Our planet is shrouded in an electrically conducting layer of free electrons and ions — a plasma. The plasma state of matter becomes an important consideration above about 50 miles altitude, where it mediates the flow of solar wind energy into our atmosphere, limits communications with spacecraft, degrades satellite navigation systems (GPS), alters chemistry in the upper atmospheric (e.g., ozone production), damages satellite electronics, and threatens the health and safety of astronauts. The plasma state remains the dominant state of matter all the way to the edge of the universe, where its property of reflecting and absorbing electromagnetic radiation presents a fundamental limit to our ability to see the beginning of time.
Plasmas become visible under certain conditions of density and energy. Optical emissions from plasmas provide important scientific insight. Examples of visible plasmas include the aurora above 100 km (the northern and southern lights), rivers of glowing plasma above 150 km (e.g.,STEVE), airglow emitting as the ionosphere recombines, lightning in the lower atmosphere, and the beautiful loops, spicules and other phenomena observed on the Sun.
In the Semeter Lab, we seek to better understand Earth’s plasma environment and our relationship with it, including societal and biological risks, technological opportunities, and implications for the original and fate of our planet. We use a diverse set of tools in this work, including radars, cameras, magnetic sensors, spacecraft measurements, computer models, and various advanced analytical techniques rooted in engineering and statistics. Some favorite items in our tool set include:
Inoherent Scatter Radar (ISR)
Low-light optical sensors (EMCCD and sCMOS cameras)
Citizen Scientists (amateur and professional photographers)
NASA spacecraft (electromagnetic fields and particles)
Physics-based computer models (GEMINI, GLOW)
Data analytics (Data fusion, inverse theory, image reconstruction, tomography).