Over the past decade, our perspective of the cosmos has changed drastically. Within the last couple of years, humans have detected thousands of planets around stars other than our own Sun (exoplanets). With the discovery of an enormous number of galaxies, we also discovered billions of stars that statistically all have a planet orbiting them. Seeing the vast Universe makes us wonder that there could be more than just life here on Earth. Maybe we are not alone in this humongous universe.
When speaking of the Universe, a question that hasn’t received that much attention yet is: how old could the oldest planetary system be?
Let’s look at the facts we already know. Our solar system is roughly 4.6 billion years old, which is quite young compared to the whole Universe which is around 13.8 billion years old. We know that the Big Bang, mostly produced Hydrogen and Helium, while Earth’s crust consists mostly of oxygen, silicon, and iron. So that means Earth couldn’t have formed right after the Big Bang. But for how long would we need to wait?
Studies have shown that to create the elements which rocky planets like Earth consist of, stars in the Universe need to first be created and then die to spread elements heavier than Hydrogen and Helium into space. For heavier elements, they are mostly produced in stellar interiors through fusion, and when the stars eventually explode and shed their layers to their surroundings. It takes thousands of years for the stars’ material to fully mix into nearby space, and afterward, this material needs to collapse and form new stars and planets.
While a correlation has been observed between the amount of time passed since the Big Bang and the amount of heavier elements in the Universe, astrophysicists are still having a hard time creating a precise duration for the number of heavy components created at what time. However, it is concluded that something like Earth could not have formed until enough stars in the Universe had exploded, and we also know that this could have happened a lot earlier than when our solar system formed.
Kepler-444 (Campante et al. 2015, ApJ) is one of the most interesting planetary systems found by astronomers in our Galaxy. The Kepler-444 consists of five rocky planets orbiting a star which is 6.6 billion years older than our solar system. This means that it could have only formed 2.6 billion years after the Big Bang. As far as we know, this system probably doesn’t harbor life since the planets that are too close to their star have liquid water. But the sole existence of Kepler-444 demonstrates that planetary systems could have formed a lot earlier in the history of the Universe than our solar system. All these facts raise the question – if alien civilizations do exist and have evolved for billions of years longer than life here on earth, then how intelligent would they be?