The trouble with impacts

The trouble with impacts is that they tend to mess everything up, from the projectile to the target to the target chamber in the gun lab when I am investigating ice and water impacts. However, there is one case where the collection of material through impacts may have skewed the expected results from an investigation into the composition of a cometary nucleus to the changes in mineral composition as a result of impact shock.

The Stardust mission was a landmark for planetary sciences as it provided the first material to be collected and recovered from a comet.

Artist impression of Stardust Space crater http://stardust.jpl.nasa.gov/photo/artist.html#row11

The space craft flew into the tail of comet Wild2 and collected material within the tail within aerogel, a synthetic porous silica gel where the liquid is replace by gas making the material 98.2% air. This material captured the material within the comets tail and then traveled back to Earth.

ksc9812074_s.jpg
The aerogel capture system on Stardust http://stardust.jpl.nasa.gov/photo/ksc981207.html

The material from the comet was travelling at around 6.2 km/s when impacting the aerogel, and a lot of material also impacted the Al foil that lay on the grid securing the aerogel capture system.

Once the Space craft was back on Earth the material within the aerogel and foil craters was analysed to discover the composition of the nucleus of a comet.

However one question that sat on the minds of people who investigate impacts such as myself was, how has the impact effects the composition of the material currently beign analysed?

This is a rather big problem, shock from impacts is known to causing melting, devolitisation, and changes to structure and event composition. Therefore is the composition of the material collect by stardust pristine or modified as a result of the impact. If modified then the science community is not investigating the composition of the comet but the results of shock altered material.

What had to be done is experimentation with in laboratory environments to understand the changes that had occurred to the Stardust material and to formulate the right corrections to mkae on the analysis results so that the composition of the comet can be determined.

This was undertaken by Foster et al, 2013 and Harriss et al, 2016. They took material of known composition, Olivine, and fired it using the light gas gun at the University of Kent at the Aerogel and Al foils used on the Stardust mission at the same speed at the material is thought to have impacted the space craft collector ~6 km/s.

Impact crater on Foils from Olivine powder from from Foster et al, (2013)

What was found was that when analysing the crater residue using RAMAN techniques the position of the Peaks of the unshot olivine grains did not match those of the olivine residues within the crater formed at a speed of ~6 km/s. This meant that the analyses by RAMAN of the Stardust grains would have produced incorrect compositional results and that a correction would be required.

This work only shows a correction is required for RAMAN analysis and has to this point only investigateed the effects on olivine minerals. The next step would be to repeat these investigations using other mineral that have been located within the collected comet material including Enstatite.

MIR Space Station – 30 Years since the launch of Continued human habitation of Space!

The International space Station is a marvel of engineering and science  and has been the basis for international collaboration of 18 countries but it owes it success to the first modual space station the Soviet Mir Space Station. Here is a short history of the Mir Space Station but for more information check out my article about the legacy of the Mir Space Station on the Conversation!

Mir was the first space craft to be assembled in space with a number of individual modules. The first three were launched between 1986 adn 1989 before the fall or the USSR and the formation of a colaboration between teh Russia and America.

1: Mir Core module – 19th Feb 1986

2: Kvant-1  – 1987

3: Kvant -2 – 1989

4: Kristall – 1990

Each of these modules were designed to undertake science investigation and experimentation, including, each of which allowed science research to be undertaken including astronomy, biological studies and growing food, all of which will show if humans are capable of undertaking, surviving and even thriving in space during long duration flights to explore beyond the moon.

A view of the Russian space station Mir on 3 July 1993 as seen from Soyuz TM-17 Jean-Pierre Haigneré – http://www.spacefacts.de/graph/drawing/drawings2/soyuz-tm-17_mir_2.jpg

Post 1991 the colaboration between America and Russia formed the Shuttle-Mir Program where the shuttle was resupplied by the Space Shuttle and the Soyuz  and manned by both Russian cosmonauts and American astronauts, the first of which arrived in 1995.

Over the next 11 years the Mir space station would be hosts to American, ESA, Japanese and Ukrainian astronauts. Two new modules were added, Spektr with 4 solar arrays and equipment for Earth observation, and Priroda was the final module to be added in 1996.

A view of the US Space Shuttle Atlantis and the Russian Space Station Mir during STS-71 as seen by the crew of Mir EO-19 in Soyuz TM-21. http://grin.hq.nasa.gov/IMAGES/LARGE/GPN-2000-001315.jpg

In 1997 failures such as a collision with a resupply ship and fires on board meant that Mir was starting to show her age. Even after the ill- fated year the station was repaired and continued to be used until it was abandoned in 1999. It was in November 2000 that decommission of the Space station was announced. The deorbit of Mir began in Jan 24th 2001 when the Space Station crashed into the South Pacific Ocean.

Break up of Mir SpaceStation in the Earths Atmosphere.

With the exception of a few mouths in 1989 Mir was permanently manned and the lessons learned from this continual habitation led to the development of the highly successful ISS and we now has a greater understanding of the effect the micro gravity has on the biology of astronauts meaning that suitable technologies and regimes can be put in place for future long duration missions into the depths of the Solar System.

How was the moon formed ? Hit and run, or one of the biggest impacts?

Our moon is an anomaly is more then one ways, firstly its the only moon with the dullest name just as Earth is Earth the moon of Earth is called Moon, even the Kerbles were creative with calling theirs Mun!

Secondly its one of the only satellites bodies currently theorised to have originated from the body it orbits, unlike other moons which are either captured or produce from ancient ring systems.

How ever the actual formation of the moon is still in debate with scientific research on the subject bringing published in science this week.

It is generally accepted that the formation of the moon and the spin on the Earth on its axis are linked and that it was an impact between two bodies, a larger Earth and the Mars size Theia that produced both these phenomenon,

The impact between the two planets caused major disruptions of both bodies and flung debris from the collision into an orbit around the crippled planet. Over time the debris comes together and forms the moon and the initial collision disrupts the rotation of the Earth so that it moves are a slower rate the previously.

There have been links between the Earth and the moon ever since Apollo astronauts brought back samples of Moon rock to analyses. The composition of the moon is similar to that predicted of a Young Earth. since the formation of the moon the Earth dynamic internal heating has changed and evolved the planets crust through millennial of plate tectonics. Where as the moon become dormant and still.

A second and most important of the evidence for the Earth and Moon originating from on body is the oxygen isotope composition.

Oxygen isotopes are used as a characterization for the different planetary bodies of the Solar System. Each meteorite family, asteroid and planet has a singular oxygen isotope composition with a few overlaps. It is this which allows scientists to discover the original of Martian and Lunar Meteorites and group other meteorites into logical families.

Basic Oxygen Isotope plot showing the TFL line (Earth and Moon) and two other meteorite groups, Martian Meteorites and the HED meteroites (http://www.psrd.hawaii.edu/Dec01/Oisotopes.html)

The oxygen isotope composition of the rock brought back from the Moon sits on what in the trade is know as the Terrestrial Fractionation Line. This TFL is the line on which all rocks from Earth fall, along with the lunar samples suggesting that the Moon and the Earth originate from the same or similar body.

However this is the crux of the matter, Earth and Moon rocks are similar but my own experiments has shown the impressive survivability of the smaller objects during an impact. Therefore the question is: Where is the material from Theia?

Recent work investigating the oxygen isotope composition of Lunar Rocks suggest that the Moon and Earth have near identical Theia contents due to their indistinguishable oxygen isotope composition meaning that the moon forming impact thoroughly mixed and homogenized the oxygen isotopes of Theia and the early Earth (Proto-earth).

Therefore there was no Hit and run collision but a high energy, high – angular -momentum impact that mixed the material of Theia with he Proto Earth distributing it homogeneously in the newly formed Moon and Earth.

 

 

Thoughts from an Impact conference

In late September I attended the Bridging the Gap Conference 2015 hosted by The University of Freiburg in Germany.

Bridging the Gap III

This was a small conference specializing in all aspects of impact cratering research and aimed to bring together the three main fields of impact cratering research together. These are:

1. Laboratory based research, such as that undertaken here at the University of Kent;

2. Fieldwork based research, where geologists investigate the outcrops of terrestrial impact craters and the remote sensing of extra-terrestrial caters;

3. Computational modelers that use software to simulate different impact scenarios and environment development.

All these fields provide vital information to the research of impact cratering but for a full understanding the three fields must work together and learn from the research of one another. Hence the Bridging the gap conference.

This three day conference included a number of oral sessions ranging from discussion the fate of the projectile, (where Jamies‘ work was presented) to target properties (where I presented my work relating to ice targets) to discussions of suevites, glasses and melt rocks.

Over all the talks were engaging and informative, with chances for discussion of different topics over coffee and lunch.

One talk of interest discussed the idea of using accessory minerals as indicators of shock in impacted rocks, given by colleagues at the University of Portsmouth who we shall bee looking forward to collaborating with on this work. In addition the a proposal for a new Shock pressure Classification scheme highlight sciences dependence of the known and well used methods of classification thought with new developments in the field many of these old classification schemes become ill defined and require extension or revision.

Interesting work looking at the impact related winds on Mars introduced me to a new phenomenon which was wonderfully explained and discussed.

Major discussion about acoustic fluidisation and what actually is a sueavite provided entertaining discussions though out the whole conference.

Overall this conference were wonderfully put together and really did provide a change for myself and the other attendees to discuss ideas, get feed back and develop collaborations with those that investigate Impact cratering in a completely different way.

The modellers provided a wonderful morning show the rest of us what can actually be achieve using the software iSale 2, which was highly informative and interested for many of the non-modelers including myself.

To conclude I wish to say congratulation to the Thomas Kenkmann and all the conveners and the science organizing committee for putting on a great, informative conference with a great conference dinner overlooking the beautiful city of Freiburg.

 

Group Focus – PhD Student Jamie Wickham-Eade

Every so often with this blog we shall be looking at the ongoing work of one of the members of the Impact Group at the University of Kent.

First under the spot light is Jamie, a first year PhD Student who is about to start his second year but already has a lot of data and plans for his project.

Following on from the last post about the survivability of a projectile during high velocity impacts which is a subject currently not well represented in the literature, Jamie’s project is doing just that investigating the breakup of basalt projectile when impacted.

Aim of Research

The main aim of his research is to discover the state of survival of the basalt projectile at different impact speeds which lead to different levels of shock experienced by the projectile.

Why are projectile fragments important?

Projectile material has been recovered form 13 sites on earth and may form dark region on asteroids such as Vesta and non-indigenous material has been fund on the moon and recovered from inside meteorites. So there is clear evidence that the projectile can survive these real life impact and so understanding the break up and survivability of different types of impact material can help in our understanding of the development of the bodies in the Solar System.

Data collection method

He used the two stage light gas gun (see previous posts) to fire basalt cubes (hand filed by Jamie) at speed between 0.5 and 6.0 Km/s into a target of water.

Picture1
The water target holder with water ready to go into the chamber

This may not be a realistic impact but it provides the expected range of shock pressure for the projectile to experience. 

The water is collected and filtered to extract the fragments of basalt projectile that have survived the impact. The fragments are measured and recorded using a Scanning electron microscope (SEM) which allows imaging of the micron sized particles of basalt.

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Jamie working on his projectiles in the Lab ~(Source – University of Kent)

Whats the big picture here?

A novel look into the survivability of basalt at high shock pressures to render the projectile survival percentage. This can be used to compare to the amount of projectile surviving impacting on different solar system bodies. Furthermore, a look into the evolution of cumulative fragment size distributions with increasing peak shock pressure.

Jamies work will soon be presented at the up coming Bridging the Gap conference in Frieberg, Germany.

The forgotten projectiles

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 planetLife 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.

NASA/JPL-Caltech/UMD
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 materialbacteria, 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

Why Science with a Big Gun?

Who here has seen Armageddon ? Deep Impact ? The Avengers Age of Ultron ? Gravity?

These films and many others all have a major threat, a asteroid/comet/moon/ ,we shall just say a planetary body / artificial satellite, hitting the Earth or Space craft and the resulting impact causing the destruction of Earth and the end of life as we know it, similar to what happened to the poor dinosaurs.

T-Rex was a Terrible Asteroid Hunter (alexhp RedBubble)

The process of two bodies colliding in space is known as Impact cratering and has been occurring on all planetary bodies since the very early history of the Solar System.

The resulting impact craters from these dynamic events are found on all bodies in the Solar system, including Earth, and shows a detailed volatile history of our own Solar System, and such events are still happening to day with >80 000 meteorites >10 grams impacting the Earth every Year.

Saturn's moon Mimas
Large Impact crater of Saturn’s moon of Mimas – Or the Death Star…. NASA/JPL/SSI

Here at the University of Kent we have a very special piece of equipment to investigate collisions between different materials to simulate impacts that occurred in the Solar system, we have  a REALLY BIG GUN!

The Light Gas Gun at the University of Kent

It is a two stage Light Gas Gun (LGG), which can fire material up to 3 mm sq between 0.5 and 7 km/s, yes that is Kilometer per second!

Why so fast? This is to reach similar speeds to that of material in space

How does the LGG work ?

The LGG works because of the two stage mechanism, the first stage uses rifle powder within a shot gun shell similar to a normal gun. When fired the energy released from the combustion of the powder propels forward a nylon piston rather then a metal bullet.

Schematic of the LGG

The piston travels down the pump tube and compresses the light gas that is present. The compression of this gas builds up the pressure against the rupture disc until it finally fails and the release of pressure from the compressed gas propels the sabot containing the projectile material down a rifled launch tube through the blast tank and light curtains into the target chamber until impacting the target material.

The type of gas, usually H or He,  and the initial pressure are selected to produced the required speed of the impact. The light curtains are used to calculate the speed of the projectile using the simple formula below as we know the distance between the two light curtains and the time the projectile passes thought.

Speed = Distance/Time

So why do we need to fire small things at such high speeds?

The research using the LGG at the University of Kent is diverse with impact cratering being linked to a number of different fields in space and geological sciences. We are currently investigating the possibility of living organisms  surviving impact cratering events. We have also recently investigated the synthesis of amino acids from energy provided by a impact event. Check out the results HERE.

Other work includes geological changes that occur during an impact event including impact melting, loss of water.

The next Blog post will go into more detail of the research undertaken using the LGG.

So, now I hope you know why we use a big gun to investigate impact cratering events that have occurred and are occurring in the Solar System.

Need to know more? Check out these links:

University of Kent

Impact group Twitter

Impact group Youtube