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New timeline for our solar system estimated

PTI | Boston |

Astronomers have estimated the new lifetime of the solar nebula which suggests that the gas giant planets Jupiter and Saturn formed within the first four million years of our solar system's formation.

About 4.6 billion years ago, an enormous cloud of hydrogen gas and dust collapsed under its own weight, eventually flattening into a disk called the solar nebula.

Most of this interstellar material contracted at the disk's centre to form the Sun, and part of the solar nebula's remaining gas and dust condensed to form the planets and the rest of our solar system.

Now, scientists from Massachusetts Institute of Technology (MIT) in the US and their colleagues have estimated the lifetime of the solar nebula – a key stage during which much of the solar system evolution took shape.

This new estimate suggests that the gas giants Jupiter and Saturn must have formed within the first four million years of the solar system's formation.

Furthermore, they must have completed gas-driven migration of their orbital positions by this time.

Benjamin Weiss, professor at MIT and Huapei Wang, the first author of the research, studied the magnetic orientations in pristine samples of ancient meteorites that formed 4.653 billion years ago, determining that the solar nebula lasted around three to four million years.

This is a more precise figure than previous estimates, which placed the solar nebula's lifetime at somewhere between one and 10 million years.

The team came to its conclusion after carefully analysing angrites, which are some of the oldest and most pristine of planetary rocks.

Scientists view angrites as exceptional recorders of the early solar system, particularly as the rocks also contain high amounts of uranium, which they can use to precisely determine their age.

Weiss and his colleagues analysed four angrites that fell to Earth at different places and times.

All four meteorites were remarkably well-preserved, having undergone no additional heating or major compositional changes since they originally formed.

Now that the scientists have a better idea of how long the solar nebula persisted, they can also narrow in on how giant planets such as Jupiter and Saturn formed.

"The gas giants must have formed by four million years after the formation of the solar system," Weiss said.

"Planets were moving all over the place, in and out over large distances, and all this motion is thought to have been driven by gravitational forces from the gas. We are saying all this happened in the first four million years," he added.

The research was published in the journal Science.