One exoplanet may have lost its outer layers in a massive planetary collision, leaving behind a dense, iron-rich core.
Key Takeaways:
- Astronomers found the first evidence of a giant collision between exoplanets, marking a groundbreaking discovery.
- Kepler-107c is nearly three times as massive as its twin, likely due to a past planetary impact.
- The collision may have stripped Kepler-107c’s outer layers, leaving behind a dense, iron-rich core.
- Similar planetary collisions might be more common than previously thought, shaping exoplanetary systems.
- This discovery mirrors the Moon’s formation, which likely resulted from a giant impact with early Earth.
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For the first time, astronomers believe they have discovered a giant planetary collision in another star system. The groundbreaking research, published in Nature Astronomy, suggests that one exoplanet, Kepler-107c, may have lost its outer layers in a violent impact, leaving behind an unusually dense, iron-rich core.
A Perplexing Density Difference
The Kepler-107 system, located 1,700 light-years away in the constellation Cygnus, contains at least four planets orbiting a Sun-like star. Two of these planets, Kepler-107b and Kepler-107c, appear to be nearly identical in size, each about 1.5 times the radius of Earth. However, Kepler-107c is nearly three times as massive as its twin, a mystery that puzzled researchers.
Kepler-107b, the inner planet, has a mass of about 3.5 times that of Earth and a density of 5.3 grams per cubic centimeter, similar to our own planet. But Kepler-107c, which orbits slightly farther out, has a staggering mass of 9.4 Earths and a density of 12.6 grams per cubic centimeter—far denser than any planet in our solar system.
Initially, astronomers considered whether intense stellar radiation could have stripped Kepler-107b of its atmosphere, making it less massive. However, if that were the case, Kepler-107b should be denser than Kepler-107c, not the other way around. This led researchers to another, more dramatic explanation: a planetary collision.
A Violent Impact That Reshaped a Planet
Scientists believe Kepler-107c likely experienced a massive collision with another planet in the past. The impact would have stripped away much of its lighter, rocky mantle, leaving behind a dense, iron-rich core. Based on mass and radius calculations, researchers estimate that Kepler-107c could be composed of up to 70% iron.
While planetary collisions have been theorized, this marks the first time astronomers have found strong evidence for such an event beyond our solar system. However, additional studies will be needed to confirm this hypothesis.
A Familiar Story from Our Own Solar System
The idea of giant planetary collisions isn’t new. In fact, the leading theory for the Moon’s formation suggests that early Earth was struck by a Mars-sized object about 4.6 billion years ago. This impact ejected material into orbit, some of which coalesced to form the Moon.
The discovery of Kepler-107c suggests that such collisions may be common in the universe. With the continued advancement of telescopes like the James Webb Space Telescope, astronomers hope to uncover more evidence of planetary impacts, reshaping our understanding of how planets form and evolve.
