Chemical Fingerprints of Planets: What Solar Twins Tell Us About the Sun and the Galaxy
In a recent study, Giulia Martos and collaborators developed a machine learning tool to investigate the chemical composition of stars like our Sun. By analyzing 99 "solar analogs" -- stars with properties very similar to the Sun -- the team aimed to detect subtle signs left by planets and explore how typical the Sun’s chemical makeup really is. Using high-resolution spectra and a specially trained neural network, they measured precise abundances of 20 elements in each star, many of which are involved in forming rocky planets.
A Peculiar Sun?
The Sun is known to be slightly different from most solar analogs: it has a lower concentration of "refractory elements," which are materials that condense at high temperatures and form the bulk of rocky planets like Earth. This difference may be a clue that the Sun once formed planets that removed these elements from the surrounding gas, leaving the Sun slightly depleted in them. Martos and her team confirmed this pattern, finding that the Sun is more depleted in refractories than about 89% of the solar analogs studied. This strengthens the idea that planet formation can leave a chemical fingerprint on a star.
Machine Learning Meets Stellar Chemistry
To detect these faint signatures, the researchers developed a neural network that mimics a method known as differential spectroscopy, but in an automatic and much faster way. This network compares the spectrum of each star to that of the Sun and determines atmospheric parameters like temperature and gravity, as well as chemical abundances. Their results match well with earlier studies that relied on manual techniques, but the neural network was able to analyze each star in just minutes -- a major improvement in efficiency.
Correcting for Galactic History
By correcting for the natural chemical changes in our galaxy over time (called Galactic Chemical Evolution, or GCE), the authors also explored how a star’s age affects its chemistry. In doing so, they discovered hints of three distinct subpopulations within the solar analogs. These groups differed in their abundances of elements like sodium and copper and may come from different parts of the Milky Way. Their differing chemical patterns suggest that stars born in different regions of the galaxy may have unique planet-forming histories.
The Sun Among Planet Hosts
The study further compared the Sun’s chemistry to that of stars with and without known exoplanets. Interestingly, stars that host planets were more chemically similar to the Sun than stars without known planets. Still, none were quite as depleted in refractory elements as the Sun. This may suggest that the Sun experienced a relatively quiet planet formation history -- one that left behind a more pristine signature than most.
What Makes the Sun Special?
Ultimately, this work shows how advances in machine learning can push the limits of what we can learn from stellar spectra. It also raises intriguing questions about what makes our Solar System special. As more exoplanets are discovered, and more stars are studied with tools like this neural network, scientists may get closer to answering the timeless question: is the Sun just another star, or is it truly unique?
Source: Martos
