Five Earth-sized planets have been discovered in a solar system so ancient it was born not long after the dawn of time.
The system’s parent star, named Kepler-444, is 117 light years from Earth and 11.2 billion years old.
When the sun-like star was formed out of a primordial cloud of gas and dust the universe was just a fifth of its current age.
British-led astronomers have shown that it hosts five planets with diameters ranging between those of Mercury and Venus. That makes them roughly the size of Earth or somewhat smaller.
Tiago Campante, from the University of Birmingham’s School of Physics and Astronomy, said: “There are far-reaching implic-ations for this discovery. We now know that Earth-sized planets have formed throughout most of the universe’s 13.8-billion-year history, which could provide scope for the existence of ancient life in the galaxy.
“By the time the Earth formed, the planets in this system were already older than our planet is today. This discovery may now help to pinpoint the beginning of what we might call the ‘era of planet formation’.”
The chances of a super-advanced race of beings living on any of the planets are remote, however.
Each of the worlds is so close to its star that its year – the time taken to complete one orbit of the star – is less than 10 days long.
At that distance, the planets would be much hotter than Mercury and unable to support Earth-like life.
Astronomers made the discovery after poring over four years’ worth of data from the US space agency Nasa’s Kepler space telescope.
Each of the worlds is so close to its star that its year – the time taken to complete one orbit of the star – is less than 10 days long
Campante’s team conducted the research using a technique called asteroseismology, which involves ‘listening’ to vibrations caused by sound trapped within a star.
The oscillations led to tiny pulse-like changes in brightness which allowed the researchers to measure the star’s diameter, mass and age.
The planets were detected from the dimming that occurred when they transited, or passed across, the face of the star. By measuring the minute fading of light coming from the star the scientists were able to calculate the relative size of the planets.
The findings appear in The Astrophysical Journal.
Co-author Professor Bill Chaplin, from the University of Bir-mingham’s School of Physics and Astronomy, said: “The first discoveries of exoplanets around other Sun-like stars in our galaxy have fuelled efforts to find other worlds like Earth and other terrestrial planets outside our solar system.
‘We are now getting first glimpses of the variety of galactic environments conducive to the formation of these small worlds. As a result, the path towards a more complete understanding of early planet formation in the galaxy is now unfolding before us.”
Kepler-444 is a quarter of the sun’s size but bright enough to be seen with binoculars in the constellation Lyra.
Professor Steve Kawaler, a US member of the team from Iowa State University, said: “This is one of the oldest systems in the galaxy. Kepler-444 came from the first generation of stars. This system tells us that planets were forming nearly seven billion years before our own solar system.
“Planetary systems around stars have been a common feature of our galaxy for a long, long time.”