Astronomers have discovered thousands of exoplanets but have almost no idea how old most of them are. Without reliable ages, it is impossible to tell whether a planet’s size, orbit, or atmosphere is a product of its birth or of billions of years of change. This project will solve that problem by combining three types of stellar data—high-resolution spectroscopy, precise positions from the Gaia spacecraft, and subtle stellar oscillations measured by TESS and the future PLATO mission—to calculate trustworthy ages for the host stars of small exoplanets. The team will then study how the occurrence of Earth-sized and Neptune-sized planets shifts over cosmic time, testing whether planet formation is linked to the evolution of the galaxy itself. This is fundamental science: there is no immediate practical application. But understanding how common Earth-like planets are at different epochs, and how planetary systems age, will directly inform the design and targeting strategy of PLATO, Europe’s next major exoplanet mission. It also provides the first empirical framework for asking whether a planet’s history—not just its present—determines its habitability.
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The discovery of thousands of exoplanets orbiting stars other than our Sun has revealed a wide range of planetary properties, both like and unlike planets in our own solar system. One unexplored parameter to understand exoplanet characteristics is their age: the solar system is roughly 4.6 billion years old, whereas some exoplanets are of similar age, while others are as old as the universe, or were born very recently. While it is likely that the properties of planetary systems are related to their age, both due to the evolution of the galaxy shaping the formation of planetary systems, and the evolution of planetary systems and their host stars over time, the potential to understand exoplanets in this context has remained largely unexplored. This is because stellar ages are notoriously difficult to determine. Here, we will overcome this challenge by using state-of-the-art Bayesian techniques to derive reliable ages combining stellar observations from high-resolution spectroscopic observations and Gaia measurements, as well as asteroseismology from current missions such as TESS and future missions like PLATO. This will allow us to derive accurate and precise stellar ages for a large sample of small extrasolar Earth and Neptune planets. We will pair the stellar characterisation with a detailed study of planet properties, including their occurrence. By doing so, we will determine how the occurrence of Earth and Neptune planets depends on the characteristics and age of their host stars over billions of years. In doing so, we will test how planet formation can be linked to galactic evolution, and how planets evolve over time. This work will also deliver important knowledge build-up in the context of the upcoming PLATO mission, whose main focus is understanding small planets and linking their properties to precise host star ages.
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