BERLIN, April 18 (Xinhua) -- An asteroid that exploded in Earth's atmosphere in 2008 and rained down diamond-bearing rocks was part of a lost planet from the early solar system, according to a study published Tuesday.

The parent planet was about as large as Mercury or Mars, and would have existed billions of years ago before breaking up in collisions with other space rocks, according to a European research team that published their results in the scientific journal Nature Communications.

Using three types of microscopy, the researchers measured the composition of diamonds trapped within rocks left scattered in Sudan's Nubian Desert after an asteroid dubbed 2008 TC3 crashed into Earth.

They concluded the precious stones could only have been formed above pressures of some 20 gigapascals, which could only have existed on a Mars- to Mercury-sized planet.

These are two of the smallest planets in the solar system, which was forged about 4.6 billion years ago.

Farhang Nabiei, a materials scientist at the Swiss Federal Institute of Technology in Lausanne, and his colleagues said the measurements provide "the first compelling evidence for such a large body that has since disappeared."

The finding also boosts the theory that today's solar system planets were forged from the remains of large "proto-planets."

The meteorites from the collision fall into a category of space rocks called ureilites, which represent less than 1 percent of objects that collide with Earth.

The researchers suggest all ureilite asteroids were remnants of the same proto-planet.