Spallation zones are regions adjacent to the free surface of a solid where the reflection of a strong incident stress wave induces tensile stresses and ejects material at high speed. The tensile stresses add to the compressive stresses in the incident wave and partially cancel its compression, leading to high-speed ejection of lightly compressed (“shocked”) material.
Spallation of the surface following impingement of a strong shock wave was first observed in association with underground nuclear explosions. During the 1980s, accumulated evidence indicated that the SNC suite of meteorites originated on a large planet, probably Mars. Their launch raised the conundrum of how intact rocks could be ejected at high enough speed to escape from Mars (a minimum of 5 km/s) and yet escape melting or vaporization. Melosh (1984) first suggested that spallation could provide the answer. Furthermore, Melosh (1988)...
KeywordsHigh-speed ejection Lithopanspermia Meteorite impact
References and Further Reading
- Valtonen M, Nurmi P, Zheng J-Q, Cucinotta FA, Wilson JW, Horneck G, Lindegren L, Melosh J, Rickman H, Mileikowsky C (2009) Natural transfer of viable microbes in space from planets in the extra-solar systems to a planet in our solar system and vice-versa. Astrophys J 690:210–215ADSCrossRefGoogle Scholar