Astronomers have found a star system that bears striking resemblance to our inner solar system. It's a sun-like star that plays host to a system of five small exoplanets - from the size of Mercury to the size of Venus.
But there's something very alien about this compact ‘solar system'; it formed when the universe was only 20 percent the age it is now, making making it the most ancient star system playing host to terrestrial sized worlds discovered to date.
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An international collaboration of astronomers that studied NASA's Kepler Space Telescope's observations over a period of four years, quickly realized that Kepler-444 formed around 11.2 billion years ago.
Though Kepler-444 may be likened to an ancient version of our solar system, the worlds it contains are not thought to be habitable and the planets that astronomers have identified certainly do not resemble Earth. They orbit well inside the star's habitable zone at a distance only 10 percent the distance that the Earth orbits the sun.
"This system shows that planet formation could take place under very different conditions from the ones in which our solar system was formed and has implications for estimating the total number of planets in our galaxy, and other galaxies," said co-investigator Sarbani Basu of Yale University.
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Kepler detected the family of 5 rocky worlds using the transit method - the exoplanets orbited in front of their host star, causing its light to dim slightly. The worlds' physical sizes and orbital characteristics could therefore be determined.
But gauging the old age of the star (and therefore the age of the entire star system) required the researchers to use the method of asteroseismology to detect the star's natural resonances caused by sound waves trapped within the stellar interior. The resonances cause slight variations in the star's brightness that was then used to measure the star's size, mass and age.
"There are far-reaching implications for this discovery," said lead author Tiago Campante of the University of Birmingham, U.K. "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."
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Indeed, discovering a system of rocky worlds that formed around such an ancient star suggests planetary formation occurred very early in the universe. We know that when the conditions are right, like on Earth, life began to pop up on our planet 3.6 billion years ago, approximately a billion years after our planet formed from the protoplanetary disk surrounding our young sun.
So that begs the question: if rocky planets formed 11.2 billion years ago around other stars, could there be a few that did have just the right conditions for life to be sparked? If so, could alien life have already come and gone in our galaxy's history? Or could this ancient life be persisting for, potentially, 10 billion years after it first formed?
For now, we simply do not know, but studies such as these provide clues as to the possibilities of life's niches throughout the Milky Way.
Source: Yale University