Uranus and Neptune played flip-flop four billion years ago

December 12th, 2007 - 1:48 pm ICT by admin  

Washington, Dec 12 (ANI): A recent study by scientists has said that Uranus and Neptune had switched places four billion years ago, indicating that the planets in our solar system werent always in the order they are today.

Steve Desh, assistant professor in the School of Earth and Space Exploration at Arizona State University, carried out the study.

Desh based his conclusion on calculations of the surface density of the soalr nebula.

The solar nebula is the disk of gas and dust out of which all of the planets formed. The surface density (mass per area) of the solar nebula protoplanetary disk is a fundamental quantity needed to calculate everything from how fast planets grow to the types of chemicals they are likely to contain.

After going through various models on planet formation, the research team developed the Nice model, which is based on sophisticated numerical calculations of the planets’ orbits over millions of years.

It explains several aspects about the orbits of Jupiter, Saturn, Uranus and Neptune, as well as the Kuiper Belt of comets beyond, by assuming the giant planets formed a lot closer together than they’re found today. Neptune, for example, formed less than half the distance from the Sun that it orbits today. And in 50% of their simulations, Uranus and Neptune switched places, although there was no way to determine whether they did or not.

According to Desch, the Nice model implied the mass of the solar system was packed together more tightly than the minimum mass solar nebula assumed.

By spreading the masses of the planets over their original orbits, as predicted by the Nice model, he found a very smooth variation of surface density with distance from the Sun, albeit one that fell off very sharply far from the Sun. The fit varied by only a few percent from the planets’ masses, but only if Uranus and Neptune did indeed switch places.

“Neptune had to form closer to the sun than Uranus or you don’t get the smooth profile,” said Desch.

The new findings have other profound implications.

“The surface density of the solar nebula isn’t what we originally thought it is actually much higher and this has implications for where we formed and for how fast planets grow, said Desch. A higher surface density of the solar nebula means that Uranus and Neptune formed closer and faster, in only 10 million years instead of billions,” he added.

This finding is important because Uranus and Neptune contain a few Earth masses of hydrogen and helium gas, and observations of other protoplanetary disks show these gases don’t hang around for more than 10 million years.

In addition to demonstrating for the first time that all of the giant planets can grow within the lifetime of the solar nebula, the study also uncovered the reason behind the sharp variation in density with distance from the Sun.

“The distribution of mass falls off very steeply because the outer edge is constantly being boiled away through the process of photoevaporation, by the ultraviolet radiation of nearby massive stars,” said Desch. (ANI)

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