How do you measure the age of a star? It's not as easy as asking them about their birthday. Measuring the age of stars is an imprecise art if you don't have a high-quality telescope. So a team of scientists set out to precisely measure the age of stars in the Milky Way and reveal unknown details about their exoplanets.
33 stars were carefully selected from a pool of 1,200 stars with exoplanets. So how were the lucky candidates selected? Since the most accurate data we have with which to compare these stars is data on the Sun (by virtue of it being the closest star to the Earth), the selected stars had to be Sun-like. This meant that they had to oscillate in a similar way to the Sun. They had to also be bright enough for the satellite to pick up a lot of detail on its properties, including the stars' exoplanet.
Their brightness, along with other characteristics, can be compared in a database of other similar stars. This allows scientists to trace back from the stars' luminosity to an accurate estimate of their ages. This estimate can be strengthened with asteroseismology. Stars pulsate, oscillate and generally vibrate. Measuring these pulses through stars is similar to how geologists gauge the interior of the Earth from earthquakes. The Keplar satellite has been observing these variations in stars for the last four years; this data allows scientists to track how stars are changing and measure different properties of the stars. Knowing these basic details about the largest fusion reactors in the universe (stars) will hopefully help us to improve energy production on Earth. And maybe even map our history and learn about our origins.
When referring to the age of a star, scientists tend to compare it with the age of the Sun (roughly 4.57 billion years old, give or take 10 million years). The stars were found to be either down to half the solar age or 2.5 times the solar age.
As a bonus, each star had Earth-like planets, making them excellent case studies of the different relationships Earth-like planets have with their stars.
Locating the planets was a little more tricky than finding the age of the stars: their existence was determined by examining the small variations in the intensity of light emitted from the central star. As a planet passes across a star, it blocks out some of the emitted light, causing these variations. This effect can be very subtle, so it hasn't led to the detection of many planets (in fact we only know of the existence of about 2,000 exoplanets).
The planets that surrounded the stars studied had exoplanets that were comparable in size to Earth (between 0.3 and 15 Earth radii). These planets orbited stars that had an age similar to that of our Sun: up to twice the solar age. It was interesting to note that the age of the stars did not affect the size of the exoplanets: that is to say that it is possible that we can find Earth-sized exoplanets all throughout the history of our galaxy. A remarkable finding was that some of the planets that were observed are twice the age of Earth. In other words, when these older planets were the age that Earth is now, Earth was only just being born!