Rocky planets like our Earth may be far more common than previously thought, according to new research published in the journal Science Advances. It suggests that when our solar system formed, a nearby supernova (the massive explosion of a star near the end of its life) bathed it in cosmic rays containing the radioactive ingredients to make rocky, dry worlds. This mechanism could be ubiquitous across the galaxy.
Earth-like planets are thought to form from planetesimals (objects made of rock and ice) that were dried out early in the solar system’s history. This process required a lot of heat, which came primarily from the radioactive decay of short-lived radionuclides (SLRs), such as aluminum-26. Previous analysis of meteorites, which are ancient records of the early solar system, confirmed the abundance of SLRs at this time.
Flaws in previous models
However, models that explain supernovae as the sole source of these SLRs cannot accurately match the quantity of the nucleotides found in meteorites. To deliver enough radioactive material, the supernova would have to be so close to the early solar system that it would have destroyed the disk of dust and gas where the planets were forming.
To solve this mystery, Ryo Sawada of the University of Tokyo and colleagues have proposed a new concept, the immersion mechanism. The team modeled a supernova exploding about 3.2 light-years away, a safe enough distance not to destroy the planet-forming disk. When it exploded, it created a shockwave that accelerated particles, mainly protons, trapping them as cosmic rays.
According to the model, SLRs were delivered in two ways. First, the supernova directly injected some, such as iron-60, into the disk as dust grains. Second, cosmic rays collided with stable materials in the disk at such high energies that they triggered nuclear reactions that produced other SLRs, such as aluminum-26.
Is there anybody out there?
When the team ran their model, they found it matched the quantity of radioactive materials found in the meteorites. This research could have profound implications for the search for life in the universe, as the team states in their paper: “Our results suggest that Earth-like, water-poor rocky planets may be more prevalent in the galaxy than previously thought, given that 26Al abundance plays a key role in regulating planetary water budgets.”
According to the study authors, around 10% to 50% of sun-like stars may have hosted planet-forming disks with SLR abundances similar to those in our solar system. That suggests a higher number of rocky, potentially habitable worlds out there in space.
https://phys.org/news/2025-12-supernova-immersion-earth-planets-common.html
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