The Nice Model (2005): Giant Planets and the Late Heavy Bombardment

Gomes, Levison, Tsiganis and Morbidelli proposed in 2005 that the giant planets suddenly migrated about 700 million years after the planets formed, scattering debris everywhere. Their Nice model offered a cause for the Moon’s Late Heavy Bombardment and showed the giant planets did not form where they are now.

What was the Late Heavy Bombardment?

Lunar samples suggested something odd. About 700 million years after the planets formed, the rate of cratering seemed to spike, as if the inner Solar System had been hit by a sudden storm of impacts. This proposed event is called the Late Heavy Bombardment. Theories of planet formation could not naturally explain an intense bombardment so late. Several models had been put forward, but none fit into a consistent story of how the Solar System evolved.

What the paper found

• A trigger in the outer Solar System. The bombardment could be set off by a rapid migration of the giant planets, Jupiter, Saturn, Uranus and Neptune, after a long quiet period.
• A disk knocked loose. The migration destabilized a disk of planetesimals, small icy and rocky bodies, orbiting beyond the planets, and sent many of them into the inner Solar System.
• Asteroids joined in. The asteroid belt was also strongly perturbed, and its objects supplied a significant share of the impactors.
• The outer Solar System falls into place. The same model also explains features such as the orbits of the giant planets and Jupiter’s Trojan asteroids, which share Jupiter’s orbit.

How they did it

The authors used computer simulations of the young Solar System: the four giant planets plus a disk of planetesimals beyond them. In their picture the planets first went through a long quiet period. Then the system changed abruptly. As the giant planets migrated, their gravity stirred the outer disk and the asteroid belt, delivering a sudden burst of impactors to the Moon and the rocky planets.

The paper was published in Nature alongside two companion papers, by Tsiganis and colleagues and by Morbidelli and colleagues. Between them, the three papers tackled the orbits of the giant planets, Jupiter’s Trojan asteroids and the bombardment. Together they form the “Nice model,” named after the city in France where the authors worked.

Why it mattered

Three puzzles that looked unrelated got one answer. More importantly, the Nice model established that the giant planets did not form where they orbit today, and that their movement reshaped the whole Solar System. Collisions had already become central to planetary science through ideas like the giant impact that likely formed the Moon. The Nice model added large-scale migration to the toolkit.

What we know now

Planet migration is now a standard part of how astronomers explain the Solar System’s architecture. The bombardment itself is less settled: whether a sharp “cataclysm” happened at all is debated.

The outer Solar System keeps raising new dynamical questions. In 2016 Batygin and Brown argued that clustered orbits of distant Kuiper belt objects point to a hypothesized Planet Nine, which as of October 2026 has not been detected.

Who wrote it

R. Gomes, H. F. Levison, K. Tsiganis and A. Morbidelli developed the model together while working in Nice. Semantic Scholar lists about 1,590 citations for this paper (October 2026), a sign of how widely the Nice model is used.

Read the original

Gomes, R., Levison, H. F., Tsiganis, K. and Morbidelli, A. (2005). “Origin of the cataclysmic Late Heavy Bombardment period of the terrestrial planets.” Nature 435, 466-469. doi:10.1038/nature03676

Free to read: publisher PDF from Nature.