Massive Space Rock Collision Creates Unusual Exoplanet

Scientists suspect a significant impact causes the differences between twin exoplanets.
Jessica Miley

Scientists have discovered by chance the way some exoplanets get their unusual composition. It seems, like many space formations, the makeup of particular planets is due to giants impacts. The discovery was made when scientists were observing Kepler 107, a sun-like star with four orbiting planets. 

The researchers were examining each of the four planets to determine their mass. They paid particular interest to the two innermost planets of the Kepler-107 system. Each of the planets has almost the same radii, but the outer planet Kepler-107c is twice as dense as its counterpart Kepler-107b. 

How do planets form?

This is weird as it means Kepler-107c must have a larger iron core than Kepler-107b, but why? It is generally understood that planets form from the accumulation of gas and dust swirling around a young star. 

Usually denser rockier planets form closer to the star as iron does not dissipate as easily as lighter elements like hydrogen and helium. Kepler 107c is further away from its twin planet, but it is significantly heavier. 

Massive impact only plausible conclusion

After much investigation scientists conclude the only plausible reason for the unusual planet is that it is the result of a giant collision between two worlds, each about 10 times Earth’s mass. 


The researchers created a computer simulation of the hypothesized impact; simulating a collision between two rocky worlds each with a dense iron core comprising of 30 percent of their mass. 

The impact produced a single planet, whose mass was almost 70 percent iron that shares similarities with Kepler 107c. The research which has been published in Nature Astronomy was conducted by astronomers Aldo S. Bonomo and Mario Dalmasso of the Istituto Nazionale Di Astrofisica (INAF) and by Center for Astrophysics, Harvard & Smithsonian (CfA) astrophysicist Li Zeng as well as a large support team. 

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Research opens up new ways of understanding galaxy

The research is important as it expands the possibilities of understanding how other objects in our galaxy are formed. Prior to the study of Kepler, astronomists were mostly limited to examining the planets in our own solar system. 

We know that the outer planets of Jupiter, Saturn, Uranus, and Neptune were formed from cold ices and gases that made up the bulk of the material in the outer solar system. 

The inner planets of our solar system were formed out of materials that survived the Sun’s radiation, like silicates and iron.

The Kepler 107 examination tells us that there are other ways that planets can form and these birth stories have big impacts on the planets structure and density.

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