Kepler Discovers Star System with Five Earth-Sized Planets

NASA's Kepler satellite has discovered a new star system that boasts five Earth-sized planets, dating back to the dawn of our own Milky Way galaxy, new research shows.

The star, appropriately named Kepler-444, hosts five planets smaller than Earth, with sizes varying between those of Mercury and Venus. And at 11.2 billion years old, it's the oldest star with Earth-sized planets ever found, providing evidence that such planets have formed throughout the history of the Universe.

"It is extraordinary that such an ancient system of terrestrial-sized planets formed when the universe was just starting out, at a fifth its current age. Kepler-444 is two and a half times older than our solar system, which is only a youthful 4.5 billion years old," Dr. Daniel Huber, a team member from the University of Sydney, said in a press release.

"This tells us that planets this size have formed for most of the history of the Universe and we are much better placed to understand exactly when this began happening," he added.

To determine just how old Kelper-444 and its quintet of planets is, a team led by the University of Birmingham, along with researchers at the University of Sydney, used what is called asteroseismology. This technique measures oscillations, or the natural resonances of the host star caused by sound waves trapped within it.

"When asteroseismology emerged about two decades ago we could only use it on the Sun and a few bright stars, but thanks to Kepler we can now apply the technique to literally thousands of stars," Huber explained. "Asteroseismology allows us to precisely measure the radius of Kepler-444 and hence the sizes of its planets. For the smallest planet in the Kepler-444 system, which is slightly larger than Mercury, we measured its size with an uncertainty of only 100km."

Though Kepler-444 may be likened to an ancient version of our own solar system, with planets about the size of Earth, the worlds it contains are not thought to be habitable and Earth-like. However, the discovery has important implications in better understanding the Milky Way's 3.8-billion-year history.

The findings were published in The Astrophysical Journal.

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