The chemical composition of stars hosting small exoplanets (with radii less than four Earth radii) appears to be more diverse than that of gas-giant hosts, which tend to be metal-rich. This implies that small, including Earth-size, planets may have readily formed at earlier epochs in the universe’s history when metals were more scarce. We report Kepler spacecraft observations of Kepler-444, a metal-poor Sun-like star from the old population of the Galactic thick disk and the host to a compact system of five transiting planets with sizes between those of Mercury and Venus. We validate this system as a true five-planet system orbiting the target star and provide a detailed characterization of its planetary and orbital parameters based on an analysis of the transit photometry. Kepler-444 is the densest star with detected solar-like oscillations. We use asteroseismology to directly measure a precise age of 11.2 ± 1.0 Gyr for the host star, indicating that Kepler-444 formed when the universe was less than 20% of its current age and making it the oldest known system of terrestrial-size planets. We thus show that Earth-size planets have formed throughout most of the universe’s 13.8 billion year history, leaving open the possibility for the existence of ancient life in the Galaxy. The age of Kepler-444 not only suggests that thick-disk stars were among the hosts to the first Galactic planets, but may also help to pinpoint the beginning of the era of planet formation
Kepler-444’s system is not much like ours, though. Kepler-444 is slightly smaller than our sun, and its planets orbit extremely close in. The habitable zone in this system starts around 0.4 astronomical units (AU), or Earth-Sun distances. Yet the outermost planet huddles at only 0.08 AU. That’s roughly five times closer than Mercury is to our own sun.
Kepler-444 and its planets to an astounding 11.2 billion years old. That’s nearly 2.5 times as old as our solar system. None of Kepler-444’s planets are thought to be habitable, as they circle the star at a scorchingly-close distance. However, Campante said that finding those planets is a great stride forward in the search for older, habitable worlds and the best may be yet to come.
“This system gives us hope that there are other habitable worlds that we can’t detect because we don’t have enough observing timespan yet,” Campante said.
NIRC2 adaptive optics image of Kepler-444. The image was obtained using the for a total of 378 s of integration time. Declination and right ascension coordinates (J2000.0) are given along the vertical and horizontal axes, respectively.
SOURCES- Arvix, Physorg,