The volume of this fragmented material is much larger than the volume excavated by the impact (Melosh et al., 1992). The rarefaction can produce strong tensile stresses and high strain rates, triggering dynamic fragmentation (Melosh et al., 1992). This succession of shock and rarefaction sets up the flow that excavates the crater (Melosh, 1984). During a hypervelocity impact a shockwave propagates into the projectile and target and is followed by a rarefaction wave that propagates from free surfaces. Impact cratering is a ubiquitous process that dominates the evolution of ancient planetary crusts (Melosh, 1989). Understanding how thoroughly fractured ancient planetary crusts are may help us determine if and when these environments became habitable. Similarly, impacts likely shattered the crust of the ancient Earth and Mars.

This implies that the fragmented bedrock can be almost exclusively created by large-scale high-speed impacts and the lunar crust was thoroughly fractured early in its history. Impacts can break up the lunar crust down to approximately 20 km, and objects greater than 1 km in diameter are the most efficient at fragmenting the crust. We found that impacts break the lunar crust into roughly meter-sized blocks. In this study, we simulated asteroid impacts and tracked how impacts shatter the lunar crust. Despite this, the processes of fracturing and fragmentation during an asteroid impact have received little attention though. This bombardment is thought to have thoroughly shattered the lunar crust, the outermost layer of the Moon, to depths of 20 km or more. The Moon's surface has experienced eons of bombardment by asteroid impacts. This suggests that impactors from 1 to 10 km in diameter can efficiently fragment the entire lunar crust to depths of ~20 km, implying that much of the modern day megaregolith can be created by single impacts rather than by multiple large impact events. For a 10-km-diameter impactor, this surface zone extends to a depth of ~20 km and lateral distances ~300 km from the point of impact. At larger impactor sizes, overburden pressure inhibits fragmentation and only a near-surface zone is fragmented. For an impactor 1 km in diameter this zone extends to depths of 20 km. For impactors 1 km in diameter or smaller, a hemispherical zone centered on the point of impact contains meter-scale fragments. We find that fragment sizes are weakly dependent on impactor size and impact velocity. This implementation allows us to directly simulate tensile in situ impact fragmentation of the lunar crust. Here we implement the Grady-Kipp model for dynamic fragmentation into the iSALE shock physics code. Little is known about the formation and evolution of the lunar megaregolith. The full, official Eesti Laul participation rules are available here.The megaregolith of the Moon is the upper region of the crust, which has been extensively fractured by intense impact bombardment. The winner of Eesti Laul will go through to the main Eurovision Song Contest semi-finals in May and, if they make it through, to the Grand Final. Other rules include that an entry may not be authored by a greater number of non-resident writers combined than Estonian citizens or residents combined performs may be citizens, residents or non-residents of Estonia.Ī maximum of five entries can be made by the one songwriter or performer. While the preliminary round winners are to be announced at the start of November, the songs will first be present in early December, via ERR's channels, including Raadio 2 – the latter will showcase those songs which did not make it through to the final. These fees double for the last couple of days entries are open, ie. The standard entry fee is €50, or €100 for songs composed in a foreign language. The deadline for entries is as noted October 23, at noon to be precise. The 10-entry 'super-final' winner will be decided on the basis of a phone-in vote. The jury will comprise several dozen people including 'ordinary' members seen as representing the target audience, as well as people with a musical background. The best five songs from this heat will then go through, making for a grand final of 10 songs. Five of these will go straight through to the final, to be held on February 17, while 15 will enter the sole semi-final heat. This preliminary round will see a broad-based jury selecting 20 songs at the Tartu preliminary round. Tartu is European Capital of Culture, Killandi noted, while the change to one semi-final only is also the result of the current economic environment, she says. There will only be one semi-final heat,Ī preliminary round in Tartu, to be held on January 20, will precede it. This year, Eesti Laul has seen several innovations. ERR producer and presenter Karmel Killandi said: 'We are waiting entries to the competition that will represent Estonia in front of the whole of Europe, in the best way possible.'

Laul isale