An artistic vision of how the amount of iron in a star affects the planets. A normal star (green mark) is likely to have planets with a longer period (green orbit), while those rich in iron (yellow) will have short-period (yellow orbit)
Scientists from the Sloan Digital Celestial Survey have learned that the star’s chemical composition may unexpectedly affect its planetary system. The discovery was made possible by a review of Kepler, who promises to expand our understanding of the formation and development of exoplanets.
Looking through the data, the researchers noticed that stars with higher iron concentrations tend to place planets closely, where orbital periods often reach less than 8 days. But in the stars with a smaller amount of iron planets are on.
The history of the study of exoplanets began in 1995, when a group of astronomers noticed one planet around a solar-type star located 50 light-years away from us. The rate of discovery accelerated in 2009 with the advent of the Kepler space telescope, designed to detect exoplanets.
During the period of the 4-year main mission, the device managed to control thousands of stars at a time, tracking the traces of darkening starlight hinting at the transit of the planets. Kepler kept an eye on the stars all the time, therefore he marked the passage of the planets and could determine the time of the orbital path of each. And this information allows us to understand the distance between the star and the planet. The closer the world, the faster its speed. Today we know more than 3000 planets with orbital periods. Kepler is an ideal tool for finding exoplanets, but it is not intended to study the chemical composition of stars. This knowledge was obtained from the Apache Point Galactic Evolutionary Observatory (APOGEE). It collects the spectrum for each star, identifying the elements present.
All the solar stars are mostly filled with hydrogen. But some hold more iron than others. By combining information from Kepler and APOGEE, we managed to notice the relationship between the amount of iron and the planetary systems. For the first time this trend was noted in 2016.
It is surprising that iron-enriched stars have only 25% more element than others, but have such a strong influence on planetary orbits. However, many questions still remain. Does the amount of iron in a star really affect the formation of short-period planets, or do such planets just gradually migrate closer to the star? Scientists hope that further research will help find the truth.