Spatial and temporal scales of aqueous alteration in icy planetesimals

Lead Research Organisation: University of Glasgow
Department Name: School of Geographical & Earth Sciences

Abstract

This aim of this research programme is to understand better the evolution of the small bodies of rock and ice that lie in the outer parts of the solar system. These bodies are collectively called 'planetesimals', and are of great interest to planetary scientists because they have remained unchanged for most of the 4,500 million year history of the solar system. Thus, they can tell us much about how it formed and developed. This research project is concerned with planetesimals that contained liquid water, probably for a brief period soon after their formation. Pieces of these planetesimals have fallen to Earth as meteorites called 'carbonaceous chondrites', which are highly valued by scientists because their chemical compositions indicate that they are least altered rocks available for study. However, despite their very primitive chemistry, the carbonaceous chondrites are made mainly of minerals that were formed by water reacting with their parent planetesimal, and this process of aqueous alteration would be expected to have also modified the chemical composition of the rock. This contradiction between a primitive chemistry and secondary mineralogy can only be explained if water within the planetesimal was static. However, recent computer simulations of planetesimal evolution consistently predict that only the smallest bodies could have contained static water and in most it must have flowed through the rocks, modifying their chemical compositions along its path. In this research programme we will test the assumptions and predictions of these models by obtaining new information on the behavior and history of water within planetesimals using one group of carbonaceous chondrites called the CMs. These meteorites contain small crystals of minerals called carbonates that crystallized from the water. By examining the compositions, internal structures and distributions of carbonate crystals using a range of microscope-based techniques, we will address the following questions: Was the water stationary or did it flow in the same way that hot water moves through rocks on Earth? Did the water exist for only a brief period in a small body or was it present for millions of years within a larger planetesimal? Did planetesimal interiors contain water or was it present only close to their surface? Results of this research will increase our understanding of how planetesimals formed and evolved and will enable us and other scientists to assess and potentially modify the computer models of planetesimal interiors. Ultimately this work is significant for our understanding of the early history of the solar system but also of the present-day composition and internal structure of comets and asteroids. These bodies are currently the focus of a great deal of international research activity, having been visited recently by several space probes, and are targets for future unmanned and possibly manned exploration.

Publications

10 25 50
 
Description The aims of this research programme were to understand better the evolution of the small bodies of rock and ice that lie in the outer parts of the solar system that are collectively called 'planetesimals'. The focus of our work was on planetesimals that contained liquid water, pieces of which have fallen to Earth as carbonaceous chondrite meteorites. Reaction of water with these planetesimals shortly after the birth of the solar system formed minerals called carbonates, and by analysing the internal structure, distribution and chemical composition of these minerals we have sought to answer the following questions: Was the water stationary or did it flow in the same way that hot water moves through rocks on Earth? Did the water exist for only a brief period in a small body or was it present for millions of years within a larger planetesimal? Did planetesimal interiors contain water or was it present only close to their surface?

This research programme has provided much new information on when and how the water reacted with planetesimal interiors. The results have enabled us and other planetary scientists to develop new models for their evolution, and to propose novel hypotheses to be tested by the next generation of spacecraft that will study and sample primitive asteroids.

We have demonstrated that water did not react with planetesimal interiors in one brief event, but rather over several longer episodes between which the abundance and type of chemical elements in the water changed significantly. We have been able to determine very precisely when the water first appeared, and using newly discovered features called veins, we have demonstrated that the water flowed through the rock in much the same was as it does on Earth. By developing a new technique called 'calcite twin stress analysis' we found that during or soon after the time that water was present, the planetesimal interiors were compressed by high pressures caused by the impact of one or meteorites on the outer surface of the planetesimal. We have been able to measure quantify these pressures, and determine the direction in which they moved through the planetesimal.
Exploitation Route Our finds are important to others in the academic community who seek to understand the early evolution and internal structure of asteroids. They are also of particular significance to international groups who are planning missions to return samples of primitive asteroids. These missions are under the auspices of the US and Japanese space agencies and interpretation of results will rely heavily on prior understanding of the carbonaceous chondrite meteorites.
Sectors Education,Culture, Heritage, Museums and Collections

 
Description We have also shared our findings with the general public by giving lectures at the Hunterian Museum in Glasgow, holding workshops in Scottish science centers, and even by setting up a stall in a Glasgow shopping center. We hope that these events have helped to inform and inspire the general public about STFC funded science.
First Year Of Impact 2010
Sector Education,Environment
Impact Types Cultural,Societal

 
Description Paneth Trust
Amount £2,000 (GBP)
Organisation Royal Astronomical Society 
Sector Learned Society
Country United Kingdom
Start 08/2010 
End 09/2010
 
Description Paneth Trust Internship
Amount £2,000 (GBP)
Organisation Royal Astronomical Society 
Sector Learned Society
Country United Kingdom
Start 07/2010 
End 09/2010
 
Description Science in Society
Amount £4,438 (GBP)
Funding ID ST/J501748/1 
Organisation Science and Technologies Facilities Council (STFC) 
Sector Academic/University
Country United Kingdom
Start 02/2012 
End 10/2012
 
Description The Royal Society of Edinburgh
Amount £300 (GBP)
Organisation Cormac Trust 
Sector Charity/Non Profit
Country United Kingdom
Start 01/2012 
End 07/2012
 
Description Travel grants
Amount £400 (GBP)
Organisation University of Glasgow 
Sector Academic/University
Country United Kingdom
Start 08/2010 
End 09/2010
 
Description Impact experiments 
Organisation University of Kent
Department School of Physical Sciences
Country United Kingdom 
Sector Academic/University 
PI Contribution Supply of samples for hypervelocity impact experiments and interpretation of results
Collaborator Contribution Undertake hypervelocity impact experiments on meteorite analogue samples
Impact A paper with results of this work has been published: Lindgren, P., Lee, M.R., Sofe, M. and Burchell, M.J. (2011) Microstructure of calcite in the CM2 carbonaceous chondrite LON 94101: implications for deformation history during and/or after aqueous alteration. Earth and Planetary Science Letters 306, 289-298.
Start Year 2010
 
Description NanoSIMS 
Organisation Carnegie Institution for Science (CIS)
Department Department of Terrestrial Magnetism (DTM)
Country United States 
Sector Charity/Non Profit 
PI Contribution Supply of carefully characerised samples of the QUE 93005 meteorite
Collaborator Contribution Used the Carnegie Institution NanoSIMS instrument to determine the crystallization ages of carbonate minerals in the meteorite
Impact A paper with results of this work has been published: Lee, M.R., Lindgren, P., Sofe, M., Alexander, C.M.O'D. and Wang, J. (2012) Extended chronologies of aqueous alteration in the CM2 carbonaceous chondrites: evidence from carbonates in Queen Alexandra Range 93005. Geochimica et Cosmochimica Acta 92, 148-169.
Start Year 2011
 
Description Hunterian Museum talks 
Form Of Engagement Activity A talk or presentation
Part Of Official Scheme? No
Type Of Presentation Keynote/Invited Speaker
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact Presentation about meteorite impacts to an audience of the general public at the Hunterian Museum, Glasgow.

None known
Year(s) Of Engagement Activity 2010,2011
 
Description Pop up museum 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? No
Type Of Presentation Workshop Facilitator
Geographic Reach Local
Primary Audience Public/other audiences
Results and Impact Pop-up museum featuring meteorites at the St Enoch shopping Centre in Glasgow, January 2013

By doing a pop-up museum at a shopping centre, we reached out to and inspired an audience that would not normally come to science festivals.
Year(s) Of Engagement Activity 2013
 
Description Science Festival 
Form Of Engagement Activity Participation in an activity, workshop or similar
Part Of Official Scheme? Yes
Type Of Presentation Workshop Facilitator
Geographic Reach National
Primary Audience Public/other audiences
Results and Impact The estimated attendance of the two science festivals was 6000 people, of which a good proportional visited our workshop. The Stargazing Live event attracted 3000 people.

A set of resources were produced that describe the history of the solar system and the planets. We also constructed a remote controlled Mars rover and a Martian landscape for it to explore.
Year(s) Of Engagement Activity 2012