Earth-Like Rocky Planets May Be Far More Common Across the Galaxy, Scientists Say
Rocky planets similar to Earth could be far more widespread than astronomers once believed, opening new possibilities in the search for life beyond our solar system. New findings suggest a powerful cosmic process may have played a critical role in shaping dry, habitable worlds throughout the Milky Way.
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Supernova Shockwaves May Have Shaped Earth-Like Worlds
Rocky planets similar to Earth may be far more widespread than once believed, according to new research published in Science Advances. The study suggests that, during the formation of our solar system, a nearby supernova flooded the region with cosmic rays carrying radioactive elements capable of creating dry, rocky worlds. If correct, this process may be common throughout the galaxy.
How Earth-Like Planet Formed in a Radioactive Environment
Earth-like planets are thought to form from planetesimals—bodies composed of rock and ice—that lost their water early in the solar system's history. This drying process required substantial heat, supplied largely by the radioactive decay of short-lived radionuclides such as aluminium-26. Earlier analyses of meteorites, which preserve records of the early solar system, have confirmed that these radionuclides were abundant at the time.
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Flaws in Previous Models of Planet Formation
Why Earlier Supernova Theories Fell Short
However, models that rely on supernovae as the sole source of these short-lived radionuclides fail to reproduce the quantities recorded in meteorites. To supply enough radioactive material, a supernova would have needed to occur so close to the young solar system that it would have destroyed the surrounding disc of dust and gas from which the planets were forming.
The 'Immersion Mechanism' Offers a New Explanation
To resolve this puzzle, Ryo Sawada of the University of Tokyo and his colleagues have proposed a new explanation known as the immersion mechanism. In their model, a supernova explodes around 3.2 light-years away—close enough to influence the system, yet distant enough to leave the planet-forming disc intact. The blast generates a shockwave that accelerates particles, mainly protons, trapping them as cosmic rays.
A Two-Step Delivery of Life-Shaping Elements
How Cosmic Rays Created Radioactive Heat Sources
The model suggests that short-lived radionuclides were delivered through two distinct pathways. Some, including iron-60, were injected directly into the disc as dust grains. Others were created when high-energy cosmic rays collided with stable material in the disc, triggering nuclear reactions that produced radionuclides such as aluminium-26.
Is There Anybody Out There? Implications for Life Beyond Earth
When the researchers ran their model, it successfully reproduced the amounts of radioactive material measured in meteorites. The findings could have far-reaching implications for the search for life beyond Earth. As the team note in their paper, "Our results indicate that Earth-like, water-poor rocky planets may be more common in the galaxy than previously assumed, given that the abundance of aluminium-26 plays a crucial role in regulating planetary water budgets."
The authors estimate that between 10% and 50% of Sun-like stars may have hosted planet-forming discs with short-lived radionuclide levels comparable to those of our own solar system, pointing to a larger population of rocky, potentially habitable worlds.
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