About 117 light years from Earth, in the constellation Lyra, spin an orange star cooler and smaller than our own. Around that star, called Kepler-444, five small planets ranging in size from Mercury to Venus are gathered close and orbit in fewer than 10 days. The most stunning thing about this newly discovered planetary system, however, is its age. The star is about 11.2 billion years old, just a few billion years younger than the universe itself.
The system may be the oldest of its kind in our galaxy, reports Rachel Feltman for the Washington Post.
"By the time the Earth formed, the planets in this system were already older than our planet is today," says Tiago Campante, of the University of Birmingham in a press statement. "The discovery may now help to pinpoint the beginning of what we might call the 'era of planet formation.'"
Campante and his colleagues sussed out details about the star and its planets with two interesting methods. The first, stellar seismology, involves listening to sound waves within the star. "Those sound waves affect the star’s temperature, creating pulsating changes in brightness that offer clues to the star’s diameter, mass and age," explains a press statement from Iowa State University. To see the circling planets, the researchers measured the small flickers created by the planets passing in front of the star—each passage made the star minutely dimmer than it is unobscured. This method is how the Kepler spacecraft has detected 1013 confirmed planets (as of this writing) since its launch in 2009.
The new system’s venerable age puts the star’s formation in the early years of the universe. It’s the oldest known system of Earth-sized planets and proves that it is possible such planets could form during much of the Universe’s 13.8-billion-year history, the researchers note in their paper, published online at ArXiv.org. The discovery leaves "open the possibility for the existence of ancient life in the Galaxy," they write.
This possibility brings to mind another problem or question, the Fermi Paradox, which states that if life is likely to form, then the Earth should have been colonized or at least visited by intelligent life already. For Slate’s Bad Astronomy blog, Phil Plait writes:
Let’s say it takes 4 billion years for those protozoa to evolve and build spaceships. It turns out that, even with the vast distances between stars and limiting your ships to far less than the speed of light, you can colonize the entire galaxy in just a few million years. That’s far less than the age of the galaxy.
Perhaps you see the problem. If planets like Earth formed 11 billion years ago, and happened to form at the right distance for more clement conditions on the surface, life could have arisen long enough ago and started building spaceships long before the Earth even formed! They’d have planted their flags on every Earth-sized habitable planet in the Milky Way by now.
No one can really answer why we haven’t seen convincing evidence of aliens yet. It could be that life is less likely to develop than we think, that civilizations destroy themselves before they achieve interstellar travel, or even that we are the very first life in the galaxy. As Plait observes, clearly we don’t have the full picture yet. Discovering more and more about such systems as Kepler-444 and its planets will get us closer to the answer.