Fascinante découverte, avec des implications tout simplement mirobolantes:
Kepler scientists have discovered the oldest known system of rocky, Earth-sized planets in the Milky Way. This suggests that terrestrial planets have appeared throughout most of the Universe's 13.8 billion year history — a potential indication of just how ancient some extraterrestrial civilizations could be.
Sadly, these five planets are not habitable; they're all parked in tight orbits that see them revolve around their host star in fewer than 10 days. The outermost planet orbits at 0.08 AU, which is about one-fifth the size of Mercury's orbit. That's quite far from the inner edge of the system's habitable zone, which is located ~0.47 AU from the host star.
At such a close distance, these planets are much hotter than Mercury. But the discovery shows that rocky planets have been forming for a very, very long time in our galaxy — a strong sign that other systems may have been producing terrestrial planets that reside within their respective habitable zones.
Life in the Universe, therefore, may have emerged far earlier than we ever imagined.
The newly discovered planets are part of the Kepler-444 system. It formed some 11.2 billion years ago, a time when the Universe was less than 20% of its current age.
That's remarkably old, about 2.5 times older than our solar system. To put that into perspective, by the time Earth formed, these five planets were already older than our planet is today. As noted by the Kepler scientists in a release, "This discovery may now help to pinpoint the beginning of what we might call 'the era of planet formation.'"
Kepler-444 is approximately 117 light-years from Earth and about 25% smaller than our Sun. The sizes of the five planets fall between Mercury and Venus (all of which are smaller than Earth). Interestingly, Kepler-444 is so bright that it can actually be seen with binoculars.