Science | Steve Thompson

Steve Thompson
High Resolution Powder Diffraction

steve Thompson Stephen Thompson is Beamline Scientist on the Powder Diffraction beamline I11. Prior to Diamond, Stephen was a beamline scientist at the SRS, where he studied astronomical silicate via laboratory analogues using IR spectroscopy, x-ray powder diffraction, EXAFS, SAXS and x-ray reflectivity. This research focussed on the evolution of structure through thermal annealing as a means to understanding the physical conditions likely to have been prevalent in the early solar nebular prior to planetary formation. He was also closely involved with data acquisition programming and the control of sample cells and instrumentation for x-ray diffraction.

Email: Stephen Thompson
Tel: +44 (0) 1235 778546
Beamline I11: High Resolution Powder Diffraction

Key Research Areas

Solid State Astrophysics, Astromineralogy, cosmic dust, amorphous silicates, non-ambient powder diffraction

Current Research Areas

Historically regarded by astronomers as an annoying "fog", interstellar dust is now at the forefront of modern astrophysics. My own research focuses on the laboratory investigation of cosmic dust analogues. This involves their manufacture and characterisation under ambient and non-ambient conditions. Advances in astronomy, laboratory simulation and theoretical modelling have had a tremendous impact on our understanding of the physical and chemical nature, origin and evolution of interstellar grains and their significance in the evolution of galaxies, the formation of stars and planetary systems as well as the synthesis of complex organic molecules in space, which could lead to the origins of life itself.

Dust actively participates in the cycling of matter from the interstellar medium (ISM) to stars and back from stars to the ISM. Solid grains condense in the cool atmospheres of old stars, Wolf-Rayet stars, planetary nebulae, novae and supernovae and are then ejected into the diffuse ISM. Here grains, interacting with hot shocked gas, stellar UV radiation and cosmic rays, undergo various disruptive processes as they cycle between diffuse and dense cloud regions. The collapse of dense molecular clouds leads to the birth of new stars and planetary systems. At the late stages of stellar evolution, gas and newly formed dust returns to the ISM through stellar winds or supernova explosions. Dust grains therefore serve as unique markers for the prevailing physical conditions in which they are embedded and laboratory research plays a key role in modelling both the nature and evolution of cosmic dust.

For example, comets cold-formed in the region of Jupiter and beyond in the early solar nebula and, as the first planetesimals, should be repositories of pristine ISM dust left over from the formation of the Sun. However, certain comets (e.g. Halley, Hale-Bopp) showed evidence of grains with crystalline mineral structures, contrary to all observational evidence suggesting ISM grains are amorphous. One possibility is that grains close in to the nascent Sun were subjected to high temperatures (~1000 K) and crystallised before a, as yet unknown, transport mechanism delivered them to the comet forming zones. By simulating this thermal process in the laboratory and monitoring the evolution of structure as a function of both time and temperature using furnaces and various in situ synchrotron techniques we have begun to elucidate the structural contributions of the grain material to the observed spectral characteristics of their cosmic counterparts. Using, for example, the fast time-resolved capabilities of the Diamond Powder Diffraction beamline we will be able to place even tighter physical constraints on the conditions present in the early solar system prior to the formation of the Earth as well as on the origins of cometary dust.

steve thompson diagram

Mechanism of structural evolution in cosmic silicates through dehydrogenation induced polymerisation during annealing proposed by Thompson & Tang (2001). Removal of Si-OH and SiH defects, as H2 gas, from disordered SiO tetrahedral units allows them to recombine to form a silicate network.

Selected Publications

  1. Crystallisation Processes in Cosmic Silicates: Progress towards understanding structural-spectral relationships. SP THOMPSON, V VERRIENTI, S FONTI, V OROFINO, A BLANCO. Advances in Space Research, in press, 2006
  2. Crystalline comet dust: laboratory experiments on a simple silicate system. SP THOMPSON, S FONTI, C VERRIENTI, A BLANCO, V OROFINO, CC TANG. Meteoritics & Planetary Science 38, no. 3, 457-478, 2003.
  3. Laboratory study of annealed amorphous MgSiO3 using IR spectroscopy and synchrotron X-ray diffraction. SP THOMPSON, S FONTI, C VERRIENTI, A BLANCO, V OROFINO, CC TANG. Astronomy & Astrophysics 395, 705-717, 2002.
  4. Laboratory investigation of crystallisation in annealed amorphous MgSiO3. SP THOMPSON, CC TANG. Astronomy & Astrophysics 368, 721-729, 2001.