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PEBBLE2PLANET Report Summary

Project ID: 278675
Funded under: FP7-IDEAS-ERC
Country: Sweden

Final Report Summary - PEBBLE2PLANET (From pebbles to planets: towards new horizons in the formation of planets)

Planets form in protoplanetary discs of gas and dust orbiting young stars as dust grains collide and grow to ever larger bodies. The goal of this ERC Starting Grant proposal was to make significant advances in our understanding of how planets form. We achieved a number of results that shed new light on planet formation. We showed that dust grains can grow to cm-sized pebbles by condensing layers of ice at their surface, in a process akin to the formation of hail in terrestrial thunder clouds. These pebbles are important in the planet formation process because they are the building blocks of kilometer-sized planetesimals. The asteroids in the asteroid belt are such planetesimals that were left over from the planet formation epoch around the young Sun more than 4.5 billion years ago. Using 1000 years of computing time on a supercomputer - luckily spread over 4000 computer processors so that the simulation "only" took 3 months - we simulated how pebbles gather in dense groups and collapse by their mutual gravity to form planetesimals. We then showed that these planetesimals can grow to planets like our own Earth in just a few million years. This is much faster than the 100 million years traditionally thought to take to form the Earth. The key to this fast growth is that the largest planetesimals grow by accreting pebbles of mm-cm sizes, just like the ones we formed by ice condensation. The pebble accretion mechanism is a very promising new theory that can explain the formation of planets, not just in our own Solar System but also in the many planetary systems that are known to orbit other stars. I will now continue to study the formation of planets by pebble accretion through my ERC Consolidator Grant called PLANETESYS.

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