by Bo Gustafson (Astronomy)  

Gustafson holds a scaled model of a dust particle.  The microwave facility Gustafson designed and built to study scaled particles is visible in the background. 
 
 

Dust particles are the starting point of planet formation, the remnants from planet formation, and probably the "cradle" from which life developed and spread in the universe.  Theoretical modeling and observations of cosmic dust is a well-established research focus in the Department of Astronomy and has been for decades.  In the Laboratory for Astrophysics we are developing unique theoretical and experimental methods that can be used on "real" problems facing astronomy and other fields of research in the natural sciences, in medical sciences, and in engineering.  We apply these techniques in the development of innovative space instrumentation that enables missions that are truly "faster, cheaper, and better." 

    In general, there is a big gap between the idealized conditions that theoreticians can solve for and the real world that we observe.  Almost all natural and man-made particles are found to be complex structures and are usually aggregates of multiple particles less than a micrometer (one thousandth of a millimeter) across.  Most theoretical calculations of how these particles interact with light are, despite this, still based on idealized homogeneous and perfect spherical particles that are also assumed to act independently of one another.  This may be a good approximation for explaining the rainbow since it arises from a cloud of finely dispersed liquid drops pulled spherical by surface tension, but it is not a good approximation for most other real conditions.  Far from spherical, cirrus cloud particles, for example, are actually intricate angular ice crystals that can be assembled in snowflake-like complex geometries.  Volcanic dust, car exhaust, man-made smog and other types of dust are examples of irregular, complex aggregate structures.  Real applications involving such intricately shaped or closely spaced particles include a range of remote sensing applications, blood analysis and other medical analyses, pollution monitoring, and the sensing and manipulation of small particles in the food industry and manufacturing as well as in our primary interest: cosmic dust. Maybe the common view that most theoretical work is "academic" and almost unrelated to reality has some truth to it. 

An actual interplanetary dust partcle (upper right), magnified by more than 6000. 
 
 
 
 
 

     When I formed the Laboratory for Astrophysics in 1994 to study the physics of dust particles and other small bodies, there was a great need for closing the gap between modeling, both theoretical and experimental, on the one side, and real particles on the other.  The foundation for our success is an accurate and fully automated microwave facility that allows us to study light interactions in which a particle's dimensions and the light's wavelength are scaled up by a factor of 6000.  Affording great control and accuracy through the scaling (we build models of particles that are micrometers across scaled up to the size of grapes), ours is the first and only facility capable of measuring all aspects of the interaction of light with an arbitrary particle.  Its first use was to test and confirm a rigorous theoretical solution to the scattering of light by arbitrary aggregates of fully interacting spheres developed in the Laboratory for Astrophysics by Dr. Yu-lin Xu.  This long sought-after theoretical development is a big step that has allowed theoretical modeling of more realistic dust structures.  Dr. Ludmilla Kolokolova, also at the Laboratory for Astrophysics, uncovered evidence for organic compounds sublimating away from dust particles as they leave a comet, an interpretation that catches the imagination since cometary organics may have "sparked" life on this planet.  The interpretation would have been impossible to make without the laboratory data. 

     These successes have not gone unnoticed, and NASA has repeatedly approached our group to apply our results to instrumentation for the analysis of dust particles in planetary atmospheres, the outflow from icy satellites and comets, and in space.  We therefore formed an alliance for space instrumentation with collaborators worldwide including Dr. Frank Giovane at the Naval Research Laboratory.  As a result, the Laboratory for Astrophysics was funded to develop the next generation space instrumentation that is small and technically simple--with no moving parts--but that is "smart" because it uses knowledge about real particles, not before available, to analyze individual micrometer-sized specks of dust that may be suspended in thick atmospheres or could be traveling through virtually empty space at velocities measured in km/s.  NASA designated our Planetary Aerosol Monitor / Cometary Dust Analyzer (PAM/IDA) one of their sixteen "standard instruments for planetary exploration in the new millennium." 

(from left) Bo Gustafson, Ludmilla Kolokolova, Thomas Waldemarsson, Yu-lin Xu and Frank Giovane stand in front of instrumentation similar to equipment they designed and built for the "John Glenn" Space Shuttle mission. 
 

     As part of the effort, we developed test and calibration facilities as well as both a means of handling small particles and the guns to shoot these particles.  A plasma gun of our design uses a hypodermic needle for a barrel and may be the smallest hypervelocity gun in the world.  This gun launches tiny dust particles to velocities exceeding 7 km/s, the speed of the space shuttle.  The whole setup including the gun and flight path is designed to fit inside our 25-foot space simulation chamber.  Detecting, let alone analyzing, particles on this scale as they speed by is a truly mind boggling feat and our way to "reach for the stars." 

     In just a few years since its formation, our group not only built the ground facilities and developed the PAM/IDA instrument, it has also built and flown a simplified version of the instrument on the "John Glenn" space shuttle this fall.  Our unit monitored the growth of dust grains in a simulated planet forming region as part of a German microgravity experiment that is intended to eventually be a long term project on the International Space Station.  We also designed part of the dust instrument on Rosetta, the European mission to a comet, and are now negotiating to fly our PAM/IDA instrument on NASA's DS4 comet mission. 

     Given the esoteric reputation of our field, it may be ironic that, as astrophysicists, our primary activity is to close the gap between theoretical and experimental modeling with applications to a broad and well established research field that touches nearly all the sciences and to bring modeling "down to Earth."  Through establishing applications for our work in the space program and potentially in industry, we feel that we are also closing the gap between "academic work" and the "real world."