During impact cratering at hyper velocity speed (>3 km/s) the event experiences such high energies that the resulting crater provides so much information, but what about the projectile?
It seems implausible that a small projectile would produce so much destruction and then survive, but the survival of part of the projectile is required for theories of some of the fundamental questions about the beginnings of our own planet, Life on this planet, and the idea of panspermia that it is something that is worth investigating.
Panspermia – the hypothesis that life exists throughout the University and is distributed by meteoroids, asteroids, comets and contaminated spacecraft.
Here at the University of Kent Impact group we have undertaken a series of projects investigating the survivability of different material during hyper-velocity impacts.
Survivability of Space craft – Space Littering
Most space craft when landing on a planet aims to land safely, known as a soft landing, so that the delicate instruments on board remain intact so that the exploration and science can begin.
Soft landing of the Curiosity rover using the Skye Crane
However, one known mission back in 2005, called NASAs Deep Impact purposefully impacted the comet Tempel-1 to discover the internal composition of the comet. The impactor payload was made of Copper and Aluminium 4%, weighed 100 kg and impacted the comet at 10.2 km/s. The debris from the impact was analysed to discover more of the internal composition of a comet. However, the projectile was thought to be completely lost during the impact.
Point of Impact of the Deep Impact Mission on to the Temple-1 Comet (NASA/JPL-Caltech/UMD)
However, at the University of Kent we investigated just how much of the Deep Impact projectile would have survived the impact and littered the comet surface with Copper material.
We used Cu ball bearings and impacted them at range of speeds, 1 – 6 km/s, into porous water ice. After the impact the ice is melted and filtered so that any material the survived the impact could be collected.
Our work concluded that up to the impact speed of 10.2 km/s significant material survived the impact, up to 15% of the original mass.
This is a significant result that highlights the effect our own space travel may be having on the Solar System, as Temple -1 now is travelling with some exotic Cu fragments that originate from Earth. This also highlights the importance of the sterilization of space craft material to prevent accidental contamination of the planetary bodies.
Astrobiology – Survivability of biological Material
Astrobiology is the study of life or possible life forming regions in the Solar system beyond Earth. The idea of panspermia means that life would have to survive impact processes to allow them to begin thriving in the new environment.
We have been interested in this idea, led by our group leader Prof Mark Burchell, for a long while investigating the survivabillity of simple organic material, bacteria, yeast, tardigrades and even fossilized material.
Fossil Fragments identified after impacts of up to 6 km/s
All these experiments used a frozen projectile which contained the organic material which was then impacted into a ocean target (water). The water is then collected and filtered and the living state of the organisms tests.
It has been found the tardigrades can survive impacts upto 4km/s,
Yeast has a survivbility probability of 10^-3% at 7.4 km/s
Natural Material – Survivability of natural Space material
Of course Natural material form space are known to survive impacts as material that does survive are known as meteorites, however investigating the survivability and the impact speed is a field of interest.
We have done a lot of work on this subject including some exciting ongoing work looking at at the survivability of basalt projectile material which will form a blog post all of its own so Watch this Space!
However if you are eager to learn more please check out the work by Joy et al., 2012 and Asphaug, 2013 who have found evidence of projectile material within the craters on the Moon