The center of the Milky Way in infrared light, as seen by the Spitzer Space Telescope A recent study shows that fewer types of planets are more common at the fringes of our galaxy.
A team of astronomers led by Caltech’s Jon Zink used data from NASA’s Kepler space telescope to do a sort of demographic study of the galaxy.
Kepler retired from NASA when it ran out of fuel in 2018 and spent nine years observing exoplanets. During its primary and secondary missions, called Kepler and K2, the space telescope discovered more than 3,300 confirmed planets, as well as many candidates who are not yet confirmed.
Zink’s team used updated techniques to remove noise in the data and order the planet numbers. To keep the analysis consistent, only planets with orbital periods (years) of one to 40 days were included in the final slice, leaving 2,038 planets for the sample used in the study.
They then used precise star mapping from the European Space Agency’s Gaia mission to pinpoint the positions of the planets’ parent stars relative to the Milky Way.
This resulted in a “galactic location trend”. Stars rise and fall on the galactic plane over millions of years as they orbit the center of the galaxy. Those far from the galactic plane, according to the study, host fewer super-Earth or sub-Neptune exoplanets.
The article about the new discovery gives several possible reasons for this pattern. Stars, referred to in the study as “high-amplitude stars” (those that are moving further away from the Milky Way over time as they wobble in their orbits), are also likely to age as the stars age. If gravitational instability occurs in these older systems, it could cause some of their planets to be ejected. Or these systems could have different amounts of certain elements, which would primarily affect the way planets form.
Another surprising trend emerged from the study. Astronomers and planetary scientists have traditionally assumed that “sub-Saturns” (gas giants similar to Saturn, but smaller) are closely associated with Jupiter-like planets during the planet formation process.
Instead applies to circulation times of more than 10 days The study found three times as many sub-Saturns as warm Jupiters (Jupiter-like worlds, hotter than our own Jupiter, but not among the hottest). This suggests that the really close relationship during planet formation is between sub-Saturns and sub-Neptunes, not between sub-Saturns and Jovian planets.
