Astronomers discovered planetary collision in another star system.
An extremely dense planet on the star Kepler 107, 1,600 light-years from here, served as a clue for a CSI team from the skies to unravel the mystery.
The most widely held hypothesis is that the moon, our natural satellite, was formed from the wreckage of a wandering planet’s collision with Earth at the time of the origin of the Solar System – a story that you can understand it here:
A team of 52 astronomers from several countries has published in Nature Astronomy a scientific paper with evidence of a similar planetary collision that occurred in a distant stellar system, that of Kepler 107, 1,600 light-years from here.
Kepler 107 is a star similar to the Sun in size and temperature.
To conclude, they analyzed data from the Kepler space telescope itself – NASA’s retired planet hunter – as well as a surface observatory located in the Canary Islands.
It all started because of an anomaly in the diameter and density measurements of two planets orbiting around Kepler 107, called Kepler 107b and Kepler 107c (the pattern of naming exoplanets, those that orbit other stars, is to add letters to the name, its precise).
It has been discovered that Kepler 107c is an extremely solid rocky planet – twice as thick as Earth, and also double as dense as its neighbor, Kepler 107b, which is closest to the star – suggesting that it has a nucleus abnormally large made of metal.
This is strange for two reasons: one is that two neighboring planets rarely have such different densities.
Another is that when they do, the tendency is for the denser to settle closer to the star. In this case, the opposite occurs: Kepler 107b, lighter, has a more closed orbit than Kepler’s 107c.
Such situations are like charades for astronomers. They need to imagine (and model mathematically) a series of phenomena, and then evaluate which one best explains the situation that exists today.
Like detectives who deduce the perpetrator of a crime using subtle evidence – such as fingerprints and projectile capsules.
In the case of Kepler 107 and its planets, an adequate explanation for an unusual density of Kepler 107c would be that it was born of a collision between two worlds. The reason: Kepler 107c has initially been a much larger planet than his brother Kepler 107b.
Thus, both its core and its outer layers were proportionally larger (see the figure below – it is only an illustrative scheme). (Yasmin Ayumi / Superinterestant) These two planets had similar densities because the nucleus, which is the densest region, was proportional to the outer layers, which are less dense.
Remember, density, for physics, is how much weighs a little bit of a thing of a certain size. A piece of styrofoam of 1 kg takes up much more space than a portion of lead 1 kg.
The two planets were different sizes, but they had similar densities because if you took a piece of equal size from each of them and placed it on the scale, the little pieces would weigh the same thing.
One day, a violent collision with another planet took away a considerable portion of Kepler’s “shell” 107c – which was the largest planet.
It was so strong that he was about the same size as his younger brother, Kepler 107b. It turns out that, now, much of Kepler 107c has become the core.
It was a superheavy nucleus, within a much smaller planet. This disproportion between the core and outer layers left Kepler 107c much denser. And the result is the exotic star system you see today.
Chris Watson of Queen’s University in Northern Ireland told the BBC:
“We found two planets in a very similar orbit around the same star but with very different densities. One is rocky, and the other is made of a much denser material, probably iron. The only way to explain this would be that in one of them, a rocky surface has been removed by a collision.”
The article is the first scientific description of a planetary collision in a star system other than ours – which makes it, by itself, important for astronomy. But the applications of this study can go further.
If he crashed into another large object, it was because he was in an uncertain orbit and had not yet gravitationally “accommodated” himself.
Understanding the reasons for the collision, therefore, is to understand a little better how are the birth and the formation of a star system very similar to ours. As always, other worlds help us to understand ours.