Jupiter is the largest planet in our solar system and that’s because billions of years in the past it has swallowed up a planet 10 times Earth masses, said researchers from the University of Peking.
This hypothesis started from an anomaly of this planet: the core is extremely small compared to the huge size of Jupiter. In more accurate data, Jupiter is about 120 times larger than Earth, yet the core of the planet is, in the best case, 10 times larger than Earth. Chinese scientists are convinced that it was vaporized in a terrifying collision that occurred shortly after the birth of our solar system.
Heavy elements inside that primordial Jupiter as metals were vaporized at the time of impact and then mixed up with the hydrogen and helium in the atmosphere of the planet. This would be the reason why Jupiter’s atmosphere is so dense. Another Studies show that the planet Saturn was born in a similar manner.
The rocky body flattened like a pancake when it hit the gas giant, then barrelled into its core
It is believed that all solar system’ planets were born in this way: impact between dwarf planets then melted together and formed larger planets.
The Earth and Moon are the result of a gigantic collision between two planets the size of Mars and Venus. The collision took place in less than 24 hours and the temperature of the Earth was so high (7000º C), that both rock and metal melted.
Scientist paper: https://arxiv.org/abs/1007.4722.