Looking for ancient planetary worlds: the search for our roots in the cradle of the Milky Way
Since NASA launched the Kepler Mission in 2009 to find potential new Earths, there have been several out-of-this-world discoveries – with the latest great find being made by a team of astronomers led by 34-year-old Birmingham Research Fellow Dr Tiago Campante.
They have identified the most ancient planetary system in our galaxy ever discovered that contains Earth-like planets orbiting a Sun-like star. More than 11 billion years old, it hails from the dawn of the Milky Way (when there were far fewer heavy metals – the building blocks of planets – around), giving scientists their strongest hint yet that life exists elsewhere in the Universe.
News of the discovery of Kepler-444, a solar system 117 light years away with five Earth-sized planets dating back to when the Universe was less than 20 per cent of its current age, was published in The Astrophysical Journal in January 2015 and made headlines around the world.
Tiago, who headed a 40-strong team from 25 institutions across seven countries, explains how the momentous discovery was made using a powerful, rapidly growing field of astronomy called asteroseismology, which is the study of the stars by observation of their natural resonances that manifest as surface oscillations.
It has been dubbed ‘listening to the music of the stars’, because – like musical instruments – a star is able to make sound naturally in its interior and that sound gets trapped. The resulting oscillations lead to miniscule changes, or pulses, in its brightness, which allow researchers to measure its diameter, mass and age. Planets are detected from the dimming that occurs when the planets transit, or pass across, the stellar disc.
So far, more than 1,000 planets – known as extrasolar or exoplanets – have been found by Kepler in the Cygnus-Lyra constellations of the Milky Way, some of which could be capable of supporting life. But Kepler-444 takes the hunt for other life in space to a new, exciting level. Or, as Tiago puts it, ‘we’re into a different ball game’.
‘There is probably at least one confirmed solar system that’s older than 444, but its only planet is a gas giant, which means there’s no rocky surface on which life could develop,’ he explains.
Although 444’s five planets – slightly smaller than Earth – are too close to their star to support life as we know it, they nevertheless provide the biggest hint yet that there is other life ‘out there’.
This is partly due to what is called the ‘observational bias’. Kepler-444’s planets, ranging in size from Mercury to Venus, take ten of our days to orbit the star.
‘These five planets are small with short orbital periods; it’s more difficult for us to detect small planets with long orbital periods,’ says Tiago. ‘It doesn’t mean they’re not there; it means we’d have to observe for a long period of time to detect them.
‘So the discovery of 444 is telling us that planets the size of the Earth have formed since the very beginning of our galaxy; there are probably other systems with planets that do fall within the habitable, or Goldilocks, zone. If that is the case, then there’s probably ancient life in the galaxy. This discovery has strengthened that hypothesis.
‘We’re talking not only about life existing, but ancient life – life that could have been out there more than twice as long as life on Earth. If you think our planet is 4.5 billion years old and life only appeared about 3.5 billion years ago, and then you think how far we have evolved in just that time. Imagine, then, what it could mean to put billions of years of life on top of that.’
As Tiago explains in his paper, the discovery of Kepler-444 not only tells us that there may be more potential habitable solar systems in our galaxy than we first thought, but also that if life does exist elsewhere, it could be even older than we imagined.
‘What it doesn’t tell us is how common life, or potential life, is, given all the conditions you need if life is to develop,’ he points out. ‘But certainly there are Earth-sized planets out there from when the Universe was less than 20 per cent its current age.’
Portuguese-born Tiago, who fell in love with astronomy after reading Cosmos by Carl Sagan as a 14-year-old, admits he never imagined he would make such a discovery, especially so early on in his career.
‘Without a doubt it is the high point so far,’ he says, beaming. ‘I never expected this to happen.’
- This paper, titled ‘An Ancient Extrasolar System With Five Sub-Earth-Size Planets’ was originally published in ‘The Astrophysical Journal Volume 799, Issue 2’.
- The paper also received the College of Engineering and Physical Sciences Best Publication award for January 2015.