two and a half times older than our solar system, which is only a youthful 4.5 billion years old.

“This tells us that planets this size have formed for most of the history of the universe and we are much better placed to understand exactly when this began happening.”

The astronomy team used asteroseismology to determine the age of the star and planets. This technique measures oscillations, the natural resonances of the host star caused by sound waves trapped within it.

“It was clear early on that we had discovered something very unusual because we had five planets orbiting a very bright star – one of the brightest Kepler has observed,” Dr Huber said.

The planets orbit their parent star in less than 10 days, at less than one-tenth the Earth’s distance from the Sun.

Their closeness to the host star means they are uninhabitable because of the lack of liquid water and high levels of radiation.

However, discoveries such as Kepler-444 provide important clues on whether a planet truly comparable to Earth may exist.

“We’re another step closer towards finding the astronomers’ holy grail – an Earth-sized planet with a one year orbit around a star similar to our Sun,” Dr Huber said.

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