The center of the Milky Way Galaxy as seen in Infrared.Image Credit: NASA, JPL-Caltech, Susan Stolovy (SSC/Caltech) et al.

Fewer planets on the outskirts of the Milky Way?

Research reveals that the distribution of stars in the Milky Way follows a demographic pattern.


In the vast expanse of the Milky Way, not all regions are created equal when it comes to the distribution of planets. Newly unveiled research suggests a demographic trend in planet populations, possibly transforming our understanding of planet formation across different galactic territories.

While scientists have long pondered if there’s any difference in planet systems across the galaxy, recent discoveries indicate a clear distinction. Interestingly, stars located away from the bustling galactic plane, the Milky Way’s densest stellar hub, exhibit a stark paucity of two major planet types: the larger-than-Earth “Super-Earths” and the potential mini-Neptunes dubbed “sub-Neptunes”. The question that baffles astronomers: Why this disparity?

Delving into Kepler’s Galactic Census

The trailblazing Kepler Space Telescope, a NASA marvel that enjoyed nine years of tracking exoplanets, provided a wealth of data for this analysis. Led by Caltech’s Jon Zink, a team of astronomers refined Kepler’s dataset, filtering out noise and focusing on planets with orbital periods (akin to our Earth years) ranging from one to 40 days. This left a whopping 2,038 planets for evaluation.


Further clarity was achieved by leveraging the precise stellar mapping of the European Space Agency’s Gaia mission, pinpointing the exact positions of these planets’ host stars within the Milky Way. The results unveiled a remarkable “galactic location trend” – a notable dearth of Super-Earths and sub-Neptunes among stars wandering far from the galactic plane.

As these distant stars oscillate in their galactic orbits over tens of millions of years, they might age differently or have varying elemental compositions, both of which can influence planet formation. Gravitational instabilities in older star systems could lead to planets being ejected, or the unique elemental proportions might just affect planetary genesis.

Re-evaluating Planetary Relationships

The research unearthed another intriguing revelation. Previously, scientists believed sub-Saturns (scaled-down versions of our own Saturn) were intricately linked with Jupiter-like planets in the planetary formation sequence. However, this study noted a twist: For orbital periods exceeding 10 days, there were thrice as many sub-Saturns as warm Jupiters (Jupiters that are warmer than ours but not among the hottest). This suggests that perhaps, during planet formation, the real bond is between sub-Neptunes and sub-Saturns, and not between the giant Jovian worlds and sub-Saturns as earlier believed.


This research is a testament to the ever-evolving nature of space science, reminding us that the Milky Way remains a vast, mysterious domain, still holding many secrets.

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Written by Ivan Petricevic

I've been writing passionately about ancient civilizations, history, alien life, and various other subjects for more than eight years. You may have seen me appear on Discovery Channel's What On Earth series, History Channel's Ancient Aliens, and Gaia's Ancient Civilizations among others.

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