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Hypervelocity Impacts

Solar System objects collide violently due to their motion leading to high relative speeds. These are often at greater than a few km/s. Impacts at such speeds are termed hypervelocity and cause unusual degrees of damage. One odd feature of such impacts is that the projectile not only fragments, but partially melts and even starts to vaporise.

Photograph of the LGG

Fortunately despite their incredible speed, most impactors in space are small, micron sized is typical, mm size less so, and cm size very rare. But large impacts have occurred in the past (for example see the surface of the moon) and still occur at irregular intervals.

Here at Kent laboratory our studies of hypervelocity impact processes use a two stage light gas gun to fire projectiles (1 micron to 4.4 mm) at speeds between 1 to 7.5 km/s. Over the past 30 years we have fired into a wide range of targets including ices, mineral and rocky targets, aerogels and the canterbury tales.

Our in-house analysis facilities include a target chamber mounted TOF-MS, a Horiba Raman spectrometer, Hitachi S3400N SEM with EDX and A Hitachi S4700 FEG-SEM with attached Brucker X-Flash . These allow us to examine targets after impact combined with hydrocode modelling of the impact allow us to examine the processes and alterations that have occurred.

Research topics include:

Dust

Solar system dust includes natural dust and that arising from human activities in space. Kent has a long history of studying both. In the early 2000’s we made major efforts studying cometary dust as part of the NASA Stardust mission to comet Wild-2. This captured freshly emitted cometary dust grains and returned them to Earth for study. The mission also obtained samples of interstellar dust for analysis.

More recently our work has focussed on:

  • Designing new dust detectors for use in space
  • The threat of increasing human made debris in Low Earth Orbit (for a recent review click here)
  • Collection of micrometeorites here on Earth, both in Antarctica and by sampling dust in the local environment
  • Continuing to work on the Stardust cometary dust collections
  • Doing background studies for future space missions to collect dust in niche environments in the Solar System, such as the plumes of Enceladus (a satellite of Saturn which has a sub-surface ocean which sprays water into space)

    • Real time measurements of dust flux in space

    We have been working for many years on designs for new dust collectors to be placed in Earth Orbit or near the Moon. For example, Kent has been working for over a decade on a series of NASA led programme to develop new impact sensors. These require new sensors which can be placed on spacecraft and give real time readout of the impact flux.

    Currently, Dr. Penny Wozniakiewicz and Professor Burchell are collaborating with NASA, and a US company (Astroacoustics) on a project to optimise new detector technology which can return data in real time. Using the Kent two stage light gas gun we have conducted a series of tests already with more planned.

    An early example of this was the DRAGONS (USNA – PI) project which deployed an new impact sensor on the International Space Station in January 2018 (for more details click here).

    Impact work has already started at a variety of labs in the US and at Kent. We are collaborating with NASA, the US Naval Research Laboratory, US Naval Academy, and Virginia Tech. on a series of projects. Using the Kent two stage light gas gun we have conducted a series of tests already with more planned.

    Dr. Penny Wozniakiewicz also holds a UK STFC grant from GNOSIS, which co-funds a PhD studentship to help improve designs of real time dust impact detectors for use in monitoring the flux of space debris. Details of GNOSIS are here.

    It is hoped that there will be future opportunities to deploy such sensors in space in the mid-2020s.

    Collection of cosmic dust and debris in space and on Earth

    Dr. Penny Wozniakiewicz has been leading several studies for a new generation of passive dust collectors which could be flown in space. These would be retrieved at the end of their life and brought back to Earth for analysis of their contents. A review of such designs is available here.

    Cometary insights from Stardust Foils

    Dr. Penny Wozniakiewicz is also continuing experimental study of hypervelocity impacts of comet 81P/Wild (Wild 2) analogues and chondrule fragments on Al foil to compare with microscopic craters from the Stardust mission. This study aims at understanding both the chemical and physical nature of the cometary dust that impacted the armature (i.e. Aluminium foil) holding the aerogel on the Stardust dust detector.

    a) SEM-EDX chemical map of a crater creater by a chondrule fragment from the Allende carbonaceous chondrites; (b) EDX spectra of a spot analysis of an impact residue lining the bottom of the crater; (c, d, e) Mg, Si and Fe maps showing that the chondrule residue covers most of the crater.

    Ices

    The role of ice in the Solar System is of interest to members of the group including Professor Burchell. At present research has focussed on hypervelocity impact processes in ice, including studies of:

    We have also taken in interest in light flash from impacts on ice. Our first paper on this was way back in the 1990s. But recently (2020) under Dr Jon Tandy, we have started undertaking more detailed studies with more work will follow.

    Astrobiology

    Kent has a variety of research interests in Astrobiology. In the hypervelocity filed, Kent was the first to show that microorganisms could survive in hypervelocity impacts (Experimental Tests of the Impact related Aspects of Panspermia, M.J.Burchell et al., in Impacts on the Early Earth pp. 1-26, eds. I. Gilmour & C. Koeberl, pub. Springer 2000). Later we showed survival rates vs. peak shock pressure (e.g. Survival of Bacteria and Spores Under Extreme Pressures. M.J. Burchell, J.R. Mann and A.W. Bunch. Monthly Notices of the Royal Astronomical Society 352, 1273 – 1278, 2004, or or Price M.C., et al., Survival of yeast spores in hypervelocity impact events up to velocities of 7.4 km s-1. Icarus 222, 263-272, 2013).

    We also showed that ejecta from impacts could carry viable microbes (Survivability of Bacteria Ejected from Icy Surfaces after Hypervelocity Impact, M.J. Burchell, et al., Origin of Life and Evolution of the Biosphere, 33, 53 – 74, 2003).

    We have even looked at what happens to seeds in hypervelocity impacts (Survival of Seeds in Hypervelocity Impacts. Jerling A., Burchell M.J., Tepfer D. Int. J. Astrobiology 7, 217 – 222, 2008).

    Members of the group also developed a new way to synthesis amino acids. This was in impacts on ice mixtures. See Martins et al., Shock synthesis of amino acids from impacting cometary and icy planet surface analogues (Nature Geoscience 6, 1045 – 1049, 2013).

    Currently we are looking at what happens to organic biomarkers in impacts. Including the niche question of how to collect material of astrobiological interest when flying at high speed through a water plume such as those emitted by icy worlds like Enceladus or Europa. Recent papers (2021) concern basic questions such as can you identify different salts after flying through a plume (https://onlinelibrary.wiley.com/doi/full/10.1111/maps.13729), what happens to tardigrades in high-speed impacts (https://www.liebertpub.com/doi/10.1089/ast.2020.2405) and how much ice you must sample in a plume to detect biomarkers (https://www.pnas.org/content/118/37/e2106197118).

    (a, b) Example tardigrades before impact testing. Tardigrades ranged in size from 150 to 850 μm. (c) Tardigrade recovered after an impact at 0.728 km s−1. (d) Tardigrade fragment from shot at 0.901 km s−1.

    Contact Dr Penny Wozniakiewicz for further details of hypervelocity impact work at Kent.