Polymers as mimics for cosmic dust
It may not feel like it, but the Earth is moving through space at approximately 18,000 mph. Similarly, micrometeorites (also known as ‘cosmic dust’) can travel at remarkably high speeds in outer space. Typically, this corresponds to the ‘hypervelocity’ regime, which is more than 1 km per second (2,000 mph, or Mach 3). Such speeds present an opportunity for determining the chemical compositions of such fast-moving particles, because when they hit a hard solid object such as a metal, the kinetic energy of the high-speed impact breaks up the particles into their constituent atoms and/or molecular fragments. These can then be analysed by time-of-flight mass spectrometry. This is the operating principle of the Cosmic Dust Analyser (CDA), an instrument onboard the CASSINI spacecraft that has been orbiting Saturn since 2004. Part of CASSINI’s mission is to examine the chemical composition of Saturn’s famous dust rings. However, in order to do this, space scientists must be confident that the CDA instrument can really discriminate between the various know types of micrometeorites (metal, silicate, organic ice etc.). This requires careful laboratory experiments using similar-sized particles of well-known chemical composition.
Prof. Steve Armes works on the design of new polymer particles in the Chemistry Department at Sheffield University. For the last 17 years, his research team has been providing space scientists based in the UK, Germany and the USA with model plastic particles of known chemical composition. The plastic is a special type of polymer known as polypyrrole. Unlike most plastics, polypyrrole conducts electricity quite well, which enables polypyrrole particles to pick up surface charge. This enables them to be accelerated up to the hypervelocity regime using a high-field van der Graaf accelerator. The fastest moving particles developed so far by Prof. Armes can attain a speed of 38 km per second. The space scientists can use these synthetic particles to calibrate their CDA instrument and verify its performance. Prof. Armes was awarded the Royal Society of Chemistry’s Interdisciplinary Prize for his role in this long-standing collaboration in 2014 and he has just published an invited review article on this topic with some of his space scientist colleagues in Chemical Communications. For more details, please read the (open access) article here.