Bombardment of the early Solar System

Long after the planets of the Solar System formed, catastrophic collisions continued, with a climax about 4 billion years ago during an interval called the Late Heavy Bombardment. The scars of this geologic violence are evident today in the ancient cratered terrains of planetary surfaces. The interval of bombardment is thought to have shaped the terrestrial planets and moons, their atmospheres and possibly even the onset of life. In this web focus, we present research papers, overview articles and opinion pieces that discuss how large impacts influenced the evolution of the early Solar System.



Shaped by collisions p505


Melt rocks returned from the Moon date to a narrow interval of lunar bombardment about 4 billion years ago. There is now evidence to show that this so-called Late Heavy Bombardment spanned the entire Solar System.



The overprotection of Mars pp510-511

Alberto G. Fairén & Dirk Schulze-Makuch


Planetary protection policies aim to guard Solar System bodies from biological contamination from spacecraft. Costly efforts to sterilize Mars spacecraft need to be re-evaluated, as they are unnecessarily inhibiting a more ambitious agenda to search for extant life on Mars.


Progress Article

Impact bombardment of the terrestrial planets and the early history of the Solar System pp520-524


About 4 billion years ago, the terrestrial planets were bombarded by asteroids following an orbital shake-up of the outer Solar System. Lunar samples, planetary cratering records and dynamical models piece together an increasingly coherent view of this bombardment interval.


From the archive


News & Views

Planetary science: Go and catch a falling star

Erik Asphaug


Patches of deposits containing unusual mafic minerals are observed in and around some large lunar impact craters. Numerical simulations suggest that in the slowest of these impacts, asteroidal material, alien to the Moon, could have survived.

Planetary science: Earth's ancient catastrophes

Tamara Goldin


Planetary science: Kick for the cosmic clockwork

Matija Ćuk


Mercury's spin and its orbit around the Sun are tied to each other in a unique arrangement. According to a set of calculations, random asteroid impacts may have aided the planet's evolution into the current spin-orbit pattern.

Planetary science: Titan's nitrogenesis

Catherine Neish


Observations from the Cassini–Huygens mission have produced potentially contradictory constraints on the origin of Titan's atmosphere. Experiments and a simple model demonstrate that a new mechanism for late formation is plausible.



Compositional evidence for an impact origin of the Moon's Procellarum basin

Ryosuke Nakamura, Satoru Yamamoto, Tsuneo Matsunaga, Yoshiaki Ishihara, Tomokatsu Morota, Takahiro Hiroi, Hiroshi Takeda, Yoshiko Ogawa, Yasuhiro Yokota, Naru Hirata, Makiko Ohtake & Kazuto Saiki


The nearside and farside of the Moon are compositionally distinct. The detection of low-calcium pyroxene around large impact basins suggests that the huge Procellarum basin on the nearside may be an ancient impact structure and a relic scar of the violent collision that produced the lunar dichotomy.

Mercury's spin—orbit resonance explained by initial retrograde and subsequent synchronous rotation

Mark A. Wieczorek, Alexandre C. M. Correia, Mathieu Le Feuvre, Jacques Laskar & Nicolas Rambaux


The planet Mercury rotates three times about its spin axis for every two orbits around the Sun. Numerical modelling suggests that this unusual pattern could result from initial retrograde rotation that was captured into a stable synchronous orbit, and subsequent disturbance by a large impact.

Replacement and late formation of atmospheric N2 on undifferentiated Titan by impacts

Yasuhito Sekine, Hidenori Genda, Seiji Sugita, Toshihiko Kadono & Takafumi Matsui


The origin of Titan's massive nitrogen atmosphere is largely unknown. Laser-gun experiments and numerical calculations suggest that the nitrogen could have been generated by conversion from ammonia during the period of Late Heavy Bombardment.

Origin of the Ganymede–Callisto dichotomy by impacts during the late heavy bombardment

Amy C. Barr & Robin M. Canup


Jupiter's large moons Ganymede and Callisto are similar in size and composition, but different in surface and interior characteristics. Simulations with geophysical models of core formation indicate that the difference in impact energy received by the two satellites during the period of late heavy bombardment can explain the dichotomy.



High-velocity collisions from the lunar cataclysm recorded in asteroidal meteorites

S. Marchi, W. F. Bottke, B. A. Cohen, K. Wünnemann, D. A. Kring, H. Y. McSween, M. C. De Sanctis, D. P. O'Brien, P. Schenk, C. A. Raymond & C. T. Russell


Lunar samples suggest that the inner Solar System was bombarded by asteroids about 4 Gyr ago. Radiometric ages of meteorites suggest an unusual number of high-velocity asteroids at this time, consistent with a dynamical origin of the bombardment in which the asteroids were pushed by outer planet migration onto highly eccentric orbits.

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