We endeavor to create the first comprehensive characterization of meteoroids and meteoroid plasmas (i.e. meteors) in order to understand their effects on the lower ionosphere and their threat to orbiting spacecraft. Meteoroids are naturally occurring objects in space that travel between 11 and 72.8 km/s and originate primarily from comets and asteroids. On average, over 100 billion meteoroids enter Earth’s atmosphere daily with masses larger than 1 microgram. These include shower meteoroids, which are associated with a parent body, as well as sporadic meteoroids, which form the background population. Although meteoroids have a profound effect on our space environment and produce plasma densities that are orders of magnitude greater than the background ionosphere, we understand very little about their fundamental properties and their potential threat to spacecraft through impact damage. These include meteoroid mass and density that depends on orbit and velocity, the formation and distribution of irregularities in the lower ionosphere, the mass deposition rate into our atmosphere, the effects of meteoroid fragmentation on plasma formation, and the effect of the background electric and magnetic fields on plasma expansion and distribution. We seek to answer these questions by probing into the plasma that surrounds the meteoroid, known as the head echo, and behind the meteoroid, called the trail, in order to assess the threat to spacecraft.
Our approach includes both experiment and modeling. We have designed waveforms and signal processing algorithms for four high-power, large-aperture radar facilities at diverse geographic locations, including ALTAIR (Kwajalein Atoll), Arecibo Observatory (Puerto Rico), Jicamarca Observatory (Peru), and the Millstone Hill Radar (Boston area). We are also developing the first fully electromagnetic scattering model that will model the interaction of radar waves with plasmas in order to correlate detected signal strength to plasma density and meteoroid mass loss. This research, which is funded through an NSF CAREER award, addresses the National Space Weather Program’s goal of improving global ionospheric specification of the evolution of ionospheric irregularities by answering the following scientific questions:
- How much extraterrestrial material is evaporated in Earth’s atmosphere each day?
- Where does this extraterrestrial material originate and what is its bulk density?
- How does this constant bombardment of extraterrestrial material affect the physics of the upper atmosphere and ionosphere?
When a meteoroid enters the Earth's atmosphere, heats up, and ablates, a plasma forms. The plasma traveling with the meteoroid is called a meteor head, while the plasma that is left behind is called a meteor trail. By transmitting pulsed electromagnetic waves with a high-power large-aperture (HPLA) radar and measuring the waves that are scattered back, one hopes to characterize the plasma and its evolution and infer many properties of the parent meteoroid such as velocity, mass, density, and composition. The image below shows typical radar data for a meteor taken with the Jicamarca Incoherent Scatter Radar outside Lima, Peru. It plots signal to noise ratio (SNR) as a function of range and time the pulse was transmitted. The diagonal line on the left is the signal from a meteor head, while the high-SNR portion to the right is signal due to the accompanying trail.
Smaller "meteor radars" have an even longer history of observing trails. They receive what are called specular trail reflections, resulting when the radar beam is perpendicular to the meteor trail. Although the techniques are different, both radar methods provide unique insight into the meteoroid population.
Our research topics within this area range from measurement and signal processing techniques to plasma scattering models and meteoroid property calculation. Individual research projects can roughly be divided as follows:
- Improved signal processing based on the theory of compressed sensing
- Trail plasma formation, diffusion, and modeling
- Modeling of electromagnetic scattering of plasmas
- Estimating meteoroid mass, density, and size based on radar observations
- Meteoroid orbit determination and characterization of meteoroid sources