One of the greatest questions is whether life exists beyond our pale blue dot. The search extends across space and through the universe’s 13.8-billion-year history. Now, scientists have found five Earth-sized planets—all around an ancient, orange star—that suggest life in the universe could be far older than previously believed.
“We’ve never seen anything like this—it is such an old star and the large number of small planets make it very special,” Daniel Huber, an astronomer from the University of Sydney and a co-author of an Astrophysical Journal paper about the finding published this week, said in a statement.
Huber is part of a team of researchers who identified what they say is the oldest planetary system ever found. It consists of five small, rocky planets orbiting a star two and a half times as old as Earth’s sun—and dates back 11.2 billion years. Although astronomers do not believe that these planets harbor life today, they say the findings suggest terrestrial-size planets capable of hosting life may have formed much earlier than previously thought.
“Now that we know that these planets can be twice as old as Earth, this opens the possibility for the existence of ancient life in the galaxy,” Tiago Campante, the lead author and an astronomer from the University of Birmingham, told New Scientist. The star that he and his team investigated is called Kepler-444 and it is some 117 light-years away from Earth. The star is only three-fourths the size of our sun, but it has the potential to burn for 30 billion years, longevity that makes it a better candidate for supporting life. Earth's sun, by comparison, is expected to burn for only 10 billion years.
But the five planets orbit closer to Kepler-444 than Mercury does our sun, putting them outside the “Goldilocks Zone.” (Surface temperatures at those distances would be too hot to harbor life.) The scientists also said that the planets have overlapping orbits that circle around their star completely in less than 10 days. “You can imagine if you are standing on the surface of the outermost planet, at some points during the orbit you could look in the direction of the star and see all the other four planets aligned," Campante said. "It must be amazing.”
To figure out the age of the star, the Kepler spacecraft took images of Kepler-444 once every minute for four years. Astronomers used the data to observe subtle changes in the star’s brightness. By analyzing Kepler-444’s pulsations, the team could determine how fast sound traveled inside of the star, a technique known as asteroseismology. With that calculation, the team then deduced the ratio of hydrogen to helium within the star, which indicated how far along into its life cycle it is.
At 11.2 billion years old, Kepler-444 is a remnant from the first generation of stars following the Big Bang. It has been around for 80 percent of the universe’s 13.8-billion-year lifetime. Our Sun has only existed for about 4.5 billion years.
“This tells us that planets this size have formed for most of the history of the universe,” Huber said, “and we are much better placed to understand exactly when this began happening.”