The study of planetary systems is one of the most rapidly changing fields in astronomy. In just a few decades, our understanding of how planets can form has changed and expanded significantly, but we know that there’s still a lot that we don’t know. A new study fits well in this shifting paradigm as it shows that a certain type of star system should be a very popular configuration.
Stars with fewer heavy elements, or “metals”, compared to the Sun might have been overlooked as good hosts for planets. These low-metallicity stars, as they are called, can frequently have compact multi-planet systems. The fraction of these compact systems remains constant even in stars with a lot more heavy elements. Considering that the metal-poor stars are overlooked in planet-hunting, the research suggests that these configurations should be extremely common. This study is published in The Astrophysical Journal Letters.
Searches so far are been biased by telescope limitation. Metal-rich stars are easier to study and they are more likely to have gas giant planets – hot Jupiters – very close to them, which are easy to spot. But new instruments are now capable of studying the smaller planets.
These systems might also be more likely to host life, at least as we know it. First of all, they are rocky, and secondly, they might have formed much earlier than the giant planets around metal-rich, more evolved stars.
“Low-metallicity stars have been around a lot longer,” lead author John Michael Brewer, from Yale, said in a statement. “That’s where we’ll find the first planets that formed.”
An important question still without an answer is how these planets form? To be perfectly honest, there are uncertainties about how any type of planet forms, but these ones in particular are quite puzzling. What’s in these low-metallicity stars that make them good hosts for small rocky planets?
“Silicon could be the secret ingredient,” senior author Professor Debra Fischer, also of Yale, explained. “The ratio of silicon to iron is acting as a thermostat for planet formation. As the ratio increases, nature is dialing up the formation of small, rocky planets.”
As it’s often the case, more observations are necessary to better characterize these systems, and by studying these objects we might even learn something important about our own planets.