The new study shows that the normal type of planets are few on the outskirts of our Milky way galaxy.

Whether the Milky Way is made up of different ‘province’ or regions that each have their own unique families of planets? It turns out the answer is yes! A new study has found that stars on the fringes of the Milky Way possess fewer of the most common planet types. This finding suggests that the process of planet formation – and the resulting families of planets – could be different from one galactic neighborhood to the next. 

To come to this conclusion, astronomers conducted a meticulous survey of planet populations in our galaxy. They found that stars far away from the galactic plane – the thicker, pancake-like concentration of stars that is home to the densest stellar populations – show a notable lack of two of the most common types of planets. 

The two planets in question are “super-Earths” and “sub-Neptunes”, which are hulking versions of our own rocky planet (super-Earths) and smaller versions of our own Neptune (sub-Neptunes). This means that these two types of planets are far less common in the less densely populated outer reaches of the Milky Way. But why this is so remains a mystery. It could be that these types of planets just don’t form in these regions, or it could be something else entirely. Astronomers are still working to uncover what’s really going on.

A team of astronomers led by Jon Zink of Caltech have used data from NASA’s historic Kepler Space Telescope to conduct a kind of demographic survey of the galaxy. The Kepler mission has revealed many planets outside our own solar system, including over 3,300 confirmed planets, and many more candidates that have yet to be confirmed.

Using updated techniques to clean up the data, Zink’s team focused on planets with orbital periods between one and forty days, leaving 2038 planets in their sample for the galactic survey. Precision mapping from the European Space Agency’s Gaia mission was then used to discover a “galactic location trend”- stars located further away from the Milky Way have fewer super-Earth or sub-Neptune exoplanets orbiting them. 

The paper on this new discovery mentions several possible explanations for this pattern. High amplitude stars are likely older and their planets may have been expelled due to gravitational instability.It is also suggested that these systems may have different abundances of elements, which affects their ability to form planets.

Astronomers and planetary scientists have traditionally held the view that “sub-Saturns”, gas giants similar to Saturn but smaller, were closely linked to Jupiter-like planets in the process of planet formation.Was published June 1, 2023, in The Astronomical Journal, by lead author Jon K. Zink. The study, conducted by an international team of scientists led by Jon K. Zink, found that for orbital periods longer than 10 days, there were three times more sub-Saturns than warm Jupiters. This discovery suggests that the true relationship during planet formation is between sub-Saturns and sub-Neptunes, and not sub-Saturns and Jovian planets. This surprising study has further advanced our knowledge of the formation of planets and the complex interactions involved.