Solar system once harboured 'super-earths'

Researchers at the California Institute of Technology have found that our solar system may have once harboured super-earths - planets larger than the Earth but smaller than Neptune.

It means that the Earth belongs to a second generation of planets.

Those early super-earths are long gone - broken up and fallen into the Sun billions of years ago largely due to a great inward-and-then-outward journey that Jupiter made early in the solar system's history, said the paper published in the journal Proceedings of the National Academy of Sciences (PNAS).

"Our work suggests that Jupiter's inward-outward migration could have destroyed a first generation of planets and set the stage for the formation of the mass-depleted terrestrial planets that our solar system has today,"said Konstantin Batygin, planetary scientist at California Institute of Technology.

The results suggest the possibility of a new picture of the early solar system that would help to answer a number of outstanding questions about the current makeup of the solar system and of the Earth itself.

Thanks to recent surveys of exoplanets - planets in solar systems other than our own - we know that about half of Sun-like stars in our galactic neighbourhood have orbiting planets.

"Indeed, it appears that the solar system today is not the common representative of the galactic planetary census. Instead we are something of an outlier," Batygin said.

But there is no reason to think that the dominant mode of planet formation throughout the galaxy should not have occurred here.

It is more likely that subsequent changes have altered its original makeup.

The paper also suggests that the formation of gas giant planets such as Jupiter and Saturn - a process that planetary scientists believe is relatively rare - plays a major role in determining whether a planetary system winds up looking something like our own or like the more typical systems with close-in super-earths.

As planet hunters identify additional systems that harbour gas giants, the researchers will have more data against which they can check their hypothesis.