The chemical composition of Earth ’ s atmosphere has undergone substantial evolution over the course of its history .
It is possible , even likely , that terrestrial planets in other planetary systems have undergone similar changes ; consequently , the age distribution of nearby stars is an important consideration in designing surveys for Earth-analogues .
Valenti & Fischer ( 2005 ) provide age and metallicity estimates for 1039 FGK dwarfs in the Solar Neighbourhood .
Using the Hipparcos catalogue as a reference to calibrate potential biases , we have extracted volume-limited samples of nearby stars from the Valenti-Fischer dataset .
Unlike other recent investigations , our analysis shows clear evidence for an age-metallicity relation in the local disk , albeit with substantial dispersion at any epoch .
The mean metallicity increases from \sim -0.3 dex at a lookback time of \sim 10 Gyrs to \sim +0.15 dex at the present day .
Supplementing the Valenti-Fischer measurements with literature metallicity data to give a complete volume-limited sample , the age distribution of nearby FGK dwarfs is broadly consistent with a uniform star-formation rate over the history of the Galactic disk .
In striking contrast , most stars known to have ( gas giant ) planetary companions are younger than 5 Gyrs ; however , stars with planetary companions within 0.4 AU have a significantly flatter age distribution , indicating that those systems are stable on timescales of many Gyrs .
Several of the older , lower metallicity host stars have enhanced [ \alpha /Fe ] ratios , implying membership of the thick disk .
If the frequency of terrestrial planets is also correlated with stellar metallicity , then the median age of such planetary system is likely to be \sim 3 Gyrs .
We discuss the implications of this hypothesis in designing searches for Earth analogues among the nearby stars .